Immunoblot analysis of membrane antigens of Schistosoma mansoni, Schistosoma intercalatum, and Schistosoma haematobium against Schistosoma-infected patient sera

Antigens present in aqueous n-butanolic extracts (BE) of Schistosoma mansoni (Venezuelan JL strain), Schistosoma intercalatum (Cameroon EDEA strain), and Schistosoma haematobium (Yemen strain) adult worm membranes were compared in immunoblot against sera of patients infected with S. mansoni, S. intercalatum, S. haematobium, Schistosoma japonicum, or Schistosoma mekongi looking for similarities (common antigens) and differences (species-specific antigens). About 17 S. mansoni BE polypeptides (M _r ∼8 to >80 kDa) were commonly recognized by S. mansoni-infected patient sera from Venezuela, Senegal, and Ethiopia. S. intercalatum-, S. haematobium-, or S. japonicum-infected sera were almost unreactive with S. mansoni BE. Nonetheless, S. mekongi-infected sera weakly cross-reacted with a ∼10–15-kDa subset of S. mansoni BE. About 72.7% of S. intercalatum-infected patient sera reacted with a ∼19–21-kDa complex in S. intercalatum BE and cross-reacted with a similar complex in S. haematobium BE. Conversely, all S. haematobium-infected patient sera reacted with a ∼19–21-kDa complex in S. haematobium BE and cross-reacted with the ∼19–21-kDa complex in S. intercalatum BE; S. mansoni- and S. japonicum-infected patient sera did not react with S. intercalatum or S. haematobium BE. Results showed the presence of a common membrane antigen between African schistosome species and species-specific antigens in S. mansoni BE that could be useful to discriminate between species and/or to detect Schistosoma infections.     

Detection of Schistosoma mansoni membrane antigens by immunoblot analysis of sera of patients from low-transmission areas

Schistosoma mansoni surface membrane components play a relevant role in the host-parasite interaction, and some are released in vivo as circulating antigens. n-Butanol extraction favors the release of membrane antigens like alkaline phosphatase, which has been shown to be specifically recognized by antibodies from S. mansoni-infected humans and animals. In the present study, components in the n-butanol extract (BE) of the adult S. mansoni worm membrane fraction were separated by one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis (1D SDS-PAGE [15%]) and further analyzed by immunoblotting (immunoglobulin G) using defined sera. S. mansoni-infected patient sera, but not sera of uninfected patients or sera obtained from patients infected with other parasite species, specifically and variably recognized up to 20 polypeptides in the molecular mass range of approximately 8 to >80 kDa. There were some differences in the number, intensity, and frequency of recognition of the BE antigens among sera from Venezuelan sites of endemicity with a different status of schistosomiasis transmission. Antigens in the 28- to 24-kDa molecular mass range appeared as immunodominants and were recognized by S. mansoni-positive sera from all the sites, with recognition frequencies varying between 57.5 and 97.5%. Immunoblotting with BE membrane antigens resulted in a highly sensitive (98.1%), specific (96.1.0%), and confirmatory test for the immunodiagnosis of schistosomiasis in low-transmission areas.     

Identification and Purification of Specific Penicillium marneffei Antigens and Their Recognition by Human Immune Sera

Disseminated infection with the dimorphic pathogenic fungus Penicillium marneffei is increasingly seen among patients with AIDS in southeast Asian countries. Previous studies have demonstrated the presence of humoral immune responses to this fungus in patient sera; we have confirmed this work using sera from P. marneffei-infected patients (n = 21) to develop Western blots of P. marneffei cytoplasmic yeast antigen (CYA). P. marneffei CYA was then partially purified by liquid isoelectric focusing, and fractions were subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting. Immunoenzyme development of the Western blots with pooled sera from patients with P. marneffei infection and with pooled sera from patients with aspergillosis (n = 20), candidiasis (n = 10), cryptococcosis (n = 9), and histoplasmosis (n = 11) revealed three antigens with relative molecular masses of 61, 54, and 50 kDa. These antigens were specifically recognized by the pooled sera from the P. marneffei-infected patients. The 61- and 54-kDa antigens were subsequently purified to homogeneity by preparative gel electrophoresis, and the 50-kDa antigen was partially purified by the same technique. N-terminal amino acid sequencing revealed that the 61-kDa antigen had a strong homology (87% identity) with the antioxidant enzyme catalase. The three antigens were then subjected to SDS-PAGE and Western blotting and to immunoenzyme development with individual patient sera; sera from 86% of P. marneffei-infected patients recognized the 61-kDa antigen, sera from 71% recognized the 54-kDa antigen, and sera from 48% recognized the 50-kDa antigen. These specifically recognized antigens are the first to be purified from P. marneffei and can be used either singly or in combination to detect antibody responses in a large percentage of individuals infected with P. marneffei.     

