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 relate d proteins produced by activated T cells. IL-4 is a well characterized mediator of various aspects of the immune response, including anti-in flammatory effects on monocytes and macrophages, regulation of B cell function, T cell growth, and regulation of adhesion molecule expressio n 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 p arallel between IL-4 activities on human and mouse cells, IL-13 activi ties in these two systems appear to differ substantially with a notabl e absence of effect on mouse B cells. This review briefly summarizes t he current state of knowledge of the interrelated activities of IL-13 and IL-4, explores the basis of these effects at the receptor level an d attempts to rationalize the existence of these close relatives via d ifferences in their production by T cells.