Psoriatic plaques are characterized by epidermal hyperplasia and the presence of acute and chronic inflammatory cells. Active psoriatic plaques demonstrate a similar immunologic phenotype, as do ongoing cellular immune responses. Activated lymphocytes and other immune accessory cells have been detected within psoriatic plaques. Interleukin-2 receptor-positive and HLA-DR+ T cells are found in significantly higher numbers in active psoriatic plaques than in uninvolved skin or in treated plaques.1,2 The interleukin-2 receptor is a membrane protein that is present only on activated T cells and is associated with cell proliferation.3-5 HLA-DR is present on activated T cells but is also present on keratinocytes, macrophages, Langerhans cells, fibroblasts, dendritic cells, and endothelial cells in these lesions.1,2 The epidermal compartment is dramatically altered. The keratinocytes that are found in active plaques are HLA-DR+,1 γ-IP-10+,6 and I-CAM-1+,7 which is similar to the representation of these interferon gamma-induced proteins in