Characterization of precipitating antibody in equine infectious anemia.

The characterization of precipitating antibody from horses experimentally infected with equine infectious anemia (EIA) virus is reported. Precipitation was demonstrated in an agar gel, using purified virus as antigen. Precipitating antibody was present in the γ globulin fractionated from infected serum with ammonium sulfate and by diethylaminoethyl cellulose chromatography. Antibody was also recovered in the 7S globulin fraction separated with Sephadex G-200 from sera collected both early and later in the disease. When 7S globulin was added to purified antigen, precipitation between the resulting antigen-globulin complex and a reference EIA antiserum was inhibited. Precipitating antibody was first detected shortly after the first febrile reaction. At that time no neutralizing antibody was found, but the appearance of precipitating antibody coincided fairly well with that of the complement fixing (CF) antibody. In contrast to CF antibody, which usually dropped below a detectable level shortly after onset of the disease, the precipitating antibody remained detectable for at least 150 days. The relationships of precipitating antibody to the CF and neutralizing antibodies are discussed. Listed are factors indicative of the value of the immunodiffusion reaction for diagnosis of EIA.