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This paper reviews the pathogenesis of psoriasis, in particular, the immunological cascade in psoriasis. Psoriasis is an immune-mediated skin disease where the T cell plays a pivotal role in the pathogenesis of the disease. The critical steps involved in the pathogenesis include Langerhans cell activation and maturation by antigens in the skin, activation of the T cell by mature Langerhans cells, differentiation and expansion of T cells within the lymph nodes, trafficking of activated T cells from the lymph node to the skin and the subsequent release of cytokines. These cytokines are responsible for epidermal and vascular hyperproliferation and pro-inflammatory effects. Each of these steps provides an opportunity for biological agents designed to block the psoriatic immunological cascade. This paper reviews the immunopathogenesis of psoriasis. Biologic agents in psoriasis, to be published separately, reviews the new biologic therapies that aim to selectively block the immunological steps implicated in the pathogenesis of psoriasis outlined in this paper. [ABSTRACT FROM AUTHOR]

This paper reviews the new biologic agents that selectively block the immunologic steps implicated in the pathogenesis of psoriasis. Four strategies have been targeted: reduction of the number of pathogenic T cells; inhibition of T-cell activation and migration; modulation of the immune system; and blockage of the activity of inflammatory cytokines. There are three classes: monoclonal antibodies, fusion proteins and recombinant cytokines or growth factors. The actions, efficacy and side-effect profile of the biologic agents, alefacept, efalizumab, etanercept and infliximab, are reviewed. [ABSTRACT FROM AUTHOR]