Babesia bovis RON2 contains conserved B-cell epitopes that induce an invasion-blocking humoral immune response in immunized cattle

Authors: RUIZ, M - Autonomous University Of Querétaro; Suarez, Carlos; MERCADO-URIOSTEQUI, M - Autonomous University Of Querétaro; HERNANDEZ-ORTIZ, R - Instituto Nacional De Investigaciones Forestales Y Agropecuarias (INIFAP); RAMOS, J - Instituto Nacional De Investigaciones Forestales Y Agropecuarias (INIFAP); GALINDO-VELAZCO, E - University Of Colima; MOSQUEDA, J - Autonomous University Of Queretaro

Submitted to: Parasites & Vectors
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/22/2018
Publication Date: 11/3/2018
Citation: Ruiz, M.H., Suarez, C.E., Mercado-Uriostequi, M.A., Hernandez-Ortiz, R., Ramos, J.A., Galindo-Velazco, E., Mosqueda, J. 2018. Babesia bovis RON2 contains conserved B-cell epitopes that induce an invasion-blocking humoral immune response in immunized cattle. Parasites & Vectors. 11:575. https://doi.org/10.1186/s13071-018-3164-2.
DOI: https://doi.org/10.1186/s13071-018-3164-2

Interpretive Summary: Babesia bovis belongs to the phylum Apicomplexa and is the major causal agent of bovine babesiosis, the most important veterinary disease transmitted by arthropods. In Apicomplexa parasites, the interaction between the proteins AMA1 and RON2 is necessary for the invasion process, and it is a target for vaccine development. In B. bovis, the existence of AMA1 has already been reported; however, the presence of a homolog of RON2 is unknown. The aim of this study was to characterize RON2 in B. bovis. The B. bovis ron2 gene was sequenced from different B. bovis strains showing > 90% similarity, including the characteristic CLAG domain for cytoadherence in the amino acid sequence, as is described in other Apicomplexa. The transcription analysis showed similar levels of transcription between attenuated and virulent B. bovis strains, and expression of the RON2 protein was confirmed in the B. bovis T3Bo virulent strain. RON2 antibodies against selected peptides derived from the protein recognized intraerythrocytic merozoites of B. bovis. Two peptides, named P2 and P3 generated partially neutralizing antibodies that had an inhibitory effect of 28.10 % and 21.42 % on the invasion process of B. bovis in bovine erythrocytes. Consistently, this effect is additive since inhibition increased to 42.09 % when the antibodies were evaluated together. Also, the two peptides were also recognized by 83.33% and 87.77% of naturally infected cattle from endemic areas. In conclusion, the data supports RON2 as a novel B. bovis vaccine candidate antigen that contains conserved B-cell epitopes that elicit partially neutralizing antibodies.

Technical Abstract: Babesia bovis belongs to the phylum Apicomplexa and is the major causal agent of bovine babesiosis, the most important veterinary disease transmitted by arthropods. In Apicomplexa parasites, the interaction between AMA1 and RON2 is necessary for the invasion process, and it is a target for vaccine development. In B. bovis, the existence of AMA1 has already been reported; however, the presence of a homolog of RON2 is unknown. The aim of this study was to characterize RON2 in B. bovis. The B. bovis ron2 gene has a similar synteny with the orthologous gene in the B. bigemina genome. The entire ron2 gene was sequenced from different B. bovis strains showing > 90% similarity, including the characteristic CLAG domain for cytoadherence in the amino acid sequence, as is described in other Apicomplexa. The transcription analysis showed similar levels of transcription between attenuated and virulent B. bovis strains, and expression of RON2 was confirmed by Western blot in the B. bovis T3Bo virulent strain. Four conserved peptides, containing predicted B-cell epitopes in hydrophilic regions of the protein, were designed and chemically synthesized. The humoral immune response generated by the synthetic peptides was characterized in bovines, showing that anti-RON2 antibodies against peptides recognized intraerythrocytic merozoites of B. bovis. Only the peptides P2 and P3 generated partially neutralizing antibodies that had an inhibitory effect of 28.10 % and 21.42 % on the invasion process of B. bovis in bovine erythrocytes. Consistently, this effect is additive since inhibition increased to 42.09 % when the antibodies were evaluated together. Finally, P2 and P3 peptides were also recognized by 83.33% and 87.77% of naturally infected cattle from endemic areas. In conclusion, the data supports RON2 as a novel B. bovis vaccine candidate antigen that contains conserved B-cell epitopes that elicit partially neutralizing antibodies.