Antibody is responsible for the passive transfer of immunity to mice from rabbits, rats or mice vaccinated with attenuatedSchistosoma japonicumcercariae

Sera from rabbits, rats and mice multiply-vaccinated with attenuated cercariae of Schistosoma japonicum conferred high levels of resistance against challenge to naive recipient mice (up to 97, 64 and 60% respectively). Vaccinated rabbit and rat sera were given before challenge and vaccinated mouse serum 5 days after challenge. To show that the protective factors in these sera were antibodies, vaccinated rabbit and mouse sera were fractionated by protein A-Sepharose and the fractions precipitated by 50% ammonium sulphate. The protein A-Sepharose binding or non-binding fractions in vaccinated rabbit serum transferred approximately equal levels of significant resistance to mice, suggesting that both the IgG and non-IgG components of vaccinated rabbit serum are protective. The major part of the protective activity in vaccinated mouse serum was transferred to recipients by the protein A-Sepharose binding fraction, i.e. the IgG antibodies. Heat inactivation of sera at 56 degrees C for 3 h affected the protective capacity of vaccinated rat sera, but not that of vaccinated rabbit or mouse sera.