IMMUNOHISTOCHEMICAL LOCALIZATION OF THROMBOMODULIN IN NORMAL HUMAN SKIN AND SKIN TUMORS

Thrombomodulin (TM) expression has been investigated in sections of no rmal human skin, in cultured normal human keratinocytes, and in a vari ety of skin tumours. TM was present in squamous epithelial cells in th e spinous layer of normal epidermis and in the outer root sheath of ha ir follicles, but was absent in the cells of the basal layer. It appea red to be predominantly localized to the cell membrane and the interce llular bridges in these areas. Cultured normal human keratinocytes dem onstrated functionally active constitutive TM expression on their cell surface. Immunoperoxidase staining of skin tumours using anti-human T M antibodies demonstrated a typical cell membrane positivity in tumour s with squamous or hair follicle differentiation. Basal cell carcinoma s showed TM expression only in areas where incomplete squamoid metapla sia occurred. Sweat gland rumours and lesions of the melanogenic syste m failed to express TM. The localization of TM by immunostaining in va rious benign and malignant skin tumours typically correlated with thei r normal skin element of origin. The physiological significance of TM expression in the epidermis is currently undefined.