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Twenty-five-year research progress in hookworm excretory/secretory products


Hookworm infection is a major public health problem that threatens about 500 million people throughout tropical areas of the world. Adult hookworms survive for many years in the host intestine, where they suck blood, causing iron deficiency anemia and malnutrition. Numerous molecules, named excretory/secretory (ES) products, are secreted by hookworm adults and/or larvae to aid in parasite survival and pathobiology. Although the molecular cloning and characterization of hookworm ES products began 25 years ago, the biological role and molecular nature of many of them are still unclear. Hookworm ES products, with distinct structures and functions, have been linked to many essential events in the disease pathogenesis. These events include host invasion and tissue migration, parasite nourishment and reproduction, and immune modulation. Several of these products represent promising vaccine targets for controlling hookworm disease and therapeutic targets for many inflammatory diseases. This review aims to summarize our present knowledge about hookworm ES products, including their role in parasite biology, host-parasite interactions, and as vaccine and pharmaceutical targets and to identify research gaps and future research directions in this field.


Hookworms are soil-transmitted intestinal nematodes that infect nearly 500 million people in tropical regions of South America, Africa and Asia [1]. These blood-feeding nematodes cause one of the most debilitating neglected tropical disease called hookworm disease. This disease resulted in four million disability-adjusted life years (DALYs) and up to USD139 billion annual economic productivity losses [2]. Most human hookworm infections are caused by Necator americanus, Ancylostoma duodenale and Ancylostoma ceylanicum. Hookworm-associated clinical symptoms, such as abdominal pain, diarrhea, and protein malnutrition, commonly occur. However, the principal clinical symptom of hookworm disease is iron deficiency anemia (IDA) because of blood losses [3, 4]. Chronic IDA affects all ages, but it is principally deleterious to persons with low iron stores (children and women of childbearing age). Sequelae of hookworm-associated chronic IDA include impaired physical and cognitive developments in children and raised perinatal maternal/infant mortalities in pregnant women [5].

Helminth key molecules comprise those present at the parasite external surface and the excretory/secretory (ES) products [6]. The ES products are a mixture of proteins, lipids and carbohydrates that are secreted from the parasite oral orifice or outer surfaces and represent the main boundary between the helminth parasites and their hosts [7]. Hookworm ES products contain a wide range of structurally and functionally distinct molecules, mostly proteins. These molecules react with host proteins and act major functions in parasite survival and development and host-parasite relationships. Notably, these molecules are crucial for the penetration of the host, tissue migration, nourishment, reproduction, and evasion of host immunity [7]. These molecules help the parasite to survive and evade the host immunological response by inhibiting the inflammatory reaction, encouraging effector cells apoptosis, and skewing the immune response phenotype [8]. Many hookworm ES products have proven as effective hookworm vaccine candidates [9] and therapeutic targets against inflammatory and allergic diseases [10].

Because of their importance in hookworm disease pathogenesis and control, hookworm ES products have been a target for intensive study for over two decades. Molecular cloning and characterization of hookworm ES proteins began with the work of Moyle et al. [11], who isolated integrin-blocking protein called neutrophil inhibitory factor (NIF) from the canine hookworm, Ancylostoma caninum. Progress in molecular biology since then has promoted the identification of several novel molecules from hookworm ES products. However, the function of many ES molecules is still unknown. Nearly two decades ago, Loukas and Prociv [8] reviewed hookworm molecules with an immunological impact. Then, Brooker et al. [5] provided a comprehensive list of hookworm molecules but with a brief description. Later, Pearson et al. [7] discussed the role of some ES proteins in the disease molecular mechanism. Molecular biological techniques have advanced over this period and thus have identified many new molecules. This review aims to summarize our knowledge about hookworm ES products, including their functions in host-parasite interactions and as a therapeutic target, and to identify research gaps and future research directions in this field.

Ancylostoma-secretory proteins

Ancylostoma-secreted proteins (ASPs) belong to a large family of cysteine-rich secretory proteins (CRISPS), called SCP/TAPS (SCP/Tpx-1/Ag5/PR-1/Sc7), which is recognized by the Pfam domain. The SCP/TAPS family includes mammalian sperm-coating glycoprotein, glioma-pathogenesis associated protein, lizard venom ryanodine-receptors blocker, hymenopteran venom antigen 5/3 family, plant pathogenesis-related proteins, and hyphae fungal proteins [12,13,14]. Multiple ASPs are secreted from both hookworm adults and infectious larvae (L3), as shown in Table 1 and Fig. 1. ASPs harbor a single or double SCP-like extracellular domain. Two ASPs, the double-domain Ac-ASP-1 and the single-domain Ac-ASP-2, were secreted from A. caninum L3 stimulated by host-specific signals in the early infection [15, 16]. Ac-ASP-1 was the most predominant protein released from the activated L3. The biological functions of larval ASPs are still unclear. However, the fast release of Ac-ASP-1 during host invasion and its partial similarity to insect venom allergens inferred its significance in hookworm pathobiology and immunobiology [15]. Additionally, Ac-asp-2 gene abundance among nematodes and its product release by host-specific signals show its importance in nematode development and physiology and probably in the infection process [16]. Several ASP family members were upregulated in serum-stimulated infectious larvae (ssL3) compared with the free-living one [17, 18]. Therefore, ASPs might be related to the early phase of hookworm transition to parasitism [18] and complementarily regulated upon stimulation by host serum [17].

Table 1 List of hookworm excretory/secretory products with an importance in host-parasite interactions
Fig. 1

The role of hookworm excretory-secretory (ES) products in parasite biology and host-parasite interactions. Hookworm ES products are classified into molecules secreted from infective larvae (L3) (red boxes) and molecules secreted from adult worms (blue boxes)

Ac-ASP-1 and Ac-ASP-2 homologs were also isolated from the L3 stage of A. ceylanicum [19] and N. americanus [20]. The crystal structure of Na-ASP-2 revealed structural similarities to CC-chemokines, implying that Na-ASP-2 might imitate chemokines function during tissue invasion [21]. A further study recorded that Na-ASP-2 caused remarkable neutrophil recruitment [22]. Tribolet et al. [23] suggested that Na-ASP-2-induced neutrophil recruitment might help to suppress the host immunity against the parasite through two different but convergent ways because neutrophils are not only essential effector cells in acute infections but also can hinder B cell and T cell responses. Neutrophils can compete with antigen-presenting cells for antigen [24] and indirectly control T cell-dendritic cell interactions [25]. Moreover, Na-ASP-2 lowered the expression of genes involved in the B cell receptor signaling pathway by reacting with the cluster of differentiation CD79A on human B lymphocytes [23]. Na-ASP-2 antibodies in endemic areas were accompanied by lowering the risk of heavy necatoriasis. Recombinant ASP-2 raised antisera were potent in vitro inhibitors to L3 migration through tissue [26]. As a result of Na-ASP-2 protective and immunogenic characters, several studies have evaluated it as a human hookworm vaccine target [26,27,28]. However, this vaccine failed during the clinical trial due to its allergic potential [29].

In addition to ASPs secreted from hookworm larvae, adult A. caninum released four ASPs [30]. Meanwhile, the proteomic analysis of A. caninum ES products demonstrated that worms release over 30 distinct ASPs [31]. Ac-ASP-3, Ac-ASP-4, Ac-ASP-5 and Ac-ASP-6 showed distinct localization in pharyngeal and esophageal glands, cuticle, intestinal microvilli, and excretory and cephalic glands, respectively [30]. Three unique ASPs cDNAs (Ace-ASP-3-5) were cloned from A. ceylanicum by RACE-PCR technique. Ace-asp-3 and Ace-asp-5 transcription levels in serum-stimulated L3 larvae were lower than that in adult worms. Conversely, Ace-asp-4 was upregulated in ssL3 stages versus adult parasites [32]. Additional studies are required to express these genes as recombinant proteins and to test them as a possible vaccine and pharmaceutical target. Although the adult worm ASPs functions remain unknown, the release of multiple members and their abundance in adult hookworm ES products [33, 34] and intestinal transcriptomes [35, 36] imply their importance in host-parasite relationships. Furthermore, Ancylostoma species ASPs expression levels in males were higher than that in females [37], indicating that these proteins might play a role in male reproduction.


As soon as the adult hookworm attaches to the intestinal mucosa, it lacerates mucosal blood vessels and sucks blood into its buccal capsule [38, 39]. To date, several structurally related hookworm antithrombotic compounds (Table 1, Fig. 1), including anticoagulants and hookworm platelet inhibitors, have been isolated from A. caninum and A. ceylanicum [40,41,42,43,44,45,46,47,48]. Other potentially related antithrombotic activities have also been identified in secretory products of adult N. americanus [49], but the cDNAs encoding these antithrombotic factors remain to be isolated and characterized. Together, the anticoagulants and platelet inhibitors act to maintain the adult worm’s blood-feeding ability. Thus, they might represent a potential vaccine target aiming to inhibit hookworm-related intestinal bleeding and iron deficiency anemia.


Adult hookworms secrete a variety of anticoagulants, termed nematode anticoagulant peptides (NAPs), to allow the ingestion of blood liberated from lacerated capillaries. In A. caninum, three NAPs could inhibit coagulation factor VIIa/tissue factor complex, composed of Ac-APc2 [43], Ac-APc3 and Ac-APc4 [50]. Other NAPs from A. caninum inhibited factor Xa, including Ac-AP5 [41], Ac-AP6 [43] and Ac-AP12 [51], while Ac-NAP10 from A. caninum could inhibit both VIIa/tissue factor complex and Xia factor [52]. Adu-NAP4 from A. duodenale hindered both Xa and Xia factors [53], but Ace-NAP1 isolated from A. ceylanicum inhibited VIIa/tissue factor complex and fXa [48].

Ancylostoma anticoagulants, identified to date, have exhibited distinct mechanisms of action. Recombinant Ac-AP5 (rAc-AP5) specifically inhibited the factor Xa through the interaction between the inhibitor’s P1 reactive site and the coagulation factor [41]. Ac-APc2 hindered the fVIIa/TF complex through a mechanism requiring the assembly of a quaternary complex (Ac-APc2-fVIIa-TF-fXa) for the maximal inhibitory activity [54, 55]. Ac-APc2 also inhibited the prothrombinase complex, probably via the interaction with coagulation factor Xa that does not involve the enzyme’s catalytic site. By contrast, Ace-AP1 differed from Ac-AP5 and Ac-APc2 in its inhibitory activity [46]. This anticoagulant used both active site and non-active site-mediated interactions to inhibit factor Xa [48]. Both Ac-APc3 and Ac-APc4 could inhibit fVIIa/TF only in the presence of fXa as an inhibitory scaffold, similar to that formerly described for Ac-APc2 [50].

Hookworm anticoagulants were immunolocalized to adult worms cephalic, or esophageal glands [45, 50, 51], and anticoagulant transcripts were identified in hookworm intestine cDNA libraries [35]. Thus, NAPs might facilitate blood-feeding by preventing thrombosis at the intestinal attachment site [56, 57] and maintaining the host blood liquid status while passing through the parasite gut [41]. Inhibitors of fVIIa/TF and fXa were localized to distinct structures within adult A. caninum, suggesting its complementary rather than redundant actions [50]. Hookworm anticoagulants represent a target for novel antithrombotic therapy. The anticoagulant NAPc2 from A. caninum decreased the development of deep vein thrombosis [58] and inhibited tumor growth and metastasis in mice [59].

Hookworm platelet inhibitors

A powerful platelet inhibitor family, called hookworm platelet inhibitors (HPI), was isolated from soluble extracts of adult A. caninum [47]. HPI inhibited coagulation by hindering the platelet aggregation and their adherence to fibrinogen and collagen. This inhibitory action occurs via the blockage of the fibrinogen receptor integrin GPIIb/IIIa (αIIbβ3) and the collagen receptor integrin GPIa/IIa (α2β1) [44]. Ac-HPI from A. caninum showed a significant similarity to other ASPs in the amino acid sequence [47] and crystal structure [60]. Despite its native structure, Escherichia coli-expressed recombinant Ac-HPI could not inhibit human platelet adhesion to fibrinogen or collagen. Consequently, Ac-HPI might need post-translational modification or exhibit a different biological role [60]. HPI native protein was detected in A. caninum extracts and ES products, and immunolocalized to the adult worm cephalic glands, indicating its release at the intestinal attachment site [47]. Recently, our group has cloned HPI from A. ceylanicum (Ace-HPI) with a 91% amino acid sequence homology to Ac-HPI. Ace-hpi transcripts were most abundant in adults, followed by ssL3s and L3 stages, with a significant difference. Unlike Ac-HPI, E. colli-expressed recombinant Ace-HPI protein inhibited the platelet aggregation [61], supporting the role of Ace-HPI in hookworm blood-feeding.


