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Genetic diversity and immunogenicity of the merozoite surface protein 1 C-terminal 19-kDa fragment of Plasmodium ovale imported from Africa into China

Parasites & Vectors volume 14, Article number: 583 (2021) Cite this article

Abstract

Background

Merozoite surface protein 1 (MSP1) plays an essential role in erythrocyte invasion by malaria parasites. The C-terminal 19-kDa region of MSP1 has long been considered one of the major candidate antigens for a malaria blood-stage vaccine against Plasmodium falciparum. However, there is limited information on the C-terminal 19-kDa region of Plasmodium ovale MSP1 (PoMSP119). This study aims to analyze the genetic diversity and immunogenicity of PoMSP119.

Methods

A total of 37 clinical Plasmodium ovale isolates including Plasmodium ovale curtisi and Plasmodium ovale wallikeri imported from Africa into China and collected during the period 2012–2016 were used. Genomic DNA was used to amplify P. ovale curtisi (poc) msp119 (pocmsp119) and P. ovale wallikeri (pow) msp119 (powmsp119) genes by polymerase chain reaction. The genetic diversity of pomsp119 was analyzed using the GeneDoc version 6 programs. Recombinant PoMSP119 (rPoMSP119)-glutathione S-transferase (GST) proteins were expressed in an Escherichia coli expression system and analyzed by western blot. Immune responses in BALB/c mice immunized with rPoMSP119-GST were determined using enzyme-linked immunosorbent assay. In addition, antigen-specific T cell responses were assessed by lymphocyte proliferation assays. A total of 49 serum samples from healthy individuals and individuals infected with P. ovale were used for the evaluation of natural immune responses by using protein microarrays.

Results

Sequences of pomsp119 were found to be thoroughly conserved in all the clinical isolates. rPoMSP119 proteins were efficiently expressed and purified as ~ 37-kDa proteins. High antibody responses in mice immunized with rPoMSP119-GST were observed. rPoMSP119-GST induced high avidity indexes, with an average of 92.57% and 85.32% for rPocMSP119 and rPowMSP119, respectively. Cross-reactivity between rPocMSP119 and rPowMSP119 was observed. Cellular immune responses to rPocMSP119 (69.51%) and rPowMSP119 (52.17%) induced in rPocMSP119- and rPowMSP119-immunized mice were found in the splenocyte proliferation assays. The sensitivity and specificity of rPoMSP119-GST proteins for the detection of natural immune responses in patients infected with P. ovale were 89.96% and 75%, respectively.

Conclusions

This study revealed highly conserved gene sequences of pomsp119. In addition, naturally acquired humoral immune responses against rPoMSP1 were observed in P. ovale infections, and high immunogenicity of rPoMSP119 in mice was also identified. These instructive findings should encourage further testing of PoMSP119 for rational vaccine design.

Graphical abstract

Background

Malaria is one of the most severe infectious diseases that threaten human health. According to the World Health Organization, there were 229 million clinical cases of malaria and 490,000 deaths from this disease in 2019 [1]. Plasmodium ovale is one of the five species of Plasmodium that regularly infect humans, and accounts for 0.5–10.5% of all malaria cases [2]. It is geographically distributed in sub-Saharan Africa and the Western Pacific Region and is classified into two subspecies: Plasmodium ovale curtisi and Plasmodium ovale wallikeri [2, 3]. Plasmodium ovale has a similar morphology and life cycle to Plasmodium vivax [2]. The prevalence of P. ovale malaria is underestimated because of the low density of these parasites in infected subjects, mild clinical symptoms (e.g. fever), and mixed infections with other species of Plasmodium [2, 4, 5]. However, P. ovale infection can evolve into severe malaria with severe anemia and may become fatal, especially in areas where malaria is endemic [6, 7]. Although there have been impressive achievements in research for P. falciparum malaria vaccines [8,9,10], no widely effective vaccine exists for P. ovale malaria. China has eliminated malaria within its borders [11], and was very recently certified as officially free of malaria by the World Health Organization. However, as a consequence of economic growth and deepening of the global trade the number of cases of malaria imported into China, including cases of P. ovale infection, increased in recent years [12,13,14].

During the invasion of human erythrocytes by malaria parasites, the merozoite surface proteins (MSPs) (including MSP1) are exposed to the host immune system [15]. Moreover, antibodies targeting MSP1 have been observed in individuals from malaria-endemic areas and have been shown to confer immunity [16,17,18]. The molecular weight of MSP1 is approximately 200 kDa [19]. The MSP1 protein undergoes two proteolytic cleavage steps during invasion of the erythrocytes. In the first step, MSP1 is cleaved into four polypeptides (with molecular weights of 83 kDa, 30 kDa, 38 kDa, and 42 kDa). Subsequently, the 42-kDa fragment is cleaved into 33-kDa (MSP133) and 19-kDa (MSP119) fragments; the latter remains attached to the merozoite surface and enters the erythrocytes [20,21,22]. Several studies have identified limited polymorphism in the C-terminal 19-kDa region of both P. falciparum MSP1 (PfMSP119) [23,24,25] and P. vivax MSP1 (PvMSP119) [26, 27]. Genetic conservation within vaccine candidate antigens is advantageous for vaccine development as it helps to reduce antigenic escape [27, 28]. Moreover, antibodies against PfMSP119 can prevent the invasion of merozoites into erythrocytes [29]. Antibodies to PfMSP119 have been associated with protection from malaria in pregnant women, infants and older children naturally infected with P. falciparum [30,31,32]. These instructive findings imply that MSP119 is a promising candidate antigen for a blood-stage vaccine.

Genetic polymorphisms of MSP1 in clinical P. ovale isolates from Thailand were analyzed and showed low sequence diversity [33]. However, there is a paucity of information on PoMSP119. In the present study, sequences of pomsp119 from clinical P. ovale curtisi and P. ovale wallikeri isolates from patients with P. ovale malaria imported into China from Africa were investigated. In addition, the immunogenicity of PoMSP119 was assessed in mice, and the levels of immune responses against PoMSP119 assessed in serum samples of patients infected with P. ovale.

Methods

Collection of samples

Blood samples of febrile patients who had returned from work in malaria-endemic areas of sub-Saharan Africa during the period 2012–2016, and who were confirmed for P. ovale curtisi or P. ovale wallikeri infection by polymerase chain reaction (PCR) tests [13], were obtained from local hospitals in Jiangsu Province, China [34, 35]. Genomic DNA was extracted from the blood samples for PCR amplification of pomsp119 genes. In addition, serum samples of the P. ovale-infected patients (n = 29) who had returned from Africa and those of healthy individuals (n = 20) from China were also obtained from the local hospitals of Jiangsu Province.