Circulating antigens in schistosomiasis: detection of 31/32-kDa proteins in sera from patients infected with Schistosoma japonicum,S. mansoni,S. haematobium,or S. intercalatum

A sandwich enzyme-linked immunosorbent assay (ELISA) was developed to detect 31/32-kDa schistosome proteins as circulating antigens in sera from schistosomiasis patients. A monoclonal antibody was used as a capture antibody and rabbit antiserum raised against purified 31/32-kDa proteins was the detecting antibody. Positive results were obtained with patients infected with Schistosoma japonicum (88%; n=69), S. mansoni (80%; n=56), S. haematobium (100%; n=40), or S. intercalatum (94%; n=65). Sera from uninfected Chinese and African individuals and from Chinese patients with trichinosis, cysticercosis, or paragonimiasis did not react in the assay. This ELISA appears to be valuable in diagnosing infections by all major human schistosome species.     

Enzyme-linked crossed immunoelectrophoresis: a technique for detection of allergens and their respective antibodies in human schistosomiasis

A method is described which allows the demonstration of allergens in complex antigens and their respective antibodies. Schistosoma mansoni antigens are separated in agarose by 2-dimensional electrophoresis, using an anti-S. mansoni serum from goats in the second dimension. After extensive washing test serum is spread over the gel and allowed to bind to the precipitated antigens. After further extensive washing, horseradish peroxidase-coupled anti-IgE antibodies are put on the plate and allowed to react. Bound antiserum is visualized with tetramethylbenzidine as a substrate.In pooled sera from schistosomiasis patients at least 7 antigen fractions of adult S. mansoni and 2 of cercarial antigen reacted with IgE antibodies. No reaction was found in normal sera.     

A monoclonal antibody against Schistosoma haematobium soluble egg antigen: efficacy for diagnosis and monitoring of cure of S. haematobium infection

A monoclonal antibody (mAb), 2F/11F, raised against Schistosoma haematobium soluble egg antigen (SEA) was found to be nonreactive with S. mansoni SEA or other parasite antigens (Fasciola hepatica, Echinococcus granulosus). This IgG₁ mAb recognized a repetitive epitope on S. haematobium SEA in the molecular-weight regions of 70, 42, and 35 kDa. It was employed as both an antigen-capture and a biotinylated detection antibody in a sandwich enzyme-linked immunosorbent assay (ELISA) for the detection of circulating schistosome antigen (CSA) and had a detection limit of <1 ng S. haematobium SEA/ml. CSA levels were measured in serum and urine samples from 116 S. haematobium-infected rural students before therapy and at 4, 8, and 12 weeks after praziquantel treatment. Serum and urine samples from 50 S. mansoni -infected patients, 15 patients harboring other parasites, and 30 noninfected individuals were also assessed. CSA was detected in 90.5% of serum samples and 94% of urine samples from S. haematobium-infected patients. CSA was undetectable in serum from the 15 patients harboring other parasites and in 94% of serum samples and 84% of urine samples from S. mansoni-infected patients. In the S. haematobium-infected group a positive correlation was detected between CSA levels in serum and urine samples and the egg load per 10 ml urine. A significant reduction in CSA levels was detected in serum and urine samples after praziquantel therapy. CSA was undetectable in 87% of serum samples and 81.5% of urine samples from schistosomiasis haematobium patients at 12 weeks post-treatment. These data demonstrate that the use of mAb 2F/11F for detection of CSA provides a sensitive method for the immunodiagnosis and monitoring of cure of schistosomiasis haematobium. Received: 5 December 1998 / Accepted: 26 June 1999     

Development and Evaluation of a Western Blot Kit for Diagnosis of Schistosomiasis

