Immunopathogenesis of psoriasis: news in an old concept.

Twenty years ago, a concept of psoriasis pathogenesis was proposed in which epidermal proliferation of psoriatic lesions was the consequence of immunological abnormalities. This concept has subsequently been supported by the remarkable efficacy of immunosuppressive drugs. Moreover, recent experimental data indicate that activated psoriatic lymphocytes are capable of inducing keratinocyte proliferation. However, we have still to explain the mechanism by which lymphocytes act on keratinocytes and to find out what antigenic material could be responsible for their activation.