Protective immunity of blood plasma fraction containing Babesia rodhaini exoantigens in mice

抄録

Babesia spp. are major hemoprotozoan parasites in animals. Exoantigens, which are soluble antigens released by the parasites during their asexual development, have been successfully applied for the development of a vaccine against babesiosis. In this study, we examined the ability of exoantigens to induce protective immunity in mice against a rodent Babesia parasite, Babesia rodhaini. The BALB/c mice immunized with the blood plasma fraction of B. rodhaini-infected mice (B. rodhaini exoantigens) showed a significant decrease in the lethal rate when challenged with B. rodhaini. Western blot analysis with anti-B. rodhaini exoantigen immune serum specifically detected at least eleven proteins in the lysate of B. rodhaini-infected erythrocytes. Next, a cDNA expression phage library of B. rodhaini was immunoscreened with the anti-B. rodhaini exoantigen immune serum, and three positive cDNA clones were obtained. However, compared to control mice, the mice immunized with each of these recombinant proteins expressed in E. coli or insect cells did not show significantly prolonged survivals after the challenge infection. These findings indicated that B. rodhaini-derived exoantigens contain vaccine candidates inducible of protective immunity in mice, but further investigation is needed to identify the target antigens responsible for the protection.