Murine NK cell cultures: effects of interleukin-2 and interferon on cell growth and cytotoxic reactivity.

Abstract Murine spleen cell populations were stimulated in vitro with 50 µg of poly l:C and 24 h later, were transferred to medium containing lnterleukin-2 (IL-2). Under these conditions, cytotoxic cells could be maintained indefinitely. Removal of mature T cells at the initiation of culture, by treatment with anti-Thy 1.2 antibody in the presence of complement, was without effect on the development of cytotoxic cells. Cells harvested from such cultures exhibited surface markers characteristic of NK cells (Thy 1 +, asialo GMI +, Lyt 2−). Concordant with the display of NK phenotypic markers, the cytotoxic cells lysed YAC-1 lymphoma cells and an NK-susceptible clone (27v) of the L5178Y lymphoma, but did not lyse clone 27av cells, an NK-insusceptible variant of L5178Y. Studies involving the addition of graded doses of mouse fibroblast interferon (IF) to mouse spleen cells, showed maximal potentiating effects of 103 U/culture, with significantly less augmentation of NK cytotoxicity at higher IF concentrations. When partially purified IL-2 was concomitantly added, IL-2 and IF were at least additive in their effects at all IF concentrations. Several observations suggested that IL-2 itself, like IF, was capable of augmenting NK cell-mediated cytotoxicity. Thus, preparations of IL-2, which lacked IF, caused a rapid increase in NK cell activity. Additionally, the ability to augment cytotoxicity was removed from IL-2 preparations not only by absorption with IL-2 receptor-bearing cells, but also by precipitation with a monoclonal antibody directed against IL-2. One explanation for the cooperation between IF and IL-2 was suggested by the finding that spleen cell population exposed to IF showed a markedly augmented ability to bind IL-2, suggesting that IF may cause an increased display and/or affinity of IL-2 receptors. Furthermore, T cell-depleted spleen cells cultured in IF and IL-2 possessed readily demonstrable Thy 1 antigen, suggesting that these agents either modulate the display of cell surface macromolecules or, perhaps, that they potentiate T cell differentiation in vitro.