Cellular immune response in the blood of cats is restricted to autochthonous feline sarcoma virus-transformed cells.

The blood-borne cytotoxic cellular immune response of cats to autochthonous fibroblasts transformed with feline sarcoma virus (FeSV) was examined. Peripheral blood lymphocytes (PBL) from immune animals were assayed for cytotoxic activity using a 51Cr release microcytotoxicity assay. The time courses for appearance of cytotoxic cells were similar for all cats: effector lymphocytes appeared in the blood 7 days after immunization; peak activity occurred about day 16, and cytotoxic PBL were no longer detectable by 35 days. The specificity of cytotoxic lymphocytes was studied using autochthonous and allogeneic targets. PBL from each of five immunized cats killed autochthonous transformed fibroblast (ATF) targets, but the immune lymphocytes were not cytotoxic for non-transformed autochthonous fibroblasts, for allogeneic fibroblasts transformed with FeSV, or for an allogeneic lymphoma cell line which produces feline leukemia virus (FeLV). Specific restriction of target-cell killing to the ATF occurred at all effector:target-cell ratios tested, and was maintained throughout prolonged assay incubation periods. The results suggest that for cytotoxicity to occur it is necessary for the immune lymphocytes to recognize a combination of virus-associated antigens and "self" antigens on the ATF. The similarities between this restricted killing and that caused by cytotoxic T lymphocytes in other mammalian systems are discussed.