The immune response of cattle to Babesia bovis (syn. B. argentina). Studies on the nature and specificity of protection.

Studies of the immune response to Babesia bovis (syn. B. argentina) in Bos taurus cattle, using the passive transfer of serum from immune animals, indicated that an effector mechanism was mediated by antibodies which reacted with the parasitized erythrocytes. During removal from the peripheral blood, the parasites did not show reduced viability on subinoculation into other non-infected animals, and thus were not dead or irreversibly damaged at this time. It was concluded that opsonization of infected erythrocytes was probably the basis of protection by the system. There was some evidence that minor variation of the protective antigen(s) occurred within strains of the parasite but this had little effect on the efficiency of the host's immune response. However, there was no cross-protection between the antibodies against different strains. These interstrain differences in antibody specificity were reconciled with earlier observations that cross-immunity commonly occurs between different strains in infected animals. It was concluded that the mechanism of cross-immunity relied on priming of the host's immune system by the protective antigen(s) of the strain so that a secondary response against the heterologous strain occurred soon after challenge.