A large family of hookworm proteases was highly represented in ES products of A. caninum [31] and N. americanus [34]. These proteases belonged to the three nematode proteases classes (aspartic, cysteine and metalloproteases), presented in Table 1 and Fig. 1. Many hookworm proteases have been contributed to the digestion of free hemoglobin (Hb), thus called hemoglobinases, through a multi-enzyme-synergistic cascade of proteolysis [62]. These hemoglobinases are mostly attached to the adult worm gut and not secreted in ES products. Hence, we do not discuss them in this review.

Aspartic proteases

Cathepsin D-like aspartic proteases from A. caninum (Ac-APR-1) and N. americanus (Na-APR-1) cleaved intact Hb at numerous distinct sites [63, 64]. Several studies have shown that these proteases act functions in the hookworm biology other than blood-feeding. Necator americanus larvae secretion had aspartic protease activity that digested skin macromolecules (fibronectin, collagen, elastin and laminin). Hindering this activity with pepstatin A inhibited larval migration through the skin [65]. Ac-APR-1 and Na-APR-1 mRNAs were expressed in both L3 and adult stages of A. caninum and N. americanus [63]. Later, it had been demonstrated that both proteases can also digest skin macromolecules and serum proteins. Some substrates from permissive definitive hosts were cleaved more easily than those from non-permissive hosts [66]. Williamson et al. [66] linked this difference in substrate preferences to the conformational difference in the S3 pocket residues. Ac-APR-1 and Na-APR-1 raised antisera partially inhibited hookworm L3 migration via hamsters’ skin, indicating these enzymesʼ roles in the invasion of host connective tissue [66]. Us-APR-1 was cloned from hookworm Uncinaria stenocephala using the RACE-PCR method, yielding a 52-kDa protein homologous to APRs from related hookworms. Western blotting using Us-APR-1 raised antisera identified Us-APR-1 protein in the adult U. stenocephala extract and its homologous protease in A. ceylanicum L3 and adult extract and ES products [67]. Us-APR-1 cross-reactivity to its homolog in A. ceylanicum might help to develop a single recombinant-APR vaccine to cross-protect against several canine hookworms [67]. The presence of Us-APR-1 in U. stenocephala ES products has not been tested, but it contains a signal peptide, suggesting that it is a secretory protein. Although genes encoding A. ceylanicum APR-1 predominated in A. ceylanicum intestinal transcriptome [36], more studies are required to clone, express and characterize this enzyme.

A distinct aspartic protease isolated from N. americanus (Na-APR-2) was more related to nematode-specific aspartic proteases (nemepsins) family than to cathepsin D. Na-APR-2 was detected only in the gut lumen and amphidial and excretory glands of adult worms [68], indicating its secretory nature. The ability of recombinant Na-APR-2 to digest Hb and serum proteins from humans was nearly twice its ability to digest that from the nonpermissive host (dog). Na-APR-2 raised antiserum inhibited 50% of N. americanus L3 migration in the skin [68], which stimulates the further investigation of this enzyme as a vaccine candidate.

Cysteine proteases

Hookworm secretions exhibited cysteine proteinase activity that degraded the synthetic cathepsin L-specific substrate (Z-Phe-Arg-AMC) but not the cathepsin B and H substrates (Z-Arg-Arg-AMC and Z-Arg-AMC) [69]. Later, a cathepsin B cysteine protease (Ac-CP-1) was cloned and sequenced from adult A. caninum [70], but no studies identified cathepsin L cysteine protease genes. Ac-CP-1 crystal structure differed from that of human cathepsin B in the substrate binding and specificity; Ac-CP-1 more favorably cleaved Phe-Arg than Arg-Arg. These results explain why the hookworm CPs, although structurally similar to cathepsin B, show a cathepsin L-like activity [71]. Ac-CP-1 was localized in esophageal, cephalic and excretory glands [70], identified in ES products [31], and showed protease activity [70]. Thus, Ac-CP-1 might promote the digestion of intestinal mucosal plug engulfed by the parasite at the attachment site.


Metalloproteases are among the highly represented proteins in ES products of adult hookworms [31]. Hookworm metalloproteases secreted as ES products mainly belong to astacin-like zinc-metalloprotease (MTP) class. The activated Ancylostoma caninum L3 secretes Ac-MTP-1 that aids in the larval tissue migration by hydrolyzing fibronectin, gelatin, laminin and collagen [72, 73]. Ac-MTP-1 was immunolocalized to glands in the esophagus and the channels connecting the esophagus to the cuticle, and its specific antisera inhibited larval migration [72]. These findings support the role of Ac-MTP-1 in the larval migration and the infection process. Additionally, adult hookworm secretes astacin-like zinc metalloproteases, including Ac-MTP-2 from A. caninum and Ace-MTP-2 from A. ceylanicum. Ac-MTP-2 showed a proteolytic activity and was localized to the esophageal glands. Hence, it is suggested to degrade the intestinal plug engulfed in the adult worm buccal capsule [74]. In vitro, Ace-MTP-2 stimulated macrophages to release TNFα and IFNγ [75], indicating its function in host-parasite interactions.

Protease inhibitors

Adult hookworms produce multiple protease inhibitors, which were highly represented in the transcriptome of adult hookworms such as N. americanus [76]. Hookworm protease inhibitors can be classified into Kunitz-type protease inhibitors, trypsin inhibitor-like protein, tissue inhibitor of metalloprotease, and aspartyl protease inhibitors (Table 1, Fig. 1). Some of these protease inhibitors are involved in disease pathogenesis.

Kunitz-type protease inhibitors

Kunitz-type protease inhibitors (KIs) are widely distributed among eukaryotes. These protease inhibitors carry single or multiple cysteine-rich Kunitz domains and display inhibitory activity against one or more serine proteases, including pancreatic trypsin [77]. Adult hookworm ES products showed a KI-similar inhibitory activity, inhibiting pancreatic elastase, trypsin and chymotrypsin [78]. This finding suggests that protease inhibitors are secreted by adult worms at the site of attachment probably to aid in the parasite survival and the hookworm-related anemia pathogenesis by hindering host intestinal proteases [78]. Later, a 7.9-kDa Ace-KI-1, with a single Kunitz domain, was isolated from A. ceylanicum and showed a potent-binding inhibitory action on neutrophil elastase, trypsin, chymotrypsin and pancreatic elastase. This unique, broad-spectrum activity indicates that Ace-KI-1 contributes to both immune modulation and protection against host intestinal proteases [78]. Ace-KI-1 was immunolocalized to the adult hookworm subcuticle, supporting its in vivo role in inhibiting intestinal proteases on worm surfaces [79]. A large multiple domain KI (84.9 kDa) was cloned and expressed from adult A. caninum (Ac-KPI-1). Both Ace-KI-1 and Ac-KPI-1 had a hydrophobic signal peptide and lacked a transmembrane domain in their deduced amino acid sequences, suggesting that these molecules are secreted [80]. Ac-KPI-1 contained 12 Kunitz domains with a high similarity to extracellular matrix proteins contributing to insect cellular remodeling and morphogenesis [81]. However, the exact role of this protein is yet to be identified.

Along with Ace-KI-1 and Ac-KPI-1, cDNA encoding two KPI types, single- (1D) and multiple-domain (12D) KPI were isolated from Ancylostoma species. These KPI comprised Ab-KPI (1D) and Ab-KPI (12D) from A. braziliense, Ace-KPI (1D) from A. ceylanicum and Ac-KPI (1D) from A. caninum. The transcription of both types of KPI was higher in males than in females [37], suggesting the possible role of these molecules in male reproduction. In addition to serine-protease inhibitors’ role in hookworm protection from the host intestinal proteolysis, they have been linked to the hookworm-related malnourishment and growth delay. This hypothesis was supported by immunization studies on Ace-KI-1 [79].

Trypsin inhibitor-like protein

A distinct member of serine protease inhibitors (Adu-TIL-1) was cloned from A. duodenale. Adu-TIL-1 contained two trypsin inhibitor-like (TIL) domains similar to the Ascaris family of serine protease inhibitors. This protease inhibitor was localized to the cuticular surface, esophagus, and intestine of the adult worms [82]. Although Adu-TIL-1 detection in ES products has not been investigated, the detection of a signal peptide in its sequence supports its extracellular secretion by the adult worm. The two TIL domains of Adu-TIL-1 showed varying inhibitory activities against human neutrophil elastase and pancreatic trypsin, suggesting its role in A. duodenale survival [82]. Further studies to characterize this molecule in other hookworms are necessary.

Tissue inhibitor of metalloprotease

Mammals secrete many matrix metalloproteases (MMPs) from immune cells and gut epithelium at the inflammation site. These metalloproteases help in remodeling extracellular matrix and are controlled by tissue inhibitors of metalloproteases (TIMPs). TIMPs are the major proteins secreted by adult hookworms, accounting for 6% of the total ES products [83]. Among them, Ac-TMP-1 (16 kDa) and Ac-TMP-2 (27.7 kDa) were isolated from adult A. caninum ES products [83, 84]. Further evidence suggested that hookworm-secreted TIMPs are involved in the immune-modulation of host immune system, which has been used to treat allergic or auto-immune diseases as major components of helminth therapy. Therefore, Ac-TMP-2 was re-named as Ac-AIP-2 (anti-inflammatory protein) for the treatment of asthma [85]. No MMP-inhibitory action has been recorded for Ac-TMP-1, whereas it hindered an endogenous metalloprotease, Ac-MTP-2 [74]. Ac-TMP-1 stimulated dendritic cells to release inflammatory cytokines and differentiate into suppressor T cells (CD4+ and CD8+) [86], indicating its immunosuppressive role. Ac-TMP-2 was localized to the adult parasite cephalic and esophageal glands [84], enhancing the theory about Ac-TMPs release to function at the attachment site [7]. Recombinant Ac-TMP-2 was highly immunoreactive and inhibited several human MMPs, such as MMP-2, MMP-7 and MMP-13 [84], but its function in host immune regulation remains unclear.

Aspartyl protease inhibitors

Nematodes aspartyl protease inhibitors are highly immunoreactive and have been proposed as potential vaccine targets. A member of the nematode aspartyl protease inhibitors (Aspins) family, named aspartyl protease inhibitor (API-1) was cloned from A. caninum and A. ceylanicum L3. Ac-api-1 mRNA was detected in all life-cycle stages, but the protein was only translated in adult A. caninum ES products. Ac-API-1 was mainly localized in the adult hookworm pseudocoelomic fluid. Soluble, yeast-expressed Ac-API-1 could not inhibit a hookworm aspartyl protease or pepsin but inhibited nearly 30% of the proteolytic activity in adult ES products. These data suggest that Ac-API-1 hinders an unknown, putative aspartyl protease from adult hookworms or may be secreted as an enzyme-inhibitor complex [87]. Thus, the substrate of this molecule needs to be determined.


The degradation of hemoglobin (Hb) releases iron-carrying heme and hematin, that can be lethal to hookworm through the production of reactive oxygen species (ROS) [88]. ROS are also released from host immune effector cells in their response to hookworm infection [89]. Therefore, hookworm secretes multiple antioxidant compounds, which might protect the worm exposed cuticular surfaces through neutralization of ROS generated from Hb digestion and host immune cells.

Glutathione S-transferases

Glutathione S-transferases (GSTs) have been suggested to detoxify the iron-carrying heme and hematin by creating homodimers to chelate these compounds. GSTs (Na-GST-1, Na-GST-2 and Na-GST-3), with a high heme-binding affinity, were isolated from N. americanus extracts and ES products [90]. Crystallography of N. americanus GSTs showed that these molecules can homodimerize in solution to produce large heme-binding cavities [91]. Goud et al. [92] expressed Na-GST-1 in the yeast Pichia pastoris and purified it by three chromatography phases, producing a 23.7-kDa protein with a 51% yield and a 98% purity. Furthermore, a 24 kDa Ac-GST-1 was cloned from adult A. caninum [93], and its homologous enzyme has been isolated from A. ceylanicum [94]. Ac-gst-1 mRNA was detectable in all developmental stages, but its protein was only detectable in adult worm extracts and ES products [93]. These results indicate that this mRNA might be transcribed but not expressed or expressed at undetectable levels in non-blood feeding phases. Ac-GST-1 was shown to localize to the hookworm hypodermis and muscles and mildly to the intestine. The recombinant enzyme showed a high-affinity hematin binding site [93]. GSTs proposed function in heme detoxification triggered several studies to evaluate them as vaccine antigens [28, 90, 93, 95].

