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.     

Bordetella pertussis Filamentous Hemagglutinin Enhances the Immunogenicity of Liposome-Delivered Antigen Administered Intranasally

In an attempt to increase the immunogenicity of mucosally delivered antigens, we incorporated the Bordetella pertussis filamentous hemagglutinin (FHA) adhesin into liposomes containing the glutathione S-transferase of Schistosoma mansoni (Sm28GST) as a model antigen. Outbred mice immunized twice intranasally with liposomes containing a constant suboptimal dose of Sm28GST and increasing doses of FHA produced anti-Sm28GST antibodies in a FHA dose-dependent manner. The addition of 3 μg of FHA to the liposomes induced more than 10-fold-higher anti-Sm28GST antibody titers, compared to those induced by liposomes without FHA. The presence of FHA did not alter the nature of the humoral immune response, and the sera contained anti-Sm28GST immunoglobulin G1 (IgG1), IgG2a, and IgG2b. However, anti-Sm28GST IgA was only detected when at least 3 μg of FHA was added to the preparation. These results show a promising potential for FHA to enhance the immunogenicity of mucosally administered antigens incorporated into liposomes.     

Systemic and Mucosal Immune Responses after Intranasal Administration of Recombinant Mycobacterium bovis Bacillus Calmette-Guérin Expressing Glutathione S-Transferase from Schistosoma haematobium

A major goal of current vaccine development is the induction of strong immune responses against protective antigens delivered by mucosal routes. One of the most promising approaches in that respect relies on the use of live recombinant vaccine carriers. In this study, Mycobacterium bovis BCG was engineered to produce an intracellular glutathione S-transferase from Schistosoma haematobium (Sh28GST). The gene encoding Sh28GST was placed under the control of the mycobacterial hsp60 promoter on a replicative shuttle plasmid containing a mercury resistance operon as the only selectable marker. The recombinant Sh28GST produced in BCG bound glutathione and expressed enzymatic activity, indicating that its active site was properly folded. Both intraperitoneal and intranasal immunizations of BALB/c mice with the recombinant BCG resulted in strong anti-Sh28GST antibody responses, which were enhanced by a boost. Mice immunized intranasally produced a mixed response with the production of Sh28GST-specific immunoglobulin G1 (IgG1), IgG2a, IgG2b, and IgA in the serum. In addition, high levels of anti-Sh28GST IgA were also found in the bronchoalveolar lavage fluids, demonstrating that intranasal delivery of the recombinant BCG was able to induce long-lasting secretory and systemic immune responses to antigens expressed intracellularly. Surprisingly, intranasal immunization with the BCG producing the Sh28GST induced a much stronger specific humoral response than intranasal immunization with BCG producing the glutathione S-transferase from Schistosoma mansoni, although the two antigens have over 90% identity. This difference was not observed after intraperitoneal administration.     

Protective immunity induced in rat schistosomiasis by a single dose of the Sm28GST recombinant antigen: Effector mechanisms involving IgE and IgA antibodies

Rats immunized by a single dose of the recombinant Sm28GST antigen, using either aluminium hydroxide or Bacillus Calmette-GuSrin adjuvant, were significantly protected (up to 59% reduction in worm burden) against a challenge infection with Schistosoma mansoni cercariae. A follow-up study of the humoral response revealed the presence of high levels of IgE and IgA antibodies together with specific IgG. Sera from once Sm28GST-immunized rats induced a cytotoxic response for schistosomula targets in the presence of normal rat eosinophils, similar to the one induced by sera from twice immunized rats. Depletion or competition studies indicated the participation of both IgE and IgA antibodies in eosinophil-dependent cytotoxicity mechanisms. These results suggest the existence, in immunized rats exhibiting protection against schistosomiasis, of an original effector mechanism implying eosinophils and IgA antibodies, together with documented effector mechanisms involving IgE and eosinophils. In addition, they raise questions concerning the role of IgA antibodies in schistosomiasis.     

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.     

Infection with Salmonella typhimurium modulates the immune response to Schistosoma mansoni glutathione-S-transferase.

