Cats represent an unusually valuable model for studying the role of the immune response to
leukemia,
lymphoma, and other mesodermal
neoplasms. The agents that cause spontaneous
feline leukemias,
lymphomas, and
fibrosarcomas, the
feline leukemia and
sarcoma viruses, are well characterized. A specific
tumor cell membrane
antigen, designated the
feline oncornavirus-associated cell membrane antigen (
FOCMA) has also been described.
Feline leukemia and feline sarcoma viruses are antigenically indistinguishable, and
FOCMA is common for both. Both laboratory-induced and spontaneous
feline leukemias,
lymphomas, and
fibrosarcomas are available for study. A clear correlation has been shown between the resistance of cats to development of lethal
tumors following inoculation of feline
sarcoma virus and the presence of high humoral antibody titers to
FOCMA. The geometric mean antibody titer to
FOCMA for cats that resisted growth of
fibrosarcomas was more than 20-fold higher than the mean for cats that succumbed to lethally progressing
tumors. Cats with induced or spontaneous
leukemia or
lymphoma also have either no detectable
FOCMA antibody or very low levels. Conversely, some cats resist development of
leukemia or
lymphoma following natural exposure to feline leukemia virus in
leukemia cluster households, and these cats have high
FOCMA antibody titers. These results support the concept of a natural immunosurveillance mechanism against
leukemia or
lymphoma development in an outbred mammalian species.