Preface [Hot topic: Psoriasis (Guest Editor: Giampiero Girolomoni)]

Psoriasis is a chronic inflammatory skin disease affecting 1-3% of the general population worldwide. Although in many patients the disease is mild and can be easily controlled with topical treatments, in about one third of cases the disease is severe with a high impact on patients' quality of life. Complex genetic predisposition and a variety of trigger factors are both important elements in disease expression and are presented in chapter 1 and 2. Psoriasis is an immune mediated disorder, with IFN-γ-producing type 1 T cells playing a fundamental role in disease pathogenesis, although the nature of the antigen towards which the immune response is directed remains elusive. Intrinsic, genetically-determined keratinocyte defects are also important to explain their abnormal behavior, and a number of mediators locally produced in the skin is involved in disease pathogenesis (chapter 3). Recently, a variety of biological agents targeting T cells or inflammatory cytokines have been proved to be very effective in the therapy of psoriasis (chapters 6, 9, 10 and 11). Indeed, psoriasis is serving as a very useful model for testing the ability of new biologicals to treat extracutaneous immune-mediated disorders. Moreover, a number of new drugs are under development with the objective of blocking T cell recruitment into the skin (chapters 7 and 8), or keratinocyte proliferation and cytokine production (chapters 12, 13 and 14).