PCR amplification and sequencing of pomsp1 19

A total of 37 clinical P. ovale isolates (P. ovale curtisi, n = 20; P. ovale wallikeri, n = 17) were collected for PCR amplification (Additional file 1: Table S1). Sequences of P. ovale curtisi (poc) msp1 (pocmsp1) (KC137343) and P. ovale wallikeri (pow) msp1 (powmsp1) (KC137341) genes from the GenBank database of the National Centre for Biotechnology Information were used as reference sequences [33, 34]. The 258-bp sequences of pomsp119 were identified via matching with similar sequences, as previously reported [36, 37], and were amplified by nested PCR. The first-round primers were as follows: pomsp119 forward (5′-AGT AAG GAA AAA GAT TTG ACA A-3′) and pomsp119 reverse (5′-AAG TAA GTT AAA TAG GAT GAT-3′). The primers for the nested PCR were as follows: pomsp119 forward (5'-ATG GGA TCT AAA CAT AAA TGT-3') and pomsp119 reverse (5'-GAA AAC ACC TTC GAA GAA TGG-3'). All the amplification reactions had the same reaction conditions, as follows: 98 °C for 3 min, followed by 35 cycles of 98 °C for 10 s, 45 °C for 1 min, and 72 °C for 1 min, and final extension at 72 °C for 5 min. PCR products were electrophoresed on 1.2% agarose gels for visualization under an ultraviolet transilluminator (ChemiDoc MP; Bio-Rad), then purified and sequenced by Genewiz (Suzhou, China). In addition, PCR-amplified fragments were also cloned into the pUC57 vector and sequenced by Genewiz using the following primers: M13F, 5′-TGT AAA ACG ACG GCC AGT-3′; M13R, 5′-CAG GAA ACA GCT ATG AC-3′. To evaluate genetic diversity within sequences of different isolates, sequences of pocmsp119 and powmsp119 were aligned using GeneDoc version 2.7.0.

Recombinant expression and purification of proteins

Genes including pocmsp119 and powmsp119 were subcloned into the pGEX-6p-1 expression vector which contained a glutathione S-transferase (GST)-tag fusion protein. Recombinant pGEX-6p-1pomsp119 were transferred into Escherichia coli strain BL21 pLysS cells to express PoMSP119 proteins. Colonies of recombinants were cultured in Luria Bertani broth supplemented with ampicillin 50 µg/ml by shaking at 250 r.p.m. at 37 °C until the optical density (OD) at 600 nm reached 0.6–0.8. To induce the expression of recombinant PoMSP119 (rPoMSP119) proteins, isopropyl β-D-1-thiogalactopyranoside (0.1 mM) (TransGen Biotech, Beijing, China) was added and the culture was allowed to grow for another eight hours. Proteins were purified by Tanlen-bio Scientific (Wuxi, China). The rPoMSP119-GST proteins were separated using 10% sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS–PAGE) and detected via western blot and Coomassie brilliant blue staining (Beyotime Biotech, China). For western blot analysis, the proteins were electrophoresed on a polyvinylidene difluoride (PVDF) membrane (Immobilon; Millipore Sigma). Nonspecific bindings were blocked by incubation with 5% skimmed milk in Tris-buffered saline supplemented with 0.1% Tween-20 (TBST) at room temperature for 2 h. The membranes were incubated with anti-GST rabbit monoclonal antibody (CWBio Biotech) as the primary antibody at 1:2000 dilution overnight at 4 °C, and then washed three times with 0.1% TBST. Horseradish peroxidase (HRP)-conjugated goat anti-rabbit immunoglobulin G (IgG) (CWBio Biotech) was used as the secondary antibody for detection (at 1:5000 dilution for 1 h). Finally, the membranes were visualized using the ChemiDoc MP imaging system (Bio-Rad).

Immunization of mice

Female BALB/c mice (Cavens; Changzhou, China) aged 6–8 weeks were intraperitoneally injected with 50 μg of rPocMSP119-GST, rPowMSP119-GST, GST, or phosphate-buffered saline (PBS) mixed with Freund’s complete adjuvant (Sigma, San Francisco, CA) as the primary immunization. The same amount of recombinant protein was mixed with incomplete Freund’s adjuvant then injected at days 21 and 42 after the initial injection to boost immunization. Mouse serum samples were collected and stored at − 80 ℃ on days 0, 7, 14, 28, 35, and 49 after the initial injection.

Western blot analysis was performed to detect antibodies directed against rPoMSP119-GST from the sera of immunized mice. Concretely, rPoMSP119–GST and GST proteins were transferred from SDS-PAGE onto PVDF membranes. The membranes were incubated with the sera of mice immunized with rPoMSP119-GST as the primary antibody, with sera of the GST immunized group, or with the sera of those injected with PBS, the negative control group, and then incubated with HRP-conjugated goat anti-mouse IgG (Cowin Biotech) at 1:5000 dilution for detection.

Enzyme-linked immunosorbent assay

Levels of IgG antibodies against rPoMSP119-GST and GST in the sera of immunized mice were evaluated through enzyme-linked immunosorbent assay (ELISA) as previously described [35, 38]. For the assays, 50 ng of rPoMSP119-GST or GST was immobilized on 96-well plates overnight at 4 °C in coating buffer (15 mM sodium carbonate and 35 mM sodium bicarbonate in distilled water) and blocked with 5% (weight/volume) non-fat milk in TBST at room temperature for 2 h. A 100-µl volume of a twofold serial dilution (1:10,000 to 1:5,120,000) of anti-rPoMSP119-GST or anti-GST mouse sera was added to each well and incubated for 1 h at room temperature. The plates were washed three times with PBS containing 0.1% of Tween-20 (PBST) then incubated with HRP-conjugated goat anti-mouse IgG antibodies (Southern Biotech) at 1:5000 dilution for 1 h at room temperature. Finally, the plates were washed again and incubated with 100 µl of 3,3’,5,5’-tetramethylbenzidine (Invitrogen) substrate for 8 min in the dark, and the reaction was stopped with 50 µl of 2 M H2SO4 in each well. The absorbance was read at 450 nm. All samples were tested in duplicate and the mean absorbance was calculated.

