Characterisation of a tumour-specific antigen on the surface of feline lymphosarcoma cells

Abstract

IN domestic cats, regression of tumours originally induced by inoculation of feline sarcoma virus (FeSV) as well as the resistance to feline leukaemia virus (FeLV)-induced lymphosarcoma in the natural environment are correlated with high titres of antibody to the feline oncornavirus-associated cell membrane antigen (FOCMA)1–4. FOCMA is present on FeLV-producing and nonproducing feline lymphosarcoma (LSA) cells and FeSV-infected fibrosarcoma cells but is absent from FeLV-infected normal cells. This finding is consistent with the interpretation that FOCMA represents an FeLV or FeSV-induced transformation-specific protein5–7. Other workers have initiated studies of the biochemical nature of FOCMA derived from cytoplasmic extracts of cells of a heterologous species (mink) nonproductively transformed by FeSV8–10. However, our primary interest has been to analyse FOCMA expressed on naturally occurring LSA cells from pet cats. We describe here the identification of a hitherto unrecognised protein on the surface of feline LSA cells and cultured transformed feline lymphoblastoid cells which exhibits antigenic determinants in common with FOCMA. The molecular weight of this protein is approximately 70,000. Our data agree with the accumulating evidence that FOCMA is distinct from all FeLV and RD114-coded virion antigens4,6–11.