We evaluated the performance of Western blot (WB) analysis using commercially available antigen strips and compared the results with those of indirect hemagglutination (IHA) and indirect immunofluorescence (IFAT) for the serodiagnosis of human schistosomiasis. The antigen preparation was a crude extract of Schistosoma mansoni. The WB profile characteristics of schistosomiasis were characterized by comparing the results for 58 serum samples from patients with parasitologically proven S. mansoni (n = 12) and S. haematobium (n = 46) infections and 37 individuals with probable cases of schistosomiasis but with only positive serology results. The specificity of WB analysis was assessed by testing 12 serum samples from healthy subjects, 67 serum samples from patients with other proven helminthic and protozoan infections, and 16 serum samples from patients with autoantibodies. Six immunodominant bands (65, 70, 80, 95, 110, and 120 kDa) were revealed with sera from patients with schistosomiasis. The presence of three or more bands in the range 65 to 120 kDa, with the exception of the 100-kDa band, was considered diagnostic for Schistosoma infection and had a specificity of 100% in our series. In patients with proven schistosomiasis, the sensitivity of WB analysis was 84.5%, whereas those of IFAT and IHA were 65.5 and 72.9%, respectively. For serologically proven cases, the sensitivity of WB analysis was 97.3%. The overall sensitivity and specificity for both groups of patients were 89.5 and 100%, respectively, with positive and negative predictive values of 100 and 91.3%, respectively. We conclude that WB analysis is a useful technique for the immunological diagnosis of schistosomiasis.     

Comparative evaluation of Schistosoma mansoni,Schistosoma intercalatum,and Schistosoma haematobium alkaline phosphatase antigenicity by the alkaline phosphatase immunoassay (APIA)

To know if alkaline phosphatase (AP) from schistosomes other than Schistosoma mansoni can be used as diagnostic marker for schistosomiasis in alkaline phosphatase immunocapture assay (APIA), we comparatively tested n-butanol extracts of adult worm membranes from a Venezuelan (JL) strain of S. mansoni (Ven/AWBE/Sm); a Cameroonian (EDEN) strain of Schistosoma intercalatum (Cam/AWBE/Si) and a Yemeni strain of Schistosoma haematobium (Yem/AWBE/Sh). APIA was evaluated with sera of patients from Venezuela, Senegal, and Gabon infected with S. mansoni, from Gabon infected with S. intercalatum or S. haematobium, from Chine infected with Schistosoma japonicum and from Cambodian patients infected with Schistosoma mekongi. Results indicate that 92.5 % (37/40) of Venezuela sera, 75 % (15/20) of Senegal sera, 39.5 % (17/43) of S. haematobium sera, and 19.2 % (5/26) S. intercalatum sera were APIA-positive with the Ven/AWBE/Sm preparation. APIA with the Cam/AWBE/Si preparation showed that 53.8 % of S. intercalatum-positive sera had anti-AP antibodies, and 51.2 %?S. haematobium-positive sera cross-immunocapturing the S. intercalatum AP. APIA performed with Yem/AWBE/Sh showed that 55.8 %?S. haematobium sera were positive. Only two out of nine S. japonicum sera were APIA-positive with the Ven/AWBE/Sm and Cam/AWBE/Si, and no reaction was observed with Cambodian S. mekongi-positive sera. AP activity was shown to be present in all the schistosome species/strains studied. The use of APIA as a tool to explore the APs antigenicity and the presence of Schistosoma sp. infections through the detection of anti-Schistosoma sp. AP antibodies in a host, allowed us to demonstrate the antigenicity of APs of S. mansoni, S. intercalatum, and S. haematobium.     

Serum levels of circulating anodic antigen and circulating cathodic antigen detected in mice infected withSchistosoma japonicum orS. mansoni

Serum concentrations of circulating anodic antigen (CAA) and circulating cathodic antigen (CCA) were studied in mice infected with eitherSchistosoma japonicum orS. mansoni cercariae. Sera from uninfected mice were negative for both antigens. CAA was detectable in theS. japonicum-infected mice as early as at 2 weeks post-infection (p.i.), and levels were higher in these animals than in theS. mansoni-infected group during the full study period. At the moment of perfusion, 10 weeks p.i., a median of 9 and 29 worms, respectively, were recovered from theS. japonicum-andS. mansoni-infected mice, and the median CAA levels were 326 and 27 ng/ml, respectively. In contrast, CCA levels were much lower in theS. japonicum-infected group (27 ng/ml) as compared with theS. mansoni-infected mice (282 ng/ml). These results suggest an important difference betweenS. japonicum andS. mansoni infections in CAA and CCA production and/or clearance and indicate a significant role for CAA in the diagnosis of human schistosomiasis japonicum.     

