Characterization of Schistosoma mansoni monoclonal antibodies which block in-vitro killing: failure to demonstrate blockage of immunity in vivo.

We have characterized various anti-schistosomular surface MoAbs previously shown to partially block in-vitro killing of schistosomula by human sera and eosinophils (Dunne et al. 1987). Immunodiffusion analysis showed that four IgM and one IgG3 MoAbs recognized periodate sensitive epitopes on the same molecular species present in schistosomular antigen but their patterns of reactivity with soluble egg antigen demonstrated that at least three distinct epitopes were involved. SDS-PAGE analysis showed the IgMs to react with 125I-labelled surface antigens of Mr 35,000-38,000 and Mr 20,000, and the IgG3 to react with an Mr 38,000 antigen. In spite of their effect in vitro, transfer of the IgM MoAbs at the time of challenge of mice vaccinated with irradiated cercariae or of mice injected with an unrelated (anti-Mr 16,000) protective MoAb failed to produce in-vivo blocking. Similarly, injection of Schistosoma mansoni eggs, prior infection with worms of one sex, or passive transfer of serum from single-sex infected mice failed to influence the resistance conferred by vaccination with irradiated cercariae.