The protein encoded by this gene is a component of the innate immune system. CD14 exists in two forms, one anchored to the membrane by a glycosylphosphatidylinositol 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 (4GLP.pdb) reveals a monomeric, bent solenoid structure containing a hydrophobic amino-terminal pocket.
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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^Ranoa DR, Kelley SL, Tapping RI (2013). "Human LBP and CD14 independently deliver triacylated lipoproteins to TLR1 and TLR2 and enhance formation of the ternary signaling complex.". J. Biol. Chem.74 (epub): epub. doi:10.1074/jbc.M113.453266. PMID23430250.
^CD14 Is Expressed and Released as Soluble CD14 by Human Intestinal Epithelial Cells In Vitro: Lipopolysaccharide Activation of Epithelial Cells Revisited.
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^Yu, B; Wright S D (1995). "LPS-dependent interaction of Mac-2-binding protein with immobilized CD14". J. Inflamm. (UNITED STATES) 45 (2): 115–25. ISSN1078-7852. PMID7583357.
Kelley SL, Lukk T, Nair SK, Tapping RI (2013). "The Crystal Structure of Human Soluble CD14 Reveals a Bent Solenoid with a Hydrophobic Amino-Terminal Pocket". Journal of Immunology190 (3): 1304–1311. doi:10.4049/jimmunol.1202446. PMID23264655.