A comparative study of Toxoplasma gondii seroprevalence in three healthy Chinese populations detected using native and recombinant antigens

  • Xiaojing Sun1,

    Affiliated with

    • Huijun Lu1,

      Affiliated with

      • Boyin Jia1,

        Affiliated with

        • Zhiguang Chang1,

          Affiliated with

          • Shuai Peng1,

            Affiliated with

            • Jigang Yin1,

              Affiliated with

              • Qijun Chen1Email author and

                Affiliated with

                • Ning Jiang1Email author

                  Affiliated with

                  Parasites & Vectors20136:241

                  DOI: 10.1186/1756-3305-6-241

                  Received: 22 July 2013

                  Accepted: 18 August 2013

                  Published: 20 August 2013

                  Abstract

                  Background

                  Toxoplasmosis is one of the most common parasitic zoonoses. The seroprevalence of Toxoplasma gondii infection in humans varies widely worldwide. Detection of Toxoplasma-specific antibodies has been a gold standard method for both epidemiological investigation and clinical diagnosis. Genetic investigation indicated that there is a wide distribution of different genome types or variants of the parasite prevalent in different areas. Thus the reliability of using antigens from parasites of a single genome type for diagnosis and epidemiology purposes needs to be extensively evaluated.

                  Methods

                  In this study, the prevalence of T. gondii infection among 880 clinically healthy individuals in China was systematically tested using crude soluble native antigens and purified recombinant antigens of type I and II T. gondii. The T. gondii-specific IgG and IgM in the sera was further confirmed using commercial Toxoplasmosis Diagnosis Kits and Western blot assays.

                  Results

                  The sero-prevalence of T. gondii-specific IgG detected with crude native Type I and type II antigens was 12.2% and 11.3% respectively. Whereas the overall prevalence was more than 20% when combined with the results obtained with recombinant tachyzoite and bradyzoite antigens. There was an obvious variation in immune-recognition of parasite antigens among the individuals studied.

                  Conclusions

                  The general prevalence of anti-T. gondii IgG in the study population was likely much higher than previously reported. The data also suggested that there is more genetic diversity among the T. gondii isolates in China. Further, combination of recombinant antigens with clear immuno-recognition will be able to generate more sensitive diagnostic results than those obtained with crude antigens of T. gondii tachyzoites.

                  Keywords

                  Toxoplasma gondii Prevalence Antigens China

                  Background

                  Toxoplasma gondii is an intracellular parasite that can infect domestic, wild, and companion animals, and it also commonly infects humans [1]. The importance of this parasite in food safety, human health and animal husbandry has been well recognized. Though T. gondii infection in humans with a normal immune competence is asymptomatic in most cases, the parasites do pose threats to individuals who are immunocompromised, such as HIV carriers [2]. It has been estimated that up to one third of the world’s population has been infected by T. gondii with an endemicity from around 10% to 70% [1, 35] and the prevalence is higher in warm and humid areas [68]. In several studies, patients with schizophrenia were found to have a higher tendency of T. gondii infection [912], but there has been no conclusive correlation between T. gondii infection and psychiatric disease [13].

                  Toxoplasma gondii displays significant genetic diversity in different geographical regions [1416]. Currently, toxoplasmosis is diagnosed primarily by demonstrating parasite-specific IgM or IgG antibodies in serum samples. Most of the commercially available tests use T. gondii native antigens derived from the fast growing tachyzoites which may result in variations in accuracy of detection. Recombinant antigens have been suggested as diagnostic reagents but their reliability may need extensive experimental validation [17, 18]. Further, T. gondii remains dormant as bradyzoites in immune competent individuals, which can convert to tachyzoites when the host immune defense system is compromised, and tachyzoites and bradyzoites do display different antigenic profiles [19]. Thus it is critical to select accurate antigens for diagnostic and epidemiological purposes.

                  In this study, we investigated the level of anti-T. gondii IgG and IgM in the sera of more than 800 Chinese individuals living in the southern and northern regions of China, comparing crude antigens of RH (Type I) and ME49 (Type II) strains and 12 recombinant antigens of either Type I or Type II T. gondii. The purpose is to compare the sensitivity and consistency in detection of T. gondii specific antibodies in the same set of samples with different antigens.

