Nitric oxide and IL-10 production induced by PIII--a fraction of Schistosoma mansoni adult worm antigenic preparation--associated with downregulation of in vitro granuloma formation.

Identification and characterization of Schistosoma mansoni antigens that can provide protective immunity, as well as an investigation of their role in host-parasite interaction, is crucial for understanding the complex immunoregulatory events that modulate granuloma formation in schistosomiasis. Previous work by our laboratory identified a fraction of S. mansoni soluble adult worm antigenic preparation (SWAP), named PIII, obtained by anionic chromatography on fast protein liquid chromatography (FPLC). This fraction was able to elicit significant in vitro cell proliferation and at the same time lower in vitro and in vivo granuloma formation when compared either to SWAP or to soluble egg antigens (SEA). In the present work, we investigate some biological activities of PIII, such as the stimulation of nitric oxide (NO) and cytokine production. Our data demonstrated that SEA, SWAP and specially PIII were able to induce a time-dependent increased NO production during in vitro granuloma reaction. Besides that, PIII evoked increased IL-10 production, but not IL-2 or IFNgamma. Collectively, our results indicate the possibility that the modulation role of PIII on in vitro granuloma might be mediated in part by its ability to induce the higher production, initially of IL-10, and lately of NO.     

Signal transduction events in human peripheral blood mononuclear cells stimulated by Schistosoma mansoni antigens

Activation of protein tyrosine kinases (PTKs) is a common step of T cell stimulation. However, the relationship between PTKs and activation of peripheral blood mononuclear cells (PBMC) from intestinal chronic schistosomiasis patients has not been explored yet. In this study, we investigated the participation of Lck and ZAP-70 protein tyrosine kinases (PTKs), as well as PLC-gamma1 and Shc proteins in PBMC activation by Schistosoma mansoni antigens. PBMC were stimulated with SEA (soluble egg antigen) or SWAP (soluble worm preparation), lysed, precipitated with specific antibodies and the level of tyrosine phosphorylation evaluated. Our results show that Lck and Shc were phosphorylated upon stimulation of the cells with SWAP, as well as with SEA. However, the phosphorylation level was more pronounced in SWAP than in SEA-stimulated cells. Phosphorylation of ZAP-70 was observed only in SWAP stimulated cells. Additionally, PLC-gamma1 phosphorylation was not observed in PBMC stimulated with SEA. Together, these results indicate that SEA and SWAP induce PBMC proliferation through distinct intracellular signaling pathways. Moreover, the weaker response of PBMC to SEA compared to SWAP stimulation suggests down-regulation of cells from intestinal chronic schistosomiasis patients to SEA, which may occur during immunomodulation to S. mansoni response.     

Human immune response in schistosomiasis: the role of P24 in the modulation of cellular reactivity to Schistosoma mansoni antigens

Schistosome antigenic components are being tested as vaccine candidates with various degrees of success, but there are only few reports using multivalent antigens to stimulate an appropriate immune response that leads to resistance or granuloma modulation. We investigated the in vitro response of peripheral blood mononuclear cells (PBMC) from chronic intestinal schistosomiasis individuals to PIII, a multivalent antigen prepared from Schistosoma mansoni adult worm antigen, and response to P24, a single antigen obtained from PIII. Treatment of PBMC with either PIII or P24 caused significant decrease in cellular proliferation and granuloma formation induced by S. mansoni antigens, and a significant elevation in IL-10 and TNF-alpha but not in IFN-gamma production. Moreover, P24 promoted an elevation in TNF-alpha level on the in vitro granuloma reaction, when cocultured with polyacrylamide beads (PB) coupled to S. mansoni antigens. These findings suggest that, besides inducing protective immunity, PIII and P24 antigens seem to be important in the regulation of in vitro granuloma formation through stimulation of IL-10 and TNF-alpha production in human schistosomiasis. The more pronounced effect of P24 on reducing the in vitro granulomatous reaction could be associated with a balance between IL-10 and TNF-alpha production.     

