Effect of recombinant human interleukin 4 on human monocyte activity

Recombinant human interleukin 4 (rhuIL-4), a lymphokine that reportedly stimulates tumoricidal activity in mouse macrophages, is currently undergoing clinical studies to determine its efficacy in the treatment of cancer. IL-4 is known to participate with other cytokines to regulate growth and differentiation of various hematopoietic cells as well as modulate the immune response. Little is known about the effect of rhuIL-4 on human monocyte tumoricidal activity. The purpose of these studies was to examine the effect of rhuIL-4 on human peripheral blood monocytes. Peripheral blood monocytes isolated from normal donors failed to demonstrate tumoricidal activity or interleukin 1 secretion after treatment with rhuIL-4 in vitro. Furthermore, monocyte-mediated cytotoxicity induced by recombinant human gamma-interferon plus muramyl dipeptide was suppressed in a dose-dependent manner by rhuIL-4. This reduction in cytotoxicity corresponded to a reduction in IL-1 production and secretion. Further investigation of rhuIL-4 and its role in the cytokine network is necessary for the development of effective immunotherapy in cancer patients.