Immunomolecular Characterization of MIC-1, a Novel Antigen in Babesia bigemina, Which Contains Conserved and Immunodominant B-Cell Epitopes that Induce Neutralizing Antibodies.

Babesia bigemina is one of the most prevalent species causing bovine babesiosis around the world. Antigens involved in host cell invasion are vaccine targets for this disease but are largely unknown in this species. The invasion process of Babesia spp. into erythrocytes involves membrane proteins from the apical complex. A protein stored in the micronemes, called Micronemal Protein 1 (MIC-1), contains a sialic acid binding domain that participates in the invasion process of host cells and is a vaccine candidate in other apicomplexan parasites. It is not known if there is a homologous gene for mic-1 in B. bigemina. Therefore, the aim of this study was to characterize the mic-1 gene homologue in Babesia bigemina. A gene was found with a microneme adhesive repeat (MAR) domain in the predicted amino acid sequence. Transcription was determined by reverse transcription polymerase chain reaction (RT-PCR). Subsequently, antibodies against peptides containing conserved B-cell epitopes were used to confirm the expression of MIC-1 in intraerythrocytic merozoites. The presence of anti MIC-1 antibodies in cattle naturally infected with B. bigemina was determined and up to 97.4% of the cattle sera (113 out of 116) identified MIC-1 using enzyme-linked immunosorbent assay (ELISA) methods. Finally, antibodies against MIC-1 were able to block 70% merozoite invasion in-vitro.