DMC1: A Monoclonal Antibody Produced from Histiocytosis X Cells Which Reacts with the Native CD1a Molecule of Human Epidermal Langerhans Cells

Human epidermal Langerhans cells express two (CDla and CDlc) of the three human thymic cell surface differentiation antigens (CD1a, CD1b, and CD1c). The first cluster of differentiation antigens (CD1) is defined by a group of monoclonal antibodies (MCA). All these MCA were obtained after immunization of mice or rats with human cortical thymocytes. 0KT6 MCA (a CDla MCA) was the first to be described as reactive with human epidermal Langerhans cells. We produced a murine MCA, called DMC1, after immunization with proliferating Langerhans cells of Eosinophilic Granuloma of the bone (Histiocytosis X). In tissues DMC1 MCA reacted with epidermal dendritic cells (Langerhans cells) in the skin and cortical thymocytes in the thymus as observed on indirect immunofluorescence. At the ultrastructural level, DMC1 MCA was specific for Birbeck granule-containing Langerhans cells and did not react with melanocyte and keratinocyte populations. The quantitative analysis of immunoelectron labeling and the cytofluorometric study showed that the intensity of labeling was inversely correlated with the concentration of trypsin used in the preparation of epidermal cell from skin samples. DMC1 MCA precipitated a protein with a relative mass of 49 000 (CD1a molecule) from lysates of iodinated epidermal Langerhans cells under reducing conditions. It recognized the original CD1a molecule (M_r 49 000) but not the membrane breakdown product of CD1a (M_r 27 000) brought about by trypsin.