Thrombomodulin expression on dermal cells in normal and psoriatic skin

Abstract The various subsets of dermal cells with a dendritic appearance can be identified by phenotypic differences in cell markers. We report on the morphology and tissue distribution of dermal cells detected with a monoclonal antibody against thrombomodulin in histological sections of normal arm and scalp skin and psoriatic skin. Double staining with antibodies to factor XIIIa, CD34 and CD68 was also employed in scalp biopsies to elucidate the relationship between thrombomodulin⁺ dermal cells and dermal dendrocytes and macrophages described by others. Thrombomodulin⁺ dermal cells in normal arm skin had little cytoplasm with fine branched dendrites and tended to be localized just beneath the epidermis. In scalp skin these cells had longer, more numerous dendrites and were distributed in the papillae and perivascular adventitial dermis primarily in the upper and central reticular dermis. In psoriatic skin, thrombomodulin⁺ dermal cells had an increased cytoplasmic volume with stout, less branched dendrites and appeared in the papillae and among inflammatory cells. Dermal cells detectable by thrombomodulin expression were factor XIIIa^–, CD34^– and CD68^–, and seemed to represent a distinct subset of dermal cells which may function in tissue repair. However, thrombomodulin⁺ dermal cells and factor XIIIa⁺ dendrocytes were frequently seen close together and could act cooperatively to regulate extravascular thrombin homeostasis in both normal and pathological dermal environments.