Reactivity of IgE in humanSchistosoma mansoni sera toS. mansoni antigens

Sera fromSchistosoma mansoni-infected human patients were tested for total IgE levels and specific IgE and IgG antibodies toS. mansoni adult worm, cercaria, and egg antigen by ELISA. Of 50 sera, 28 were investigated by enzyme-linked crossed immunoelectrophoresis (ELCIE) to detect IgE reactivity to individual adult worm extract components. All sera showed increased total IgE levels. Specific IgE antibody levels to the different antigens varied; they were significantly correlated with each other but independent from total IgE. No correlation was found between specific IgG and any of the IgE antibody levels. Testing of the 28 individual sera by ELCIE revealed heterogeneous patterns. Seven sera were found to be non-reactive: three reacted with one precipitate, and the others reacted with between two and nine precipitates. However, in no case were identical patterns recognized, although four antigens reacted with about 80% of the sera. The number of bands detected by the individual sera depended neither on the levels of total IgE nor on those of specific IgE.Supported by the Bundesministerium für Forschung und Technologie der Bundesrepublik Deutschland (grant PTB 8324)     

Immunization with rP22 induces protective immunity against Schistosoma mansoni: effects on granuloma down-modulation and cytokine production

Schistosomiasis remains a significant public health problem in tropical countries and it is recognized as the most important human helminth infection in terms of morbidity and mortality. Although the existing antischistosomal drugs are highly effective, they do not prevent against reinfection or granuloma formation. Therefore, vaccine strategies are essential for the control of schistosomiasis. Our group recently identified the recombinant (r) P22 protein, a component of the adult worm protein fraction PIII that has been shown to engender protective and immunomodulatory effects on murine schistosomiasis. A cDNA clone encoding rP22 was isolated from a Schistosoma mansoni adult worm cDNA library using anti-PIII rabbit serum; it exhibited complete identity with S. mansoni Sm21.7 EF-hand antigen. Confocal microscopy revealed that rP22 is a tegument protein localized on the surface of S. mansoni miracidia and adult worms. Mice immunized with rP22 exhibited a 51% and 22.5% decrease in adult worm burden and in hepatic eggs, respectively. Additionally, rP22 vaccine produced a reduction in 60% of liver granuloma size and 71% of fibrosis in mice, suggesting that rP22 might contribute to down-modulate granulomatous hypersensitivity to S. mansoni eggs. Protective immunity in mice was associated with high titers of rP22-specific IgG antibodies; elevated production of IFN-γ, TNF-α and IL-10; and a reduced level of IL-4. In conclusion, these findings indicate that rP22-based vaccines could be useful to elicit protection and reduce pathology associated to schistosomiasis.     

Isolation and characterization of surface antigens from Schistosoma mansoni schistosomula

Surface antigens of Schistosoma mansoni schistosomula were isolated using antibodies produced in rat and human schistosomiasis. Three immunoreactive surface proteins of 40 000, 37 000 and 32 000 daltons were identified by SDS—PAGE analysis of immune complexes formed by incubation of a detergent extract of surface labelled schistosomula with infected rat sera. Surface antigens of similar molecular weight were also isolated when using sera of patients with schistosomiasis. Binding of schistosomula surface antigens to specific antibodies was substantially inhibited by components released by adult worms. The results suggest that these schistosomula surface antigens could be involved in the immune response against challenge infection but their protective role in immunity still remains to be determined.     

Characterization of the Glycoprotein Antigens Which Mediate the Schistosoma japonicum Circumoval Precipitin Reaction

