Polyclonal antibody characterization of Babesia caballi antigens.

In a previous study diagnostic B. caballi antigens with apparent molecular mass of 50 and 48 kDa were identified. Another antigen of 141 kDa was recognized by most but not all B. caballi sera tested. Here a further characterization of the three antigens is reported. Rabbits were vaccinated with gel-purified antigens and monospecific antibodies were obtained for the 141 and 48 kDa antigens. Antibodies raised against the 50 kDa antigen cross-reacted with the 48 kDa antigen, suggesting that these two antigens bear unique as well as common epitopes. After two-dimensional electrophoresis the 50 and 48 kDa antigens were present as horizontal bands over a pH range from approximately 5.0-7.0 with focused spots at a pH of 5.5 and 5.9, respectively. The 141 kDa antigen was not present after two-dimensional electrophoresis. None of the three antigens could be identified as a glycoprotein. Judging from the immunofluorescence antibody test staining pattern obtained with the rabbit sera the 141 kDa antigen is present on the surface of infected erythrocytes. The 50 and 48 kDa antigens are located in the parasite itself and probably not on the surface of infected erythrocytes. The punctate staining pattern observed with the 48 kDa antiserum suggests that this antigen might be located in or associated with the apical complex of the parasite.