The affinity test of the anti-rPoMSP119-GST IgG antibody was performed in accordance with the above-mentioned ELISA test with the exception that the test here was repeated in a 96-well plate coated with the same recombinant proteins. More specifically, sera were incubated for 90 min at room temperature, following by washing of one of the plates with PBST while the other plate was first incubated with 100 µl of TBST containing 6 M urea for 10 min at room temperature before final washing with PBST. Finally, all the plates were incubated with HRP-conjugated goat anti-mouse IgG antibodies at 1:5000 dilution for 1 h at room temperature. The reaction was stopped with 50 µl of 2 M H2SO4 in each well and absorbance was measured at 450 nm. The avidity index (AI) was calculated as follows [39]:

$${\text{AI}}\, = \,\left( {{\text{OD45}}0{\text{ of a sample treated with 6}} {\text{Murea}}/{\text{OD45}}0{\text{ of a sample not treated with 6}} {\text{Murea}}} \right)\, \times \,{1}00$$

Lymphocyte proliferation assays

Assays for lymphocyte proliferation were performed using Cell Counting Kit-8 (CCK-8; Beyotime Biotech), as previously described [35, 40]. Briefly, lymphocytes from mice immunized with rPoMSP119-GST, GST and PBS (5 × 105 cells/well) were treated with 10 µL of rPocMSP119-GST (5 µg/mL), 10 µL of rPowMSP119-GST (5 µg/mL), 10 µL of GST (5 µg/mL) or 10 µL of concanavalin A (ConA; 2 μg/mL) as the positive control in 96-well flat-bottomed microtiter plates then incubated for 72 h at 37 °C with 5% CO2. A 10-µl volume of CCK-8 was added to each well and the plates were incubated at 37 °C for 2 h. Finally, cell proliferation was measured at 450 nm by a microplate reader.

Screening of serum samples

Serum samples from 29 cases of P. ovale-infected and 20 healthy individuals were screened by well-type amine arrays. The screening was performed as previously described [41, 42]. Briefly, modified glass slides (75 × 25 mm,) were prepared for the protein arrays (CapitalBio, Beijing, China) and warmed to room temperature before use. Teflon tapes with holes were pasted on array glass slides to ensure integrity of the array. One microliter of rPocMSP119-GST, rPowMSP119-GST and GST solution in PBS (100 ng/µl) was spotted into each well of the arrays and incubated for 2 h at 37 °C. Array slides were washed three times with PBST for 10 min and were blocked with 5% of bovine serum albumin in PBST at 37 °C for 2 h. The arrays were washed again and probed with 1 µl of serum samples at 1:200 dilution. Finally, 1 µl of Alexa Fluor 546 goat anti-human IgG (10 ng/µl; Invitrogen) in PBST was added to the arrays for antibody detection. The intensity of the serological responses was measured by a fluorescent microarray scanner (CapitalBio). The positive cut-off value was calculated as the mean fluorescence intensity (MFI) of negative controls plus 2 SD. A Mann–Whitney U-test was performed to compare differences in MFI between groups.

Statistical analysis

GraphPad Prism software (version 5.0; GraphPad Software) was used for the statistical analyses and graphing. An unpaired two-tailed Student t-test was used for the comparison of mean values between samples; differences were considered statistically significant when P-values < 0.05.

Results

Genetic description and PCR analysis of pomsp1 19

The full lengths of PocMSP1 (KC137343) and PowMSP1 (KC137341) were predicted to be 1727 and 1672 amino acids, respectively [34]. Following the proteolytic cleavage of MSP1, schematic diagrams of PocMSP1 and PowMSP1 were divided into seven domains as follows: signal peptide, 83-kDa domain, 30-kDa domain, 38-kDa domain, 33-kDa domain, 19-kDa domain, and glycolphosphatidylinositol (GPI) (Fig. 1a, b). Sequence alignment of amino acids between PocMSP119 and PowMSP119 showed only one amino acid difference for each (amino acids located at positions 1640 and 1585 in PocMSP1 and PowMSP1, respectively) (Fig. 1c). Clinical P. ovale curtisi and P. ovale wallikeri isolates (n = 20 and n = 17, respectively) that were used as sources of genomic DNA for PCR amplification are listed in Additional file 1: Table S1. PCR products of pomsp119 genes were successfully amplified and showed a single 258-bp band on electropherograms (Fig. 2a). Alignment of pomsp119 sequences from all isolates showed no amino acid mutation (Additional file 2: Fig S1), suggesting that pomsp119 was completely conserved across the isolates.

Fig. 1
figure 1

a, b Schematic diagram of protein structure and alignment of the C-terminal 19-kDa region of Plasmodium ovale merozoite surface protein 1 (PoMSP119) amino acid (aa) sequences. a, b Signal peptide (SP; black), glycophosphatidylinositol (GPI; red), and expression area (gray) of proteins. c Alignment of amino acid sequences of Plasmodium ovale curtisi (Poc) MSP119 (PocMSP119) and Plasmodium ovale wallikeri (Pow) MSP119 (PowMSP119)

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Fig. 2
figure 2

a, b Polymerase chain reaction (PCR) amplification of pomsp119, and expression and purification of recombinant PoMSP119 (rPoMSP119)-glutathione S-transferase (GST) proteins. a The pocmsp119 and powmsp119 genes were amplified by PCR. b Purified rPoMSP119-GST (~ 37 kDa) was resolved by 10% sodium dodecyl sulfate–polyacrylamide gel electrophoresis. c Western blot analysis of rPoMSP119-GST using an anti-GST rabbit monoclonal antibody. 1 Purified rPocMSP119-GST protein, 2 purified rPowMSP119-GST protein, M marker; for other abbreviations, see Fig. 1

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Expression, purification, and analysis of rPoMSP119-GST proteins

The molecular weight of rPoMSP119-GST was estimated as approximately 35 kDa (including the molecular weights of PocMSP119/PowMSP119 and pGEX-6p-1 expression vector containing a GST-tag fusion protein, estimated as 9 and 26 kDa, respectively). Recombinant proteins were efficiently expressed and purified, as shown in Fig. 2b, and presented in SDS-PAGE as a single band of approximately 37 kDa. Western blot analysis confirmed the expression of rPoMSP119-GST proteins (Fig. 2c).

Mice-derived antibodies against rPoMSP119-GST recognized the recombinant proteins

To verify whether anti-rPoMSP119-GST antibodies were produced in the sera of immunized mice, we performed an immunoblot for a specific ~ 37-kDa band of purified rPoMSP119-GST proteins. As expected, sera from mice immunized with rPocMSP119-GST and rPowMSP119-GST detected rPocMSP119-GST and rPowMSP119-GST, respectively (Fig. 3a, b). In addition, sera from mice immunized with GST could also recognize the recombinant proteins (Fig. 3c). No band was found for the recombinant proteins treated with sera from mice immunized with PBS (negative control). These results indicated that rPoMSP119-GST could induce anti–rPoMSP119-GST antibodies in mice.

