Immunity to Babesia in mice. II. Cross protection between various Babesia and Plasmodium species and its relevance to the nature of Babesia immunity.

Mice immunized against B. rodhaini by means of a drug-controlled infection were subsequently resistant to infection with B. microti and B. ratti. In the reciprocal experiments the protection against B. rodhaini was less effective. B. rodhaini immunized mice were also considerably protected against P. vinckei infection, whereas protection against P. berghei did not occur. Antibody determinations indicated that the heterologous protection cannot be explained by the occurrence of cross-reacting antibodies. Because of similarity with the non-specific suppression of babesiosis in BCG-infected mice, the same effector mechanism is postulated to explain the infection-induced homologous and heterologous protection. Unlike non-specifically induced protection, the induction of acquired resistance by means of a drug-controlled B. rodhaini infection is thymus-dependent.