In vivo interleukin 2 administration augments the generation of alloreactive cytolytic T lymphocytes and resident natural killer cells

Interleukin 2 (IL 2) is a T cell growth factor that has been shown to modulate several in vitro immune responses. Produced by T cells, the lymphokine has been highly purified and used in a series of in vivo studies to examine the effect of IL 2 on murine cytotoxic T cell (CTL) and natural killer (NK) cell reactivity. By employing an immunization protocol known to generate CTL activity against allogeneic tumors, in vivo administration of highly purified IL 2, either in concert, with or 2 days after, tumor administration, resulted in an augmented CTL response as compared to effector cells harvested from untreated, alloimmunized control animals. Characterization of the effector cells responsible for the augmented cytolytic activity showed them to be of the T cell lineage and to be specific for the appropriate immunizing tumor cell. Furthermore, we were able to demonstrate that administration of purified IL 2 to naive, non-antigen-challenged recipients resulted in substantial potentiation of NK cell activity. The augmented cytolytic reactivity was mediated by NK cells as evidenced by effector cell lysis of NK-susceptible but not NK-insusceptible tumor targets. The results of these studies suggest IL 2 functions in vivo as an immune response regulator and may have a beneficial effect as an in vivo immunopotentiator.