Superoxide dismutases

Parasites also produce antioxidant enzymes called superoxide dismutases (SODs), which catalyze the conversion of superoxide anions into hydrogen peroxide and molecular oxygen. The toxic hydrogen peroxide can be removed by several enzymes, including peroxidase, glutathione peroxidase and catalase, which were detected in adult A. ceylanicum extracts [96]. Complementary DNAs encoding SODs have been cloned from multiple parasitic nematodes, such as Onchocerca volvulus [97], Haemonchus contortus [98], Brugia [99] and Toxocara canis [100]. Activated leukocytes release ROS, including superoxide anion, as a part of their antiparasitic activity. Thus, it has been proposed that SOD is expressed by parasitic helminths as an enzymatic defense against ROS immune-effector mechanisms [101, 102]. Nitric oxide interacts with superoxide anions to produce the hydroxyl radical. Therefore, parasite SOD might act as a defensive link between host nitric oxide and ROS-dependent attack because it might reduce host nitric oxide-dependent hydroxyl radical production by mopping up host-derived superoxide anions [103]. Cu/Zn SOD activity was detected in N. americanus ES products [104] and adult A. ceylanicum extract [96]. However, further research is necessary to clone the cDNAs encoding these proteins from hookworms and to elucidate their biological functions.


Peroxiredoxins (PRXs), also called peroxidoxin or thiol-specific antioxidants, are antioxidants conserved in prokaryotes and eukaryotes. Hookworms secrete peroxiredoxins, a family of peroxidases important for protection against ROS. Parasite PRXs can also act as signaling molecules and chaperones [90]. A peroxiredoxin (Ace-PRX-1) was cloned from A. ceylanicum (Table 1, Fig. 1). Ace-prx-1 transcript was more abundant in adults than in eggs and larvae, and its protein was only detected in adult worm extracts and ES products [90]. Thus, Ace-prx-1 mRNA might be translated only in the blood-feeding stages, the only exposed stages to oxidation by heme. Parasite PRXs can detoxify extremely reactive oxygen species, such as hydroxyl radicals and hydrogen peroxide, and reactive nitrogen species [105], suggesting that hookworm PRXs defensive role is complementary to SOD protective role by detoxifying SOD produced hydrogen peroxide. Although PRXs secreted from other helminths (Schistosoma mansoni and Fasciola hepatica) were suggested to stimulate macrophage activation and Th2 helper cell differentiation [106], the immunomodulatory role of secreted Ace-PRX-1 remains to be explored.


Adult hookworms secrete many molecules with a potential immunomodulatory function, such as neutrophil inhibitory factor, macrophage migration inhibitory factor and calreticulin (Table 1, Fig. 1). These molecules might inhibit the inflammatory reaction, promote effector cells apoptosis and skew the immune response phenotype; as a result, they can help the parasite survival inside the host [8]. Recently, hookworm ES products have been evaluated as a therapeutic target. These products contain immunoregulatory properties, which can suppress inflammatory diseases such as inflammatory bowel diseases, colitis, asthma and other allergic diseases (reviewed by Navarro et al. [10]).

Neutrophil inhibitory factor

Neutrophil inhibitory factor (NIF) is a novel, 41 kDa cysteine-rich glycoprotein, with no significant sequence similarity to any previously identified protein, was isolated from adult A. caninum [11]. It might be used by the hookworm to minimize the local inflammation so that the parasite is protected from the host immune response. Hookworm NIF is a specific β2-integrin CR3 antagonist, which bound neutrophils through the CD1lb A-domain, preventing them from recognizing CR3 ligands and mediating phagocytosis [107]. Also, Ac-NIF could inhibit CD11b/CD18-dependent neutrophil function by preventing the activated neutrophils from adhering to vascular endothelium and releasing H2O2 [11]. Further studies showed that recombinant Ac-NIF (rAc-NIF) could block the adherence of neutrophils to fibrinogen by binding the neutrophil I domain of CD11b/CD18 [108]. Additionally, NIF hindered the aggregation of phorbol ester-activated JY lymphoblastoid cells, only expressed in the active CD11a. Thus, NIF antiadhesive action might be caused by inhibition of both CD11a and CD11b β2 integrins on neutrophils [109]. Although divergent homologs of NIF were identified as expressed sequence tags (ESTs) from adult N. americanus [110], their roles have not been explored yet.

Ac-NIF has been studied as a possible therapeutic agent. The Ac-NIF expression caused β-Integrin blockage, which prevented neutrophil activation, migration and sequestration, and subsequently prevented tissue inflammation and lung injury in mice [111]. A combination of rAc-NIF and anti-CD11a/CD18 monoclonal antibody significantly reduced neutrophil accumulation and moderately decreased dermal edema in rats with a reverse passive Arthus reaction [112]. In a rodent focal cerebral ischemia model, rAc-NIF administration for 48 h had a significant neuroprotective action [113]. This action was caused by lowering neutrophil number within the tissue, suggesting rAc-NIF potential therapeutic properties in stroke [113]. Additionally, Ac-NIF selectively inhibited the trans-endothelial migration of eosinophils in vitro and air passages eosinophilia in OVA-induced lung allergic reaction [114].

Macrophage migration inhibitory factor

Macrophage migration inhibitory factor (MIF) is a pro-inflammatory cytokine originally detected as an activated T cell product and then revealed to exert various biological functions [115]. Mammalian MIF inhibits macrophages’ random migration and can counteract anti-inflammatory and immunosuppressive effects of glucocorticoids [116]. MIF stimulates cytokines release from macrophages, T cell proliferation, and the secretion of nitric oxide, matrix metalloproteases, cyclooxygenase 2 and prostaglandin E2 [117,118,119]. An ortholog of the human MIF was isolated from A. ceylanicum (Ace-MIF). Ace-MIF could antagonize the mammalian MIF for attaching to its cell surface receptor CD74. Consequently, Ace-MIF is assumed to modulate the host immune responses against skin-penetrating larvae and adult worm attached to the small intestine. Immunoblotting detected the native Ace-MIF in L3 and adult worm extracts and ES products, the parasitic stages that must challenge host immunity [120]. These data provide a probable tool for reducing hookworm survival and disease pathogenesis through selective inhibition of the hookworm cytokine. However, further research is required to isolate and characterize the homologs of this protein in other hookworm species.


Calreticulin is a highly conserved and multifunctional calcium-binding protein, which is present in all cells of higher creatures, except erythrocytes. Numerous calreticulin-associated functions in parasites were reviewed by Ferreira et al. [121]. These functions include calcium storage, chaperoning, integrin-mediated signaling and cell adhesion, modulating gene expression, as well as inhibiting T cells and natural killer cells perforin pore formation, tumor growth, angiogenesis, and C1q-dependent complement activation [121]. Hookworm calreticulin was originally identified as a key allergen reacting with IgE from N. americanus-infected patients [122]. Later, calreticulin was cloned, expressed, and purified from adult N. americanus extracts. Although calreticulin transcripts were detected in L3, L4 and adult stages, the protein was only detected in adult worm extracts and ES products. Recombinant calreticulin was a specific binding-inhibitor for the hemolytic capacity of human complement C1q [123]. Therefore, calreticulin might play a role in inhibiting the host immune reaction through blocking complement activation. However, further studies are required to isolate and characterize this molecule from Ancylostoma species.

Other ES products

Excretory/secretory proteins

A unique 12.9 kDa major secretory protein, called A. ceylanicum excretory/secretory protein 1 (Ace-ES-1), was purified and cloned from adult A. ceylanicum (Table 1). Ace-ES-1 was more abundant than other proteins in A. ceylanicum ES products, indicating its possible key role in disease pathogenesis. Although Ace-ES-1 was strongly immunogenic and reacted to A. ceylanicum-infected hamster serum [124], its biological role is still unclear. Thereafter, an 11.7 kDa protein (Ace-ES-2) was cloned from adult A. ceylanicum ES products (Table 1). This protein showed a netrin-like fold similarity to that of the TIMP family [125, 126]. Adult worms secreted Ace-ES-2 at the intestinal attachment site soon after infection [125] and before parasites feed on blood [127]. Although Ace-ES-2 had no significant inhibitory effect on MMPs or complement-mediated cell lysis, the highly acidic surface on Ace-ES-2 implies its potential role as a cytokine decoy receptor [126]. Ace-ES-2 was highly immunogenic in infected animals and induced protection when administered as an oral vaccine [125], but whether this molecule has an immunomodulatory function needs to be analyzed.

C-type lectins

Lectins represent a family of related proteins that regulate crucial cell functions via attaching to carbohydrates. One member of this family is C-type lectins (C-TLs), which are recognized by their calcium requirements for the optimal biological activity [128]. This sugar-binding protein family (C-TLs) serves as glycoprotein ligand receptors. C-TLs are located in serum and on endothelial and immune cells (B and T cells) to share in orchestrating the immune system [129]. Proteomic analysis of A. caninum ES products identified lectins, including three C-type lectins, as one of the highly represented proteins [31]. C-TLs transcripts, with a sequence homology to host immune system lectins (CD23 and P-selectin), were identified in adult N. americanus [110, 130]. Additionally, analysis of N. americanus and A. caninum intestinal transcriptomes reported C-type lectins as abundant transcripts [35]. A cDNA encoding a secreted C-TL (Na-CTL-2) was cloned from N. americanus and expressed only in adult worms [131].

C-TLs might inhibit the local inflammatory reaction to hookworm feeding in the intestine by antagonizing host lectins for attaching to inflammatory ligands [8]. Another hypothesis is that C-TLs in hookworms and other hematophagous parasites might have an anticoagulant activity similar to C-TLs in snake venom [8]. Moreover, a male-sex-specific C-type lectin was cloned from A. ceylanicum (Ace-CTL-1) and could bind N-acetyl-d-glucosamine (a constituent of eukaryotic egg cell membranes) in vitro. Ace-CTL-1 was detected in male extracts and sperms and immunolocalized to the testis in males and growing embryos in females [128], suggesting its role in reproduction. Recently, the blockage of CTL receptors on human dendritic cells (DC) has interfered with N. americanus larval exsheathment and DC sequestration around the sheath. These data showed DC-CTL role in the L3 exsheathment and evasion from DCs immune recognition [132]; however, the effect of hookworm-derived C-type lectins on host DC and larval exsheathment is yet to be determined.


All nematodes, either parasitic or free-living, carry cholinergic motor neurons, so they may use acetylcholinesterase (AChE) to lysis acetylcholine [8]. In addition to neuronal AChE, many parasitic nematodes, including hookworms, secrete AChE into the in vitro culture medium [133]. Immunohistochemistry has confirmed that the enzyme is originated from cephalic and esophageal glands of adult hookworms [133, 134]. AChE purified from adult N. americanus ES products showed a specific activity on acetylthiocholine iodide [133] and was homologous to Caenorhabditis elegans AChE class B [135]. Nevertheless, hookworm AChE should be carefully tested against a wider spectrum of substrates compared with free-living nematode AChE [136]. Western blotting demonstrated a significant difference in reaction to AChE-immunized rabbit serum between ES products of N. americanus males and females [133]. This sex difference suggests that AChE might help in, or be modified by, genital tract secretions [136], but this role has not been confirmed yet.

Although AChE release from parasitic nematodes is well accepted, its biological functions are argumentative [133]. Several functions have been anticipated for nematode nonneuronal AChE. This enzyme might play a role in host gut peristalsis inhibition, enteric secretory mechanisms control [137], immunomodulation, cell development, intestinal wound healing, and choline production for biosynthesis [138]. AChE immunogenicity was first confirmed in a volunteer inoculated with four doses of N. americanus L3 over 27 months [139]. AChE-specific antibodies were identified 12 weeks following the second dose, boosted by following infections and dropped after treatment [139], which excluded AChE as a vaccine candidate [136]. Furthermore, AChE activity was identified in A. caninum and A. tubaeforme [140, 141] but at a concentration significantly lower than those in N. americanus [142]. The three hookworm species have a similar impact on host gut peristalsis, indicating that AChE might not inhibit gut motility but might act a yet unidentified function [136]. AChE genes were cloned from the rodent nematode Nippostrongylus brasiliensis [137], while there are no available data about the cloning of AChE from hookworms.

