Regulation of cell proliferation and differentiation by interferons.

The interferons are a widely studied group of proteins which were first identified by their ability to protect cells against virus infections (Stewart, 1979). They are synthesized and secreted by a variety of cell types in response to several classes of inducers (notably virus infections) and exert their effects in vivo as a result of interaction with other cells in distant parts of the body. In this sense the interferons are analogous to the polypeptide hormones. A functional similarity with hormones is further emphasized by the recent identification in target cells of specific membrane receptors for interferons and by the multiplicity of biological effects which result from the interactions of the interferons with these receptors. In recent years it has become clear that the interferons are capable of influencing cellular physiology and behaviour in a number of ways. Their effects include inhibition of cell growth and proliferation, regulation of the expression of specific genes, modulation of cell differentiation, and activation of certain cell types in the immune system (e.g. macrophages and natural killer cells). The mechanisms underlying the antiviral actions of the interferons have been widely studied and frequently reviewed (Baglioni, 1979; Hovanessian, 1979; Lengyel, 1982; Sen, 1982). In contrast, information concerning the effects of interferons on cell proliferation and differentiation has only been obtained during the last decade, as our understanding ofmechanisms ofgrowth regulation and gene expression in eukaryotes in general has increased. This review aims to summarize the current situation regarding these actions of the interferons and suggests areas in which our perception of such control of cell function may be expected to increase.