Schistosoma mansoni PIII antigen modulates in vitro granuloma formation by regulating CD28, CTLA-4, and CD86 expression in humans

We investigated the in vitro responses of peripheral blood mononuclear cells (PBMC) from intestinal chronic schistosomiasis patients to PIII, a multivalent antigen prepared from Schistosoma mansoni adult worm. PIII decreased cellular proliferation and granulomatous reaction. Moreover, induced the reduction of IFN-gamma levels and increased IL-10 production. To better understand the mechanism through which the observed suppression occurs, the present study focused on the phenotypic pattern displayed by PBMC treated with PIII in an in vitro granuloma assay. Expression of the surface markers CD28, CTLA-4 and CD86 by lymphocytes and monocytes were analyzed by flow cytometry. Our results demonstrated a significant decrease of CD28+CD4+ and CD28+CD8+ T-cell percentage stimulated by PIII compared to its non-infected counterparts. This suppressive effect was related to a significant increase in the percentage of T-cells expressing CTLA-4. PIII also promoted a significant increase in the percentage of cells expressing CD86. Indeed, our results demonstrated that PIII was capable of modulating in vitro granuloma reaction, and this event was related to the balance of IL-10, IFN-gamma and CD28, CTLA-4, CD86 bringing new insight to the immunoregulation of granulomatous hypersensitivity in human schistosomiasis.     

Cytokine Regulation of Human Immune Response to Schistosoma mansoni: Analysis of the Role of IL-4, IL-5 and IL-10 on Peripheral Blood Mononuclear Cell Responses

The role of cytokines on the in vitro proliferative response of peripheral blood mononuclear cells (PBMC) from Schistosoma mansoni infected patients to soluble egg (SEA) and adult worm antigens (SWAP) were evaluated. The results obtained demonstrated that the proliferative response of PBMC from chronic intestinal (INT) patients to SEA and SWAP is increased by the blockage of IL-10 with specific monoclonal antibodies (MAb). The effects of these antibodies were readily reversed by the addition of recombinant IL-10. In contrast, no effect was observed on the PBMC response of acute and hepatosplenic patients (HS) in the presence of anti-IL-10. Anti-IL-4 antibodies decreased the PBMC response of the intestinal (INT) and HS individuals to SEA and SWAP, and the PBMC response of acute patients to SEA but not to SWAP. Addition of anti-IL-5 MAb did not decrease the PBMC response of acute patients to SEA or SWAP. These results suggested that IL-10 has an important role in the modulation of the immune response in chronic asymptomatic patients and that this cytokine may be an important factor in controlling morbidity.     

Expression of a Schistosoma mansoni 28-kilodalton glutathione S-transferase in the livers of transgenic mice and its effect on parasite infection.

Schistosomiasis is a debilitating tropical disease for which an effective vaccine is needed. A 28-kDa glutathione S-transferase from Schistosoma mansoni (Sm28GST) has been shown to induce protective immunity. Sm28GST possesses significant sequence identity to mammalian GST isoforms. In order to study self-reactivity in mice immunized with Sm28GST and the concomitant phenomena of immune tolerance and epitope suppression, as well as their consequences for the protective immunity induced by this vaccination, we developed transgenic (Tg) mice that express Sm28GST under the control of a part of the mouse transferrin gene promoter. A study of (P28)Tg mice showed that the expression of Sm28GST was strictly localized in pericentrolobular hepatocytes. No histological change, inflammatory infiltrates, or modification of seric L-aspartate: 2-oxoglutarate aminotransferase concentration was observed over an 18-month period, despite a cross-reactivity between Sm28GST and a mouse molecule of 30 kDa. The immunoglobulin G anti-Sm28GST response of (P28)Tg mice immunized with recombinant Sm28GST was lower (P < 0.001) than that observed in non-(P28)Tg littermates and inversely proportional of Sm28GST liver expression. The response of non-(P28)Tg mouse spleen cells to Sm28GST stimulation was greater (P < 0.01) than that observed with (P28)Tg mouse spleen cells. (P28)Tg mice infected with 40 S. mansoni furcocercariae harbored more worms (P < 0.05) than did non-(P28)Tg control mice. The increase in the level of infection in (P28)Tg mice was reflected in concomitant increases in the numbers of adult worms and schistosome eggs found in livers and intestines after whole-body perfusion at 56 days postinfection, but no relative increase in the fertility of individual female worms was observed. The results obtained argue for the involvement of Sm28GST in reducing levels of infection and support the view that this enzyme has a central role in the maintenance of parasite viability, at least during its migration through host tissues.     

