Interleukin 13 elicits a subset of the activities of its close relative interleukin 4.

Interleukin 13 (IL-13) and interleukin 4 (IL-4) are two closely related proteins produced by activated T cells. IL-4 is a well characterized mediator of various aspects of the immune response, including anti-inflammatory effects on monocytes and macrophages, regulation of B cell function, T cell growth, and regulation of adhesion molecule expression on endothelial cells. IL-13, a more recently characterized cytokine, appears to exhibit IL-4-like activities on monocytes, macrophages and human B cells, but has no effect on T cells. While there is a close parallel between IL-4 activities on human and mouse cells, IL-13 activities in these two systems appear to differ substantially with a notable absence of effect on mouse B cells. This review briefly summarizes the current state of knowledge of the interrelated activities of IL-13 and IL-4, explores the basis of these effects at the receptor level and attempts to rationalize the existence of these close relatives via differences in their production by T cells.