                  Methods

                  Study populations and serum samples

                  880 serum samples from clinically healthy individuals were collected in Changchun, Daqing and Shanghai areas in China from July 2006 to June 2012 as described previously [20]. The sera were collected with the consent of the volunteers. The study was carried out with permission from the Ethical Committee of Institute of Zoonosis, Jilin University, China.

                  Antigens

                  Soluble native parasite antigens: T. gondii tachyzoites of RH and ME49 strains were cultivated in BHK (baby hamster kidney) cell lines as described earlier [21]. Briefly parasites released from host cells were harvested, washed in PBS and lysed by sonication. The insoluble component such as cell debris was eliminated by centrifugation (12,000 rpm for 30 min) and the soluble proteins, respectively termed RH-Ag and ME49-Ag were collected and diluted to a final concentration of 1 mg/ml in PBS for the serological test.

                  Recombinant antigens: To generate the recombinant antigens, the coding sequences of T. gondii, which including tachyzoite-specific (SAG1, SAG5A and SAG5D), bradyzoite-specific (BAG1, BSR4 and SRS9) and common antigens (MIC6, SRS4, GRA5, SUS1, SAG3, and SRS8) likely expressed in both tachyzoites and bradyzoites were amplified by the Polymerase Chain Reaction (PCR). Their accession numbers and primer sequences are listed in Table 1. Genomic DNA was isolated from the tachyzoites of the T. gondii RH and ME49 strains and was used as the template for PCR amplification of the coding sequences. The PCR reaction was carried out in a 25 μl reaction mixture containing 10 μM of each primer, 2.5 mM of each dNTP, 1.25 U of Ex Taq DNA polymerase (TAKARA), 0.5 μg DNA template, and 1 × Ex Taq buffer. The touchdown PCR was performed on the PCR System (Applied Biosystems, CA, USA) with a program of initial denaturation for 4 min at 94°C; 35 cycles of 94°C for 45 s, annealing for 45 s (initial temperature 61°C, then decreasing by 0.3°C/cycle), and 72°C for 2 min; and a final extension at 72°C for 10 min. The PCR products were respectively cloned into the plasmid pGEX-4T-1 (GE Healthsystems, Uppsala, Sweden) and PET-28a (Qiagen, Düsseldorf, Germany) to construct recombinant plasmids, which were subsequently confirmed by sequencing. The plasmids with correct sequences were transformed into BL21 competent cells and the His-tag and GST-tag fusion proteins were expressed and purified according to a standard protocol as described [22]. They were respectively named as RH-rAg, ME49-rAg and RH/ME49-rAg. The recombinant proteins were diluted to a final concentration of 1 mg/ml in PBS for the serological test.
                  Table 1

                  Primer sequences used in the Polymerase Chain Reaction (PCR)

                  Gene name

                  NCBI accession no.

                  Primer sequence (5’-3’)

                  Amplified product (bp)

                  SAG5D

                  AY190528.1

                  F-GATGCGACCGGAACGACCC

                  981

                    

                  R-ATATGTGCCAAGAAAGACA

                   

                  SAG5A

                  AF013968.3

                  F-GAGGTAACGAATGTTCTG

                  1002

                    

                  R-GTATGCACCGAAAGAAACA

                   

                  MIC6

                  AF110270.1

                  F-TCCCCGTTTTTTGCCTTTC

                  792

                    

                  R-ATGTCCACTTCCTTCCTC

                   

                  SRS4

                  XM_002366109.1

                  F-CCACATGAAGGTAGTTTG

                  1068

                    

                  R-GTAGGAACCAGCAAGAAGC

                   

                  GRA5

                  EU918733.1

                  F-TCAACGCGTGACGTAGGG

                  132

                    

                  R-TCCAGTCACCGCTGCTC

                   

                  SAG1

                  AY217784.1

                  F-TCGGATCCCCCTCTTGTT

                  867

                    

                  R-CGCGACACAAGCTGCGAT

                   

                  SUS1

                  U77677.1

                  F-TCTCCTCTTTCGATGGCC

                  1131

                    

                  R-GACGGCACCAAACATAGC

                   

