Natural immunity in cats to feline leukemia viral antigens.

An isotopic antiglobulin assay was developed to measure antibodies in "normal" cats to FOCMA, a cell surface antigen associated with immunity to FeLV-induced tumors. The assay was shown to be specific for detecting FOCMA antibody by several criteria including a correlation with cell membrane immunofluorescence and absorption tests. Antibody to FOCMA developed following FeLV infection and was expressed in heterologous species. In combination with an assay for antibody to FeLV p30, the major virion structural protein, 200 cats sera from three different geographic areas were examined for evidences of FeLV-type-C-virus infection. Approximately 17% of all sera examined contained antibody to FOCMA. Antibodies directed to the FeLV p30 were detected in 8 of the sera and only in cats with FOCMA antibody. The correlation in cat sera between antibody to FOCMA and FeLV p30 antigen suggests that both are associated with the same process, infection with FeLV type-C-virus. The relationship of the observed pattern of antibody response is discussed in relation to other horizontally transmitted RNA-containing viruses.