Characterization of a Feline Leukemia Viral Cell Membrane Antigen Reactive with Feline Sera

Abstract

Cats which have been infected with FeLV and which have recovered without disease or persistent viremia are at a low to negligible risk for subsequent development of FeLV-associated neoplasia. To evaluate the immunologic correlates of this protection, cat sera from various free-living populations were shown by immunoprecipitation of FL74 cell surface proteins to react with an 85,000 dalton cell surface protein, p85. All sera from non-viremic cats with FL74 cell membrane immunofluorescence reactivity greater than 1:32 precipitated p85. The reactivity of p85 and concomitant cell membrane reactivity could be completely removed from serum with freshly purified, undisrupted FeLV and could be blocked with specific antisera to known virion envelope glycoproteins, demonstrating that p85 contains determinants of the FeLV envelope glycoprotein. The reactivity to p85 could also be removed with FeLV-infected feline and nonfeline cells but not with cells nonproductively transformed by the feline sarcoma virus. These data strongly suggest that a major cell membrane antibody in feline sera is directed to the major FeLV envelope glycoprotein expressed on the surface of cells infected with FeLV but not FeSV. The relationship of this reactivity to the previously and presently defined anti-“FOCMA” reactivity is discussed.