                  SAG3

                  JF312642.1

                  F-GAGCACGGACTGTTCGTCG

                  1035

                    

                  R-GGCAGCCACATGCACAAGG

                   

                  BAG1

                  XM_002365075.1

                  F-ATGGCGCCGTCAGCATCGC

                  687

                    

                  R-CTTCACGCTGATTTGTTGCT

                   

                  BSR4

                  XM_002369844.1

                  F-GATAATCTTCTTGAAGGAC

                  1038

                    

                  R-GGCGGCCGCGCTAGAGGC

                   

                  SRS8

                  XM_002371596.1

                  F-GAACAACTCGGCGAAGG

                  1077

                    

                  R-AAGGGAACCGGCAAGAAGC

                   

                  SRS9

                  AF465609.2

                  F-GACAGTCTGCATGAAGGA

                  1077

                    

                  R-CAATGAAGCAACAACGAAC

                   

                  Serological assay

                  Indirect ELISA assays were performed to measure the anti-T. gondii IgG level according to the standard protocol [23]. All reaction steps except coating and washing were performed at 37°C. Briefly, Maxisor micro-ELISA plates (Nalge Nunc International, IL, USA) were coated with 50 μl per well of the T. gondii antigens (RH-Ag, ME49-Ag and 12 recombinant antigens, respectively) in a concentration of 5 μg/ml at 4°C overnight. The plates were washed five times with PBS containing 0.05% Tween 20 and blocked for 3–4 h at 37°C with 100 μl per well of 0.5% BSA in PBS. After washing, 50 μl of each serum sample, diluted at 1:50 was added to the well in triplicates for 1 h. Alkaline phosphatase-labelled goat antihuman IgG (Sigma, St. Louis, USA, 1:2000 dilution) was added to the well after washing. Finally, 50 μl of NPP [4-Nitrophenyl phosphate disodium salt hexahydrate] (Sigma, St. Louis, USA) and 9.7% diethanolamine (pH 9.8) were used to detect antigen-antibody reactions. The plates were finally read in a Biotek 93 micro-ELISA auto-reader 808 at 405 nm. A human serum sample, which was previously confirmed with negative reactivity to T. gondii by the direct agglutination test was included as a negative control in every plate. The GST protein was used as control for the GST-tag fusion antigens. The cut-off point of OD value for a positive sample was set to be at least two times higher than that of the negative sample at any dilution point as described previously [20].

                  To further confirm the ELISA data, all positive and 50 randomly selected negative sera were further tested by the commercial T. gondii IgG/IgM Kits (Haitai Biological Pharmaceuticals Co., Ltd, China) that can respectively detect human IgG and IgM, and Western blot assays using soluble extract of T. gondii. The procedure of the commercial IgG/IgM kit was performed according to the manufacturer’s instruction [24]. For the purpose of Western blot assays, the parasite-derived soluble proteins were separated on a 12% SDS-PAGE gel and transferred onto nitrocellulose membranes (Bio-Rad, CA, USA). The membrane was cut into strips and incubated with the positive and negative sera (at 1:50 dilution) identified in the ELISA assays. Meanwhile, a serum of an individual previously confirmed with T. gondii infection was used as a positive control. The membrane strips were further incubated with an alkaline phosphatase-conjugated goat anti-human IgG antibody (1:20000 dilutions) after washing in TBST buffer (10 mM Tris, 150 mM NaCl, pH 8.0 and 0.05% Tween 20). Eventually, the strips were incubated with BCIP/NBT substrate solution to visualize the protein bands that were recognized by the specific antibodies.

                  Statistical analysis

                  The results were statistically analyzed using the SPSS 18.0 software package. Chi-square test was used to analyze the anti-T. gondii IgG seroprevalence by using twelve T. gondii antigens. The differences were considered to be statistically significant when the p value was less than 0.05 [20].

