Immunogenicity and sequence analysis of recombinant p58: a neutralization-sensitive, antigenically conserved Babesia bigemina merozoite surface protein.

The gene encoding the conserved, neutralization-sensitive surface protein p58 of Babesia bigemina was cloned and sequenced. An open reading frame of 1440 bases was found to encode a protein with a predicted size of 54 kDa. A transmembrane hydrophobic domain and signal peptide were present at the amino-terminus. The polypeptide encoded by a nearly full length cDNA was expressed in bacteria and contained epitope(s) reactive with anti-p58 polyclonal and monoclonal antibodies. Serum antibodies from rabbits immunized with a lysate of recombinant bacteria specifically immunoprecipitated native p58 from [35S]methionine-labeled B. bigemina antigens. In addition, the sera contained antibodies that bound to the surface of live merozoites from 4 geographically different Latin American isolates, confirming the presence and immunogenicity of conserved, surface-exposed epitopes on the recombinant polypeptide. This molecular clone will now enable immunization trials in cattle designed to better evaluate the ability of p58 to induce immune protection by vaccinating with constructs containing only conserved, neutralization-sensitive epitopes.