Macrophage specific antigen is expressed by resting microglia in the CNS but not by Langerhans cells in the skin.

Controversy exists as to whether Langerhans cells in the epidermis and resting microglia in the brain should be included among cells of the mononuclear phagocyte series (MPS). A monoclonal anti-guinea-pig macrophage antibody has been prepared that is specific for a macrophage membrane antigen and does not react with Fc receptors or Ia antigens. This antibody fails to react with Langerhans cells despite reacting with peritoneal exudate macrophages, alveolar macrophages, Kupffer cells and macrophages in infectious granulomas. It does, however, react with resting microglia in the brain. This could suggest that Langerhans cells, despite a similar bone marrow origin, are not typical cells of the MPS, whereas resting microglia share features with this cell system.