Malignant histiocytosis in infants: surface marker analysis of malignant cells in two cases.

Two infants with malignant histiocytosis, as diagnosed by morphological and cytochemical examinations of malignant cells infiltrating pleural effusion, skin, and bone marrow, are described. Surface marker analysis of the malignant cells with monoclonal antibodies showed these cells to express markers of T-lymphocytes and HLA-DR antigen, but not those of B-lymphocytes, granulocytes, or monocytes. These immunological findings demonstrated that the neoplastic cells in malignant histiocytosis of infancy may be of T-cell origin, rather than histiocytic or monocytic origin.