The BM8.1 antibody is specific for mouse F4/80 antigen, a 125 kDa transmembrane protein widely expressed by members of the mononuclear phagocyte system and considered to be a key marker for mature macrophage cells. F4/80 is differentially expressed during myeloid cell development, and may be regulated by certain cytokines within the tissue microenvironment. Other cell types shown to express this antigen include Langerhans cells, Kupffer cells and dendritic cell subsets. BM8.1 is widely used together with antibodies to CD115 (c-fms), CD11b and CD11c to identify myeloid / macrophage cells by flow cytometry.