Mechanisms of protective immunity against Schistosoma mansoni infection in mice vaccinated with irradiated cercariae. II. Analysis of immunity in hosts deficient in T lymphocytes, B lymphocytes, or complement.

Laboratory mice with genetic or induced immunodeficiencies were vaccinated with irradiated cercariae of Schistosoma mansoni and assayed 4 wk later for their resistance to challenge infection. Athymic nude mice failed to develop immunity to challenge or detectable antibody responses to schistosomula, whereas heterozygote (nu/+) controls and nude mice with thymus grafts displayed highly significant levels of resistance and anti-schistosomulum antibody. Similarly, no resistance or antibody production as observed in vaccinated mice that had been made deficient in B lymphocytes by the injection of anti-mu-chain antisera from birth. In contrast, normal levels of vaccine-induced resistance were observed in mice genetically deficient in the fifth component of complement (C5) and in mice decomplemented before challenge by treatment with cobra venom factor. These results indicate that the resistance to challenge infection induced by irradiated cercariae is both thymus and B lymphocyte dependent and therefore is likely to result from specific immune responses directed against schistosome worms. The data also argue against a role for complement in the effector mechanism of vaccine-induced immunity.