Fatty-acid and retinol-binding proteins

Nematodes, including hookworms, produce two distinct classes of fatty acid- and retinol-binding proteins (FAR, fatty acid- and retinol-binding; and NPA, nematode polyprotein antigen/allergen), as shown in Table 1, Fig. 1. These proteins might help the uptake, transfer, and metabolism of sterols, fatty acids and retinol in the parasites. FAR mRNAs were highly presented in hookworm intestinal transcriptomes [35]. Ac-FAR-1 and Ac-FAR-2 cDNAs were first cloned from a cDNA expression library using A. caninum ES products-immunized rabbit serum [143]. Then, Ace-FAR-1 and Na-FAR-1 cDNAs were isolated from adult A. ceylanicum [144] and N. americanus, respectively [145]. Ac-FAR-1 protein was only detectable in adult worm extracts and ES products [143]. Ace-far-1 mRNA was most abundant in eggs, while the protein was expressed in both sexes, only detectable in female ES products and localized in the hypodermis, ovaries, uterus, and testis. These data show that Ace-FAR-1 might help fatty acid uptake for cuticle integrity, egg generation, and embryo development [144]. On the contrary, Na-FAR-1 was localized in the male copulatory bursa and the adult worm intestine, indicating their roles in male reproduction and nutrient uptake [146]. FAR might promote the parasite infectivity and lower the intestinal mucosal IgA levels through decreasing the retinol amount required for repairing the intestinal injuries and upregulating Th2 cytokine response, respectively [143]. To identify the exact function of the hookworm FARs, further studies are required to determine what FARs bind.

A partial cDNA was cloned from the four subunits of a putative A. ceylanicum NPA (Ace-NPA). Ace-NPA protein was detectable in extracts from all life stages and ES products from both male and female nematodes. Unlike rAce-FAR-1, Ace-NPA protein extracts from L3 and adult extract were more immunoreactive than that from eggs [147]. Ace-NPA were localized to the cuticle, hypodermis and the male testis but not in the female, proposing its role in obtaining fatty acids required for the cuticle integrity and male reproduction. A single recombinant Ace-NPA subunit (rAce-NPAb) bound fatty acids with C12-C22 chain [147] but with affinity different from that of rAce-FAR-1 [144]. This difference in Ace-NPA expression, localization, and binding affinity from that of Ace-FAR-1 indicates a distinct function for both proteins in hookworm biology [147]. However, the functional difference between Ace-NPA and Ace-FAR has not been fully understood yet.

Targets for vaccine and therapy

Strategies are frequently implemented to control hookworm infection in humans and animals due to the high morbidity caused by this infection [148]. In endemic areas, hookworm control depends on the regular treatment with benzimidazole anthelmintic drugs [149]. Unfortunately, anthelmintic drugs currently fail to control hookworm infection due to rapid re-infection and emerging benzimidazole resistance [32]. These facts have focused the attention on establishing an efficient vaccine using several hookworm ES products (Table 2).

Table 2 Summary of vaccine trials using hookworm excretory/secretory products

The early developed irradiated hookworm larval vaccine was removed from markets due to non-sterile immunity and difficult wide-scale production and distribution [8]. Hence, hookworm larval secretions, including the ASP family, constituted the next focus of interest for developing a hookworm vaccine. Recombinant Ac-ASP-1 (rAc-ASP-1) vaccine reduced hookworm burdens in mice lungs and muscles, suggesting that this vaccine produced antibodies that inhibit larval migration [150]. This study was the first to shed light on this family of proteins as vaccine targets. Following that, cross-species protection against A. caninum L3 challenge was induced using rASP-1 from the human hookworms, A. duodenale and N. americanus. This cross-protection was proportionally correlated to the sequence homology percentage between the vaccine ASP and the challenge larvae Ac-ASP-1 [151]. Conversely, Ac-ASP-2, with a 55% amino acid sequence homology to Ac-ASP-1, did not induce protection [151]. Hamsters vaccinated with recombinant Ace-ASP-2 (Ay-ASP-2) from A. ceylanicum showed significant decreases in worm burdens and the length of recovered worms was decreased [19]. Some studies have also investigated ASP from N. americanus (Na-ASP-2) as a lead vaccine candidate. In Sprague Dawley rat, vaccination with Na-ASP-2 formulated with aluminum hydroxide adjuvant (Alhydrogel) resulted in a strong and durable antibody response [152]. Moreover, the air pouch of vaccinated rats demonstrated increased levels of antigen-presenting cells and cytokines (IL-4, IL-10, IFN-γ and IL-5). Hence, this vaccine might neutralize the parasite at the inoculation site, preventing its migration into the host tissue [27]. In golden hamsters, Na-ASP-2/Alhydrogel vaccine lowered worm burdens [28]. Similarly, dog vaccination with rNa-ASP-2/Glaxo SmithKline adjuvant significantly decreased worm burdens and fecal egg counts through the release of antibodies, which inhibited larval migration [26]. It has been found that the anti-Na-ASP-2 IgE level in an endemic population was correlated with low hookworm burdens, indicating the protective association between increasing anti-ASP-2 IgE levels and the risk of heavy hookworm infection [26]. A phase 1a vaccine trial in hookworm-non-exposed adults from the USA showed that Na-ASP-2 vaccine was well-tolerated and induced a prolonged immune response [153]. By contrast, a phase 1b trial in hookworm-exposed individuals in Brazil was stopped due to the generalized urticaria developed in several volunteers harboring pre-formed Na-ASP-2-specific IgE [29]. Despite its safety alarms, Na-ASP-2 remains as an interesting vaccine candidate, especially if it is genetically modified to decrease its allergenicity or utilized as a pediatric vaccine before anti-hookworm IgE development [154].

Along with ASP-1 and ASP-2, the effect of immunization with another larval antigen Ac-MTP-1 was studied. Dogs vaccinated with rAc-MTP-1 developed pre-challenge Ac-MTP-1-specific IgG2 and IgE antibody response. After the L3 challenge, hookworm burdens and egg counts were inversely correlated to anti-Ac-MTP-1 IgG2 antibody titers, with a statistical significance, proposing that this protein provides a hopeful vaccine candidate [155].

Recently, recombinant vaccines targeting adult hookworm proteases have shown a high efficacy. A recombinant A. caninum aspartic protease (rAc-APR-1) induced significant protection in dogs, with reducing anemia, hookworm burdens, and egg counts [156]. Interestingly, rAc-APR-1 vaccine in dogs decreased adult hookworm number obtained from the small intestine and increased the worm burden from the large intestine, an unusual hookworm habitat. This change in the habitat preference proposes that Ac-APR-1-induced antibodies hindered the blood-feeding in the small intestine and thus forced worms to migrate into a more favorable habitat [157]. Worm burdens significantly dropped in Ac-APR-vaccinated hamsters challenged with a different hookworm species (N. americanus) L3 [28], suggesting that Ac-APR-1 might cross-protect against its orthologs from other hookworm species. The enzymatically inactive mutant Na-APR-1 partly protected dogs against A. caninum challenge, especially from blood loss, with significantly declined weight loss and egg counts [158]. These results were explained by the mutant Na-APR-1 ability to trigger neutralizing antibodies to both the native enzyme (Na-APR-1) and APR-1 orthologs from the other three human hookworm species [158]. Na-APR-1 (M74) administered to mice as low as 0.99 μg could trigger specific antibodies (IgG), which inhibited 89% of the native protease enzymatic activity, supporting this mutant protein as a vaccine candidate [159]. Additionally, serum from a rabbit vaccinated with U. stenocephala aspartic protease (Us-APR-1) showed cross-reactivity with an aspartic protease from a heterologous dog hookworm species, A. ceylanicum (Ace-APR-1) [67]. However, the possible APR-1 cross-protection between A. ceylanicum and U. stenocephala is still to be examined.

Hookworm GSTs are essential for parasite survival and offer promising targets for vaccine establishment. Recombinant Ac-GST-1 was highly immunogenic and could induce not only Th2-associated antibody (IgG1) and cytokine (IL-4) responses but also a strong Th1-like response indicated by the production of IFN-γ and IgG2 antibody response, suggesting Ac-GST-1 as a possible drug and vaccine target against hookworm infection [93]. Dogs vaccinated with Ac-GST-1 showed reduced worm burdens (39.4%) and egg counts (32.3%) but without statistical significance [93]. Additionally, hamsters immunized with Ac-GST-1 revealed significant worm reduction (50.6% and 53.7%) following the challenge with N. americanus larvae [28, 93]. In hamsters, rNa-GST-1 induced 32% and 39% drops in worm burdens [90]. Moreover, rNa-GST-1/Alhydrogel vaccine produced significant antigen-specific IgG responses, which were safe and well tolerated in both hookworm-naïve and exposed adults, stimulating this vaccine progress into children’s clinical trials [95]. The Na-GST-1/Alhydrogel vaccine has been proposed to act through the induction of IgG antibodies, that could be ingested by the hookworms developing inside the host intestine to block the detoxifying action of parasite Na-GST-1, thus allowing free heme to accumulate and damage the worm [95]. Recently, Brelsford et al. [160] have tested Na-GST-1/Alhydrogel vaccine immunogenicity and relative potency during storage. Although a 90% blockage of Na-GST-1 catalytic activity has been attained in animals vaccinated with stored Na-GST-1, a lower blockage percentage has been detected in immunized humans. Additionally, anti-Na-GST-1 antibodies obtained from volunteers from a hookworm non-endemic area exhibited more potent catalytic activity inhibition than those from volunteers from a hookworm-endemic area [160].

Some individual hookworm molecules with a possible role as immunomodulators were evaluated as vaccine candidates, such as Ace-KI and calreticulin. Recombinant Ace-KI-1 partially protected hamsters against the growth delay, with no detectable effect on anemia. These findings suggest that Ace-KI might contribute to hookworm-related malnourishment and growth delay pathogenesis by causing intestinal malabsorption [79]. Mice injected intraperitoneally with free calreticulin showed a 43–49% decrease in worm burdens in the lungs, with low serum IgE levels and intermediate levels of lung eosinophilia. However, calreticulin encapsulated in poly-lactide-coglycolide microparticles induced anti-calreticulin IgG1 and IgE levels and lung eosinophilia higher than that induced by free calreticulin but without protective immunity. These results indicate that calreticulin-protective immunity depends on an unknown mechanism other than the classical Th2 reaction, and alternative adjuvants should be explored [161].

Other ES products have been evaluated as vaccine candidates. Oral vaccination with Ace-ES-2 decreased anemia and improved the recovery rate in hamsters, implying that the parasite was neutralized by an anti-Ace-ES-2 immune reaction [125]. The oral Ace-FAR-1 vaccine significantly decreased the worm burden in hamsters, showing its possible function in hookworm biology and as a valuable vaccine target [144].

Some studies have suggested that combining multiple antigens may provide an effective vaccine development strategy to improve protection and/or disease symptoms in the host. Ace-ASP-2 and Ace-MTP-1 cocktail vaccine decreased worm burdens and egg counts and significantly enhanced Hb levels and body weight in hamsters compared with the single-antigen vaccine [162]. Currently, a divalent human hookworm vaccine consisted of Na-GST-1 and Na-APR-1 (M74) is under establishment by the Sabin Vaccine Institute Product Development Partnership. Both single antigen vaccines are in Phase 1 trials [163].


Advances in molecular biology over the last 25 years resulted in the identification of numerous hookworm ES products, with diverse structures and functions. Many ES molecules help in host invasion, tissue migration, blood-feeding, nutrient acquisition, reproduction, embryo-development, host defense and immune modulation. Several hookworm ES products have been studied as potential vaccine and drug targets. Despite the tremendous progress in the study of hookworm ES products in recent decades, many key issues need to be further addressed. For example, the role of many molecules is still unclear, such as ASPs, Ace-ES-1, Ace-ES-2, Ac-KPI-1 and AChE. The substrate of Ac-API-1 needs to be determined. No studies have examined hookworm C-type lectin effects on host lectins and DC, larval exsheathment, and blood clotting. Similarly, the role of hookworm peroxiredoxins in immunomodulation remains to be analyzed. There are no available data about the cloning of SODs and AChE from hookworms. In addition, cDNA encoding calreticulin and C-TLs have not been cloned from Ancylostoma species. Proteomic analysis of ES products from adult A. caninum and N. americanus were previously conducted. However, proteomic analysis of ES products from other hookworm species and different life stages would uncover new molecules important in hookworm pathogenesis and vaccine development. Moreover, some molecules, with host defense and immunomodulatory roles, have not been tested as vaccine candidates, including TIMPs, MIF, NIF, SODs and PRXs. Targeting of molecules involved in blood-feeding, such as NAP and HPI, as vaccine candidates might prevent hookworm anemia. Although some hookworm ES products showed its efficacy as anti-inflammatory and antithrombotic agents, the hookworm protein therapy is yet to be fully explored.

Availability of data and materials

All data generated or analyzed during this study are included in the article.





iron deficiency anemia


Ancylostoma secretory protein


serum-stimulated infectious larvae


nematode anticoagulant peptide


hookworm platelet inhibitor


aspartic protease


cysteine protease


astacin-like zinc metalloprotease


Kunitz-type protease inhibitor


trypsin inhibitor-like protein


aspartyl protease inhibitor


tissue inhibitor of metalloprotease


matrix metalloprotease


glutathione S-transferase


superoxide dismutase




neutrophil inhibitory factor


macrophage migration inhibitory factor


C-type lectin




fatty acid- and retinol-binding protein


nematode polyprotein antigen/allergen


  1. 1.

