Langerhans cells (LC) were reported to function as the antigen-presenting cells in the skin. They express immune response gene-associated antigens on their cell membranes. These cells seem to mediate contact sensitivity in vivo and the antigen- specific response of T lymphocytes in vitro. Langerhans cells also have surface receptors for the Fc portion of immunoglobulin G (IgG) and for the third component of complement, C3. They originate from the bone marrow, but details about the precursors of LC are not known. This antibody reacts specifically to human LC. The protein recognized by this antibody was mainly in the membranes of Birbeck granules and related structures. Langerhans cells are dendritic cells (antigen-presenting immune cells) of the skin and mucosa, and contain large granules called Birbeck granules. They are present in all layers of the epidermis, but are most prominent in the stratum spinosum. They also occur in the papillary dermis, particularly around blood vessels, as well as in the mucosa of the mouth, foreskin, and vagina. They can be found in other tissues, such as lymph nodes, particularly in association with the condition Langerhans cell histiocytosis (LCH).