Fig. 3
figure 3

a–d Detection of antibodies in the sera of mice immunized with rPoMSP119-GST. a–c Western blot analyses for the detection of rPoMSP119-GST proteins by using antibodies from the sera of mice immunized with rPoMSP119-GST and GST proteins. d Western blot analysis using antibodies from the sera of mice immunized with PBS. 1 Purified rPocMSP119-GST protein, 2 purified rPowMSP119-GST protein, 3 purified GST protein. For abbreviations, see Figs. 1 and 2

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Immunized mouse-generated anti-rPocMSP119, anti-rPowMSP119, and anti-GST sera also cross-reacted with the rPoMSP119 proteins and with GST (Fig. 3a–c). Sera from mice immunized with rPocMSP119-GST could recognize rPowMSP119-GST and GST (Fig. 3a). Similarly, sera from mice immunized with rPowMSP119-GST could also recognize rPocMSP119-GST and GST (Fig. 3b). These results showed that anti–rPocMSP119-GST and anti–rPowMSP119-GST antibodies had the ability to cross-react with PocMSP119 and PowMSP119 antigens.

Levels of immune responses in mice immunized with rPoMSP119-GST

To measure levels of immune responses against rPoMSP119-GST or PBS (negative control) in mice, ELISA was performed using rPoMSP119-GST and GST proteins as the coating antigens. The results showed that both rPocMSP119-GST and rPowMSP119-GST were immunogenic (Fig. 4). The average antibody titers were determined by ELISA at 49 days after the first intraperitoneal injection. The proteins rPocMSP119-GST and rPowMSP119-GST induced comparable antibody responses, with end-point titers ranging from 1:10,000 to 1:2,560,000 (Fig. 4a). After three consecutive immunizations, high IgG antibody responses were induced in mice immunized with rPoMSP119-GST (Fig. 4b, c). The titration curves for GST were indicative of low responses compared to those for rPoMSP119-GST proteins. In addition, in comparison to immunization with rPoMSP119-GST proteins, GST immunization failed to induce high IgG antibody responses in mice, and PBS induced no IgG antibody response at all. These results suggested that immunization of mice with rPoMSP119-GST proteins induced higher levels of IgG antibodies (rPocMSP119-GST, mean avidity, 92.57%, P = 0.0024; rPowMSP119-GST, mean avidity, 85.32%, P = 0.014) than immunization of mice with GST (mean avidity, 37.84%) (Fig. 4d). However, there was no statistically significant difference in immune response between the rPocMSP119-GST and rPowMSP119-GST groups of mice (P > 0.05).

Fig. 4
figure 4

a–e Immune responses in mice immunized with rPoMSP119-GST. a Sera from immunized mice were multiply diluted (from 1:10,000 to 1:5,120,000), and the data are expressed as average optical density (OD) values. b Increasing trend of immunoglobulin G (IgG) levels detected using ELISA. c Specific immune responses in sera from mice immunized with different proteins confirmed by testing the interaction between antibodies and rPocMSP119-GST, rPowMSP119-GST and GST. The mean OD shows the strength of specific immune responses. d Avidity indices of anti-rPoMSP119-GST IgG determined by ELISA. e Splenocytes from immunized mice were stimulated with recombinant proteins, and concanavalin A (ConA) was used as a positive control. * P < 0.05, ** P < 0.01, *** P < 0.001; not significant (ns) P > 0.05. For other abbreviations, see Figs. 1 and 2

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Cellular immune responses induced by rPoMSP119-GST were assessed through spleen lymphocyte proliferation assays. The proliferation of splenocytes in vitro under rPocMSP119-GST, rPowMSP119-GST, GST, and ConA (positive control) stimulations was determined. Cell proliferation induced by rPocMSP119-GST was 69.51% and that induced by rPowMSP119-GST was 52.17%. Collectively, rPoMSP119-GST proteins induced a stronger proliferation response of spleen cells (rPocMSP119-GST, P = 0.0471; rPowMSP119-GST, P = 0.026) than ConA. GST failed to induce cell proliferation (P < 0.00001; Fig. 4e).

Cross‑reactivity of rPoMSP119-GST proteins with anti‑rPoMSP119-GST antibodies

We examined cross-reactivity between rPocMSP119-GST and rPowMSP119-GST using ELISA. rPocMSP119-GST could recognize IgG of sera from mice immunized with rPowMSP119-GST (Fig. 5a, d), with no significant difference observed in cross-reactivity and avidity indices of cross-reaction (P > 0.05). However, anti-GST IgG antibodies showed a significantly lower level of cross-reactivity and avidity indices of cross-reaction with rPocMSP119-GST than in reaction of rPocMSP119-GST with anti-rPocMSP119-GST IgG (P < 0.001; Fig. 5a, d). In addition, the cross-reactivity and affinity of anti-rPocMSP119-GST antibodies and rPowMSP119-GST showed no significance difference in comparison to the reaction of rPowMSP119-GST with anti-rPowMSP119-GST antibodies (Fig. 5b, e). Unexpectedly, rPocMSP119-GST and rPowMSP119-GST showed a significantly higher cross-reactivity and affinity than those of GST with anti-GST antibodies (P < 0.05) (Fig. 5c, f). These results suggested that either rPocMSP119-GST or rPowMSP119-GST had the ability to recognize and bind with high-affinity antibodies induced in mice immunized with rPoMSP119-GST.

Fig. 5
figure 5

a–e Cross-reactivity of rPoMSP119-GST proteins with antisera from mice immunized with rPoMSP119-GST. a Cross-reactivity of rPowMSP119-GST and GST with sera of mice immunized with rPocMSP119-GST protein. b Cross-reactivity of rPocMSP119-GST and GST with sera of mice immunized with rPowMSP119-GST protein. c Cross-reactivity of rPoMSP119-GST with sera from mice immunized with GST protein. c–e Avidity indices of cross-reaction to anti-rPoMSP119-GST IgG [positive control (PC)]. The data are shown as the mean OD (the OD reflects the magnitude of the immune response). * P < 0.05, ** P < 0.01, *** P < 0.001; ns P > 0.05. For other abbreviations, see Figs. 1, 2 and  4

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Humoral immune responses to rPoMSP119-GST in P. ovale infections

Naturally acquired humoral immune responses in patients infected with P. ovale were assessed against rPoMSP119-GST. Protein microarrays were used to screen anti-rPoMSP119-GST antibodies in 29 serum samples from P. ovale-infected individuals and 20 serum samples from healthy individuals (Additional file 3: Table S2). Patients infected with P. ovale showed significantly higher MFI of total IgG against rPocMSP119-GST and rPowMSP119-GST than healthy individuals (P < 0.0001) (Fig. 6a, b). Anti-rPocMSP119-GST antibodies showed sensitivity and specificity of 89.96% (MFI value of 26/29 patient samples > cut-off value of 5752.4) and 75% (MFI value of 15/20 healthy samples < 5752.4), respectively. Anti-rPowMSP119-GST antibodies showed sensitivity and specificity of 89.96% (MFI value of 26/29 patient samples > cut-off value 7092) and 75% (MFI value of 15/20 healthy samples < cut-off value 7092), respectively. However, no statistically significant difference was observed in the MFI of total IgG against GST protein between P. ovale-infected and healthy individuals (P = 0.5964; Fig. 6c). These results showed that both rPocMSP119-GST and rPowMSP119-GST are targets of signatures of exposure and immunity.

