IMMUNOHISTOCHEMICAL COMPARISON OF CUTANEOUS HISTIOCYTOSES AND RELATEDSKIN DISORDERS - DIAGNOSTIC AND HISTOGENETIC RELEVANCE OF MS-1 HIGH-MOLECULAR-WEIGHT PROTEIN EXPRESSION

Twenty-nine cases of Langerhans cell histiocytosis (LCH), non-Langerha ns cell histiocytoses (N-LCH), non-infectious granulomas, and fibrobla st-related lesions were examined with a panel of monoclonal and polycl onal antibodies on freshly frozen tissue sections to characterize the macrophage phenotype of N-LCH syndromes. MS-1 high molecular weight ex tracellular protein, specific for sinusoidal endothelial cells and den dritic perivascular macrophages in normal human organs, was expressed by N-LCH cells but was not found in LCH cells, epithelioid cells in sa rcoidosis, or palisading histiocytes in granuloma annulare. The subcel lular location of MS-1 protein, i.e., cytoplasmic vs. peripheral/extra cellular, allowed discrimination of small and large (foamy or multinuc leated) N-LCH cells. MS-1-positive cells, which were found intermingle d in cellular dermatofibromas but not in fibrous dermatofibromas, diff ered from MS-1-positive N-LCH cells by their dendritic morphology, and thus rather resembled their normal dermal counterparts. A preserved f unctional relationship of these two MS-1-positive cell types was indic ated by the fact that N-LCH and cellular dermatofibromas were the only lesions found to be highly vascularized. As expected, CD1a showed hig h specificity for LCH, while CD34 was predominantly expressed by fibro blast-related lesions; in cellular dermatofibromas, CD34 and MS-1 expr ession partially overlapped. The other antigens tested showed non-spec ific or overlapping patterns of expression. In conclusion, assessment of MS-1 protein expression (in addition to assessment of CD1a and CD34 ) promises to be of diagnostic value in the discrimination of N-LCH fr om related skin disorders, and it may indicate a common differentiativ e pathway for most N-LCH disease entities.