A novel neutralization sensitive and subdominant RAP-1-related antigen (RRA) is expressed by Babesia bovis merozoites

SUAREZ, C.E.; LAUGHERY, J.M.; BASTOS, R.G.; JOHNSON, W.C.; NORIMINE, J..; ASENZO, ; BROWN, W.C.; JACOBSEN FLORIN-CHRISTENSEN, M.; GOFF, W.

PARASITOLOGY

CAMBRIDGE UNIV PRESS

Año: 2011 vol. 138 p. 809 - 818

0031-1820

Objective: The Babesia bovis genome encodes a rap-1 related gene denominated RAP-1 related antigen (RRA). In this study, we analyzed the pattern of expression,immunogenicity and functional relevance of RRA.Methods: Phylogenetic analysis was performed using the program Phylip. Expression of  rra was analyzed by Northern blots, RT-PCR, immunoprecipitation, Western blots and immunofluorescence. RRA antigenicity was tested by T-cell proliferation and Western blot analysis, and functional relevance was determined in an in vitro neutralization assay.Results: RRA is more closely related to RAP-1b of Babesia bigemina than to B. bovis RAP-1, and it is highly conserved among distinct strains. Transcriptional analysis suggests lower numbers of rra transcripts compared to rap-1. Immunoprecipitation of metabolically labeled B. bovis proteins with antibodies against synthetic peptides representing predicted antigenic regions of RRA confirmed the expression of a ~43 kDa RRA in cultured merozoites. Antibodies present in B. bovis hyperimmune sera, but not in field infected cattle sera, reacted weakly with recombinant RRA, and no significant stimulation was obtained using recombinant RRA as antigen in T-cell proliferation assays, indicating that RRA is a subdominant antigen. Antibodies against RRA synthetic peptides reacted with merozoites using immunofluorescence, and are able to significantly inhibited erythrocyte invasion in in vitro neutralization tests, suggesting functional relevance for parasite survival. Conclusion: B. bovis express a novel subdominant RAP-1-like molecule that maycontribute to erythrocyte invasion and/or egression by the parasite.