Interleukin-2 can induce suppression of human natural killer cell cytotoxicity.

By interaction with monocytes, interleukin-2 (IL-2) suppressed natural killer (NK) cell cytotoxicity (NKCC) of human, Percoll-fractionated, low-density mononuclear cells. The NK-suppressive effect of IL-2 was independent of de novo formation of prostaglandins or protein since it was unaffected by treatment with indomethacin and cycloheximide, respectively. A monoclonal antibody to the p55 (beta) moiety of the IL-2 receptor (anti-Tac/anti-CD25) blocked IL-2-induced NKCC suppression but did not affect the NK-enhancing effect of the lymphokine. We conclude that IL-2 exerts a monocyte-dependent, IL-2 beta-receptor mediated suppressive influence on human NK cells.