Immunohistochemical analysis of chronic discoid and subacute cutaneous lupus erythematosus--relation to immunopathological mechanisms.

An immunohistochemical analysis of skin biopsies was performed in 18 patients with cutaneous lupus erythematosus (LE), using the alkaline phosphatase and monoclonal anti-alkaline phosphatase method (APAAP). The study group was subdivided on the basis of clinical criteria into 10 patients with chronic discoid LE (CDLE) and eight patients with subacute cutaneous LE (SCLE). Using a panel of monoclonal antibodies the following results were obtained: (i) ICAM-1 was expressed on epidermal keratinocytes, dermal inflammatory cells, and endothelial cells in most biopsies, whereas LFA-1 was confined to the dermis. Attachments between keratinocytes or endothelial cells and activated T lymphocytes via ICAM-1/LFA-1 may be a possible mechanism of target/effector recognition in cutaneous LE. (ii) HLA-DR was expressed on epidermal keratinocytes and cells of the dermal infiltrate, but not on endothelial cells. HLA-DR+ cells probably function as antigen-presenting cells, leading to major histocompatibility complex-restricted cellular cytotoxicity in cutaneous LE. (iii) Interleukin 2 receptor expression on dermal inflammatory cells was weak, indicating non-specific activation of T lymphocytes. (iv) The dermal inflammatory cells were T lymphocytes, mainly of the helper/inducer subtype. B lymphocytes were rarely found in the dermis. In general, no significant immunohistochemical differences were found between CDLE and SCLE, suggesting that these variants represent clinical subtypes rather than different pathogenetic entities.