The immunological basis of psoriasis.

Evidence that psoriasis is an immune-mediated disorder comes from laboratory studies, clinical observation, and use of targeted therapies. Immunohistochemical studies have shown that the majority of T cells in psoriatic plaques are CD45RO+ memory-effector T cells that migrate into skin in recognition of an as yet undetermined antigen. There is also a predominance of Th1 cytokines, namely interferon gamma, in psoriatic plaques, in contrast to the predominance of Th2 cytokines found in atopic dermatitis. The efficacy of therapeutic agents that target T cells, such as anti-CD4+ monoclonal antibodies, cyclosporin, and interleukin-2 fusion toxin, has provided further substantial evidence that psoriasis is a T-cell-mediated disease. New T-cell targeted approaches and cytokine modulation are advancing basic science in providing an understanding of the evidence for the importance of the immune process in the biology of psoriasis.