Langerhans cells react with pan-leukocyte monoclonal antibody: ultrastructural documentation using a live cell suspension immunoperoxidase technique.

Langerhans cells are generally regarded as members of an Ia+ dendritic cell system capable of potent accessory cell function in immune responses. While it has been shown that murine Langerhans cells are bone marrow-derived, the ontogenic relationships among human Langerhans cells, other dendritic cells, macrophages, and leukocytes in general have yet to be fully clarified. Recently, several pan-leukocyte monoclonal antibodies have been produced which react with the human leukocyte common antigen. This antigen resembles the murine T200 antigen and is expressed by all leukocyte subtypes but not by nonhematopoietic cells. Using an immunoperoxidase technique for staining suspensions of live skin cells, we have documented Langerhans cell reactivity with pan-leukocyte monoclonal antibody L3B12 at the ultrastructural level. Reactivity with this highly sensitive and specific pan-leukocyte marker supports the concept of the human Langerhans cell as a specialized form of bone marrow-derived mononuclear leukocyte and defines an immunologic feature common to dendritic cells, macrophages, and leukocytes that is not shared by other cell types. This finding is discussed in the context of other recent data concerning the immunologic phenotype of Langerhans cells. Since the immunoultrastructural method employed does not require cell fixation of any kind prior to immunologic staining, it should prove particularly useful for studying cell surface antigens that are adversely affected by fixation.