Human Schistosomiasis: Modulation of In Vitro Granulomatous Hypersensitivity and Lymphocyte Proliferative Response by Macrophages Undergoing Differentiation

The mechanisms associated with the modulation of immune response in the chronic phase of human schistosomiasis mansoni infection are complex and involve many cell types. In the present paper the authors demonstrate that antigenic stimulation of peripheral blood mononuclear cells (PBMC) from chronic-intestinal schistosomiasis mansoni patients with polyacrylamide beads (PB) conjugated to Schistosoma mansoni soluble egg antigens (PB-SEA) or adult worm antigen preparation (PB-SWAP) were able to induce a statistically significant increase on the in vitro multinucleated giant cell (MGC) formation after the 15th day in culture. A correlation between an increase in the number of MGC and a decrease in in vitro granuloma formation index to PB-SEA and PB-SWAP was observed. Moreover, the authors demonstrated a down-regulation of lymphocyte proliferative responses to S. mansoni antigens, during the differentiation pathway of monocytes towards MGC formation, due to a decrease in the antigen-presenting capacity of these cells. These phenomena also correlate with a concomitant decrease in the expression of HLA-DR and CD54 adhesion molecules on the surface of MGC. The results suggest that differentiation of monocytes to MGC may be one of the immunoregulatory mechanisms involved in the down-regulation of the granuloma reaction against S. mansoni eggs.     

Effect of combined praziquantel and recombinant glutathione S-transferase on resistance to reinfection in murine Schistosomiasis mansoni

This study was undertaken to evaluate the effect of recombinant Schistosoma mansoni-26 Glutathione S-transferase (rSm 26 GST) or soluble egg antigen (SEA) alone and in addition to praziquantel (PZQ) on the state of resistance to S. mansoni reinfection. The associated changes in the immune responses were evaluated. The experimental group of mice were injected intravenously before S. mansoni infection (80 cercariae/mouse) either with rSm26 GST (1 microgx4) or SEA (10 microgx4) in addition to PZQ (2x500 mg/kg) administered 6 weeks post-infection. Seven control groups were used, three of them were the infected (80 cercariae/mouse), the challenged (240 cercariae/mouse) and the infected challenged controls (80+240 cercariae/mouse). The rest of the four groups were the treated controls receiving: the GST-Lyzate, rSmGST, SEA and PZQ in the same doses and at the same timings. Challenge infection was conducted for all the groups 8 weeks post-infection. Animals were sacrificed 3 weeks post-challenge. After sacrifice animals were perfused and percentage resistance to reinfection was calculated. Immune responses were assessed by the measurement of hepatic granuloma diameter, intralesional T-cell phenotypes and serum immunoglobulin isotypes. The highest percentage of resistance to reinfection was observed in rGST-treated group while the lowest percentage of resistance was detected in PZQ-treated group. Whereas in mice receiving combined rGST or SEA and PZQ, percentage resistance to reinfection was significantly higher than that in PZQ treated mice. The remarkable reduction in granuloma diameter in rGST-treated group with or without PZQ was associated with decrease in the intralesional L(3)T(4)(+) and increase in Lyt(2)(+) T-cell phenotypes. However, no special relationship was observed between the percentage of resistance and the changes in granuloma diameter or intralesional T-cell phenotypes. The increase in percentage resistance to reinfection was found accompanied by increased anti SWAP IgE. Combined rGST and PZQ provided the complementary goals of improved state of resistance to reinfection 'which was compromized after cure with PZQ' and the maximal reduction in granuloma diameter.     

Schistosoma mansoni: cell-mediated immunity evaluated by antigen-induced leukocyte adherence inhibition assay

Peripheral blood leukocytes (PBL) from schistosomiasis patients fail to adhere to glass in the presence of soluble egg antigens (SEA) or soluble worm adult antigenic preparation (SWAP). These leukocytes are non-reactive with S. mansoni unrelated antigens (C. albicans and bovine albumin). Supernatants obtained from cultures of mononuclear cells of patients with antigens were able to inhibit granulocyte adherence to glass. The inhibition of antigen-induced adherence (LAI assay) was not observed when PBL or supernatants were obtained from normal subjects or from schistosomiasis patients after chemotherapy. These results show that under the conditions tested, leukocytes appear to react directly with SEA or SWAP thus losing their property of adherence to glass.     

