Following mitogen stimulation (phytohemagglutinin or concanavalin A), feline lymphocytes were maintained in medium containing feline interleukin 2. Lymphocyte lines derived from the blood of feline leukemia virus-infected cats contained cells 50 to 90% of which expressed virus antigens, but lymphocyte lines derived from uninfected cats remained virus free. Leukemia virus-positive and -negative lymphocyte lines retained total dependence upon the presence of interleukin 2 for finite life spans of 20 to 40 cell divisions. Cell-doubling times and surface properties (membrane immunoglobulin negative, guinea pig red cell rosette positive) of all T-cell lines were similar. All cat lymphocyte lines rapidly developed strong but nonspecific cytotoxic effects against a variety of established cat target lines, including normal and leukemia virus-infected fibroblasts and virus-producing lymphomas. Attempts to infect virus-negative lymphocytes with leukemia virus in vitro produced lines containing 1 to 4% of infected cells; subsequently, this level of infection remained constant. Within observation limits, the characteristics of feline leukemia virus-infected and normal cat T-cells were similar. Leukemia virus infection did not predispose target lymphocytes to exhibit properties in vitro that might be associated with preneoplastic change, such as rapid or infinite cell division or development of independence from interleukin 2 regulation.
This study was supported by USPHS Grants R01 CA 24608 and R01 CA 34394 awarded by the National Cancer Institute, Department of Health and Human Services.