The circumoval precipitin test is a serological test used for diagnosis of schistosomiasis japonica. Soluble egg antigens of Schistosoma japonicum block the formation of the circumoval precipitin by serum from infected humans. Consequently, circumoval precipitin inhibition was used to monitor purification of the soluble egg antigens of S. japonicum. Crude egg antigens were separated into protein and glycoprotein fractions by lectin chromatography on concanavalin A Sepharose. The glycoprotein fraction produced two intense precipitin lines upon immunodiffusion analysis with human chronic infection sera. The protein fraction produced two faint precipitin lines which did not cross-react with those of the glycoprotein fraction. The glycoprotein fraction contained 90% of the circumoval precipitin inhibitory activity. Isoelectric focusing of ¹²⁵I-labeled concanavalin A Sepharose fractions revealed at least four groups of potential S. japonicum antigens, termed JAG I, II, and III, and a JAG IV complex. These had isoelectric points ranging from 3.2 to 6.7. In these respects, the S. japonicum egg antigen glycoproteins are similar to those of Schistosoma mansoni. The glycoproteins were further separated by diethylaminoethyl ion-exchange chromatography. On immunodiffusion analysis it was found that one of the strong Ouchterlony precipitin lines was associated with glycoproteins that did not adsorb to diethyl-aminoethyl columns, whereas the second Ouchterlony precipitin was heterodisperse, being present in the first, second, and third of the four peaks eluted from the diethylaminoethyl column. Immunoelectrophoresis of the diethylaminoethyl fractions demonstrated that the antigen present in highest concentration in soluble egg antigen glycoproteins, JAG II, was extremely heterodisperse in its behavior on diethylaminoethyl columns. This is unlike the S. mansoni antigens which can be easily separated by diethylaminoethyl ion-exchange chromatography.     

Salmonella typhimurium exacerbates injuries but resolves fibrosis in liver and spleen during Schistosoma mansoni infection

BackgroundIn most developing or undeveloped countries, patients are often co-infected with multiple pathogens rather than a single pathogen. While different pathogens have their impact on morbidity and mortality, co-infection of more than one pathogen usually made the disease outcome different. Many studies reported the co-infection of Schistosoma with Salmonella in pandemic areas. However, the link or the underlying mechanism in the pathogenesis caused by Schistosoma-Salmonella co-infection is still unknown.MethodsIn this study, Salmonella typhimurium (S. typhimurium) was challenged to Schistosoma mansoni (S. mansoni)-infected mice. Further experiments such as bacterial culture, histopathological examination, western blotting, and flow cytometry were performed to evaluate the outcomes of the infection. Cytokine responses of the mice were also determined by ELISA and real-time quantitative PCR.ResultsOur results demonstrated that co-infected mice resulted in higher bacterial excretion in the acute phase but higher bacterial colonization in the chronic phase. Lesser egg burden was also observed during chronic schistosomiasis. Infection with S. typhimurium during schistosomiasis induces activation of the inflammasome and apoptosis, thereby leading to more drastic tissue damage. Interestingly, co-infected mice showed a lower fibrotic response in the liver and spleen. Further, co-infection alters the immunological functioning of the mice, possibly the reason for the observed pathological outcomes.ConclusionCollectively, our findings here demonstrated that S. mansoni-infected mice challenged with S. typhimurium altered their immunological responses, thereby leading to different pathological outcomes.     

Susceptibility of neonate mice born to Schistosoma mansoni-infected and noninfected mothers to subsequent S. mansoni infection

The present study tested the hypothesis that prenatal exposure of neonate Outbred albino mice to Schistosoma mansoni antigens (Ags) or antibodies (Abs) modulates their immunity against postnatal responses to infection. Persistence of maternal S. mansoni Abs and/or Ags in mice born to S. mansoni-infected mothers (IF-IMs) and noninfected mothers (IF-NMs) for up to 8 weeks after delivery was investigated. A higher level of anti-S. mansoni IgG Ab was detected in sera of 1-week-old mice born to IF-IM compared to controls. Then, immunoglobulin (Ig)G gradually decreased to the eight week. No anti-S. mansoni IgM Ab was detected in sera of these offspring at any week after delivery. Schistosoma Ags were detected in liver and kidney tissues of mice born to infected mothers. However, Ags decreased markedly till the sixth week in the liver but increased significantly at the sixth week in the kidney. Eight-week-old mice born to infected and noninfected mothers were infected with 200 S. mansoni ceracriae. Their sera and livers were collected for testing IgG and granuloma formation 6 weeks postinfection. Worms were collected via portal perfusion and counted. Anti-S. mansoni IgG level, size and number of liver granuloma, and worm burden were significantly reduced in the offspring of infected mothers. These data suggest that in utero exposure of Outbred albino mice to S. mansoni may attenuate the pathogenesis of S. mansoni in subsequent challenge.     

