RON2, a novel gene in Babesia bigemina, contains conserved, immunodominant B-cell epitopes that induce antibodies that block merozoite invasion

Authors: MOSQUEDA, JUAN - Autonomous University Of Querétaro; HIDALGO-RUIZ, MARIO - Autonomous University Of Queretaro; CALVO-OLVERA, D.A. - Autonomous University Of Querétaro; HERNANDEZ-SILVA, D.J. - Autonomous University Of Querétaro; Ueti, Massaro; MERCADO-URIOSTEGUI, M.A - Autonomous University Of Querétaro; RODRIGUEZ, ANGELINA - Autonomous University Of Queretaro; RAMOS-ARAGON, J.A. - Instituto Nacional De Investigaciones Forestales Y Agropecuarias (INIFAP); HERNANDEZ-ORTIZ, RUBIN - Instituto Nacional De Investigaciones Forestales Y Agropecuarias (INIFAP); KAWAZU, SHIN-ICHIRO - Obihiro University Of Agriculture And Veterinary Medicine; IGARASHI, IKUO - Obihiro University Of Agriculture And Veterinary Medicine

Submitted to: Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/7/2019
Publication Date: 9/13/2019
Citation: Mosqueda, J., Hidalgo-Ruiz, M., Calvo-Olvera, D., Hernandez-Silva, D., Ueti, M.W., Mercado-Uriostegui, M.A., Rodriguez, A., Ramos-Aragon, J.A., Hernandez-Ortiz, R., Kawazu, S.I., Igarashi, I. 2019. RON2, a novel gene in Babesia bigemina, contains conserved, immunodominant B cell epitopes that induce antibodies that block merozoite invasion. Parasitology. 146(13):1646-1654. https://doi.org/10.1017/S0031182019001161.
DOI: https://doi.org/10.1017/S0031182019001161

Interpretive Summary: Bovine babesiosis is the most important veterinary disease transmitted by ticks in tropical and subtropical regions. In this study, we identified a protein that is conserved among B, bigemina Mexico.isolates. Sera from B. bigemina naturally infected bovines were screened by indirect ELISA for the presence of RON2-specific antibodies and recognized multiple conserved B cell epitopes. We tested if antibodies specific for these peptides inhibited the growth of B. bigemina in an in vitro system. We showed an inhibitory effect of RON2-specific antibodies on the invasion of red blood cells by B. bigemina. RON2 is a novel antigen for B. bigemina vaccine development which contains conserved, immunodominant B cell epitopes that induce antibodies capable of blocking merozoite invasion into red blood cells.

Technical Abstract: Bovine babesiosis is the most important veterinary disease transmitted by ticks in temperate regions of the world. In Plasmodium falciparum, another apicomplexan parasite, the interaction of the rhoptry neck protein 2 (RON2) with the apical membrane antigen-1 (AMA-1), has been described to play a key role in the erythrocyte invasion process. To date RON2 has not been described in Babesia bigemina, the causal agent of bovine babesiosis in the Americas. With the use of bioinformatic tools, we found a ron2 orthologous gene of P. falciparum in the B. bigemina genome. The amplification and sequencing of ron2 was obtained from a field strain of B. bigemina. RON2 encodes a 1351 amino acid long polypeptide with an identity of 64% (98% coverage) with RON2 of B. bovis and contains the CLAG domain for cytoadherence, which is conserved in other apicomplexa. B. bigemina ron2 is transcribed and expressed in blood stages. B. bigemina RON2 localizes at anterior end of the merozoite as determined by indirect immunofluorescence. Sera from B. bigemina-infected bovines were screened by indirect ELISA for the presence of RON2-specific antibodies and showed the recognition of conserved B cell epitopes. Finally, in vitro neutralization assays demonstrated an inhibitory effect of RON2-specific antibodies on the invasion ofr ed blood cells by B. bigemina. Therefore, RON2 is a novel antigen in B. bigemina and contains conserved, immunodominant B cell epitopes, which induce antibodies that block merozoite invasion with a potential consideration as a vaccine candidate.