                  Results and discussion

                  In this study, the prevalence of anti-T. gondii antibodies (primarily IgG) in 880 individuals was detected using tachyzoite-derived crude parasite antigens of RH (RH-Ag, type I) and ME49 (ME49-Ag, Type II), and 12 recombinant antigens (Rec-Ag) of T. gondii. The prevalence of anti-T. gondii IgG in the study population obtained with crude antigens was 12.2% and 11.3%, respectively (Table 2). We have previously investigated T. gondii prevalence in clinical healthy individuals with crude antigens of the RH strain T. gondii, the results obtained in this study was consistent with our previous study [20]. However, among the 173 samples which were positive, only 20 samples were positive by both RH-Ag and ME49-Ag (Table 2 and Figure 1), suggesting strong strain-specific immune-response in the population. Though the data reflected the exposure of T. gondii in the investigated population, the actual seroprevalence of infection may be under represented due to the fact that both RH-Ag and ME49-Ag were generated from tachyzoites. It is well known that T. gondii remains as the relatively quiescent bradyzoite stage in immuocompetent hosts, and comparative studies indicated that bradyzoites and tachyzoites do have different gene expression profiles, which may result in differences in elicitation of host immune responses [25]. However, due to technical difficulties in obtaining enough bradyzoites, the currently diagnostic antigens have all been obtained from the fast growing tachyzoites.
                  Table 2

                  Positive serum number and prevalence of anti- T. gondii IgG detected with different antigens

                  Strain of T. gondii

                  Antigen names

                  Stage and location

                  Number of samples (n = 880) with anti-T. gondii IgG and prevalence (%)

                  Independent positive rate

                  Cross-positive rate

                  Combined positive rate

                  Inter-strains

                  RH

                  RH-Ag

                  Tachyzoite crude antigens

                  107 (12.2%)

                    

                  ME49

                  ME49-Ag

                  Tachyzoite crude antigens

                  99 (11.3%)

                    
                   

                  SAG5D

                  Tachyzoite, surface

                  87 (9.9%)

                  17.5%

                   

                  SAG5A

                  Tachyzoite surface

                  93 (10.6%)

                  RH-rAg

                  MIC6

                  Microneme

                  96 (10.9%)

                  SRS4

                  Surface

                  98 (11.2%)

                   

                  GRA5

                  Dense granule

                  91 (10.4%)

                  15.6%

                  SAG1

                  Tachyzoite surface

                  93 (10.6%)

                  ME49-rAg

                  SUS1

                  Surface

                  93 (10.6%)

                  28.2%

                  SAG3

                  Surface

                  96 (10. 9%)

                  BAG1

                  Bradyzoite, cytoplasmic

                  131 (14.9%)

                  RH/ME49-rAg

                  BSR4

                  Bradyzoite, surface

                  94 (10.7%)

                  19.2%

                  SRS8

                  Surface

                  104 (11.8%)

                  SRS9

                  Bradyzoite, surface

                  97 (11.0%)

                  http://static-content.springer.com/image/art%3A10.1186%2F1756-3305-6-241/MediaObjects/13071_2013_Article_1026_Fig1_HTML.jpg
                  Figure 1

                  Number of positive sera in a clinically healthy population detected with three kinds of antigen. A shows the numbers and percentage (in bracket) of 394 sera with T. gondii-specific IgG detected by the crude antigens of RH, ME49 strain and recombinant antigens. B shows the numbers and percentage (in bracket) of the 208 positive sera with T. gondii-specific IgG detected by the recombinant antigens (RH-rAg, ME49-rAg, RH/ME49-rAg).

                  To test the differences in seroprevalence with tachyzoite- and bradyzoite-derived antigens, twelve recombinant antigens including three tachyzoite-specific, three bradyzoite-specific and six antigens likely expressed by both tachyzoites and bradyzoites (Table 2). These antigens have been previously proved to be immunogenic and frequently recognized by human antibodies [2628]. The seroprevalence of specific IgG to the individual recombinant antigens were around 10%, with one exception, the positive rate (14.9%) of BAG1-GST was significantly higher than that observed with other recombinant antigens or even crude antigens (p < 0.05) (Table 2). Thus immuno-recognition of BAG1 is likely more prominent than other bradyzoite antigens during chronic infection. BAG1 was a 30 kDa cytosolic protein which is only expressed in the bradyzoites [29, 30]. Immunological studies suggested that BAG1 was very immunogenic and could induce early humoral and cell-mediated immune responses upon infection in humans [31]. Thus it is not so surprising to observe a most prominent recognition of BAG1 by the sera compared to other tachyzoite- and bradyzoite-derived antigens.