Immune response polarization is controlled by several factors, including cytokines, antigen-presenting cells, antigen dose, and others. We have previously shown that adjuvants and live vectors play a critical role in polarization. Thus, immunization with the Schistosoma mansoni 28-kDa glutathione-S-transferase (Sm28-GST) in aluminum hydroxide induced a type 2 cytokine profile and the production of immunoglobulin G1 (IgG1)- and IgE-specific antibodies. In contrast, mice infected with recombinant Salmonella typhimurium expressing Sm28-GST developed a type 1 cytokine profile and produced IgG2a-specific antibodies against Sm28-GST and Salmonella antigens. In this study, to determine if S. typhimurium not expressing Sm28-GST would still influence the type of the response against this antigen, we compared the profiles of the immune responses generated against Sm28-GST administered in alum in mice infected and not infected with S. typhimurium. Infected mice generated both IgG1 and IgG2a antibodies against Sm28-GST, while noninfected mice produced only IgG1 anti-Sm28-GST antibodies. Moreover, interleukin-4 (IL-4) mRNA expression in infected mice was near background levels, while gamma interferon (IFN-gamma) mRNA expression in coinfected mice was significantly higher than in mice immunized with Sm28-GST in alum only. However, after antigen-specific stimulation in vitro with Sm28-GST, levels of IL-4 and IFN-gamma cytokine production were similar in the two groups of mice. These results suggest that (i) the immune milieu produced during an infection may modify the response against an irrelevant antigen and (ii) isotype switching may be influenced by the cytokine environment of a bystander immune response, even though the specific antigen-driven cytokine production is not modified. Thus, the isotypic profile is not always an absolute reflection of the cytokines produced by antigen-specific Th cells.     

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.     

用噬菌体肽库筛选重组日本血吸虫线粒体相关蛋白的表位

目的：筛选和鉴定重组的日本血吸虫（中国大陆株）线粒体相关蛋白rSj38的表位。方法：用纯化的rSj338/26GST免疫家兔获得抗rSj338/26GST的多克隆抗体IgG，将抗体进一步纯化，获得抗rSj338单特异多克隆抗体IgG。用纯化抗rSj338抗体对噬菌体12肽库进行5轮免疫学筛选，挑取克隆。采用Western blot免疫识别，核苷酸序列测定分析其获得的表位并与rSj338/26GST进行同源性比较。将获得的不同表位的阳性克隆分别免疫小鼠，并采用Western blot及dot-ELISA方法筛选能刺激小鼠产生较高滴度抗rSj338抗体的阳性克隆，并将阳性噬菌体免疫的小鼠血清对纯化的rSj338/26GST,26GST，日本血吸虫成虫及虫卵抗原进行Western blot识别。结果：经5轮免疫学筛选后挑取的32个克隆，用Western blot方法30个克隆能被抗rSj338抗体识别，核苷酸序列分析发现共有11种表位，与rSj338无一级结构的同源性。经动物免疫初步实验筛选。共获得4个免疫原性较强的阳性克隆，其免疫鼠血清均可识别rSj338/26GST，日本血吸虫成虫及虫卵抗原。结论：获得了4种日本血吸虫中国大陆株线粒体相关蛋白rSj338的表位，均为模拟表位，这将为日本血吸虫病的疫苗研究开辟新的途径。     

Differential induction of lupus associated antinuclear antibodies in MRL mice by monoclonal anti-Sm antibodies.

The effect of monoclonal autoantibodies on immunoregulation was investigated in MRL/MpJ-lpr/lpr mice. Passive transfer of KSm2 (a monoclonal IgG2a antibody directed against the 16 kD polypeptide of Sm) induced IgG antibodies to the other major immunoreactive polypeptides of Sm (28 and 29 kD) in all mice studied, and to polypeptides of the closely related antigen nRNP/Sm in 63% of the mice. In addition an increment in IgG anti-dsDNA antibodies, and in IgA and IgM anti-Sm antibodies, over control levels was observed. These effects were not due to polyclonal activation since anti-histone antibody levels were unaffected. Two other IgG2a monoclonal antibodies: KSm5 (directed against the 28 and 29 kD Sm polypeptides) and OX 12 (directed against an irrelevant antigen) failed to modulate the autoimmune responses of the mice in any way. These results demonstrate specific antibody-mediated connectivity between B cell clones producing autoantibodies against three distinct antigens.     

Relationship of Impairment of Schistosome 28-Kilodalton Glutathione S-Transferase (GST) Activity to Expression of Immunity to Schistosoma mattheei in Calves Vaccinated with Recombinant Schistosoma bovis 28-Kilodalton GST

Sera from calves vaccinated with the recombinant Schistosoma bovis-derived 28-kDa glutathione S-transferase (28GST) and subsequently naturally or experimentally exposed to Schistosoma mattheei were studied for their content of specific immunoglobulin G (IgG) and IgA antibodies to recombinant S. bovis 28GST as well as for their capacity to inhibit the enzymatic activity of the antigen. The results were analyzed in regard to the presence (natural infection) or absence (experimental infection) of a protective effect(s) (reductions in worm burden, egg load, fecal egg counts, and excretion of viable eggs) toward S. mattheei challenge. Under such conditions, no differences in the IgG- and IgA-specific antibodies to recombinant S. bovis 28GST or in the ability to block the catalytic function of the antigen between the two groups were recorded. Nevertheless, correlation analysis between the specific antibody responses to recombinant S. bovis 28GST and the inhibition of GST activity suggested an association with IgG in experimentally infected vaccinated animals, while in naturally infected vaccinated calves, the inhibitory activity appeared to be linked to a greater degree with IgA. These results suggest that in contrast to schistosomiasis in humans, IgG antibodies in calves with schistosomiasis may exhibit inhibitory functions toward GST enzymatic activity or have a modulatory effect on IgA antibody properties. Furthermore, sera from animals immunized with recombinant S. bovis 28GST recognized the native S. mattheei 28GST and achieved comparable levels of inhibition of activity of recombinant S. bovis 28GST and S. matthei 28GST, indicating the presence of cross-reactive epitopes on these two molecules.     

