New concepts in the pathogenesis and treatment of psoriasis: key roles for IL-23, IL-17A and TGF-β1

Psoriasis is a complex inflammatory skin disease that is thought to be mediated by T helper (Th)1 cells that secrete interferon-γ. Interestingly, recent advances by cellular immunologists have identified a new distinct type of T cell, called a Th17 cell, that plays an essential pathogenic role in several classic autoimmune inflammatory diseases previously believed to be Th1 diseases. Recent data also suggest that Th17 cells play a key role in psoriasis pathogenesis. Cytokines that are critical to the development, survival, proliferation, and function of Th17 cells include transforming growth factor β1 (initial differentiation), interleukin-23 (survival and proliferation), and interleukin-17A (proinflammatory effector function). If psoriasis is proven to be a Th17 disease and not a Th1 disease, these cytokines will be attractive targets for future therapies for individuals with psoriasis. These new concepts regarding psoriasis pathogenesis and treatment are the focus of this review.