[Langerhans cells: methods of identification]

Since their first description by P. Langerhans in 1868, the identification of these "clear dendritic cells of the epidermis" has been facilitated by the discovery of specific markers: enzymes ATP ase, endogenous peroxidase; Birbek granules, an ultrastructural organelle described in 1961; immunological membrane markers shared with the Macrophage-Monocyte-Histiocyte system (1977): receptors for the Fc fragment of the immunoglobulins and for complement, HLA-DR (la) antigen. In the skin, the Langerhans cell represents the epidermal equivalent of the macrophage, forming in conjunction with keratinocytes, a reticulo-epithelial system: the fact that the Langerhans cell is marked by the glial S-100 protein suggests that the Langerhans cell represents a monocyte sub-population, morphologically and functionally different from tissue-histiocytes; recently the discovery of membrane antigens defined by monoclonal antibodies: OKT 6, OKT 11 and BL 6, suggests that Langerhan 's cells may be considered as "distinct" macrophages, that have acquired antigenic differenciation in thymic and epidermic epithelia. The nosologic connection between Langerhans cells and "indeterminate cells of the epidermis" remains unclear.