Induction of protective immunity against Schistosoma mansoni by a non-living vaccine. VI. Antigen recognition by non-responder mouse strains

Previous studies have shown that many strains of mice develop partial resistance to Schistosoma mansoni as a result of intradermal vaccination with soluble schistosome antigens plus BCG. However, P and BALB/c mice are non-responsive to this intradermal vaccination protocol. In this study, humoral and cellular responses to schistosome antigens in vaccinated P and BALB/c mice were compared to those in protected C57BL/6 mice to identify an immune correlate to resistance in this model. Levels of circulating IgG and IgM antibodies to soluble adult worm antigens, as measured by ELISA, were comparable between strains. Moreover, Western blot analysis revealed no qualitative differences in antibody reactivity, with sera from vaccinated animals of all three strains recognizing the antigen previously identified as Sm-97 (paramyosin). However, vaccinated P and BALB/c mice showed specific defects in cell-mediated immunity to schistosome antigens, including decreased production of macrophage-activating lymphokines and an inability to produce activated macrophage effector cells in vivo at the site of antigen challenge. These observations strengthen our hypothesis that the intradermal vaccine acts through induction of T-cell-mediated immune resistance mechanisms.