Fig. 6
figure 6

a–c Analysis of humoral immune responses to rPoMSP119-GST in Plasmodium ovale infections. a IgG responses to rPocMSP119-GST in patients infected with P. ovale and in healthy individuals. b IgG responses to rPowMSP119-GST in patients infected with P. ovale and in healthy individuals. c IgG responses to GST in P. ovale-infected patients and in healthy individuals. * P < 0.05, ** P < 0.01, *** P < 0.001; ns P > 0.05. For abbreviations, see Figs. 1, 2 and  4

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Discussion

Molecules of blood-stage malaria parasites are components of interest for the development of effective malaria vaccines [43]. Several merozoite surface proteins are regarded as promising malaria vaccine candidates because they are targets of host immune selection and play essential roles in erythrocyte invasion [28, 44]. In the first rodent model used to study a malaria vaccine, MSP1 was proven to provide protection against challenge infection [45]. That study showed that after MSP1 undergoes proteolytic cleavage only MSP119 is carried into the invaded erythrocytes. In a later study, antibodies against MSP119 were shown to prevent merozoites from invading erythrocytes in vitro [20]. Antigenic diversity increases the difficulty of developing an effective malaria vaccine, as it helps parasites to escape from host immune responses [46]. In the present study, sequences of pomsp119 were completely conserved in 20 P. ovale curtisi and 17 P. ovale wallikeri clinical isolates. These results are consistent with those from previous studies which reported genetic conservation of msp119 across malaria parasites [33, 36, 37]. Immune-mediated selection pressure is an important mechanism as it may lead to antigenic diversity [47]. In the present study, we found that the C-terminal region of PoMSP119 is under relatively lower selective pressure than the N-terminal of PoMSP1, which has also been shown to have low genetic diversity [34].

Antibodies play an important role in protection against clinical disease. Earlier studies suggested that antibody responses to PfMSP119 might protect children from high levels of blood-stage parasitemia and clinical malaria [32]. In the present study, cross-reaction between rPocMSP119-GST and rPowMSP119-GST was detected. This cross-reaction indicates that rPocMSP119 and rPowMSP119 share similar antigenic determinants and, therefore, PoMSP119 might possess species-specific efficacy as a vaccine candidate. In addition, as rPoMSP119-GST protein contains the GST tag, rPocMSP119-GST and rPowMSP119-GST could be detected by using the sera of mice immunized with GST protein as a non-specific control. Of the five classes of immunoglobulins, IgG is well-known as one that plays a critical role in malaria immunity [48]. A significantly higher level of IgG antibodies was detected in the sera of mice immunized with rPoMSP119-GST proteins than in the sera of the control group of mice immunized with GST protein (Fig. 4), which showed that rPoMSP119-GST induced immune responses in mice. There was no significant difference in cross-reactivity between anti-rPocMSP119-GST IgG and anti-rPowMSP119-GST IgG antibodies, while the affinity index of anti-rPoMSP119-GST IgG was higher than that of the GST group in the cross-reactivity and autoantigen binding test (Fig. 5). These findings imply that antibodies induced in mice immunized with rPoMSP119-GST can bind tightly to antigens and tend to mature. Although anti-GST antibodies were induced in mice immunized with GST protein, affinity maturation was not promoted. High-affinity antibodies are advantageous in a number of biological functions [49]. A better understanding of cellular responses can help in the development of effective blood-stage vaccine candidates for malaria. Lymphocytes play a key role in the immune system and have been shown to be specific for immune responses to infectious microorganisms and other foreign substances [50]. Lymphocyte proliferation assays are widely used to determine T cell immune responsiveness to an antigenic stimulus. The current study showed that rPocMSP119-GST could stimulate the proliferation of T cells (Fig. 4f). This result is particularly instructive as it proves that rPocMSP119-GST can induce cellular immune responses in mice, and more importantly, proves the immunogenicity of rPoMSP119-GST in mice.

A number of studies have reported serologic analyses that investigated IgG antibodies against specific antigens of P. falciparum and P. vivax to assess infection incidence and immunity levels [17, 51, 52]; however, the question of response specificity has not been fully explored. In this study, we also analyzed humoral immune responses in P. ovale infections. Most of the P. ovale-infected serum samples showed positive antibody responses to rPoMSP119-GST, with a high sensitivity (89.96%) and specificity (75%). The differences in immune responses were not related to the presence of GST protein as no significant difference was observed in the MFI of total IgG against GST protein between P. ovale-infected and healthy individuals (Fig. 6). These data confirmed the antigenicity of rPoMSP119-GST, which may indirectly reflect or contribute to protection against P. ovale malaria infection as humoral immune responses are partly involved in preventing clinical malaria [53]. Seroepidemiological studies have been particularly informative in areas of low transmission where the sensitivity of surveys for prevalence of malaria parasites is impacted by the low number of parasite-infected individuals [54]. Previous studies have used PfMSP119 and PvMSP119 as serological markers to detect the prevalence of malaria parasites [55, 56]. Due to the limited number of serum samples in the present study we were not able to compare differences in the signal of serological responses with respect to other criteria such as gender and parasite density. However, PoMSP119 as a biomarker of exposure is worthy of further study.

Conclusions

This study demonstrated that pomsp119 sequences were completely conserved in clinical P. ovale curtisi and P. ovale wallikeri isolates. Furthermore, the immunogenicity of rPoMSP119 in mice was comprehensively analyzed. The informative results presented here contribute to the knowledge base for the development of a PoMSP119-based vaccine. In addition, the naturally acquired antibody responses against rPoMSP119 shown here indicate that further study of PoMSP119 could provide new insights for serological research. The cross-reactivity of PoMSP119 with sera from patients infected with P. falciparum or P. vivax needs to be explored in future studies, as does the clinical protection against malaria afforded by anti-PoMSP119 antibodies.

