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

Diego Hernández-Silva,Ruben Hernández-Ortiz,Massaro Ueti,Miguel Mercado-Uriostegui,Juan Mosqueda,Gabriela Aguilar-Tipacamú,Juan Ramos-Aragón,Uriel Valdez-Espinoza

doi:10.3390/vetsci5020032

Abstract

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.

Highlights

Bovine babesiosis is a tick-borne disease that is distributed in the tropical and subtropical regions of the world [1]
An mRNA sequence uploaded in the Genbank after our initial studies confirmed these findings. (Accession number: XM_012914667.1) The predicted peptide sequences translated from all the strains were aligned against the putative Micronemal Protein 1 (MIC-1) from the Australian strain
The results showed that when the Babesia bigemina culture was incubated with antibodies against each of the three Microneme proteins (MICs)-1 peptides, a statistically significant difference was observed in the reduction of parasitemia in comparison to the culture supplemented with pre-immunization serum (Figure 3)

Summary

Introduction

Bovine babesiosis is a tick-borne disease that is distributed in the tropical and subtropical regions of the world [1]. It has been suggested that they participate in the initial contact with the membrane of the host cell, followed by the reorientation of the apical complex and the release of proteins from rhoptries. The release of these proteins allows the parasite to penetrate the target cell [7,8,9]. MICs are key mediators for cell-cell interaction due to the adhesion domains they possess They are considered adhesin proteins and are well conserved among the different species of apicomplexan parasites [5,10]

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Conclusion