Humoral immune reactivity to feline leukemia virus and associated antigens in cats naturally infected with feline leukemia virus.

The humoral antibody response of cats infected naturally with feline leukemia virus (FeLV) was measured by an enzymelinked immunosorbent assay. Cats that became persistently viremic developed lower antibody levels than did cats which recovered from the infection. Cats that were viremic for 2 to 36 weeks prior to recovery had variable enzyme-linked immuno sorbent assay values that overlapped with the values seen in both nonviremic and persistently viremic cats. There was a strong correlation between antibody levels against FeLV and antibodies to feline oncornavirus-associated cell membrane antigen in sera from cats which recovered from FeLV infection but not in sera from cats that were persistently viremic. Sera from persistently viremic and recovered cats were analyzed by a combination of gel electrophoresis and enzymelinked immunosorbent assay, a procedure which permitted the levels of antibodies to each of the protein components of purified FeLV to be quantitated. Sera from recovered cats contained antibodies reactive against the five major FeLV struc tural proteins (gp73, p27, p15, p12, p10) and against eight additional antigenic components with apparent molecular weight values of 58,000, 47,000, 36,000, 24,000, 17,000, 15,700, 12,000, and 8,500. The major antibody reactivity was directed against the 58,000-dalton protein. Sera from persist ently viremic cats also contained antibodies to all of these components but at a significantly reduced level. The 17,000- and 15,700-dalton proteins were cross-reactive with a monoclonal antibody to the p15(E) of murine leukemia virus, and the 47,000-dalton protein appeared to be antigenically related to actin. The 58,000-, 36,000-, and 24,000-dalton species contained gag gene homology as judged by their cross-reactivity with sera specific for gag proteins. Feline on cornavirus-associated cell membrane antigen reference sera were found to exhibit high reactivity against p15(E). It is concluded that antibodies specific for not only gp73 but also for gag gene-coded proteins and polyproteins are impor tant in protection against FeLV infection.