ABSTRACT
Effects of interleukin-2 (IL-2) on the natural killer (NK) activities of BALB/c mouse and Wistar rat spleen cells were compared. While mouse spleen cells cultured alone rapidly lost NK activity, co-culture with IL-2 resulted in a marked enhancement of NK activity. In contrast, the levels of NK activity of rat spleen cells cultured alone increased and remained high for 3 days and declined thereafter. Addition of human recombinant IL-2 or purified rat IL-2 did not influence the NK levels in rat spleen cell bulk cultures. Both IL-2 preparations were however biologically active as shown by their capacities to induced proliferation in rat spleen cells. Rat spleen cells suppressed the IL-2 activation of mouse spleen cells in a dose dependent manner, indicating a suppressor influence generated by rat spleen cells. Culture supernatants of rat spleen cells cultured with or without IL-2 for 3 or 5 days could also suppress the mouse spleen NK activation in response to IL-2. The suppressor activity could be concentrated on a 5K MW cut-off Amicon filter indicating that the molecular weight of the factor is more than 5000. These results indicate that a suppressor of IL-2 induced NK activation of mouse spleen cells is released by cultured rat spleen cells.