Use of wogonin as a cooperative drug with praziquantel to better combat schistosomiasis

BackgroundSchistosomiasis is one of the most devastating tropical diseases in the world. Currently, praziquantel (PZQ) represents the best pharmacological option for the treatment of schistosomiasis as it effectively kills the worm. However, the inability to reverse established liver damages often makes treatment futile. In the current study, we investigate whether combining the use of wogonin, a compound that was found to be liver-protective, with PZQ can attribute to the greatest beneficial effect in Schistosoma mansoni-infected mice.MethodsTo determine the protective effect of PZQ-wogonin treatment on S. manosni-infected mice, histopathological analysis was done to evaluate the granuloma size and fibrotic areas in the liver. Western blotting was performed to analyze several injuries-related markers including fibrotic markers, inflammasomes, and apoptotic markers. Scanning electron microscopy was done to evaluate the effect of wogonin on the worms, and the worm and egg burden was calculated.ResultsOur results showed that PZQ-wogonin treatment significantly improved liver histopathology of S. mansoni-infected mice. Further analysis showed that PZQ-wogonin combinations are more effective in reducing fibrosis, inflammation, and apoptosis in the liver than that of individual drug use. Furthermore, our results revealed that wogonin is anthelmintic; and it works better with PZQ in reducing hepatic egg burden, further lessen the disease progression.ConclusionIn general, this combinatorial strategy may represent a new and effective approach to schistosomiasis treatment.     

Enzyme-Linked Immunosorbent Assay To Differentiate the Antibody Responses of Animals Infected with Brucella Species from Those of Animals Infected with Yersinia enterocolitica O9

Enzyme-linked immunosorbent assays using antigens extracted from Brucella abortus with n-lauroylsarcosine differentiated natural Brucella-infected animals from Brucella-vaccinated or Yersinia enterocolitica O9-infected animals. A field trial in Mongolia showed cattle, sheep, goat, reindeer, camel, and human sera without infection could be distinguished from Brucella-infected animals by conventional serological tests.     

Rapid Detection of a Schistosoma mansoni Circulating Antigen Excreted in Urine of Infected Individuals by Using a Monoclonal Antibody

Schistosoma circulating antigens were used to indicate the infection intensity and to assess cure. An immunoglobulin G2a (IgG2a) mouse monoclonal antibody was used in a fast dot-enzyme-linked immunosorbent assay (ELISA; FDA) for rapid and simple diagnosis of schistosomiasis in the field. Seven hundred Egyptians were parasitologically examined for Schistosoma mansoni and other parasitic infections. A rectal biopsy was done as a “gold standard” for individuals showing no S. mansoni eggs in their feces. Egg counts were obtained by the Kato smear method for only 100 of 152 individuals with eggs in their feces. Specific anti-schistosome IgG antibodies were evaluated in sera by ELISA. Urine samples from the 700 individuals were tested by FDA for detection of the circulating antigen. The assay showed a sensitivity of 93% among 433 infected individuals and a specificity of 89% among 267 noninfected individuals. FDA showed the highest efficiency of antigen detection (91%) compared with the efficiency of antibody detection by ELISA (75%) and stool analysis (60%). In addition, FDA detected infected patients with 20 eggs/g of feces. Also, the sensitivity of FDA ranged from 90 to 94% among samples from patients with different clinical stages of schistosomiasis. All the assay steps can be completed within 30 min at room temperature for 96 urine samples. The monoclonal antibody identified a 74-kDa antigen in different antigenic extracts of S. mansoni and Schistosoma haematobium and in the urine of infected individuals. In addition, a 30-kDa degradation product was identified only in the urine samples. On the basis of these results, FDA should be used as a rapid tool for the sensitive and specific diagnosis of Schistosoma infection.     

Expression of a 28-Kilodalton Glutathione S-Transferase Antigen of Schistosoma mansoni on the Surface of Filamentous Phages and Evaluation of Its Vaccine Potential

A cloning and expression system that allows display of proteins on the surface of filamentous phages was exploited to display a 28-kDa glutathione S-transferase (Sm28GST) antigen of the human parasite Schistosoma mansoni. The phage-displayed Sm28GST (pdGST) was immunoreactive and was recognized by immune sera, suggesting that the Sm28GST protein displayed on the surface of phages potentially maintains native conformation. Subsequent immunization studies showed that mice can develop high titers of antibodies against pdGST and do not require any additional adjuvant for immunization. Isotype analysis suggested that the pdGST immunization predominantly induced immunoglobulin G2b (IgG2b), IgG3, and IgM anti-GST antibodies in mice. Furthermore, the pdGST immunization was found to confer about 30% protection after a challenge infection with 100 cercariae of S. mansoni in BALB/c mice. These findings suggest that phage display is a simple, efficient, and promising tool to express candidate vaccine antigens for immunization against infectious agents.