Epithelium‐lining macrophages are spindle‐shaped cells which line the epidermis and hair follicles. We studied the distribution and phenotype of this hitherto neglected member of the dermal monocyte/macrophage system in 25 lesional psoriatic, and five normal skin biopsies. Epithelium‐lining macrophages were inconspicuous in normal skin, whereas their number was increased in almost two thirds of psoriatic cases; in nine out of 25 lesional skin biopsies, these flattened cells formed an almost continuous single‐cell row at the dermo‐epidermal junction.

Immunophenotyping revealed that these cells expressed the leucocyte common antigen CD45. and the macrophage markers CD14, CD36 and CD4, but not CD11b. Epithelium‐lining macrophages strongly expressed HLA‐DR‐antigens and CD 11a, but lacked the Langerhans cell marker CD1, and CD34. The dermal dendrocyte marker factor XIIIa was expressed in only a minority of these cells.

It is concluded that epithelium‐lining macrophages represent a separate subset of dermal monocytes/macrophages with a distinct tissue localizaton and immunophenotype. Their restricted distribution and close association with the epidermis may suggest a role in the regulation of epidermal growth. Alternatively, the expression of several immune‐associated molecules may indicate that epithelium‐lining macrophages are involved in the antigen‐dependent or‐independent activation of T cell.