Availability of data and materials

The data supporting the conclusions of this article are included within the article and its additional files. The new sequences identified in this study have been deposited in GenBank with the accession numbers MZ766552-MZ766553.

Abbreviations

ELISA:

Enzyme-linked immunosorbent assay

GPI:

Glycophosphatidylinositol

GST:

Glutathione S-transferase

IgG:

Immunoglobulin G

MSP1:

Merozoite surface protein 1

PCR:

Polymerase chain reaction

SDS-PAGE:

Sodium dodecyl sulfate–polyacrylamide gel electrophoresis

References

  1. World Health Organization. World malaria report 2019. Geneva. 2020. http://www.who.int/malaria/publications/world_malaria_report/en/.

  2. Collins WE, Jeffery GM. Plasmodium ovale: parasite and disease. Clin Microbiol Rev. 2005;18:570–81.

    Article  PubMed  PubMed Central  Google Scholar 

  3. Sutherland CJ, Tanomsing N, Nolder D, Oguike M, Jennison C, Pukrittayakamee S, et al. Two nonrecombining sympatric forms of the human malaria parasite Plasmodium ovale occur globally. J Infect Dis. 2010;201:1544–50.

    Article  CAS  PubMed  Google Scholar 

  4. Mueller I, Zimmerman PA, Reeder JC. Plasmodium malariae and Plasmodium ovale—the “bashful” malaria parasites. Trends Parasitol. 2007;23:278–83.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  5. Oguike MC, Betson M, Burke M, Nolder D, Stothard JR, Kleinschmidt I, et al. Plasmodium ovale curtisi and Plasmodium ovale wallikeri circulate simultaneously in African communities. Int J Parasitol. 2011;41:677–83.

    Article  PubMed  PubMed Central  Google Scholar 

  6. Kotepui M, Kotepui KU, Milanez GD, Masangkay FR. Severity and mortality of severe Plasmodium ovale infection: a systematic review and meta-analysis. PLoS ONE. 2020;15:e0235014.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  7. Dini S, Douglas NM, Poespoprodjo JR, Kenangalem E, Sugiarto P, Plumb ID, et al. The risk of morbidity and mortality following recurrent malaria in Papua, Indonesia: a retrospective cohort study. BMC Med. 2020;18:28.

    Article  PubMed  PubMed Central  Google Scholar 

  8. Vandoolaeghe P, Schuerman L. The RTS, S/AS01 malaria vaccine in children 5 to 17 months of age at first vaccination. Expert Rev Vaccines. 2016;15:1481–93.

    Article  CAS  PubMed  Google Scholar 

  9. Kassegne K, Abe EM, Chen JH, Zhou XN. Immunomic approaches for antigen discovery of human parasites. Expert Rev Proteomics. 2016;13:1091–101.

    Article  CAS  PubMed  Google Scholar 

  10. Kaslow DC. Malaria vaccine research & innovation: the intersection of IA2030 and zero malaria. NPJ Vaccines. 2020;5:109.

    Article  PubMed  PubMed Central  Google Scholar 

  11. Chen JH, Fen J, Zhou XN. From 30 million to zero malaria cases in China: lessons learned for China-Africa collaboration in malaria elimination. Infect Dis Poverty. 2021;10:51.

    Article  PubMed  PubMed Central  Google Scholar 

  12. Zhou S, Li Z, Cotter C, Zheng C, Zhang Q, Li H, et al. Trends of imported malaria in China 2010–2014: analysis of surveillance data. Malar J. 2016;15:39.

    Article  PubMed  PubMed Central  Google Scholar 

  13. Cao Y, Wang W, Liu Y, Cotter C, Zhou H, Zhu G, et al. The increasing importance of Plasmodium ovale and Plasmodium malariae in a malaria elimination setting: an observational study of imported cases in Jiangsu Province, China, 2011–2014. Malar J. 2016;15:459.

    Article  PubMed  PubMed Central  Google Scholar 

  14. Xia J, Wu D, Sun L, Zhu H, Li K, Zhang J, et al. Characteristics of imported Plasmodium ovale spp. and Plasmodium malariae in Hubei Province, China, 2014–2018. Malar J. 2020;19:264.

    Article  PubMed  PubMed Central  Google Scholar 

  15. Ladda R, Aikawa M, Sprinz H. Penetration of erythrocytes by merozoites of mammalian and avian malarial parasites 1969. J Parasitol. 2001;87:470–8.

    CAS  PubMed  Google Scholar 

  16. Osier FH, Fegan G, Polley SD, Murungi L, Verra F, Tetteh KK, et al. Breadth and magnitude of antibody responses to multiple Plasmodium falciparum merozoite antigens are associated with protection from clinical malaria. Infect Immun. 2008;76:2240–8.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  17. Fowkes FJ, Richards JS, Simpson JA, Beeson JG. The relationship between anti-merozoite antibodies and incidence of Plasmodium falciparum malaria: a systematic review and meta-analysis. PLoS Med. 2010;7:e1000218.

    Article  PubMed  PubMed Central  Google Scholar 

  18. Richards JS, Arumugam TU, Reiling L, Healer J, Hodder AN, Fowkes FJ, et al. Identification and prioritization of merozoite antigens as targets of protective human immunity to Plasmodium falciparum malaria for vaccine and biomarker development. J Immunol. 2013;191:795–809.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  19. Cooper JA. Merozoite surface antigen-I of Plasmodium. Parasitol Today. 1993;9:50–4.

    Article  CAS  PubMed  Google Scholar 

  20. Blackman MJ, Heidrich HG, Donachie S, McBride JS, Holder AA. A single fragment of a malaria merozoite surface protein remains on the parasite during red cell invasion and is the target of invasion-inhibiting antibodies. J Exp Med. 1990;172:379–82.

    Article  CAS  PubMed  Google Scholar 

  21. Blackman MJ, Whittle H, Holder AA. Processing of the Plasmodium falciparum major merozoite surface protein-1: identification of a 33-kilodalton secondary processing product which is shed prior to erythrocyte invasion. Mol Biochem Parasitol. 1991;49:35–44.

    Article  CAS  PubMed  Google Scholar 

  22. Holder AA, Blackman MJ, Burghaus PA, Chappel JA, Ling IT, McCallum-Deighton N, et al. A malaria merozoite surface protein (MSP1)-structure, processing and function. Mem Inst Oswaldo Cruz. 1992;87:37–42.

