Feline oncornavirus-associated cell-membrane antigen (FOCMA): distinction between FOCMA and the major virion glycoprotein.

Abstract

The humoral antibody response of feline leukemia virus (FeLV)exposed cats to the feline oncornavirusassociated tumor cell-membrane antigen (FOCMA) is directly correlated with immunosurveillance against tumor development under natural conditions. By means of membrane immunofluorescence and radioimmunoprecipitation, the antibody response to FOCMA was found to be independent of the antibody response to the major envelope and core proteins of FeLV, gp70 and p3. This was especially true for healthy viremic cats, wbere antigenemia with circulating FeLV gp7O and p30 apparently binds any free antibody to these proteins, but high levels of FOCMA antibody are often concurrently present. Exhaustive in vitro absorption of highly immune nonviremic serum with gp70 and p30 also failed to remove FOCMA antibody activity. These results indicate that FOCMA is not one of these major FeLV structural proteins.

Humans have antibodies capable of recognizing oncoviral glycoproteins: demonstration that these antibodies are formed in response to cellular modification of glycoproteins rather than as consequence of exposure to virus.

“…The presence of these determinants was found to be independent of the known evolutionary relationships of oncoviruses (24)(25)(26)(27)(28)(29) (1980) glycosylation exhibits species specificity (34)(35)(36)(37). We also observed a striking pattern of species specificity with respect to the cell in which a virus was grown and the ability of human sera to recognize its envelope glycoprotein.…”

Pseudotypes of feline sarcoma virus contain an 85,000-dalton protein with feline oncornavirus-associated cell membrane antigen (FOCMA) activity.

“…Surveys of cat sera have shown no concordance between titers of antibodies to FOCMA and those to viral gp7O, p30 (3,10), or reverse transcriptase (unpublished observations). Thus, FOCMA appears to be distinct from the major FeLV structural proteins.…”

“…Adsorption of cat antisera reactive to FOCMA with disrupted FeLV (3,9) or with two proteins (gp70 and p30) purified from virions (10) fails to reduce the anti-FOCMA titers. Surveys of cat sera have shown no concordance between titers of antibodies to FOCMA and those to viral gp7O, p30 (3,10), or reverse transcriptase (unpublished observations).…”

Feline oncornavirus-associated cell membrane antigen: evidence for an immunologically crossreactive feline sarcoma virus-coded protein.

“…Analysis of anti-FOCMA titers in sera of virus-exposed cats has suggested that development of antibody directed against FOCMA may constitute an immunosurveillance defense against tumor development (1, 3). Although the nature of FOCMA is unknown, recent findings indicate that it is distinct from both the major 30,000 molecular weight (Mr) FeLV structural antigen (p30) (4,5) and the 70,000 Mr envelope glycoprotein (gp7O) (5). The possibility that FOCMA may be distinct from all FeLV-coded structural proteins is suggested by the demonstration that nontransformed FeLV-infected fibroblasts and normal lymphoid cells fail to express FOCMA (6,7).…”

“…Double-Antibody Radioimmunoprecipitation and Competition Immunoassays. Radioimmunoprecipitation and competition immunoassays for FeLV gag gene-coded structural proteins of Mr 30,000 (p30), 15,000 (p15), 12,000 (p12), and 10,000 (plO) (8) and the 70,000 Mr env gene-coded glycoprotein, gp7O (5), were performed by the double-antibody procedure as described (5,8).…”