    Pullan RL, Smith JL, Jasrasaria R, Brooker SJ. Global numbers of infection and disease burden of soil transmitted helminth infections in 2010. Parasit Vectors. 2014;7:37.

    PubMed  PubMed Central  Article  Google Scholar 

  2. 2.

    Jourdan PM, Lamberton PH, Fenwick A, Addiss DG. Soil-transmitted helminth infections. Lancet. 2018;391:252–65.

    PubMed  Article  Google Scholar 

  3. 3.

    Traub RJ. Ancylostoma ceylanicum, a re-emerging but neglected parasitic zoonosis. Int J Parasitol. 2013;43:1009–15.

    PubMed  Article  Google Scholar 

  4. 4.

    George S, Levecke B, Kattula D, Velusamy V, Roy S, Geldhof P, et al. Molecular identification of hookworm isolates in humans, dogs and soil in a Tribal area in Tamil Nadu, India. PLoS Negl Trop Dis. 2016;10:e0004891.

    PubMed  PubMed Central  Article  CAS  Google Scholar 

  5. 5.

    Brooker S, Bethony J, Hotez PJ. Human hookworm infection in the 21st century. Adv Parasitol. 2004;58:197–288.

    PubMed  PubMed Central  Article  Google Scholar 

  6. 6.

    Hewitson JP, Grainger JR, Maizels RM. Helminth immunoregulation: the role of parasite secreted proteins in modulating host immunity. Mol Biochem Parasitol. 2009;167:1–11.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  7. 7.

    Pearson MS, Tribolet L, Cantacessi C, Periago MV, Valero MA, Jariwala AR, et al. Molecular mechanisms of hookworm disease: stealth, virulence, and vaccines. J Allergy Clin Immunol. 2012;130:13–21.

    CAS  PubMed  Article  Google Scholar 

  8. 8.

    Loukas A, Prociv P. Immune responses in hookworm infections. Clin Microbiol Rev. 2001;14:689–703.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  9. 9.

    Chen C-C, Louie S, McCormick BA, Walker WA, Shi HN. Helminth-primed dendritic cells alter the host response to enteric bacterial infection. J Immunol. 2006;176:472–83.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  10. 10.

    Navarro S, Ferreira I, Loukas A. The hookworm pharmacopoeia for inflammatory diseases. Int J Parasitol. 2013;43:225–31.

    CAS  PubMed  Article  Google Scholar 

  11. 11.

    Moyle M, Foster DL, McGrath DE, Brown SM, Laroche Y, De Meutter J, et al. A hookworm glycoprotein that inhibits neutrophil function is a ligand of the integrin CD11b/CD18. J Biol Chem. 1994;269:10008–15.

    CAS  PubMed  Google Scholar 

  12. 12.

    Van Loon LC, Van Strien EA. The families of pathogenesis-related proteins, their activities, and comparative analysis of PR-1 type proteins. Physiol Mol Plant Pathol. 1999;55:85–97.

    Article  Google Scholar 

  13. 13.

    Kovalick GE, Griffin DL. Characterization of the SCP/TAPS gene family in Drosophila melanogaster. Insect Biochem Mol Biol. 2005;35:825–35.

    CAS  PubMed  Article  Google Scholar 

  14. 14.

    Yamazaki Y, Hyodo F, Morita T. Wide distribution of cysteine-rich secretory proteins in snake venoms: isolation and cloning of novel snake venom cysteine-rich secretory proteins. Arch Biochem Biophys. 2003;412:133–41.

    CAS  PubMed  Article  Google Scholar 

  15. 15.

    Hawdon JM, Jones BF, Hoffman DR, Hotez PJ. Cloning and characterization of Ancylostoma-secreted protein. A novel protein associated with the transition to parasitism by infective hookworm larvae. J Biol Chem. 1996;271:6672–8.

    CAS  PubMed  Article  Google Scholar 

  16. 16.

    Hawdon JM, Narasimhan S, Hotez PJ. Ancylostoma secreted protein 2: cloning and characterization of a second member of a family of nematode secreted proteins from Ancylostoma caninum. Mol Biochem Parasitol. 1999;99:149–65.

    CAS  PubMed  Article  Google Scholar 

  17. 17.

    Moser JM, Freitas T, Arasu P, Gibson G. Gene expression profiles associated with the transition to parasitism in Ancylostoma caninum larvae. Mol Biochem Parasitol. 2005;143:39–48.

    CAS  PubMed  Article  Google Scholar 

  18. 18.

    Datu BJD, Gasser RB, Nagaraj SH, Ong EK, OʼDonoghue P, McInnes R, et al. Transcriptional changes in the hookworm, Ancylostoma caninum, during the transition from a free-living to a parasitic larva. PLoS Negl Trop Dis. 2008;2:e130.

    PubMed  PubMed Central  Article  CAS  Google Scholar 

  19. 19.

    Goud GN, Zhan B, Ghosh K, Loukas A, Hawdon J, Dobardzic A, et al. Cloning, yeast expression, isolation, and vaccine testing of recombinant Ancylostoma-secreted protein (ASP)-1 and ASP-2 from Ancylostoma ceylanicum. J Infect Dis. 2004;189:919–29.

    CAS  PubMed  Article  Google Scholar 

  20. 20.

    Goud GN, Bottazzi ME, Zhan B, Mendez S, Deumic V, Plieskatt J, et al. Expression of the Necator americanus hookworm larval antigen Na-ASP-2 in Pichia pastoris and purification of the recombinant protein for use in human clinical trials. Vaccine. 2005;23:4754–64.

    CAS  PubMed  Article  Google Scholar 

  21. 21.

    Asojo OA, Goud G, Dhar K, Loukas A, Zhan B, Deumic V, et al. X-ray structure of Na-ASP-2, a pathogenesis-related-1 protein from the nematode parasite, Necator americanus, and a vaccine antigen for human hookworm infection. J Mol Biol. 2005;346:801–14.

    CAS  PubMed  Article  Google Scholar 

  22. 22.

    Bower MA, Constant SL, Mendez S. Necator americanus: the Na-ASP-2 protein secreted by the infective larvae induces neutrophil recruitment in vivo and in vitro. Exp Parasitol. 2008;118:569–75.

    CAS  PubMed  Article  Google Scholar 

  23. 23.

    Tribolet L, Cantacessi C, Pickering DA, Navarro S, Doolan DL, Trieu A. Probing of a human proteome microarray with a recombinant pathogen protein reveals a novel mechanism by which hookworms suppress B-cell receptor signaling. J Infect Dis. 2015;211:416–25.

    CAS  PubMed  Article  Google Scholar 

  24. 24.

    Yang CW, Strong BS, Miller MJ, Unanue ER. Neutrophils influence the level of antigen presentation during the immune response to protein antigens in adjuvants. J Immunol. 2010;185:2927–34.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  25. 25.

    Yang X, Gao X. Role of dendritic cells: a step forward for the hygiene hypothesis. Cell Mol Immunol. 2011;8:12–8.

    PubMed  Article  Google Scholar 

  26. 26.

    Bethony J, Loukas A, Smout M, Brooker S, Mendez S, Plieskatt J, et al. Antibodies against a secreted protein from hookworm larvae reduce the intensity of hookworm infection in humans and vaccinated laboratory animals. FASEB J. 2005;19:1743–5.

    CAS  PubMed  Article  Google Scholar 

  27. 27.

    Mendez S, D’Samuel A, Antoine A, Ahn S, Hotez P. Use of the air pouch model to investigate immune responses to a hookworm vaccine containing the Na-ASP-2 protein in rats. Parasite Immunol. 2008;30:53–6.

    CAS  PubMed  Google Scholar 

  28. 28.

    Xiao S, Zhan B, Xue J, Goud GN, Loukas A, Liu Y, et al. The evaluation of recombinant hookworm antigens as vaccines in hamsters (Mesocricetus auratus) challenged with human hookworm, Necator americanus. Exp Parasitol. 2008;118:32–40.

    CAS  PubMed  Article  Google Scholar 

  29. 29.

    Diemert DJ, Pinto AG, Freire J, Jariwala A, Santiago H, Hamilton RG, et al. Generalized urticaria induced by the Na-ASP-2 hookworm vaccine: implications for the development of vaccines against helminths. J Allergy Clin Immunol. 2012;130:169–76.

    CAS  PubMed  Article  Google Scholar 

  30. 30.

    Zhan B, Liu Y, Badamchian M, Williamson A, Feng J, Loukas A. Molecular characterisation of the Ancylostoma-secreted protein family from the adult stage of Ancylostoma caninum. Int J Parasitol. 2003;33:897–907.

    CAS  PubMed  Article  Google Scholar 

  31. 31.

    Mulvenna J, Hamilton B, Nagaraj SH, Smyth D, Loukas A, Gorman JJ. Proteomics analysis of the excretory/secretory component of the blood-feeding stage of the hookworm, Ancylostoma caninum. Mol Cell Proteomics. 2009;8:109–21.

    CAS  PubMed  Article  Google Scholar 

  32. 32.

    Siwińska A, Bąska P, Daniłowicz-Luebert E, Januszkiewicz K, Długosz E, Wędrychowicz H, et al. Cloning and molecular characterization of cDNAs encoding three Ancylostoma ceylanicum secreted proteins. Acta Parasitol. 2013;58:112–8.

    PubMed  Article  CAS  Google Scholar 

  33. 33.

    Morante T, Shepherd C, Constantinoiu C, Loukas A, Sotillo J. Revisiting the Ancylostoma caninum secretome provides new information on hookworm-host interactions. Proteomics. 2017;17:1700186.

    Article  CAS  Google Scholar 

  34. 34.

    Logan J, Manda SS, Choi YJ, Field M, Eichenberger R, Mulvenna J, et al. Comprehensive analysis of human hookworm secreted proteins using a proteogenomic approach. bioRxiv. 2018.

    Article  Google Scholar 

  35. 35.

    Ranjit N, Jones MK, Stenzel DJ, Gasser RB, Loukas A. A survey of the intestinal transcriptomes of the hookworms, Necator americanus and Ancylostoma caninum, using tissues isolated by laser microdissection microscopy. Int J Parasitol. 2006;36:701–10.

    CAS  PubMed  Article  Google Scholar 

  36. 36.

    Wei J, Damania A, Gao X, Liu Z, Mejia R, Mitreva M, et al. The hookworm Ancylostoma ceylanicum intestinal transcriptome provides a platform for selecting drug and vaccine candidates. Parasit Vectors. 2016;9:518.

    PubMed  PubMed Central  Article  CAS  Google Scholar 

  37. 37.

    Costa AFDV, Gasser RB, Dias SRC, Rabelo ÉML. Male-enriched transcription of genes encoding ASPs and Kunitz-type protease inhibitors in Ancylostoma species. Mol Cell Probes. 2009;23:298–303.

    CAS  PubMed  Article  Google Scholar 

  38. 38.

    Kalkofen UP. Attachment and feeding behavior of Ancylostoma caninum. Z Parasitenkd. 1970;33:339–54.

    CAS  PubMed  Article  Google Scholar 

  39. 39.

    Kalkofen UP. Intestinal trauma resulting from feeding activities of Ancylostoma caninum. Am J Trop Med Hyg. 1974;23:1046–53.

    CAS  PubMed  Article  Google Scholar 

  40. 40.

    Cappello M, Clyne LP, McPhedran P, Hotez PJ. Ancylostoma factor Xa inhibitor: partial purification and its identification as a major hookworm-derived anticoagulant in vitro. J Infect Dis. 1993;167:1474–7.

    CAS  PubMed  Article  Google Scholar 

  41. 41.

    Cappello M, Vlasuk GP, Bergum PW, Huang S, Hotez PJ. Ancylostoma caninum anticoagulant peptide: a hookworm-derived inhibitor of human coagulation factor Xa. Proc Natl Acad Sci USA. 1995;92:6152–6.

    CAS  PubMed  Article  Google Scholar 

  42. 42.

    Cappello M, Hawdon JM, Jones BF, Poindexter Kennedy W, Hotez PJ. Ancylostoma caninum anticoagulant peptide: cloning by PCR and expression of soluble, active protein in E. coli. Mol Biochem Parasitol. 1996;80:113–7.

    CAS  PubMed  Article  Google Scholar 

  43. 43.

    Stassens P, Bergum PW, Gansemans Y, Jespers L, Laroche Y, Huang S, et al. Anticoagulant repertoire of the hookworm Ancylostoma caninum. Proc Natl Acad Sci USA. 1996;93:2149–54.