                  On further analysis of the serum samples which were positive in the ELISA test, surprisingly it was found that the samples did not all overlapped or consistently react with the three kinds of antigen (Figure 1A). Among the 394 positive samples, 107 sera were positive with RH-Ag, 99 were positive with ME49-Ag and 248 were positive with the recombinant antigens. 20 samples which accounted for only 5.1% of all positive samples were detected by both RH-Ag and ME49-Ag. 20 samples, 5.1% of all positive sera, were detected by both RH-Ag and the Rec-Ags, and 26 sera, 6.6% of all positive samples, were detected by both ME49-Ag and the Rec-Ags (Figure 1A). Only 6 samples were positively detected in reactions with all three kinds of antigen and accounted for 1.5% of all positive samples. The reason that rAgs were more sensitive than native antigens may be due to the low concentration of the immunogenic components in the crude antigens. During T. gondii infection, a broad range of parasite antigens will be presented to the host immune system, thus the detection sensitivity using crude antigens will be affected by factors such as antibody affinity, antigen variation, inter-antigen interaction, and strain-specific responses. Similar results have been reported in previous studies [32, 33].

                  Analysis of the ELISA results in the assays with recombinant antigens of RH and ME49 strains showed, however, more overlapping between different strains (Figure 1B and Table 2). Among the 248 positive samples detected with the 12 recombinant antigens of either RH-, ME49- or common (RH/ME49) type, 71 samples were positive in reactions with all three types of antigen, which accounted for 28.6% of all positive samples, even though the detection rates with strain-specific rAgs were higher. The data further supported the finding that a combination of several immune-dominant antigens will generate a higher diagnostic efficiency [32]. In contrast, 6.9% of the positive sera samples were detected by both RH-rAg and ME49-rAg, 11.3% were detected by both RH-rAg and common RH/ME49-rAg, and 9.7% were detected by both ME49-rAg and RH/ME49-rAg.

                  To determine the reliability of the ELISA results based on recombinant antigens, the 284 positive sera were further validated with two commercial Toxoplasma gondii IgG/IgM Kits and Western blot assays. 85.1% and 43.5% of the positive samples previously identified by the ELISA assay were confirmed by the com-IgG and com-IgM kit, respectively, whereas a 2% and 0% positive rate were found in the selected negative serum samples (P < 0.01) (Table 3). The data suggested, in one aspect, that half of the individuals may be recently infected by T. gondii at the sample time. In another aspect, a combination of antigens with different parasite strains will be needed to achieve a higher diagnostic efficiency and a broader coverage. Western blot assays showed that 71.7% and 81.5% of the ELISA positive samples were found to be immunoreactive with the native proteins of RH and ME49 strain, respectively (Table 3), which further supported the ELISA data. Examples of Western blots were shown in Figure 2 with variation in recognition of multiple bands (Figure 2A) and single bands (Figure 2B) by the serum samples. These results, again, suggested that the immune recognition of T. gondii antigens varied among different individuals.
                  Table 3

                  The positive rates of samples detected with the commercial T. gondii IgG/IgM Kits and Western blot

                   

                  Number of positive sera by ELISA

                  Number of negative sera by ELISA

                  P value

                   

                  (n = 248)

                  (n = 50, randomly selected)

                   
                   

                  positive

                  negative

                  positive

                  negative

                  (Among serum samples)

                   

                  n

                  %

                  n

                  %

                  n

                  %

                  n

                  %

                   

                  com-IgG Kit

                  211

                  85.1

                  37

                  14.9

                  1

                  2

                  49

                  98

                  P < 0.01

                  com-IgM Kit

                  108

                  43.5

                  140

                  56.5

                  0

                  0

                  50

                  100

                  WB-RH

                  178

                  71.7

                  70

                  28.3

                  1

                  2

                  49

                  98

                  WB-ME49

                  202

                  81.5

                  46

                  18.5

                  5

                  10

                  45

                  90

                  P < 0.05

                  http://static-content.springer.com/image/art%3A10.1186%2F1756-3305-6-241/MediaObjects/13071_2013_Article_1026_Fig2_HTML.jpg
                  Figure 2

                  Western blot analysis of serum samples. A shows the examples where the serum samples recognized multiple bands of T. gondii proteins. B shows the example of the serum samples that recognized a dominant T. gondii protein. NC: negative control; PC: positive control; M: pre-stained Protein Molecular Weight Marker.

