Psoriasis: a disease of abnormal Keratinocyte proliferation induced by T lymphocytes.

Psoriasis affects 2% of the population in Western countries. Its aetiology and pathogenesis remain unknown but suggestions include abnormalities of blood vessels, neural components, epidermal cell cycle time or maturation of keratinocytes. More recently autoimmune reactions have been implicated involving stratum corneum antibodies(1) and antibodies to nuclei of basal epidermal cells(2). However, there is no convincing evidence that any of these abnormalities are of primary nature. In this article, Helgi Valdimarsson and his colleagues propose that the process leading to psoriatic lesions is triggered by T lymphocytes within the epidermal compartment. They envisage that psoratic lesions erupt where epidermal influx of antigen-carrying Langerhans cells and helper T lymphocytes overrides the normal epidermal suppressor mechanism.