Neospora caninum: Identification of 19-, 38-, and 40-kDa surface antigens and a 33-kDa dense granule antigen using monoclonal antibodies

Neospora caninum, a coccidian parasite closely related to Toxoplasma gondii , can infect a broad host range and is regarded as an important cause of bo vine abortion worldwide. In the present study, four antigens of N. caninum were partially characterized using monoclonal antibodies. Immunofluorescenc e of viable tachyzoites as well as the immunoprecipitation of antigens extr acted from tachyzoites previously labeled by surface biotinylation revealed that three of these antigens with apparent molecular weights of 40, 38, an d 19 kDa are located in the outer surface membrane of this parasite stage. Further evidence for the surface localization of the 38-kDa antigen was obt ained by immunoelectron microscopy. In addition to the surface molecules, a n antigen located in dense granules and in the tubular network of the paras itophorous vacuole was detected by another monoclonal antibody. When tachyz oite antigens separated under nonreducing conditions were probed on Western blots, this antibody reacted mainly with a 33-kDa antigen. Immunohistochem ical analysis of infected tissue sections indicated that the 33-kDa dense g ranule antigen is present in both tachyzoites and bradyzoites, while the 38 -kDa surface antigen from tachyzoites seems to be absent in bradyzoites. (C ) 1999 Academic Press.