                  Conclusions

                  In this study, we compared the immunorecognition of three kinds of T. gondii strain- and developmental status-specific antigens with the same set of sera. Results clearly showed that there were strikingly differences in the recognition of these antigens among the samples. The prevalence of anti-T. gondii IgG obtained with crude native RH-Ag and ME49-Ag was similar, whereas the prevalence obtained with recombinant antigens (rAgs) was significantly higher than that of the crude antigens. More importantly, the number of sera that cross-reacted with the three kinds of antigen was low, accounting for only 1.5% of the positive samples. Nevertheless the recombinant antigens had shown a significantly higher consistency in detection of T. gondii-specific IgG in the serum samples. Thus, the general prevalence of anti-T. gondii IgG was likely much higher than previously reported. The data further supported the conclusion that there is more genetic diversity among the T. gondii isolates in China [1416], which argue for the necessity of the establishment of a method that can detect most, if not all, of the variant specific antibodies.

                  Declarations

                  Authors’ Affiliations

                  (1)
                  Key Laboratory of Zoonosis, Ministry of Education, Jilin University

                  References

                  1. Montoya JG, Liesenfeld O: Toxoplasmosis. Lancet. 2004, 363 (9425): 1965-1976. 10.1016/S0140-6736(04)16412-X.View ArticlePubMed
                  2. Walle F, Kebede N, Tsegaye A, Kassa T: Seroprevalence and risk factors for Toxoplasmosis in HIV infected and non-infected individuals in Bahir Dar, Northwest Ethiopia. Parasit Vectors. 2013, 16; 6 (1): 15-View Article
                  3. Alvarado-Esquivel C, Torres-Castorena A, Liesenfeld O, Garcia-Lopez CR, Estrada-Martinez S, Sifuentes-Alvarez A, Marsal-Hernandez JF, Esquivel-Cruz R, Sandoval-Herrera F, Castaneda JA: Seroepidemiology of Toxoplasma gondii infection in pregnant women in rural Durango, Mexico. J Parasitol. 2009, 95 (2): 271-274. 10.1645/GE-1829.1.View ArticlePubMed
                  4. Liu Q, Wei F, Gao S, Jiang L, Lian H, Yuan B, Yuan Z, Xia Z, Liu B, Xu X: Toxoplasma gondii infection in pregnant women in China. Trans R Soc Trop Med Hyg. 2009, 103 (2): 162-166. 10.1016/j.trstmh.2008.07.008.View ArticlePubMed
                  5. Flegr J, Preiss M, Klose J, Havlicek J, Vitakova M, Kodym P: Decreased level of psychobiological factor novelty seeking and lower intelligence in men latently infected with the protozoan parasite Toxoplasma gondii Dopamine, a missing link between schizophrenia and toxoplasmosis?. Biol Psychol. 2003, 63 (3): 253-268. 10.1016/S0301-0511(03)00075-9.View ArticlePubMed
                  6. Garcia JL, Navarro IT, Ogawa L, de Oliveira RC, Kobilka E: Seroprevalence, epidemiology and ocular evaluation of human toxoplasmosis in the rural zone Jauguapita (Parana) Brazil. Rev Panam Salud Publica. 1999, 6 (3): 157-163.View ArticlePubMed
                  7. Coelho RA, Kobayashi M, Carvalho LB: Prevalence of IgG antibodies specific to Toxoplasma gondii among blood donors in Recife, Northeast Brazil. Rev Inst Med Trop Sao Paulo. 2003, 45 (4): 229-231.View ArticlePubMed
                  8. Tian YM, Dai FY, Huang SY, Deng ZH, Duan G, Zhou DH, Yang JF, Weng YB, Zhu XQ, Zou FC: First report of Toxoplasma gondii seroprevalence in peafowls in Yunnan Province, Southwestern China. Parasit Vectors. 2012, 19 (5): 205-View Article
