Abstract
Substantial evidence during the past years has indicated that keratinocytes play an active role in the generation and expression of protective immune responses and immunopathological reactions in the skin. In resting keratinocytes, immune mediators are barely detectable. Upon stimulation by environmental, physical or chemical stimuli, a significant increase in the release of pro-inflammatory mediators can be observed both in vitro and in vivo. The outcome of many skin reactions, however, critically depends on the cross-talk between infiltrating T cells and keratinocytes. Indeed, T-cell-derived lymphokines have been identified as the most effective triggers of keratinocyte expression of soluble and membrane molecules, which in turn are, themselves, responsible for the recruitment and local activation of T cells and other leukocytes, leading to the eventual amplification of the inflammatory reaction.