    CAS  PubMed  Article  Google Scholar 

  44. 44.

    Chadderdon RC, Cappello M. The hookworm platelet inhibitor: functional blockade of integrins GPIIb/IIIa (αIIbβ3) and GPIa/IIa (α2β1) inhibits platelet aggregation and adhesion in vitro. J Infect Dis. 1999;179:1235–41.

    CAS  PubMed  Article  Google Scholar 

  45. 45.

    Harrison LM, Córdova JL, Cappello M. Ancylostoma caninum anticoagulant peptide-5: immunolocalization and in vitro neutralization of a major hookworm anti-thrombotic. Mol Biochem Parasitol. 2001;115:101–7.

    CAS  PubMed  Article  Google Scholar 

  46. 46.

    Harrison LM, Nerlinger A, Bungiro RD, Córdova JL, Kuzmič P, Cappello M. Molecular characterization of Ancylostoma inhibitors of coagulation factor Xa: hookworm anticoagulant activity in vitro predicts parasite blood feeding in vivo. J Biol Chem. 2002;277:6223–9.

    CAS  PubMed  Article  Google Scholar 

  47. 47.

    Del Valle A, Jones BF, Harrison LM, Chadderdon RC, Cappello M. Isolation and molecular cloning of a secreted hookworm platelet inhibitor from adult Ancylostoma caninum. Mol Biochem Parasitol. 2003;129:167–77.

    PubMed  Article  CAS  Google Scholar 

  48. 48.

    Mieszczanek J, Harrison LM, Cappello M. Ancylostoma ceylanicum anticoagulant peptide-1: role of the predicted reactive site amino acid in mediating inhibition of coagulation factors Xa and VIIa. Mol Biochem Parasitol. 2004;137:151–9.

    CAS  PubMed  Article  Google Scholar 

  49. 49.

    Furmidge B, Horn L, Pritchard D. The anti-haemostatic strategies of the human hookworm Necator americanus. Parasitology. 1996;112:81–7.

    PubMed  Article  Google Scholar 

  50. 50.

    Mieszczanek J, Harrison LM, Vlasuk GP, Cappello M. Anticoagulant peptides from Ancylostoma caninum are immunologically distinct and localize to separate structures within the adult hookworm. Mol Biochem Parasitol. 2004;133:319–23.

    CAS  PubMed  Article  Google Scholar 

  51. 51.

    Jiang D, Zhan B, Mayor RS, Gillespie P, Keegan B, Bottazzi ME, et al. Ac-AP-12, a novel factor Xa anticoagulant peptide from the esophageal glands of adult Ancylostoma caninum. Mol Biochem Parasitol. 2011;177:42–8.

    CAS  PubMed  Article  Google Scholar 

  52. 52.

    Li D, He Q, Kang T, Yin H, Jin X, Li H, et al. Identification of an anticoagulant peptide that inhibits both fXIa and fVIIa/tissue factor from the blood-feeding nematode Ancylostoma caninum. Biochem Biophys Res Commun. 2010;392:155–9.

    CAS  PubMed  Article  Google Scholar 

  53. 53.

    Gan W, Deng L, Yang C, He Q, Hu J, Yin H, et al. An anticoagulant peptide from the human hookworm, Ancylostoma duodenale that inhibits coagulation factors Xa and XIa. FEBS Lett. 2009;583:1976–80.

    CAS  PubMed  Article  Google Scholar 

  54. 54.

    Buddai SK, Toulokhonova L, Bergum PW, Vlasuk GP, Krishnaswamy S. Nematode anticoagulant protein c2 reveals a site on factor Xa that is important for macromolecular substrate binding to human prothrombinase. J Biol Chem. 2002;277:26689–98.

    CAS  PubMed  Article  Google Scholar 

  55. 55.

    Bergum PW, Cruikshank A, Maki SL, Kelly CR, Ruf W, Vlasuk GP. Role of zymogen and activated factor X as scaffolds for the inhibition of the blood coagulation factor VIIa-tissue factor complex by recombinant nematode anticoagulant protein c2. J Biol Chem. 2001;276:10063–71.

    CAS  PubMed  Article  Google Scholar 

  56. 56.

    Cappello M, Harrison L, Bungiro R Jr, Chadderdon R, Milstone A, Nerlinger A, et al. Molecular pathogenesis of hookworm anemia: prospects for a disease-based vaccine. J Parasitol. 2003;89:S158–64.

    Google Scholar 

  57. 57.

    Hotez PJ, Ghosh K, Hawdon JM, Narasimhan S, Jones B, Shuhua X, et al. Experimental approaches to the development of a recombinant hookworm vaccine. Immunol Rev. 1999;171:163–71.

    CAS  PubMed  Article  Google Scholar 

  58. 58.

    Lee AY, Vlasuk GP. Recombinant nematode anticoagulant protein c2 and other inhibitors targeting blood coagulation factor VIIa/tissue factor. J Intern Med. 2003;254:313–21.

    CAS  PubMed  Article  Google Scholar 

  59. 59.

    Zhao J, Aguilar G, Palencia S, Newton E, Abo A. rNAPc2 inhibits colorectal cancer in mice through tissue factor. Clin Cancer Res. 2009;15:208–16.

    CAS  PubMed  Article  Google Scholar 

  60. 60.

    Ma D, Francischetti IM, Ribeiro JM, Andersen JF. The structure of hookworm platelet inhibitor (HPI), a CAP superfamily member from Ancylostoma caninum. Acta Crystallogr F Struct Biol Commun. 2015;71:643–9.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  61. 61.

    Huang Y, Abuzeid AMI, Liu Y, He L, Zhao Q, Yan X, et al. Identification and localization of hookworm platelet inhibitor in Ancylostoma ceylanicum. Infect Genet Evol. 2020;77:104102.

    CAS  PubMed  Article  Google Scholar 

  62. 62.

    Williamson AL, Lecchi P, Turk BE, Choe Y, Hotez PJ, McKerrow JH, et al. A multi-enzyme cascade of hemoglobin proteolysis in the intestine of blood-feeding hookworms. J Biol Chem. 2004;279:35950–7.

    CAS  PubMed  Article  Google Scholar 

  63. 63.

    Williamson AL, Brindley PJ, Abbenate G, Prociv P, Berry C, Girdwood K, et al. Cleavage of hemoglobin by hookworm cathepsin D aspartic proteases and its potential contribution to host specificity. FASEB J. 2002;16:1458–60.

    CAS  PubMed  Article  Google Scholar 

  64. 64.

    Harrop SA, Prociv P, Brindley PJ. Acasp, a gene encoding a cathepsin D-like aspartic protease from the hookworm Ancylostoma caninum. Biochem Biophys Res Commun. 1996;227:294–302.

    CAS  PubMed  Article  Google Scholar 

  65. 65.

    Brown A, Girod N, Billett EE, Pritchard DI. Necator americanus (human hookworm) aspartyl proteinases and digestion of skin macromolecules during skin penetration. Am J Trop Med Hyg. 1999;60:840–7.

    CAS  PubMed  Article  Google Scholar 

  66. 66.

    Williamson AL, Brindley PJ, Loukas A. Hookworm cathepsin D aspartic proteases: contributing roles in the host-specific degradation of serum proteins and skin macromolecules. Parasitology. 2003;126:179–85.

    CAS  PubMed  Article  Google Scholar 

  67. 67.

    Wasyl K, Zawistowska-Deniziak A, Bąska P, Wędrychowicz H, Wiśniewski M. Molecular cloning and expression of the cDNA sequence encoding a novel aspartic protease from Uncinaria stenocephala. Exp Parasitol. 2013;134:220–7.

    CAS  PubMed  Article  Google Scholar 

  68. 68.

    Williamson AL, Brindley PJ, Abbenante G, Datu BJ, Prociv P, Berry C. Hookworm aspartic protease, Na-APR-2, cleaves human hemoglobin and serum proteins in a host-specific fashion. J Infect Dis. 2003;187:484–94.

    CAS  PubMed  Article  Google Scholar 

  69. 69.

    Dowd AJ, Dalton JP, Loukas AC, Prociv P, Brindley PJ. Secretion of cysteine proteinase activity by the zoonotic hookworm Ancylostoma caninum. Am J Trop Med Hyg. 1994;51:341–7.

    CAS  PubMed  Article  Google Scholar 

  70. 70.

    Harrop SA, Sawangjaroen N, Prociv P, Brindley PJ. Characterization and localization of cathepsin B proteinases expressed by adult Ancylostoma caninum hookworms. Mol Biochem Parasitol. 1995;71:163–71.

    CAS  PubMed  Article  Google Scholar 

  71. 71.

    Brinkworth RI, Brindley PJ, Harrop SA. Structural analysis of the catalytic site of AcCP-1, a cysteine proteinase secreted by the hookworm Ancylostoma caninum. Biochim Biophys Acta. 1996;1298:4–8.

    PubMed  Article  Google Scholar 

  72. 72.

    Williamson AL, Lustigman S, Oksov Y, Deumic V, Plieskatt J, Mendez S, et al. Ancylostoma caninum MTP-1, an astacin-like metalloprotease secreted by infective hookworm larvae, is involved in tissue migration. Infect Immun. 2006;74:961–7.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  73. 73.

    Zhan B, Hotez PJ, Wang Y, Hawdon JM. A developmentally regulated metalloprotease secreted by host-stimulated Ancylostoma caninum third-stage infective larvae is a member of the astacin family of proteases. Mol Biochem Parasitol. 2002;120:291–6.

    CAS  PubMed  Article  Google Scholar 

  74. 74.

    Feng J, Zhan B, Liu Y, Liu S, Williamson A, Goud G, et al. Molecular cloning and characterization of Ac-MTP-2, an astacin-like metalloprotease released by adult Ancylostoma caninum. Mol Biochem Parasitol. 2007;152:132–8.

    CAS  PubMed  Article  Google Scholar 

  75. 75.

    Baska P, Wisniewski M, Krzyzowska M, Dlugosz E, Zygner W, Gorski P, et al. Molecular cloning and characterisation of in vitro immune response against astacin-like metalloprotease Ace-MTP-2 from Ancylostoma ceylanicum. Exp Parasitol. 2013;133:472–82.

    CAS  PubMed  Article  Google Scholar 

  76. 76.

    Cantacessi C, Mitreva M, Jex AR, Young ND, Campbell BE, Hall RS, et al. Massively parallel sequencing and analysis of the Necator americanus transcriptome. PLoS Negl Trop Dis. 2010;4:e684.

    PubMed  PubMed Central  Article  CAS  Google Scholar 

  77. 77.

    Ascenzi P, Bocedi A, Bolognesi M, Spallarossa A, Coletta M, De Cristofaro R, et al. The bovine basic pancreatic trypsin inhibitor (Kunitz inhibitor): a milestone protein. Curr Protein Pept Sci. 2003;4:231–51.

    CAS  PubMed  Article  Google Scholar 

  78. 78.

    Milstone AM, Harrison LM, Bungiro RD, Kuzmic P, Cappello M. A broad spectrum Kunitz type serine protease inhibitor secreted by the hookworm Ancylostoma ceylanicum. J Biol Chem. 2000;275:29391–9.

    CAS  PubMed  Article  Google Scholar 

  79. 79.

    Chu D, Bungiro RD, Ibanez M, Harrison LM, Campodonico E, Jones BF, et al. Molecular characterization of Ancylostoma ceylanicum Kunitz-type serine protease inhibitor: evidence for a role in hookworm-associated growth delay. Infect Immun. 2004;72:2214–21.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  80. 80.

    Briggs MS, Gierasch LM. Molecular mechanisms of protein secretion: the role of the signal sequence. Adv Protein Chem. 1986;38:109–80.

    CAS  PubMed  Article  Google Scholar 

  81. 81.

    Hawdon JM, Datu B, Crowell M. Molecular cloning of a novel multidomain Kunitz-type proteinase inhibitor from the hookworm Ancylostoma caninum. J Parasitol. 2003;89:402–7.

    CAS  PubMed  Article  Google Scholar 

  82. 82.

    Jin X, Deng L, Li H, Zhang Z, He Q, Yang C, et al. Identification and characterization of a serine protease inhibitor with two trypsin inhibitor-like domains from the human hookworm Ancylostoma duodenale. Parasitol Res. 2011;108:287–95.

    PubMed  Article  Google Scholar 

  83. 83.

    Zhan B, Badamchian M, Meihua B, Ashcom J, Feng J, Hawdon J, et al. Molecular cloning and purification of Ac-TMP, a developmentally regulated putative tissue inhibitor of metalloprotease released in relative abundance by adult Ancylostoma hookworms. Am J Trop Med Hyg. 2002;66:238–44.