                  9. Hinze-Selch D, Daubener W, Eggert L, Erdag S, Stoltenberg R, Wilms S: A controlled prospective study of Toxoplasma gondii infection in individuals with schizophrenia: beyond seroprevalence. Schizophr Bull. 2007, 33 (3): 782-788. 10.1093/schbul/sbm010.PubMed CentralView ArticlePubMed
                  10. Yolken RH, Bachmann S, Ruslanova I, Lillehoj E, Ford G, Torrey EF, Schroeder J: Antibodies to Toxoplasma gondii in individuals with first-episode schizophrenia. Clin Infect Dis. 2001, 32 (5): 842-844. 10.1086/319221.View ArticlePubMed
                  11. Cetinkaya Z, Yazar S, Gecici O, Namli MN: Anti-Toxoplasma gondii antibodies in patients with schizophrenia–preliminary findings in a Turkish sample. Schizophr Bull. 2007, 33 (3): 789-791. 10.1093/schbul/sbm021.PubMed CentralView ArticlePubMed
                  12. Hamidinejat H, Ghorbanpoor M, Hosseini H, Alavi SM, Nabavi L, Jalali MH, Borojeni MP, Jafari H, Mohammadaligol S: Toxoplasma gondii infection in first-episode and inpatient individuals with schizophrenia. Int J Infect Dis. 2010, 14 (11): e978-e981. 10.1016/j.ijid.2010.05.018.View ArticlePubMed
                  13. Torrey EF, Bartko JJ, Lun ZR, Yolken RH: Antibodies to Toxoplasma gondii in patients with schizophrenia: a meta-analysis. Schizophr Bull. 2007, 33 (3): 729-736. 10.1093/schbul/sbl050.PubMed CentralView ArticlePubMed
                  14. Zhou P, Zhang H, Lin RQ, Zhang DL, Song HQ, Su C, Zhu XQ: Genetic characterization of Toxoplasma gondii isolates from China. Parasitol Int. 2009, 58 (2): 193-195. 10.1016/j.parint.2009.01.006.View ArticlePubMed
                  15. Zhou P, Nie H, Zhang LX, Wang HY, Yin CC, Su C, Zhu XQ, Zhao JL: Genetic characterization of Toxoplasma gondii isolates from pigs in China. J Parasitol. 2010, 96 (5): 1027-1029. 10.1645/GE-2465.1.View ArticlePubMed
                  16. Dubey JP, Zhu XQ, Sundar N, Zhang H, Kwok OC, Su C: Genetic and biologic characterization of Toxoplasma gondii isolates of cats from China. Vet Parasitol. 2007, 145 (3–4): 352-356.View ArticlePubMed
                  17. Kotresha D, Noordin R: Recombinant proteins in the diagnosis of toxoplasmosis. APMIS. 2010, 118 (8): 529-542.PubMed
                  18. Macedo AG, Cunha JP, Cardoso TH, Silva MV, Santiago FM, Silva JS, Pirovani CP, Silva DA, Mineo JR, Mineo TW: SAG2A protein from Toxoplasma gondii interacts with both innate and adaptive immune compartments of infected hosts. Parasit Vectors. 2013, 5 (6): 163-View Article
                  19. Gross U, Holpert M, Goebel S: Impact of stage differentiation on diagnosis of toxoplasmosis. Ann Ist Super Sanita. 2004, 40 (1): 65-70.PubMed
                  20. Xiao Y, Yin J, Jiang N, Xiang M, Hao L, Lu H, Sang H, Liu X, Xu H, Ankarklev J: Seroepidemiology of human Toxoplasma gondii infection in China. BMC Infect Dis. 2010, 7 (10): 4-View Article
                  21. Lindstrom I, Kaddu-Mulindwa DH, Kironde F, Lindh J: Prevalence of latent and reactivated Toxoplasma gondii parasites in HIV-patients from Uganda. Acta Trop. 2006, 100 (3): 218-222. 10.1016/j.actatropica.2006.11.002.View ArticlePubMed
                  22. Jiang N, Cai P, Yin J, Hao L, Lu H, Wang X, Wang H, Chen Q: Characterization of antibody responses to the Sj23 antigen of Schistosoma japonicum after infection and immunization. Acta Trop. 2010, 116 (1): 9-14. 10.1016/j.actatropica.2010.04.015.View ArticlePubMed
