Suppression of activity of mouse natural killer (NK) cells by activated macrophages from mice treated with pyran copolymer

Treatment of young mice with pyran copolmyer caused a substantial decrease in natural killer (NK) cell activity at 7 days. The decrease in cytotoxicity was associated with the presence of splenic suppressor cells, capable of inhibiting in vitro the NK activity of spleen cells from normal mice. The suppressor cells appeared to be macrophages, being plastic‐adherent, phagocytic and radioresistant, and lacking demonstrable Thy 1.2 antigen. Sonicates or culture supernatants of adherent spleen cells from pyran‐treated mice were also able to inhibit NK activity, suggesting that suppressor cells act by release of soluble factors.