    CAS  PubMed  Article  Google Scholar 

  84. 84.

    Zhan B, Gupta R, Wong SP, Bier S, Jiang D, Goud G, et al. Molecular cloning and characterization of Ac-TMP-2, a tissue inhibitor of metalloproteinase secreted by adult Ancylostoma caninum. Mol Biochem Parasitol. 2008;162:142–8.

    CAS  PubMed  Article  Google Scholar 

  85. 85.

    Navarro S, Pickering DA, Ferreira IB, Jones L, Ryan S, Troy S, et al. Hookworm recombinant protein promotes regulatory T cell responses that suppress experimental asthma. Sci Transl Med. 2016;8:362ra143.

    PubMed  Article  CAS  Google Scholar 

  86. 86.

    Cuellar C, Wu W, Mendez S. The hookworm tissue inhibitor of metalloproteases (Ac-TMP-1) modifies dendritic cell function and induces generation of CD4 and CD8 suppressor T cells. PLoS Negl Trop Dis. 2009;3:e439.

    PubMed  PubMed Central  Article  CAS  Google Scholar 

  87. 87.

    Delaney A, Williamson A, Brand A, Ashcom J, Varghese G, Goud GN, et al. Cloning and characterisation of an aspartyl protease inhibitor (API-1) from Ancylostoma hookworms. Int J Parasitol. 2005;35:303–13.

    CAS  PubMed  Article  Google Scholar 

  88. 88.

    Brophy P, Pritchard D. Metabolism of lipid peroxidation products by the gastro-intestinal nematodes Necator americanus, Ancylostoma ceylanicum and Heligmosomoides polygyrus. Int J Parasitol. 1992;22:1009–12.

    CAS  PubMed  Article  Google Scholar 

  89. 89.

    Nguyen JB, Pool CD, Wong CYB, Treger RS, Williams DL, Cappello M, et al. Peroxiredoxin-1 from the human hookworm Ancylostoma ceylanicum forms a stable oxidized decamer and is covalently inhibited by conoidin A. Chem Biol. 2013;20:991–1001.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  90. 90.

    Zhan B, Perally S, Brophy PM, Xue J, Goud G, Liu S, et al. Molecular cloning, biochemical characterization, and partial protective immunity of the heme-binding glutathione S-transferases from the human hookworm Necator americanus. Infect Immun. 2010;78:1552–63.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  91. 91.

    Asojo OA, Homma K, Sedlacek M, Ngamelue M, Goud GN, Zhan B. X-ray structures of Na-GST-1 and Na-GST-2 two glutathione S-transferase from the human hookworm Necator americanus. BMC Struct Biol. 2007;7:42.

    PubMed  PubMed Central  Article  CAS  Google Scholar 

  92. 92.

    Goud GN, Deumic V, Gupta R, Brelsford J, Zhan B, Gillespie P, et al. Expression, purification, and molecular analysis of the Necator americanus glutathione S-transferase 1 (Na-GST-1): a production process developed for a lead candidate recombinant hookworm vaccine antigen. Protein Expr Purif. 2012;83:145–51.

    CAS  PubMed  Article  Google Scholar 

  93. 93.

    Zhan B, Liu S, Perally S, Xue J, Fujiwara R, Brophy P. Biochemical characterization and vaccine potential of a heme-binding glutathione transferase from the adult hookworm Ancylostoma caninum. Infect Immun. 2005;73:6903–11.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  94. 94.

    Hang J, He L, Abuzeid AMI, Huang Y, Liu Y, Yan X, et al. Molecular characterization and tissue localization of glutathione S-transferase from adult Ancylostoma ceylanicum. J Helminthol. 2020;94:e118.

    CAS  PubMed  Article  Google Scholar 

  95. 95.

    Diemert DJ, Freire J, Valente V, Fraga CG, Talles F, Grahek S, et al. Safety and immunogenicity of the Na-GST-1 hookworm vaccine in Brazilian and American adults. PLoS Negl Trop Dis. 2017;11:e0005574.

    PubMed  PubMed Central  Article  CAS  Google Scholar 

  96. 96.

    Batra S, Singh SP, Gupta S, Katiyar JC, Srivastava VM. Reactive oxygen intermediates metabolizing enzymes in Ancylostoma ceylanicum and Nippostrongylus brasiliensis. Free Radic Biol Med. 1990;8:271–4.

    CAS  PubMed  Article  Google Scholar 

  97. 97.

    James ER, McLean D, Perler F. Molecular cloning of an Onchocerca volvulus extracellular Cu-Zn superoxide dismutase. Infect Immun. 1994;62:713–6.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  98. 98.

    Liddell S, Knox D. Extracellular and cytoplasmic Cu/Zn superoxide dismutases from Haemonchus contortus. Parasitology. 1998;116:383–94.

    CAS  PubMed  Article  Google Scholar 

  99. 99.

    Tang L, Ou X, Henkle-Dührsen K, Selkirk ME. Extracellular and cytoplasmic Cu/Zn superoxide dismutases from Brugia lymphatic filarial nematode parasites. Infect Immun. 1994;62:961–7.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  100. 100.

    Tetteh KK, Loukas A, Tripp C, Maizels RM. Identification of abundantly expressed novel and conserved genes from the infective larval stage of Toxocara canis by an expressed sequence tag strategy. Infect Immun. 1999;67:4771–9.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  101. 101.

    Brophy PM, Pritchard DI. Parasitic helminth glutathione S-transferases: an update on their potential as targets for immuno- and chemotherapy. Exp Parasitol. 1994;79:89–96.

    CAS  PubMed  Article  Google Scholar 

  102. 102.

    Maizels RM, Bundy DA, Selkirk ME, Smith DF, Anderson RM. Immunological modulation and evasion by helminth parasites in human populations. Nature. 1993;365:797–805.

    CAS  PubMed  Article  Google Scholar 

  103. 103.

    Brophy PM, Pritchard DI. Immunity to helminths: ready to tip the biochemical balance? Parasitol Today. 1992;8:419–22.

    CAS  PubMed  Article  Google Scholar 

  104. 104.

    Taiwo FA, Brophy PM, Pritchard DI, Brown A, Wardlaw A, Patterson LH. Cu/Zn superoxide dismutase in excretory-secretory products of the human hookworm Necator americanus. An electron paramagnetic spectrometry study. Eur J Biochem. 1999;264:434–8.

    CAS  PubMed  Article  Google Scholar 

  105. 105.

    Barr SD, Gedamu L. Role of peroxidoxins in Leishmania chagasi survival. Evidence of an enzymatic defense against nitrosative stress. J Biol Chem. 2003;278:10816–23.

    CAS  PubMed  Article  Google Scholar 

  106. 106.

    Donnelly S, O’Neill SM, Stack CM, Robinson MW, Turnbull L, Whitchurch C, et al. Helminth cysteine proteases inhibit TRIF-dependent activation of macrophages via degradation of TLR3. J Biol Chem. 2010;285:3383–92.

    CAS  PubMed  Article  Google Scholar 

  107. 107.

    Rieu P, Ueda T, Haruta I, Sharma CP, Arnaout MA. The A-domain of beta 2 integrin CR3 (CD11b/CD18) is a receptor for the hookworm-derived neutrophil adhesion inhibitor NIF. J Cell Biol. 1994;127:2081–91.

    CAS  PubMed  Article  Google Scholar 

  108. 108.

    Muchowski PJ, Zhang L, Chang ER, Soule HR, Plow EF, Moyle M. Functional interaction between the integrin antagonist neutrophil inhibitory factor and the I domain of CD11b/CD18. J Biol Chem. 1994;269:26419–23.

    CAS  PubMed  Google Scholar 

  109. 109.

    Lo SK, Rahman A, Xu N, Zhou MY, Nagpala P, Jaffe HA, et al. Neutrophil inhibitory factor abrogates neutrophil adhesion by blockade of CD11a and CD11b β2 integrins. Mol Pharmacol. 1999;56:926–32.

    CAS  PubMed  Article  Google Scholar 

  110. 110.

    Daub J, Loukas A, Pritchard D, Blaxter M. A survey of genes expressed in adults of the human hookworm, Necator americanus. Parasitology. 2000;120:171–84.

    CAS  PubMed  Article  Google Scholar 

  111. 111.

    Xu N, Rahman A, Minshall RD, Tiruppathi C, Malik AB. β2-Integrin blockade driven by E-selectin promoter prevents neutrophil sequestration and lung injury in mice. Circ Res. 2000;87:254–60.

    CAS  PubMed  Article  Google Scholar 

  112. 112.

    Rote WE, Dempsey E, Maki S, Vlasuk GP, Moyle M. The role of CD11/CD18 integrins in the reverse passive Arthus reaction in rat dermal tissue. J Leukoc Biol. 1996;59:254–61.

    CAS  PubMed  Article  Google Scholar 

  113. 113.

    Jiang N, Moyle M, Soule HR, Rote WE, Chopp M. Neutrophil inhibitory factor is neuroprotective after focal ischemia in rats. Ann Neurol. 1995;38:935–42.

    CAS  PubMed  Article  Google Scholar 

  114. 114.

    Schnyder-Candrian S, Maillet I, Le Bert M, Brault L, Jacobs M, Ryffel B, et al. Neutrophil inhibitory factor selectively inhibits the endothelium-driven transmigration of eosinophils in vitro and airway eosinophilia in OVA-induced allergic lung inflammation. J Allergy. 2012;2012:245909.

    Article  CAS  Google Scholar 

  115. 115.

    Leng L, Bucala R. Insight into the biology of macrophage migration inhibitory factor (MIF) revealed by the cloning of its cell surface receptor. Cell Res. 2006;16:162–8.

    CAS  PubMed  Article  Google Scholar 

  116. 116.

    Aeberli D, Leech M, Morand EF. Macrophage migration inhibitory factor and glucocorticoid sensitivity. Rheumatology. 2006;45:937–43.

    CAS  PubMed  Article  Google Scholar 

  117. 117.

    Sampey AV, Hall PH, Mitchell RA, Metz CN, Morand EF. Regulation of synoviocyte phospholipase A2 and cyclooxygenase 2 by macrophage migration inhibitory factor. Arthritis Rheum. 2001;44:1273–80.

    CAS  PubMed  Article  Google Scholar 

  118. 118.

    Mitchell RA, Metz CN, Peng T, Bucala R. Sustained mitogen-activated protein kinase (MAPK) and cytoplasmic phospholipase A2 activation by macrophage migration inhibitory factor (MIF). Regulatory role in cell proliferation and glucocorticoid action. J Biol Chem. 1999;274:18100–6.

    CAS  PubMed  Article  Google Scholar 

  119. 119.

    Onodera S, Nishihira J, Iwabuchi K, Koyama Y, Yoshida K, Tanaka S, et al. Macrophage migration inhibitory factor up-regulates matrix metalloproteinase-9 and -13 in rat osteoblasts. Relevance to intracellular signaling pathways. J Biol Chem. 2002;277:7865–74.

    CAS  PubMed  Article  Google Scholar 

  120. 120.

    Cho Y, Jones BF, Vermeire JJ, Leng L, DiFedele L, Harrison LM, et al. Structural and functional characterization of a secreted hookworm macrophage migration inhibitory factor (MIF) that interacts with the human MIF receptor CD74. J Biol Chem. 2007;282:23447–56.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  121. 121.

    Ferreira V, Molina MaC, Valck C, Rojas Á, Aguilar L, Ramı́rez G, et al. Role of calreticulin from parasites in its interaction with vertebrate hosts. Mol Immunol. 2004;40:1279–91.

    CAS  PubMed  Article  Google Scholar 

  122. 122.

    Pritchard DI, Brown A, Kasper G, McElroy P, Loukas A, Hewitt C, et al. A hookworm allergen which strongly resembles calreticulin. Parasite Immunol. 1999;21:439–50.

    CAS  PubMed  Article  Google Scholar 

  123. 123.

    Kasper G, Brown A, Eberl M, Vallar L, Kieffer N, Berry C, et al. A calreticulin-like molecule from the human hookworm Necator americanus interacts with C1q and the cytoplasmic signalling domains of some integrins. Parasite Immunol. 2001;23:141–52.

    CAS  PubMed  Article  Google Scholar 

  124. 124.

    Bungiro RD, Harrison LM, Cappello M. Ancylostoma ceylanicum excretory/secretory protein 1: purification and molecular cloning of a major secretory protein from adult hookworms. Mol Biochem Parasitol. 2002;119:147–51.

    CAS  PubMed  Article  Google Scholar 

  125. 125.