    Article  PubMed  Google Scholar 

  23. Kang Y, Long CA. Sequence heterogeneity of the C-terminal, Cys-rich region of the merozoite surface protein-1 (MSP-1) in field samples of Plasmodium falciparum. Mol Biochem Parasitol. 1995;73:103–10.

    Article  CAS  PubMed  Google Scholar 

  24. Miller LH, Roberts T, Shahabuddin M, McCutchan TF. Analysis of sequence diversity in the Plasmodium falciparum merozoite surface protein-1 (MSP-1). Mol Biochem Parasitol. 1993;59:1–14.

    Article  CAS  PubMed  Google Scholar 

  25. Qari SH, Shi YP, Goldman IF, Nahlen BL, Tibayrenc M, Lal AA. Predicted and observed alleles of Plasmodium falciparum merozoite surface protein-1 (MSP-1), a potential malaria vaccine antigen. Mol Biochem Parasitol. 1998;92:241–52.

    Article  CAS  PubMed  Google Scholar 

  26. Thakur A, Alam MT, Sharma YD. Genetic diversity in the C-terminal 42 kDa region of merozoite surface protein-1 of Plasmodium vivax (PvMSP-1(42)) among Indian isolates. Acta Trop. 2008;108:58–63.

    Article  CAS  PubMed  Google Scholar 

  27. Murhandarwati EEH, Herningtyas EH, Puspawati P, Mau F, Chen SB, Shen HM, et al. Genetic diversity of merozoite surface protein 1–42 (MSP1–42) fragment of Plasmodium vivax from Indonesian isolates: rationale implementation of candidate MSP1 vaccine. Infect Genet Evol. 2020;85:104573.

    Article  CAS  PubMed  Google Scholar 

  28. Kassegne K, Komi Koukoura K, Shen HM, Chen SB, Fu HT, Chen YQ, et al. Genome-wide analysis of the malaria parasite Plasmodium falciparum isolates from Togo reveals selective signals in immune selection-related antigen genes. Front Immunol. 2020;11:552698.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  29. Guevara Patino JA, Holder AA, McBride JS, Blackman MJ. Antibodies that inhibit malaria merozoite surface protein-1 processing and erythrocyte invasion are blocked by naturally acquired human antibodies. J Exp Med. 1997;186:1689–99.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  30. Branch OH, Udhayakumar V, Hightower AW, Oloo AJ, Hawley WA, Nahlen BL, et al. A longitudinal investigation of IgG and IgM antibody responses to the merozoite surface protein-1 19-kiloDalton domain of Plasmodium falciparum in pregnant women and infants: associations with febrile illness, parasitemia, and anemia. Am J Trop Med Hyg. 1998;58:211–9.

    Article  CAS  PubMed  Google Scholar 

  31. Okech BA, Corran PH, Todd J, Joynson-Hicks A, Uthaipibull C, Egwang TG, et al. Fine specificity of serum antibodies to Plasmodium falciparum merozoite surface protein, PfMSP-1(19), predicts protection from malaria infection and high-density parasitemia. Infect Immun. 2004;72:1557–67.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  32. Egan AF, Morris J, Barnish G, Allen S, Greenwood BM, Kaslow DC, et al. Clinical immunity to Plasmodium falciparum malaria is associated with serum antibodies to the 19-kDa C-terminal fragment of the merozoite surface antigen, PfMSP-1. J Infect Dis. 1996;173:765–9.

    Article  CAS  PubMed  Google Scholar 

  33. Putaporntip C, Hughes AL, Jongwutiwes S. Low level of sequence diversity at merozoite surface protein-1 locus of Plasmodium ovale curtisi and P. ovale wallikeri from Thai isolates. PLoS ONE. 2013;8:e58962.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  34. Chu R, Zhang X, Xu S, Chen L, Tang J, Li Y, et al. Limited genetic diversity of N-terminal of merozoite surface protein-1 (MSP-1) in Plasmodium ovale curtisi and P. ovale wallikeri imported from Africa to China. Parasit Vectors. 2018;11:596.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  35. Uwase J, Chu R, Kassegne K, Lei Y, Shen F, Fu H, et al. Immunogenicity analysis of conserved fragments in Plasmodium ovale species merozoite surface protein 4. Malar J. 2020;19:126.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  36. Birkenmeyer L, Muerhoff AS, Dawson GJ, Desai SM. Isolation and characterization of the MSP1 genes from Plasmodium malariae and Plasmodium ovale. Am J Trop Med Hyg. 2010;82:996–1003.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  37. Priest JW, Plucinski MM, Huber CS, Rogier E, Mao B, Gregory CJ, et al. Specificity of the IgG antibody response to Plasmodium falciparum, Plasmodium vivax, Plasmodium malariae, and Plasmodium ovale MSP119 subunit proteins in multiplexed serologic assays. Malar J. 2018;17:417.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  38. Zhang X, Chu R, Xu S, Fu H, Tang J, Chen L, et al. Immunogenicity analysis of genetically conserved segments in Plasmodium ovale merozoite surface protein-8. Parasit Vectors. 2019;1:164.

    Article  Google Scholar 

  39. Eberhardt MK, Chang WL, Logsdon NJ, Yue Y, Walter MR, Barry PA. Host immune responses to a viral immune modulating protein: immunogenicity of viral interleukin-10 in rhesus cytomegalovirus-infected rhesus macaques. PLoS ONE. 2012;7:e37931.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  40. Cheng Y, Shin EH, Lu F, Wang B, Choe J, Tsuboi T, et al. Antigenicity studies in humans and immunogenicity studies in mice: an MSP1P subdomain as a candidate for malaria vaccine development. Microbes Infect. 2014;16:419–28.

    Article  CAS  PubMed  Google Scholar 

  41. Chen JH, Jung JW, Wang Y, Ha KS, Lu F, Lim CS, et al. Immunoproteomics profiling of blood stage Plasmodium vivax infection by high-throughput screening assays. J Proteome Res. 2010;3:6479–89.

    Article  Google Scholar 

  42. Kassegne K, Zhang T, Chen SB, Xu B, Dang ZS, Deng WP, et al. Study roadmap for high-throughput development of easy to use and affordable biomarkers as diagnostics for tropical diseases: a focus on malaria and schistosomiasis. Infect Dis Poverty. 2017;6:130.