Immune Responses during Human Schistosomiasis Mansoni

Splenocytes from 25 patients with severe hepatosplenic schistosomiasis mansoni were obtained after therapeutic splenectomy. Spleen cells were phenotyped and analysed for responsiveness to mitogens or heterogeneous schistosome-derived antigenic preparations (eggs, SEA; adult worms, SWAP; cercariae, CERC) in blastogenesis assays and lymphokine production systems, and were compared with peripheral blood mononuclear cells (PBMN). Splenic lymphocytes were 55% T lymphocytes (sheep erythrocyte rosette-positive) and 37% surface immunoglobulin-positive B lymphocytes. The mean T4+:T8+ ratio of these splenocytes was 1.0. Phytohaemagglutinin stimulated spleen cell production of the lymphokine mitogenic factor, but exposure to SEA or SWAP did not. Spleen cell and PBMN blastogenic responses to SEA and SWAP were sometimes, but not always in accord. Removal of plastic adherent cells allowed the non-adherent spleen cells of 30-40% of the patients to respond substantially more vigorously to SEA, SWAP and CERC. Spleen cells from a subgroup of 20-30% of the patients failed to respond to the schistosomal antigens regardless of removal of adherent cells. Spleen cell responses to gram-negative lipopolysaccharide peaked on day 5 or 6 of culture, and were augmented by adherent cell removal. Pokeweek mitogen-stimulated responses were optimal on day 5 of culture. Spleen cells from most severe, hepatosplenic schistosomiasis mansoni patients do not respond well to schistosomal antigens or B-cell mitogens. The splenic responses of many of these patients were elevated by the removal of adherent spleen cells.     

Induction of Cytotoxic T-Cell Activity by the Protective Antigen of Schistosoma mansoni Sm28GST or its Derived C-Terminal Lipopeptide

In a previous work the authors demonstrated that immunization with Schistosoma mansoni 28-kDa glutathion-S-transferase (Sm28GST) was able to reduce hepatic damage in infected mice and that the adoptive transfer of Sm28GST-specific T cells reproduced the protective effect obtained with the recombinant molecule. In the present paper, the authors show that Sm28GST is also able to stimulate an antigen-specific, cytotoxic T-cell response against Sm28GST-pulsed P815 target cells in normal mice and that effector cells induced in vivo were classical Class I MHC-restricted CD8⁺ lymphocytes. The authors found no spontaneous CTL activity against Sm28GST-pulsed target cells during the course of the infection by S. mansoni although Sm28GST is expressed at different developmental stages of the parasite. It was observed, however, that immunization with Sm28GST is sufficient to elicit a significant level of CTL response for 6 weeks in infected mice. The role of these Class I MHC-restricted CD8⁺ lymphocytes in the protection observed precisely at the same period in immunized mice remains to be elucidated. The authors also observe that immunization with the lipopeptidic form of the C-terminal peptide of the molecule (190–211 peptide) led to a CTL activation comparable to that observed after immunization with the whole molecule demonstrating the feasibility of using a synthetic lipopeptide as immunogen for a CTL response against Sm28GST epitopes. Moreover, like Sm28GST-specific CTLs, 190–211 lipopeptide-specific cells were also Class I MHC-restricted lymphocytes.     

Molecular cloning and tissue distribution of a 26-kilodalton Schistosoma mansoni glutathione S-transferase

A Schistosoma mansoni cDNA library was constructed from the mRNA of adult worms in the expression vector lambda gt11 and screened with a rabbit antiserum raised against the 26-kDa S. mansoni glutathione S-transferase isoforms (Sm GST 26). Two clones were selected and the nucleotide sequences deduced. The predicted amino acid sequence, specified by these cDNAs, shows strong homology with a Schistosoma japonicum 26 kDa glutathione S-transferase and a lower level of homology with mammalian glutathione S-transferase class mu isoenzymes (EC 2.5.1.18). No significant homology score was found with a 28-kDa S. mansoni glutathione S-transferase (Sm GST 28). A study of the tissue distribution of the cloned Sm GST 26 by immunoelectron microscopy shows similarities to Sm GST 28 in that they are present in the tegument and in subtegumentary parenchymal cells. However, a major difference exists in the protonephridial region in which Sm GST 26 is present in the cytoplasmic digitations localized in the apical chamber delineated by the flame cell body, suggesting that Sm GST 26 may be actively excreted by adult worms.     

Protective effect of rSm28GST-specific T cells in schistosomiasis: role of gamma interferon.

