Protection of Cats Against Feline Leukemia Virus-Positive and Virus-Negative Tumors by Complement-Dependent Antibody23

Abstract

Antibodies to feline oncornavirus-associated cell membrane antigen (FOCMA) were measured as complement-dependent antibody (CDA) by ⁵¹Cr release and by immunofluorescence in sera from 1,482 cats. CDA to FOCMA (CDA-FOCMA) was not detected in any of 335 cats isolated from feline leukemia virus (FeLV) exposure. but it was present in 55 and 57% of healthy viremic and virus-free cats. respectively. living continuously in multicat households where FeLV infection was endemic. Of singly housed pet cats tested, the antibody was detected in 30–45%. By comparison, the prevalence of CDA-FOCMA was 12% in FeLV-infected cats with leukemia and 13% in leukemic cats with no detectable evidence of FeLV infection; these prevalences both differed significantly from appropriate control groups (P<0.01). Furthermore, the mean antibody titer in the few leukemic cats with detectable CDA-FOCMA was one-half that found in comparable non leukemic cats. Antibody appeared in 71% of experimental cats inoculated with feline sarcoma virus following tumor regression, but it was detected in only 6% of cats bearing progressing tumors. Lack of detectable CDA-FOCMA in tumor-bearing cats was not attributable to the presence of circulating blocking factors and in most cases it could not be explained by passive absorption of antibody by tumor. Three of 4 fresh tumor cell preparations from naturally occurring lymphomas and 1 feline lymphoma cell line that did not replicate virus or express FeLV antigens were lysed by some CDA-FOCMA-positive sera but not by normal sera. The data are consistent with a common immune surveillance mechanism in cats, mediated by lytic antibody and complement, which is directed at naturally arising feline leukemias whether or not they express virus antigens.