Genetic control of immune response to a purified Schistosoma mansoni antigen. I. Effect of MHC class II antigens on the cellular, humoral and protective responses

Experimental models of Schistosoma mansoni infection

Experimental models of Schistosoma mansoni infections in mammals have contributed greatly to our understanding of the pathology and pathogenesis of infection. We consider here hepatic and extrahepatic disease in models of acute and chronic infection. Experimental schistosome infections have also contributed more broadly to our understanding of granulomatous inflammation and our understanding of Th1 versus Th2 related inflammation and particularly to Th2-mediated fibrosis of the liver.

A mimotope peptide-based vaccine against Schistosoma mansoni: synthesis and characterization

A panel of four mimotopes of the epitope recognized by the highly protective monoclonal antibody against Schistosoma mansoni (152-66-9B) was obtained by screening a solid-phase 8mer random peptide library. Three of the four mimotopes (p28, p29 and p30) were efficiently recognized in an in vitro radioimmunoassay by the monoclonal antibody and by sera from infected mice and one (p30) induced in vitro proliferation of primed lymphocytes. When the mimotopes were conjugated to bovine serum albumin (BSA) and the conjugates used to immunize C57BL/6J mice, only the p30-BSA-induced antibodies which were effective at complement-mediated killing of schistosomula. The level of complement-mediated killing obtained with the anti-p30 antibodies was comparable to that seen with serum from mice immunized with the protective 9B-antigen. Furthermore, following challenge infection of mimotope-BSA-immunized mice, a greater than 40% reduction in worm burden was observed in p30-BSA-immunized mice, a level comparable to that seen following immunization with the intact 9B-antigen. These results show that a simple synthetic peptide immunogen comprising an eight-amino acid mimotope of a conformational epitope on the 9B-antigen can induce protective immune responses against S. mansoni that are comparable to those obtained following immunization with the far more complex intact antigen. This mimotope may well represent a potential component of a synthetic peptide vaccine against S. mansoni. The inclusion of other B-cell- and T-cell-stimulating synthetic epitopes in such a vaccine, together with a more appropriate carrier, adjuvant and delivery systems may well result in a level of protection even greater than that seen with the single mimotope.

Proteosome delivery of a protective 9B-antigen against Schistosoma mansoni

We have previously characterized a stage specific, partially protective protein denoted 9B-antigen. This antigen is of 450 kDa in its native form but upon SDS-PAGE in reducing conditions it exhibits two subunits of 30 kDa and 45 kDa. The 9B-antigen is localized at the surface of schistosomula and persists at the surface of lung schistosomula. The 9B-antigen is also localized in internal organs of a vital function in the parasite such as flame cells and cytoplasmic tubes. Infected individuals or mice vaccinated with irradiated cercariae recognize the 9B-antigen. We have previously shown that when injected with complete Freunds adjuvant, the 9B-antigen can induce 40% protection against challenge infection. In this study we have used a more effective delivery system for this antigen. The 9B-antigen was coupled to proteosomes derived from meningoccocal outer membrane proteins. Vaccination of mice with this complex increased the protection level to 60%. Sera from these vaccinated mice induced high levels of complement mediated cytotoxicity of the parasite. Since the proteosomes are approved for human use, these results are promising towards the development of a vaccine against schistosomiasis.

Synthesis and characterization of a protective peptide-based vaccine against Schistosoma mansoni

Two synthetic peptides, corresponding to the N-terminal sequence of the 45-kDa subunit of the protective 9B antigen of Schistosoma mansoni and differing in only one amino acid residue, were synthesized. These peptides were recognized by the protective monoclonal antibody 152-66-9B, as well as by sera of mice and humans infected with schistosomiasis. The peptides were coupled to a protein carrier and used for immunization. One of the peptides, 9B-peptide1, induced in mice significant protection against challenge infection, manifested in a 40 to 50% reduction in worm burden.

MHC-restriction of antibody responses to an 86 kilodalton antigen of Schistosoma mansoni

The previously observed MHC-restriction of the antibody response to an 86kDa S. mansoni antigen has been investigated in more detail. The I-A locus of the H-2 complex has been implicated as conferring responder or non-responder status on mice expressing the k and b alleles respectively. Inheritance of responsiveness was dominant over non-responsiveness. An additional level of complexity was observed in the p86 antibody responder status of individuals within a responding inbred strain. This could not be accounted for directly by the level of patent infection, but showed an inverse correlation with the level of egg output in H-2k mice. Differential antibody responsiveness to other antigens, between individuals of the same strain, occurred independently of the differential responsiveness to p86.

Genetic control of immune response to a purified Schistosoma mansoni antigen. II. Establishment and characterization of specific I-A and I-E restricted T-cell clones

T-cell lines and clones specific for a partially protective schistosome antigen (9B antigen) were established from mice immunized with such antigen. The H-2 congenic strains B10.A which express both I-A and I-E class II gene products of the major histocompatibility complex (MHC) and B10.A(4R) which only express I-A molecules were used in these studies. The specific T-cell lines recognized the 9B antigen in the context of either A or E molecules, but both class II antigens were necessary for maximal stimulation of the T-cell lines in lymphocyte proliferation assays. T-cell clones were derived from these lines and their MHC restriction was investigated. Both I-A and I-E restricted clones could be isolated. All clones were specific for 9B antigen showing different degrees of cross-reactivity with a total schistosome extract (CA sonicate). A correlation between the fine specificity of the clones and the expression of class II antigens was demonstrated. Clones specific for 9B antigen, or which reacted to the same extent with 9B antigen and CA sonicate, were I-A restricted, whereas clones which proliferated more in the presence of CA sonicate were all I-E restricted. This suggests that I-E restricted clones recognize more cross-reactive epitopes than I-A restricted clones. These antigen-specific T-cell clones should provide a useful tool for examining the role of class II antigens in the modulation of protective immune response during Schistosoma mansoni infection.