Immunohistochemical study of the abnormal cells in Langerhans cell histiocytosis (histiocytosis x).

The immunophenotypic properties of the abnormal cells in routine specimens from 16 cases of Langerhans cell histiocytosis (LCH) were examined. In five cases, cryostat sections were also available. The abnormal cells expressed a similar phenotype and were positive for HLA-DR, S-100 protein, peanut agglutinin (PNA), CD1a, CD4 and several macrophage-associated markers, including CD11c, CDw32 and CD68 (the latter detectable in routine sections with antibody KP1). Staining with CD14, CD35 (C3b receptor), and CD11b (C3bi receptor) was negative with the exception of one of the cases in which a proportion of the cells showed faint positivity with CD11b. Staining for pan-T-cell (CD2, CD3, CD5) and pan-B-cell (CD19, CD22) antigens was negative in all lesions. It is concluded that LCH expresses a characteristic phenotype with some heterogeneity with regard to macrophage markers and that immunohistochemical methods in cryostat sections and routine specimens form a useful supplement to other techniques for the diagnosis of this condition.