Immunization with a single dose of 50 micrograms of recombinant Schistosoma mansoni 28-kDa glutathione-S-transferase (rSm28GST) was able to induce a reduction in the worm burden, the number of eggs, and the degree of hepatic fibrosis as quantified by the measurement of collagen content in the liver of S. mansoni-infected mice. No relationship was found between anti-Sm28GST immunoglobulin G and immunoglobulin A titers and the levels of protection obtained. Adoptive transfers of Sm28GST-specific total, CD4+, or CD8+ T cells reproduced the protective effect obtained with the recombinant molecule. Moreover, experiments studying in vivo T-cell depletion demonstrated that anti-CD4- or anti-CD8-treated mice showed a significant decrease in the protective effect conferred, suggesting a role of the two T-cell subpopulations in the expression of Sm28GST-mediated protection against hepatic damage. Sm28GST-specific cells produced little interleukin-4 and high levels of gamma interferon. Treatment of immunized mice with anti-gamma interferon antibody totally suppressed the Sm28GST-induced protective effect and led to the rapid death of infected animals, suggesting a role for this cytokine in the expression of the protective immunity obtained after immunization with rSm28GST.     

Obtention of a human primary humoral response against schistosome protective antigens in severe combined immunodeficiency mice after the transfer of human peripheral blood mononuclear cells

Peripheral blood mononuclear cells (PBMC) from healthy donors were injected into C.B.-17 severe combined immunodeficiency (scid) mice which were subsequently immunized with crude Schistosoma mansoni adult worm antigenic preparation (SWAP) or with recombinant S. mansoni 28-kDa glutathione transferase (r-Sm-28-GST) antigen. PBMC from a S. mansoni-infected patient were also transferred. The specific human anti-SWAP and anti-Sm-28-GST antibody responses were monitored. The presence in both cases of human specific antibodies in scid mouse sera was determined by enzyme-linked immunosorbent assay and Western blotting techniques using anti-human immunoglobulin reagents. No antibodies were detected in these sera using anti-mouse immunoglobulin antisera. These antibodies were functional since a cytotoxic activity against schistosomula was observed when monocytes were incubated with scid mouse sera positive for anti-Sm-28-GST antibodies.     

Differential responsiveness of humans with early-stage schistosomiasis haematobium to Schistosoma haematobium soluble adult-worm and egg antigens

Schoolchildren (7–8 years old) infected with Schistosoma haematobium were tested for lymphocyte proliferative responses, in vitro granuloma formation (IVGF), and cytokine release in T-cell Western assays and for serum antibody reactivity by enzyme-linked immunosorbent assay (ELISA) and immunoblotting against S. haematobium soluble adult-worm (SAWA) and egg (SEA) antigens. The lymphoproliferative response rate of individual subjects against 10 SAWA and 15 SEA electroseparated bands ranged from 0 to 33?% and from 11 to 66?%, respectively. The SAWA bands essentially failed to elicit significant IVGF, in contrast to the SEA bands, all of which were capable of inducing IVGF from peripheral blood mononuclear cells (PBMC) of 30–80?% of individual donors. The exclusive ability of SEA bands to induce IVGF could not be attributed to selective release of interleukin 2 (IL-2), IL-4, or interferon-gamma, as SEA and SAWA bands were capable of eliciting release of a similar array of cytokines in supernatants of 4-day PBMC cultures. The antibody response to SEA was stronger than that to SAWA, yet the proportion of SAWA bands binding humoral antibodies of individual donors was significantly larger than that observed for SEA. The study thus suggests that humans with early-stage S. haematobium infection respond poorly to SAWA but mount strong cellular immune responses to SEA that result in granuloma and antibody formation.     

Establishment and characterization of an antigen-specific T-cell line from liver granulomas of Schistosoma mansoni-infected mice.

Granulomatous inflammations in schistosomiasis mansoni are the result of T-cell-mediated reactions to soluble egg antigens (SEA) secreted by parasite ova. To study TDH effector cell function, a granuloma T-cell line was established from collagenase-digested liver granulomas of acutely infected CBA/J mice. Dispersed nonadherent granuloma cells were cultured with feeder layer cells and SEA or with feeder layer cells alone in alternate cycles for 32 weeks. The granuloma T-cell line was L3T4+ Lyt-1+. In vitro, the SEA-stimulated T cells showed proliferation and interleukin 2 production. One million T cells adoptively transferred SEA-specific footpad swelling, and 7.5 X 10(6) T cells adoptively transferred granulomatous hypersensitivity to injected ova or SEA-coated beads. Anti-L3T4 monoclonal antibody blocked the SEA-specific cell proliferation. Depletion of L3T4+ cells abrogated, while that of Lyt-1+ cells diminished the adoptive transfer of SEA-specific footpad swelling. These experiments demonstrate that the granuloma T-lymphocyte population contains TDH-type effector cells. Establishment of an SEA-specific granuloma T-cell line will allow the study of the effector functions of the hitherto uncharacterized intralesional granuloma T lymphocyte.     