                  23. Balsari A, Poli G, Molina V, Dovis M, Petruzzelli E, Boniolo A, Rolleri E: ELISA for toxoplasma antibody detection: a comparison with other serodiagnostic tests. J Clin Pathol. 1980, 33 (7): 640-643. 10.1136/jcp.33.7.640.PubMed CentralView ArticlePubMed
                  24. Glor SB, Edelhofer R, Grimm F, Deplazes P, Basso W: Evaluation of a commercial ELISA kit for detection of antibodies against Toxoplasma gondii in serum, plasma and meat juice from experimentally and naturally infected sheep. Parasit Vectors. 2013, 5 (6): 85-View Article
                  25. Lyons RE, McLeod R, Roberts CW: Toxoplasma gondii tachyzoite-bradyzoite interconversion. Trends Parasitol. 2002, 18 (5): 198-201. 10.1016/S1471-4922(02)02248-1.View ArticlePubMed
                  26. Sun XM, Ji YS, Elashram SA, Lu ZM, Liu XY, Suo X, Chen QJ, Wang H: Identification of antigenic proteins of Toxoplasma gondii RH strain recognized by human immunoglobulin G using immunoproteomics. J Proteomics. 2012, 21 (77): 423-432.View Article
                  27. Amerizadeh A, Khoo BY, Teh AY, Golkar M, Abdul Karim IZ, Osman S, Yunus MH, Noordin R: Identification and real-time expression analysis of selected Toxoplasma gondii in-vivo induced antigens recognized by IgG and IgM in sera of acute toxoplasmosis patients. BMC Infect Dis. 2013, 13 (1): 287-10.1186/1471-2334-13-287.PubMed CentralView ArticlePubMed
                  28. Amerizadeh A, Idris ZM, Khoo BY, Kotresha D, Yunus MH, Karim IZ, Saadatnia G, Teh AY, Noordin R: Identification of Toxoplasma gondii in-vivo induced antigens by cDNA library immunoscreening with chronic toxoplasmosis sera. Microb Pathog. 2013, 54: 60-66.View ArticlePubMed
                  29. Bohne W, Gross U, Ferguson DJ, Heesemann J: Cloning and characterization of a bradyzoite-specifically expressed gene (hsp30/bag1) of Toxoplasma gondii, related to genes encoding small heat-shock proteins of plants. Mol Microbiol. 1995, 16 (6): 1221-1230. 10.1111/j.1365-2958.1995.tb02344.x.View ArticlePubMed
                  30. Parmley SF, Weiss LM, Yang S: Cloning of a bradyzoite-specific gene of Toxoplasma gondii encoding a cytoplasmic antigen. Mol Biochem Parasitol. 1995, 73 (1–2): 253-257.View ArticlePubMed
                  31. Di Cristina M, Del Porto P, Buffolano W, Beghetto E, Spadoni A, Guglietta S, Piccolella E, Felici F, Gargano N: The Toxoplasma gondii bradyzoite antigens BAG1 and MAG1 induce early humoral and cell-mediated immune responses upon human infection. Microbes Infect. 2004, 6 (2): 164-171. 10.1016/j.micinf.2003.11.009.View ArticlePubMed
                  32. Araujo PR, Ferreira AW: High diagnostic efficiency of IgM-ELISA with the use of multiple antigen peptides (MAP1) from T. gondii ESA (SAG-1, GRA-1 and GRA-7), in acute toxoplasmosis. Rev Inst Med Trop Sao Paulo. 2010, 52 (2): 63-68. 10.1590/S0036-46652010000200001.View ArticlePubMed
                  33. Pietkiewicz H, Hiszczynska-Sawicka E, Kur J, Petersen E, Nielsen HV, Stankiewicz M, Andrzejewska I, Myjak P: Usefulness of Toxoplasma gondii-specific recombinant antigens in serodiagnosis of human toxoplasmosis. J Clin Microbiol. 2004, 42 (4): 1779-1781. 10.1128/JCM.42.4.1779-1781.2004.PubMed CentralView ArticlePubMed

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                  This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://​creativecommons.​org/​licenses/​by/​2.​0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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