IDENTIFICATION AND CHARACTERIZATION OF NEOSPORA-CANINUM TACHYZOITE ANTIGENS USEFUL FOR DIAGNOSIS OF NEOSPOROSIS

The purpose of the present study was to identify antigens of the proto zoan parasite Neospora caninum that could be used for the diagnosis of neosporosis in domestic animals. As revealed by immunoblotting, immun e sera from a wide range of animal species exhibited a similar recogni tion pattern of four major and several minor N. caninum antigens. In c ontrast to preinoculation sera, all tested immune sera recognized nonr educed immunodominant 17-, 29-, 30-, and 37-kDa antigens. A 46-kDa pro tein which showed faint recognition by preimmune sera also exhibited a strong response by immune sera. Immunolocalization of the four immuno dominant N. caninum antigens was investigated by immunogold electron m icroscopy using monospecific polyclonal antisera. The 17-kDa antigen a ppears to be associated,vith the body part of the rhoptries, while the 29- and 30-kDa antigens were associated with the dense granules, netw ork, and limiting membrane of the parasitophorous vacuole. Studies wer e also conducted to compare antibody responses to N. caninum and the r elated protozoan Toxoplasma gondii. Although N. caninum and T. gondii (RH strain) tachyzoites shared a Pew cross-reacting antigens, the immu nodominant antigens of both parasites were not recognized by heterolog ous sera. Also, immunogold staining with rabbit anti-Neospora hyperimm une serum exhibited almost no labeling of external membranes of Neospo ra tachyzoites compared with the very marked labeling seen when Toxopl asma tachyzoites (RH strain) were incubated with rabbit anti-Toxoplasm a hyperimmune serum. These unique antigenic differences should be usef ul in developing a diagnostic assay for N. caninum.