Th17 cells: a new paradigm for cutaneous inflammation.

Inflammatory processes of the skin have classically been segregated to either the cell-mediated, T-helper type 1 (Th1) or the humoral (Th2) branch of the immune system. The recent addition of Th17 cells, a novel T-helper cell named for its secretion of interleukin (IL)-17, to current thinking in autoimmunity has resulted in a significant paradigm shift in immunological thinking. Collectively, Th17 cytokines have been found to stimulate cutaneous immune reactions through an activation of a wide range of downstream inflammatory mediators and an induction of immune cell and keratinocyte proliferation as well as angiogenesis. Newly developed treatment modalities for neutralizing the Th17 branch of the immune system are proving to be valuable additions to the current therapeutic armamentarium. Here we describe a new schema for dermatologic T-cell-mediated immunity. We elucidate experiments confirming the presence of Th17 cells, followed by a discussion of their relevance to cutaneous inflammation and psoriasis.