CD14, also called monocyte differentiation antigen CD14, is a co-receptor protein for bacterial lipopolysaccharide. It is a component of the innate immune system, enhancing responses to infection by sensitizing host cells to bacterial lipopolysaccharide and other microbial products. Binding to LPS activates the release of cytokines. CD14 has a membrane-bound form and a soluble form. It is expressed on macrophages, monocytes (specific marker for monocytic differentiation), neutrophils, dendritic cells, and enterocytes; the soluble form is secreted by the liver and by monocytes. Staining is used to identify monocytes and macrophages in normal tissues and leukemias (eg, acute monoblastic, acute myelomonocytic). References: Science. 1990;249(4975):1431-1433. PMID: 1698311; Immunity. 1994;1(6):509-516. PMID: 7534618; J Hepatol. 1999;31(3):435-442. PMID: 10488701; Infect Immun. 1998;66(3):1135-1141. PMID: 9488406; Am J Clin Pathol. 2011;135(5):720-730. doi: 10.1309/AJCPZ46PMMAWJROT; -Leukemia. 2006;20(7):1321-1324. doi: 10.1038/sj.leu.2404242