FUNCTIONS OF IL-4 AND CONTROL OF ITS EXPRESSION

IL-4 has been called the ''prototypic immunoregulatory cytokine.'' Lik e many cytokines, it can affect a variety of target cells in multiple ways. IL-4 has an important role in regulating antibody production, he matopoiesis and inflammation, and the development of effector T-cell r esponses. It is produced only by a subset of activated hematopoietic c ells, including T cells and Fc epsilon RI(+) mast cells and basophils. Based on the different tissue distribution and access to distinct tar get cells, IL-4 derived from T and Fc epsilon RI(+) cells may have qui te different effects on these immunological processes. In view of this , as well as the clear correlation of aberrant expression with disease , it is of interest to understand the signals that regulate IL-4 expre ssion in a cell-specific manner. Recently, progress has been made in d efining the T-cell- and Fc epsilon RI-receptor-mediated signals that s timulate IL-4 gene expression. These studies have demonstrated that th ere are common and cell-specific signaling pathways that regulate prod uction of this cytokine. In this review, we summarize the activities o f IL-4 defined both in vitro and in vivo and compare the signals leadi ng to IL-4 expression in cells of both T- and mast-cell lineage.