Expression of major histocompatibility complex class II molecules by dermal inflammatory cells, epidermal Langerhans cells and keratinocytes in canine dermatological disease.

The distribution of Major Histocompatibility Complex (MHC) Class II molecules in skin biopsies from 42 dogs with primary skin disease and six control dogs was examined by indirect immunohistochemical methods. Canine epidermal Langerhans cells constitutively expressed MHC Class II and the number of such cells was increased in the epidermis of dogs with discoid lupus erythematosus (n = 10), hypersensitivity dermatitis (n = 10) or deep pyoderma (n = 13) but not in eight cases of pemphigus foliaceus. Expression of MHC Class II by epidermal and follicular keratinocytes was observed in a ninth dog with pemphigus foliaceus. Within dermal inflammatory infiltrates, Class II was expressed by macrophages, dendritic cells and fibroblasts but not by neutrophils, eosinophils, mast cells or plasma cells. Only occasional dermal lymphocytes expressed surface MHC Class II, but nodular aggregates of strongly Class II-positive lymphocytes were observed within the dermis of two dogs with discoid lupus erythematosus.