CD14 exists in two forms, one anchored to the membrane by a glycosylphosphatidylinositol (GPI) tail (mCD14), the other a soluble form (sCD14). Soluble CD14 either appears after shedding of mCD14 (48 kDa) or is directly secreted from intracellular vesicles (56 kDa).
The x-ray crystal structure of human CD14 reveals a monomeric, bent solenoid structure containing a hydrophobic amino-terminal pocket.
CD14 acts as a co-receptor (along with the Toll-like receptorTLR 4 and MD-2) for the detection of bacterial lipopolysaccharide (LPS). CD14 can bind LPS only in the presence of lipopolysaccharide-binding protein (LBP).
Although LPS is considered its main ligand, CD14 also recognizes other pathogen-associated molecular patterns such as lipoteichoic acid. cluster of differentiation (CD)-14 is a
receptor for a very wide range of microbial products including lipopolysaccharide (released from Gram-negative bacteria), peptidoglycans, and lipoteichoic acid (constituents of Gram-positive bacteria).
CD14 is expressed mainly by macrophages and (at 10-times lesser extent) by neutrophils. It is also expressed by dendritic cells. The soluble form of the receptor (sCD14) is secreted by the liver and monocytes and is sufficient in low concentrations to confer LPS-responsiveness to cells not expressing CD14. mCD14 and sCD14 are also present on enterocytes. sCD14 is also present in human milk, where it is believed to regulate microbial growth in the infant gut.
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^Thomas CJ, Kapoor M, Sharma S, Bausinger H, Zyilan U, Lipsker D, et al. (November 2002). "Evidence of a trimolecular complex involving LPS, LPS binding protein and soluble CD14 as an effector of LPS response". FEBS Letters. 531 (2): 184–188. doi:10.1016/S0014-5793(02)03499-3. PMID12417309. S2CID25135963.
^Yu B, Wright SD (1995). "LPS-dependent interaction of Mac-2-binding protein with immobilized CD14". Journal of Inflammation. 45 (2): 115–125. PMID7583357.