    Bungiro RD Jr, Solis CV, Harrison LM, Cappello M. Purification and molecular cloning of and immunization with Ancylostoma ceylanicum excretory-secretory protein 2, an immunoreactive protein produced by adult hookworms. Infect Immun. 2004;72:2203–13.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  126. 126.

    Kucera K, Harrison LM, Cappello M, Modis Y. Ancylostoma ceylanicum excretory-secretory protein 2 adopts a netrin-like fold and defines a novel family of nematode proteins. J Mol Biol. 2011;408:9–17.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  127. 127.

    Bungiro RD Jr, Cappello M. Detection of excretory/secretory coproantigens in experimental hookworm infection. Am J Trop Med Hyg. 2005;73:915–20.

    PubMed  Article  Google Scholar 

  128. 128.

    Brown AC, Harrison LM, Kapulkin W, Jones BF, Sinha A, Savage A, et al. Molecular cloning and characterization of a C-type lectin from Ancylostoma ceylanicum: evidence for a role in hookworm reproductive physiology. Mol Biochem Parasitol. 2007;151:141–7.

    CAS  PubMed  Article  Google Scholar 

  129. 129.

    Weis WI, Taylor ME, Drickamer K. The C-type lectin superfamily in the immune system. Immunol Rev. 1998;163:19–34.

    CAS  PubMed  Article  Google Scholar 

  130. 130.

    Loukas A, Maizels RM. Helminth C-type lectins and host-parasite interactions. Parasitol Today. 2000;16:333–9.

    CAS  PubMed  Article  Google Scholar 

  131. 131.

    Loukas A, Brown AP, Pritchard DI. Na-ctl-2, a cDNA encoding a C-type lectin expressed exclusively in adult Necator americanus hookworms. DNA Seq. 2002;13:61–5.

    CAS  PubMed  Article  Google Scholar 

  132. 132.

    Hassan A, Pritchard DI, Ghaemmaghami AM. Human dendritic cell sequestration onto the Necator americanus larval sheath during ex-sheathing: a possible mechanism for immune privilege. Parasitology. 2018;145:1183–90.

    CAS  PubMed  Article  Google Scholar 

  133. 133.

    Pritchard D, Leggett K, Rogan M, McKean PG, Brown A. Necator americanus secretory acetylcholinesterase and its purification from excretory-secretory products by affinity chromatography. Parasite Immunol. 1991;13:187–99.

    CAS  PubMed  Article  Google Scholar 

  134. 134.

    McLaren DJ, Burt JS, Ogilvie BM. The anterior glands of adult Necator americanus (Nematoda: Strongyloidea). II Cytochemical and functional studies. Int J Parasitol. 1974;4:39–46.

    CAS  PubMed  Article  Google Scholar 

  135. 135.

    Pritchard DI, Brown A, Toutant JP. The molecular forms of acetylcholinesterase from Necator americanus (Nematoda), a hookworm parasite of the human intestine. Eur J Biochem. 1994;219:317–23.

    CAS  PubMed  Article  Google Scholar 

  136. 136.

    Prociv P. Pathogenesis of human hookworm infection: insights from a ‛newʼ zoonosis. Chem Immunol. 1997;66:62–98.

    CAS  PubMed  Article  Google Scholar 

  137. 137.

    Hussein AS, Chacón MR, Smith AM, Tosado-Acevedo R, Selkirk ME. Cloning, expression, and properties of a nonneuronal secreted acetylcholinesterase from the parasitic nematode Nippostrongylus brasiliensis. J Biol Chem. 1999;274:9312–9.

    CAS  PubMed  Article  Google Scholar 

  138. 138.

    Pritchard D. The survival strategies of hookworms. Parasitol Today. 1995;11:255–9.

    Article  Google Scholar 

  139. 139.

    Ogilvie BM, Bartlett A, Godfrey RC, Turton J, Worms M, Yeates R. Antibody responses in self-infections with Necator americanus. Trans R Soc Trop Med Hyg. 1978;72:66–71.

    CAS  PubMed  Article  Google Scholar 

  140. 140.

    Areekul S, Cheeramakara C. Acetylcholinesterase activity in different stages of Ancylostoma caninum. Southeast Asian J Trop Med Public Health. 1982;13:285–6.

    CAS  PubMed  Google Scholar 

  141. 141.

    Nwosu AB. Age-related changes in esterase and acetylcholinesterase activities of the infective larvae of Ancylostoma tubaeforme. Int J Parasitol. 1978;8:355–8.

    CAS  PubMed  Article  Google Scholar 

  142. 142.

    Wang FL, Ning KB, Wang XZ, Yang GM, Wang JY. Average values of Ancylostoma duodenale and Necator americanus cholinesterase activity in humans. Chin Med J. 1983;96:60–2.

    CAS  PubMed  Google Scholar 

  143. 143.

    Basavaraju S, Zhan B, Kennedy MW, Liu Y, Hawdon J, Hotez PJ. Ac-FAR-1, a 20 kDa fatty acid- and retinol-binding protein secreted by adult Ancylostoma caninum hookworms: gene transcription pattern, ligand binding properties and structural characterisation. Mol Biochem Parasitol. 2003;126:63–71.

    CAS  PubMed  Article  Google Scholar 

  144. 144.

    Fairfax KC, Vermeire JJ, Harrison LM, Bungiro RD, Grant W, Husain SZ, et al. Characterisation of a fatty acid and retinol binding protein orthologue from the hookworm Ancylostoma ceylanicum. Int J Parasitol. 2009;39:1561–71.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  145. 145.

    Gabrielsen M, Rey-Burusco MF, Griffiths K, Roe AJ, Cooper A, Smith BO, et al. Two crystal forms of a helix-rich fatty acid- and retinol-binding protein, Na-FAR-1, from the parasitic nematode Necator americanus. Acta Crystallogr Sec F Struct Biol Cryst Commun. 2012;68:835–8.

    CAS  Article  Google Scholar 

  146. 146.

    Rey-Burusco MF, Ibáñez-Shimabukuro M, Gabrielsen M, Franchini GR, Roe AJ, Griffiths K, et al. Diversity in the structures and ligand-binding sites of nematode fatty acid and retinol-binding proteins revealed by Na-FAR-1 from Necator americanus. Biochem J. 2015;471:403–14.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  147. 147.

    Fairfax KC, Harrison LM, Cappello M. Molecular cloning and characterization of a nematode polyprotein antigen/allergen from the human and animal hookworm Ancylostoma ceylanicum. Mol Biochem Parasitol. 2014;198:37–44.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  148. 148.

    Hotez PJ, Brooker S, Bethony JM, Bottazzi ME, Loukas A, Xiao S. Hookworm infection. N Engl J Med. 2004;351:799–807.

    CAS  PubMed  Article  Google Scholar 

  149. 149.

    Hotez PJ. Mass drug administration and integrated control for the worldʼs high-prevalence neglected tropical diseases. Clin Pharmacol Ther. 2009;85:659–64.

    CAS  PubMed  Article  Google Scholar 

  150. 150.

    Ghosh K, Hawdon J, Hotez P. Vaccination with alum-precipitated recombinant Ancylostoma-secreted protein 1 protects mice against challenge infections with infective hookworm (Ancylostoma caninum) larvae. J Infect Dis. 1996;174:1380–3.

    CAS  PubMed  Article  Google Scholar 

  151. 151.

    Sen L, Ghosh K, Bin Z, Qiang S, Thompson MG, Hawdon JM, et al. Hookworm burden reductions in BALB/c mice vaccinated with recombinant Ancylostoma secreted proteins (ASPs) from Ancylostoma duodenale, Ancylostoma caninum and Necator americanus. Vaccine. 2000;18:1096–102.

    CAS  PubMed  Article  Google Scholar 

  152. 152.

    Fujiwara R, Bethony J, Bueno L, Wang Y, Yeong Ahn S, Samuel A, et al. Immunogenicity of the hookworm Na-ASP-2 vaccine candidate: characterization of humoral and cellular responses after vaccination in the Sprague Dawley rat. Hum Vaccines. 2005;1:123–8.

    CAS  Article  Google Scholar 

  153. 153.

    Bethony JM, Simon G, Diemert DJ, Parenti D, Desrosiers A, Schuck S, et al. Randomized, placebo-controlled, double-blind trial of the Na-ASP-2 hookworm vaccine in unexposed adults. Vaccine. 2008;26:2408–17.

    CAS  PubMed  Article  Google Scholar 

  154. 154.

    Zhan B, Santiago H, Keegan B, Gillespie P, Xue J, Bethony J, et al. Fusion of Na-ASP-2 with human immunoglobulin Fcγ abrogates histamine release from basophils sensitized with anti-Na-ASP-2 IgE. Parasite Immunol. 2012;34:404–11.

    CAS  PubMed  Article  Google Scholar 

  155. 155.

    Hotez PJ, Ashcom J, Zhan B, Bethony J, Loukas A, Hawdon J, et al. Effect of vaccination with a recombinant fusion protein encoding an astacin like metalloprotease (MTP-1) secreted by host-stimulated Ancylostoma caninum third-stage infective larvae. J Parasitol. 2003;89:853–5.

    CAS  PubMed  Article  Google Scholar 

  156. 156.

    Loukas A, Bethony JM, Mendez S, Fujiwara RT, Goud GN, Ranjit N, et al. Vaccination with recombinant aspartic hemoglobinase reduces parasite load and blood loss after hookworm infection in dogs. PLoS Med. 2005;2:e295.

    PubMed  PubMed Central  Article  CAS  Google Scholar 

  157. 157.

    Hotez PJ, Ashcom J, Bin Z, Bethony J, Williamson A, Hawdon JM, et al. Effect of vaccinations with recombinant fusion proteins on Ancylostoma caninum habitat selection in the canine intestine. J Parasitol. 2002;88:684–90.

    PubMed  Article  Google Scholar 

  158. 158.

    Pearson MS, Bethony JM, Pickering DA, de Oliveira LM, Jariwala A, Santiago H, et al. An enzymatically inactivated hemoglobinase from Necator americanus induces neutralizing antibodies against multiple hookworm species and protects dogs against heterologous hookworm infection. FASEB J. 2009;23:3007–19.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  159. 159.

    Pearson MS, Jariwala AR, Abbenante G, Plieskatt J, Wilson D, Bottazzi ME, et al. New tools for NTD vaccines: a case study of quality control assays for product development of the human hookworm vaccine Na-APR-1M74. Hum Vaccin Immunother. 2015;11:1251–7.

    PubMed  PubMed Central  Article  Google Scholar 

  160. 160.

    Brelsford JB, Plieskatt JL, Yakovleva A, Jariwala A, Keegan BP, Peng J, et al. Advances in neglected tropical disease vaccines: developing relative potency and functional assays for the Na-GST-1/Alhydrogel hookworm vaccine. PLoS Negl Trop Dis. 2017;11:e0005385.

    CAS  PubMed  PubMed Central  Article  Google Scholar 

  161. 161.

    Winter JA, Davies OR, Brown AP, Garnett MC, Stolnik S, Pritchard DI. The assessment of hookworm calreticulin as a potential vaccine for necatoriasis. Parasite Immunol. 2005;27:139–46.

    CAS  PubMed  Article  Google Scholar 

  162. 162.

    Mendez S, Zhan B, Goud G, Ghosh K, Dobardzic A, Wu W, et al. Effect of combining the larval antigens Ancylostoma secreted protein 2 (ASP-2) and metalloprotease 1 (MTP-1) in protecting hamsters against hookworm infection and disease caused by Ancylostoma ceylanicum. Vaccine. 2005;23:3123–30.

    CAS  PubMed  Article  PubMed Central  Google Scholar 

  163. 163.

    Seid CA, Curti E, Jones RM, Hudspeth E, Rezende W, Pollet J, et al. Expression, purification, and characterization of the Necator americanus aspartic protease-1 (Na-APR-1 (M74)) antigen, a component of the bivalent human hookworm vaccine. Hum Vaccin Immunother. 2015;11:1474–88.

    PubMed  PubMed Central  Article  Google Scholar 

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We would like to thank our colleagues in the College of Veterinary Medicine, South China Agricultural University, Guangzhou, China.


This work was supported by the National Natural Science Foundation of China (Grant no. 31672541) and the Science and Technology Planning Project of Guangdong Province, China (Grant no. 2014A020214005).

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GL developed the concept of the paper, AMIA wrote the draft version of the review. GL, AMIA, XZ and YH contributed to the writing, editing, and revision of the manuscript. All authors read and approved the final manuscript.

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Correspondence to Guoqing Li.

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Abuzeid, A.M.I., Zhou, X., Huang, Y. et al. Twenty-five-year research progress in hookworm excretory/secretory products. Parasites Vectors 13, 136 (2020).

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  • Hookworm
  • ES products
  • Host-parasite interactions
  • Vaccine
  • Therapy