CROSS-PROTECTIVE IMMUNITY INDUCED BY BABESIA-BOVIS CLONES WITH ANTIGENICALLY UNRELATED VARIABLE MEROZOITE SURFACE-ANTIGENS

Babesia bovis merozoite surface antigen 1 (MSA-1) induces antibodies c apable of neutralizing merozoites in vitro. Both MSA-1 and the co-expr essed MSA-2 are encoded by a polymorphic multigene family and are anti genically variant among strains isolated from widely separated geograp hic regions. In this study, cross-protective immunity between two B. b ovis clones, Mexico Mo-7 and Israel-C, that have antigenically unrelat ed MSA-1 and MSA-2 surface proteins was assessed. Cattle immunized by infection with either clone were significantly protected against chall enge with the uncloned Israel Bbv strain. This indicates that epitopes capable of inducing partial protection are shared among different str ains and that immunity is not solely dependent upon MSA-1 or MSA-2. Ho wever, cattle immunized with the Israel-C clone, derived from the Isra el Bbv strain, were significantly better protected against BbV challen ge than were cattle immunized with the Mexico Mo-7 clone bearing antig enically unrelated MSA-1 and MSA-2. The significant difference in immu nity induced by the homologous strain versus an antigenically variant strain indicates that epitope variation among strains is relevant to i mmunity against babesiosis.