Expression of endomucin, a novel endothelial sialomucin, in normal and diseased human skin.

Endomucin is an endothelial sialomucin that was recently identified with the help of monoclonal antibodies raised against mouse endothelial cells. Cloning of human endomucin allowed us to generate monoclonal antibodies against soluble recombinant forms of human endomucin. In this study, we investigated the expression of this novel molecule in human skin under different conditions, using the monoclonal antibodies. In normal human skin, endomucin was detected for the monoclonal antibody L6H10 by immunoblotting, and immunohistologic analysis of wax-embedded sections revealed that this glycoprotein is expressed on capillaries, venules, and lymphatic vessels. Interestingly, staining of arterial endothelium was either weak or focal using the monoclonal antibodies against endomucin. In situ hybridization of normal human skin confirmed the expression pattern on the messenger RNA level obtained above. We further analyzed the expression of endomucin in skin biopsy specimens from patients with inflammatory skin diseases, such as atopic dermatitis, psoriasis, lichen planus, cutaneous lupus erythematosus, and T cell lymphoma as well as with vascular skin tumors, such as hemangioma, pyogenic granuloma, angiolipoma, Kaposi's sarcoma, and angiosarcoma. We found endomucin expressed on the endothelium of each tissue, concluding that this novel molecule is a new endothelial-specific marker in the study of normal and diseased human skin.