Following exposure to feline leukemia virus (FeLV), cats that resist
leukemia produce
complement dependent
antibodies (CDA) which lyse
leukemia cells in the presence of cat
complement. The CDA activity has been shown to be directed to
feline oncornavirus-associated cell membrane antigen (
FOCMA) found on the surface of most
feline leukemias. Despite the retrovirus etiology of
feline leukemia, and the ubiquity of
FOCMA expression by individual
tumors, we found that CDA activity did not cross-react when five
feline leukemia lines were compared (FL74, F422, 3272, 3281, and 79-14940). Profiles for CDA mediated lysis of the
leukemia target lines were determined for sera from 149 FeLV exposed cats, and animals were identified whose sera would selectively lyse almost any possible combination of
tumors from one to five lines tested. Cross absorption and cold target inhibition studies were performed on selected sera, and a spectrum of different
antigens was identified which included both individual determinants and
antigens shared by some of the
tumor lines.
Leukemias FL74 and F422 carried a cross-reactive determinant which was distinct from a second
antigen shared by 3272 and 3281; lines F422, 3272 and 3281 each also carried a unique
antigen.
Leukemia 79-14940 did not cross-react with other target
tumor lines. Targets of CDA mediated lysis on
leukemia cells maybe associated with normal feline
cell surface antigens, because CDA titers were sometimes reduced after serum absorption with normal cat spleen cells. The relevance of multiple
FOCMA determinants is discussed in terms of tumor escape from immunity.