IgG Subclass-Associated Differences in Anti-Schistosomal Antibody Specificity

Consecutive sera from before and after treatment were collected from 23 patients with a Schistosoma mansoni infection, seven of whom had an early infection. All sera were analysed for IgGl, IgG3 and IgG4 antibody activity against three peptides from the protein Sm 28 GST (24–43, 115–131 and 140–153 aa). In addition, sera from 14 patients, four with an early infection and 10 patients with a chronic infection, were analysed for IgG and IgA antibody activity using seven peptides derived from the protein Sm 28 GST. This molecule has previously demonstrated protective activity against infection in various experimental models.
The results are indicative of a subclass-related epitope specificity of the antibodies. Moreover, reactivity to one of the peptides (158–175 aa) was significantly associated with a chronic infectious status.     

Characterization and specificity of B-cell responses in lupus induced by Mycobacterium bovis in NOD/Lt mice.

A single dose of pasteurized Mycobacterium bovis administered intravenously to prediabetic non-obese diabetic (NOD) mice prevented the onset of type 1 diabetes but precipitated a systemic ''autoimmune rheumatic disease'' (ARD) similar to systemic lupus erythematosus. This syndrome was characterized by haemolytic anaemia, anti-dsDNA and anti-Smith antigen (Sm) antinuclear autoantibodies, increased severity of sialadenitis and glomerular immune complex deposition. Here, we examine the specificity of the autoantibody responses in M. bovis-treated NOD mice. Large amounts of antibody were detected to the Sm/ribonucleoprotein (RNP) complex, of which the 28 000 MW polypeptide appeared to be immunodominant. The IgG subclass involved in the anti-Sm response was primarily IgG2a. Antibodies against dsDNA were also detected, but the subclass of this response was mixed, with IgG2a and IgG2b being present in equal amounts. Together, these findings argue against a role for immune deviation towards T helper type 2 (Th2) responses in pathogenesis of the disease. The anti-dsDNA and anti-Sm reactivities were not mediated by polyreactive antibodies since neither antigen could cross-compete plasma antibody binding to the other in competitive enzyme-linked immunosorbent assay. The role of polyclonal B-cell activation was examined by measuring total gamma-globulin as well as IgG reactive with other nuclear antigens including Ro60, Ro52 and La, which although not a major component of the autoantibody responses in these mice, did show small but significant increases following immunization with M. bovis. Thus polyclonal stimulation, while likely to be occurring, was not directly responsible for production of anti-Sm antibodies.     

Immunization of Mice with Live-Attenuated Late Liver Stage-Arresting Plasmodium yoelii Parasites Generates Protective Antibody Responses to Preerythrocytic Stages of Malaria

Understanding protective immunity to malaria is essential for the design of an effective vaccine to prevent the large number of infections and deaths caused by this parasitic disease. To date, whole-parasite immunization with attenuated parasites is the most effective method to confer sterile protection against malaria infection in clinical trials. Mouse model studies have highlighted the essential role that CD8⁺ T cells play in protection against preerythrocytic stages of malaria; however, there is mounting evidence that antibodies are also important in these stages. Here, we show that experimental immunization of mice with Plasmodium yoelii fabb/f⁻ (Pyfabb/f⁻), a genetically attenuated rodent malaria parasite that arrests late in the liver stage, induced functional antibodies that inhibited hepatocyte invasion in vitro and reduced liver-stage burden in vivo. These antibodies were sufficient to induce sterile protection from challenge by P. yoelii sporozoites in the absence of T cells in 50% of mice when sporozoites were administered by mosquito bite but not when they were administered by intravenous injection. Moreover, among mice challenged by mosquito bite, a higher proportion of BALB/c mice than C57BL/6 mice developed sterile protection (62.5% and 37.5%, respectively). Analysis of the antibody isotypes induced by immunization with Pyfabb/f⁻ showed that, overall, BALB/c mice developed an IgG1-biased response, whereas C57BL/6 mice developed an IgG2b/c-biased response. Our data demonstrate for the first time that antibodies induced by experimental immunization of mice with a genetically attenuated rodent parasite play a protective role during the preerythrocytic stages of malaria. Furthermore, they highlight the importance of considering both the route of challenge and the genetic background of the mouse strains used when interpreting vaccine efficacy studies in animal models of malaria infection.     

