CD14
Mammalian protein found in humans
CD14 (cluster of differentiation 14) is a surface membrane protein made mostly by macrophages as part of the innate immune system. It helps to detect bacteria in the body by binding lipopolysaccharide (LPS), a pathogen-associated molecular pattern (PAMP). It is highly expressed on monocytes and macrophages, and at lower levels on neutrophils and dendritic cells.
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.
01Function
CD14 acts as a co-receptor (along with the Toll-like receptor TLR 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 CD14 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).
02Tissue distribution
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.
03Differentiation
CD14+ monocytes can differentiate into a host of different cells, including dendritic cells, a differentiation pathway encouraged by cytokines, including GM-CSF and IL-4.
04Interactions
CD14 has been shown to interact with lipopolysaccharide-binding protein.
Sources and credits
This article is adapted from the Wikipedia article “CD14”, written by its contributors and licensed under CC BY-SA 4.0. Fathomly has changed the layout, removed citation markers, navigation and maintenance notices, and adjusted punctuation. This adapted version is shared under the same license. For references, see the original article.
Images, from Wikimedia Commons:
- Protein CD14 PDB 1WWL.png by Kim JI, Lee CJ, Jin MS, Lee CH, Paik SG, Lee H, Lee JO (2005). Crystal structure of CD14 and its implications for lipopolysaccharide signaling. J Biol Chem. 2005 Mar 25;280(12):11347-51., GPL
- Toll-like receptor pathways revised.jpg by The original uploader was Subclavian at English Wikipedia., Public domain
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