Polypeptides reactive with antibodies eluted from the surface of Babesia bovis-infected erythrocytes.

A technique was sought that would enable identification of surface-exposed parasite antigens on Babesia bovis-infected erythrocytes (BbIE) that are not detectable by surface-specific immunoprecipitations. Antibodies which bind to the surface of BbIE were recovered from intact cells using a low pH wash procedure. The eluted antibodies were then used in conventional immunoprecipitation assays to identify parasite-synthesized polypeptides carrying epitopes that are exposed on the surface or are cross-reactive with such epitopes. The results of these experiments support our previous data, obtained using a surface-specific immunoprecipitation technique, in the identification of a repertoire of parasite-derived antigens on the surface of infected erythrocytes (Allred et al., 1991). In addition, two polypeptides of M(r) 68,000 and 185,000 were identified which react strongly with the eluted antibodies but which are not detected by surface-immunoprecipitation. These data illustrate the potential of this approach for identification of parasite polypeptides which carry epitopes exposed on, or cross-reactive with exposed epitopes of the infected erythrocyte surface.