Cytokine production by epithelial cells

The epithelium has long been regarded as a passive barrier intended to protect the underlying tissues. Many regulatory signals, including cytokines, that control epithelial cell proliferation and differentiation and cell function during inflammation were thought to be nonepithelial-derived. Now there is a growing appreciation that epithelial cells provide some of the impetus for their own growth and differentiation, and may also regulate the function of other cells through the elaboration of certain cytokines. Moreover, because epithelial cells serve as the interface between the organism and environment, they are in a position to signal changes in the environment. It is now clear that epithelial cells respond to injury or infection with cytokine secretion. Various approaches to detecting cytokines in normal and diseased tissue have been undertaken during the past few years to establish cytokine synthesis by different epithelia. This review will examine these recent investigations in various general contexts of epithelial cell function.