1.1.1.3　Langerhans cells

Langerhans cells are immunocompetent cells that originated from bone marrow mononuclear-macrophages and are distributed in the epidermis and hair follicle epithelium above the stratum basale，accounting for 3％-5％of the total number of epidermal cells.The density of Langerhans cells varies with the location.Generally，there are comparatively more Langerhans cells in the skin of the face and neck，while less in the palm and plantar regions.When impregnated with gold chloride，the Langerhans cells may appear as the shape of dendritic cells；however，the dopa response is negative and ATPase response is positive.Under the optical microscopy investigation，Langerhans cells are polygonal in shape，with clear cytoplasm，smaller nuclei and lobulated，abundant mitochondria，golgi bodies and endoplasmic reticulum，and lysosomes.Electron microscopy investigation demonstrates that the cytoplasm of the cells contains unique Birbeck granules，which are used to distinguish from melanocytes（Figure 1-3）.At present，it is believed that Birbeck granules are formed by the invagination of the envelope during the phagocytosis of foreign antigens by Langerhans cells，which is a phagocytic or antigen storage form for the digestion of extracellular substances.Langerhans cells can recognize，ingest，process，and present antigens to T cells.Langerhans cells also play an important role in tumor immunity.Langerhans cells have a variety of surface markers，including FcR of IgG and IgE，C3b receptors，MHC class Ⅱ antigens（HLA-DR，DP，DQ）and CD4，CD45，S-100，etc.The specific surface markers of Langerhans cells are CD1a and Langerin（CD207）（see extended reading 1）.(https://www.daowen.com)