Distribution of cell surface antigens in histiocytosis X cells. Quantitative immunoelectron microscopy using monoclonal antibodies.

We have shown previously that cells comprising the cutaneous infiltrates of histiocytes X (HXCs), like Langerhans cells (LCs), react with monoclonal anti-T6 antibody. HXCs also react with anti-T4/4b and anti-Ia-like antibodies. To further define the patterns of antibody reactivity in HXCs, we performed immunoelectron microscopy on two clear-cut cases of histiocytosis X using the immunoperoxidase technique. The reaction product of diaminobenzidine, indicating anti-T6 antibody reactivity, was easily detected along cell membranes of HXCs and at sites of possible endocytosis. Anti-T4/4b and anti-Ia antibodies had less cell membrane reactivity. Computerized image analysis aided in discriminating the patterns of anti-T6 antibody in HXCs and from LCs and confirmed that anti-T6 antibody staining was the most intense of the antibodies evaluated. These findings (1) document antigenic similarities and differences between HXCs and LCs on an ultrastructural level, (2) add support to the concept that HXCs are abnormal proliferations of LCs, and (3) demonstrate the association of the cell surface antigen, T6, with apparent endocytotic activity.