Precursors of Langerhans cells

Abstract

LC are dendritic cells localized in the supra-basal layer of the epidermis and in mucous epithelia. Their density ranges from 200 to 900 cells/mm2. Their first function is to take an antigen, process it and present the processed antigen to the lymphocytes ([1] Misery L. La cellule de Langerhans. Editions Techniques, Encycl. Méd. Chir. Dermatologie 1994;12-220-B-10). They are involved in numerous diseases.The origin of these cells has been debated but a consensus has now been reached. Langerhans cells (LC) were first described in 1868 by Paul Langerhans ([2] Über die Nerven der menschlichen Haut. Virch Arch A (Pathol Anat) 1868;44:325–337). He thought that it was a nerve cell. LC were first considered to be a component of the nervous system because their dendritic processes are similar to nerve fibers and because of their staining by gold chloride. Other authors have discussed a possible relationship with melanocytes. LC were regarded either as melanocytes, the progeny of melanocytes after division, or as melanocytes in an arrested stage of development ([3] Masson P. My conception of cellular naevi. Cancer 1951;4:9–15; [4] Fan J, Schoenfeld RJ, Hunter J. A study of the epidermal clear cells with special reference to their relationship to the cells of Langerhans. J Invest Dermatol 1959;32:445–450; [5] Zelickson AS. Granule formation in the Langerhans cell. J Invest Dermatol 1966;47:498–502). S100 protein is expressed on melanocytes, on nerve cells and on LC ([6] Cocchia D, Michetti F, Donato R. Immunochemical and immunocytochemical localization of S100 antigen in normal human skin. Nature 1981;294:85–87), but this does not imply that there is a common lineage. Subsequent research showed that this cell is in fact an immune cell.Electron microscopy has given us a new and very important insight into the nature of LC. Thus, there is no tonofilament, no desmosome and no melanosome ([7] Birbeck MS, Breathnach AS, Everall JD. An electron microscopy study of basal melanocyte and high level clear cell (Langerhans cell) in vitiligo. J Invest Dermatol 1961;37:51–63). The most important ultrastructural feature is the presence of Birbeck granules. Many experiments have pointed to a bone-marrow origin of LC and their probable relationship with the phagocytic mononuclear cell system.