    Article  PubMed  PubMed Central  Google Scholar 

  43. Duffy PE, Patrick GJ. Malaria vaccines since 2000: progress, priorities, products. NPJ Vaccines. 2020;5:48.

    Article  PubMed  PubMed Central  Google Scholar 

  44. Holder AA. Malaria vaccines: where next? PLoS Pathog. 2009;5(10):e1000638.

    Article  PubMed  PubMed Central  Google Scholar 

  45. Holder AA, Freeman RR. Immunization against blood-stage rodent malaria using purified parasite antigens. Nature. 1981;294:361–4.

    Article  CAS  PubMed  Google Scholar 

  46. malERA Refresh Consultative Panel on Tools for Malaria Elimination. malERA: an updated research agenda for diagnostics, drugs, vaccines, and vector control in malaria elimination and eradication. PLoS Med. 2017;14:e1002455.

  47. O’Donnell RA, Saul A, Cowman AF, Crabb BS. Functional conservation of the malaria vaccine antigen MSP-119 across distantly related Plasmodium species. Nat Med. 2000;6:91–5.

    Article  CAS  PubMed  Google Scholar 

  48. Megnekou R, Staalsoe T, Taylor DW, Leke R, Hviid L. Effects of pregnancy and intensity of Plasmodium falciparum transmission on immunoglobulin G subclass responses to variant surface antigens. Infect Immun. 2005;73:4112–8.

    Article  CAS  PubMed  PubMed Central  Google Scholar 

  49. Steward MW, Lew AM. The importance of antibody affinity in the performance of immunoassays for antibody. J Immunol Methods. 1985;78:173–90.

    Article  CAS  PubMed  Google Scholar 

  50. Khosravi M, Rahimi R, Pourahmad J, Zarei MH, Rabbani M. Comparison of kinetic study and protective effects of biological dipeptide and two porphyrin derivatives on metal cytotoxicity toward human lymphocytes. Iran J Pharm Res. 2017;16:1059–70.

    CAS  PubMed  PubMed Central  Google Scholar 

  51. Cutts JC, Powell R, Agius PA, Beeson JG, Simpson JA, Fowkes FJ. Immunological markers of Plasmodium vivax exposure and immunity: a systematic review and meta-analysis. BMC Med. 2014;12:150.

    Article  PubMed  PubMed Central  Google Scholar 

  52. Folegatti PM, Siqueira AM, Monteiro WM, Lacerda MV, Drakeley CJ, Braga EM. A systematic review on malaria sero-epidemiology studies in the Brazilian Amazon: insights into immunological markers for exposure and protection. Malar J. 2017;16:107.

    Article  PubMed  PubMed Central  Google Scholar 

  53. Diallo TO, Remoue F, Gaayeb L, Schacht AM, Charrier N, De Clerck D, et al. Schistosomiasis coinfection in children influences acquired immune response against Plasmodium falciparum malaria antigens. PLoS ONE. 2010;5:e12764.

    Article  PubMed  PubMed Central  Google Scholar 

  54. Cook J, Reid H, Iavro J, Kuwahata M, Taleo G, Clements A, et al. Using serological measures to monitor changes in malaria transmission in Vanuatu. Malar J. 2010;9:169.

    Article  PubMed  PubMed Central  Google Scholar 

  55. Biggs J, Raman J, Cook J, Hlongwana K, Drakeley C, Morris N, et al. Serology reveals heterogeneity of Plasmodium falciparum transmission in northeastern South Africa: implications for malaria elimination. Malar J. 2017;16:48.

    Article  PubMed  PubMed Central  Google Scholar 

  56. Rodrigues MH, Cunha MG, Machado RL, Ferreira OC Jr, Rodrigues MM, Soares IS. Serological detection of Plasmodium vivax malaria using recombinant proteins corresponding to the 19-kDa C-terminal region of the merozoite surface protein-1. Malar J. 2003;2:39.

    Article  PubMed  PubMed Central  Google Scholar 

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Acknowledgements

The authors would like to thank the local health officials of the hospitals in Jiangsu Province, China and Jiangsu Institute of Parasitic Diseases for their support in providing clinical samples of P. ovale.

Funding

This work was supported by the National Natural Science Foundation of China (81871681, 81971967); the Jiangsu Provincial Department of Science and Technology (no. BM2018020); and the National First-class Discipline Program of Food Science and Technology (JUFSTR20180101).

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  1. Qinwen Xu and Sihong Liu contributed equally to this work

Authors and Affiliations

  1. Laboratory of Pathogen Infection and Immunity, Department of Public Health and Preventive Medicine, Wuxi School of Medicine, Jiangnan University, Wuxi, Jiangsu, People’s Republic of China

    Qinwen Xu, Bo Yang, Jiachen Lu, Yifan Sun, Wenli Zhong, Miaosa Zhang, Jun Cao & Yang Cheng

  2. Key Laboratory of National Health and Family Planning Commission on Parasitic Disease Control and Prevention, Jiangsu Provincial Key Laboratory on Parasite and Vector Control Technology, Jiangsu Institute of Parasite Diseases, Wuxi, 214064, Jiangsu, People’s Republic of China

    Sihong Liu, Yaobao Liu, Guoding Zhu & Jun Cao

  3. School of Global Health, Chinese Center for Tropical Diseases Research, Shanghai Jiao Tong University School of Medicine, Shanghai, 200025, People’s Republic of China

    Kokouvi Kassegne

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Contributions

YC and JC conceived and designed the study. YBL, GDZ, JC and QBW collected the samples. QWX, SHL, BY and JCL conducted the laboratory work. QWX and KK wrote the manuscript. KK and YFS reviewed the manuscript. WLZ and MSZ analyzed the data. All authors read and approved the final manuscript.

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Correspondence to Jun Cao or Yang Cheng.

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This study was approved by the Ethics Committee of Jiangsu Provincial Key Laboratory on Parasite and Vector Control Technology, Jiangsu Institute of Parasitic Diseases (IRB00004221), Wuxi, China. The animal trial was approved by the Animal Ethics Committee of Jiangnan University [JN no. 20180615t0900930 (100)].

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Supplementary Information

Additional file 1

: Table S1. Information on imported Plasmodium ovale curtisi and Plasmodium ovale wallikeri isolates used in this study.

Additional file 2: Figure S1.

Alignments of amino acid sequences of Plasmodium ovale curtisi and Plasmodium ovale wallikeri MSP119 in all amplified clinical isolates.

Additional file 3: Table S2.

Information on serum samples from patients infected with Plasmodium ovale used for the microarrays.

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Xu, Q., Liu, S., Kassegne, K. et al. Genetic diversity and immunogenicity of the merozoite surface protein 1 C-terminal 19-kDa fragment of Plasmodium ovale imported from Africa into China. Parasites Vectors 14, 583 (2021). https://doi.org/10.1186/s13071-021-05086-6

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