Protection against Influenza Virus Infection of Mice Fed Bifidobacterium breve YIT4064

Mice fed Bifidobacterium breve YIT4064 and immunized orally with influenza virus were more strongly protected against influenza virus infection of the lower respiratory tract than ones immunized with influenza virus only. The number of mice with enhanced anti-influenza virus immunoglobulin G (IgG) in serum upon oral administration of B. breve YIT4064 and oral immunization with influenza virus was significantly greater than that upon oral immunization with influenza virus only. These findings demonstrated that the oral administration of B. breve YIT4064 increased anti-influenza virus IgG antibodies in serum and protected against influenza virus infection. The oral administration of B. breve YIT4064 may enhance antigen-specific IgG against various pathogenic antigens taken orally and induce protection against various virus infections.     

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.     

Schistosoma mansoni tetraspanning orphan receptor (SmTOR): a new vaccine candidate against schistosomiasis

One approach to fight against schistosomiasis is to develop an efficient vaccine. Schistosoma mansoni tetraspanning orphan receptor (SmTOR) might be a vaccine candidate, as it is a tegument membrane protein expressed most highly in cercariae. In this study we characterized the recombinant first extracellular domain of SmTOR (rSmTORed1) as having the expected property to bind C2 of complement similarly to a smaller peptide of the same domain, and to produce specific and high-titre antibodies in BALB/c mice immunized using complete Freund''s adjuvant/incomplete Freund''s adjuvant (CFA/IFA). Immunization was protective against parasite infection, as demonstrated by a significant decrease in worm burden in immunized BALB/c mice versus the control groups over two independent trials [64 and 45% reduction for mean adult worm burden in immunized versus phosphate-bufferd saline (PBS) injected mice]. Interestingly, infection by itself did not lead to the generation of anti-rSmTORed1 antibodies, corresponding to the low frequency of specific anti-rSmTORed1 antibodies detected in the sera of patients infected with S. mansoni (2/20; 10%). These data suggest that, as opposed to the natural infection during which SmTOR induces antibodies only rarely, immunization with its smaller first extracellular domain might be more efficient.     

Local transient induction of inflammatory cytokines after intranasal administration of recombinantBordetella pertussis

Inflammatory cytokines have been described to play a critical role in the orientation and amplification of the IgA immune response. In this study, we show that the intranasal administration of aBordetella pertussisstrain expressing the protective antigen glutathione-S-transferase ofSchistosoma mansoni(Sm28GST) induced an inflammatory response in the lungs of mice, characterized by the production of inflammatory cytokines, such as Tumor Necrosis Factor α, Interleukin-6 and Transforming-Growth Factor β. The production and the secretion of these cytokines in lung tissues were early and transient. Their presence was observed only during the first week after administration despite the persistence of the bacteria for 1 month. Two weeks after inoculation, Interleukin-10 secretion was detected in the lungs, which could explain the decrease in the production of inflammatory cytokines. These inflammation-regulating cytokines, induced in the lungs by the presence of the bacterial vector, could be part of the process generating the local immune response, in particular the anti-Sm28GST IgA response.     

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.     

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.     

Isotype responses to candidate vaccine antigens in protective sera obtained from mice vaccinated with irradiated cercariae of Schistosoma mansoni.

In experimental schistosomiasis, sera of mice multiply vaccinated with radiation-attenuated cercariae of Schistosoma mansoni passively transfer resistance against cercarial challenge to naive mice. To further characterize these sera, we tested their protective capacities in two mouse strains (C57BL/6J and CBA/J) and compared the antigen-specific isotype compositions of the different protective sera by means of the enzyme-linked immunosorbent assay. By using an array of purified schistosomal antigens, the patterns of antibody titers and isotypes differed for each experimental group and antigen. In the most-protective C57BL/6J sera, high levels of immunoglobulin G1 (IgG1), IgG2a, and IgG2b bound to heat shock protein 70 and the integral membrane protein Sm23, whereas recognition of these antigens by less-protective CBA/J sera was lower. Glutathione S-transferase (GST) was recognized predominantly by IgM antibodies of all vaccinated groups, and a significant portion of this response was directed against carbohydrate epitopes. Antibodies specific for triosephosphate isomerase, paramyosin, and Sm32 (hemoglobinase) were present in less-protective sera and thus seem less relevant for passive transfer of resistance. The results of this study suggest a contribution of IgG antibodies specific for heat shock protein 70 and Sm23, and possibly a contribution of GST-specific IgM antibodies, to the protective effect of sera from C57BL/6J mice vaccinated with irradiated cercariae.