UV Radiation and Cytokines

There is solid evidence for the existence of a complex network of interacting soluble mediators which influence immunologic and inflammatory reactions (Luger and Schwarz, 1990). These mediators include cytokines, growth factors, eicosanoids and neuropeptides. Cytokines are defined as low molecular weight (glyco) proteins that are transiently produced and exert their biologic activities via specific cell-surface receptors. Moreover, each mediator usually has multiple overlapping activities, and different factors may induce each other, or interfere with receptor expression on the target cells, thus affecting cell function in a synergistic or antagonistic way (Schwarz and Luger, 1992). Rather soon it became clear that keratinocytes, Langerhans cells as well as melanocytes have the capacity to secrete a large number of these inflammatory and immunologic mediators. The constitutive production of cytokines by keratinocytes both in vitro and in vivo is quite low, but can be enhanced by injurious stimuli such as bacterial and viral products, tumor promoters etc. An early finding during the unraveling of the cutaneous cytokine network was that ultraviolet (UV) light, in particular the UVB range (290–320 nm) is one of the most potent inducers of cutaneous cytokine production (Schwarz and Luger, 1989). As exposure to UV light leads to local and systemic inflammatory reactions and alterations of the immune response, keratinocyte derived mediators may play a relevant role in the pathogenesis of UV-induced skin reactions.