FUNCTIONAL AND IMMUNOREACTIVE THROMBOMODULIN EXPRESSED BY KERATINOCYTES

In an immunohistopathologic study using two monoclonal antibodies that recognize independent epitopes on human thrombomodulin, we detected expression of thrombomodulin on Malpighian-layer keratinocytes, but not on the basal or upper granular-layer keratinocytes. Western blotting and thrombomodulin-specific enzyme-linked immunosorbent assay performed on both shaved skin and cultured SV40-transformed keratinocytes showed the expression of full-length thrombomodulin, indistinguishable from endothelial thrombomodulin. Thrombomodulin was expressed by keratinocytes in 1 mM calcium but not in reduced calcium. A functional assay for thrombomodulin revealed that epidermal-derived thrombomodulin possessed cofactor activity for thrombin-catalyzed protein C activation. The limited pattern of expression of thrombomodulin in epidermis implies that this molecule may be a differentiation marker of keratinocytes in addition to being a potent anticoagulant in the skin.