In vitro and in vivo evidence that autoimmune reactivity to collagen develops spontaneously in Schistosoma mansoni-infected mice

Egg-induced granuloma formation in murine schistosomiasis mansoni results from vigorous anti-parasite reaction by activated T cells, macrophages, eosinophils, and fibroblasts. The present study suggests that strain-specific, autoimmune T-cell reactivity directed against host matrix proteins might also contribute to granulomatous hypersensitivity. T cells from infected C57B1/6, but not from CBA or BALB/c mice, proliferative in vitro in response to denatured collagen. T cells from uninfected mice, previously immunized with soluble egg antigen (SEA), did not respond in vitro to collagen. Spleen cells from acutely infected mice, but not chronically infected or uninfected animals, formed granulomas around collagen-coupled polyacrylamide beads in vitro. This response was blocked by anti-collagen antibodies that had no inhibitory effect on in vitro granuloma formation around SEA-coupled beads. In related in vivo studies, granuloma formation was quantitated after iv injection of SEA-, collagen-, or uncoated beads into normal or infected recipients. The mean diameter of lung granulomas induced by collagen-coupled beads in infected mice was significantly greater than the diameter of granulomas around either collagen beads in uninfected mice or uncoated beads in infected mice. these observations indicate that anti-collagen responses develop spontaneously in Schistosoma-infected mice and suggest that such reactivity might play a secondary role in granuloma formation and the pathogenesis of hepatic fibrosis.     

A monoclonal antibody blocking the Schistosoma mansoni 28-kDa glutathione S-transferase activity reduces female worm fecundity and egg viability

The protective effects of two different monoclonal antibodies (mAb) raised against the Schistosoma mansoni 28-kDa glutathione S-transferase (Sm 28 GST) were investigated. Two mAb of the same isotype (IgM) have been selected according to the blocking effect on Sm 28 GST enzymatic activity (S13) or the lack of blockade (H12). When passively transferred into Fischer rats, both S13 and H12 significantly reduced the worm burden. In BALB/c mice clear effects on female worm fecundity and egg viability were observed when the S13 mAb was transferred; these effects included significantly reduced loads of intestinal eggs, reduced egg hatching rates and an increased proportion of non-living eggs. No effect on egg production and egg hatching was observed in H12-treated mice. In addition, worm pairs recovered from S13-but not H12-treated mice laid significantly fewer eggs in vitro, and normal worm pairs incubated in vitro with the S13 mAb produced significantly fewer eggs than those incubated with H12 mAb. The impairment of egg hatching ability was also reproduced in vitro by the S13 mAb. These data suggest the existence of two different effector mechanisms induced by immunization with Sm 28 GST. The effect on the schistosome worm burden appears to be independent of GST activity whereas the effect on S. mansoni female fecundity and egg viability seems to be significantly linked to the inactivation of the enzymatic site.     

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.     

Inter-species variation of schistosome 28-kDa glutathione S-transferases.

The 28-kDa glutathione S-transferase from Schistosoma mansoni (Sm28GST) is a candidate vaccine antigen. To evaluate the antigenic and phylogenetic variations between the 28-kDa GSTs from 4 species of schistosome, we have cloned and sequenced the 28-kDa GSTs from Schistosoma haematobium (Sh28GST) and Schistosoma bovis (Sb28GST). Sb28GST and Sh28GST are more similar to each other (97%) than to Sm28GST (90%) and particularly to the 28-kDa GST from Schistosoma japonicum (Sj28GST, 77%). Antisera directed against the major Sm28GST epitopes revealed differences in the recognition of the 28-kDa GSTs from the other schistosome species suggesting that these regions have been subjected to evolutionary pressure. The consequences of such species-specific epitopes on the development of a multi-species anti-schistosome vaccine are discussed.