Suppressive Activity of Interleukin 4 on the Induction of Antigen‐specific Cytotoxic T Cells in Humans

The effect of interleukin 4 (IL 4) on the induction of cytotoxic T cells (CTL) was studied by using human peripheral blood lymphocytes in vitro. IL 4 suppressed the induction of CTL specific for allogeneic antigens in a concentration‐dependent manner. However, IL 4 did not suppress proliferative responses induced with allogeneic antigens or mitogens. The suppressive effect of IL 4 on CTL induction was observed when IL 4 was added at the early period of the CTL induction culture, but not at the later period. Furthermore, IL 4 did not suppress the effector function of CTL to target cells. IL 4 suppressed the production of IL 1 by monocytes/macrophages and the production of IL 2 and the expression of IL 2 receptors on T cells. Moreover, IL 4 suppressed the induction of lymphokine‐activated killer cells. These results suggest that IL 4 has a suppressive activity on the induction of killer cells in humans.