CD14

CD14 (is_associated_with::cluster of differentiation 14), also known as CD14, is a human is_associated_with::gene.

The is_associated_with::protein encoded by this gene is a component of the is_associated_with::innate immune system. CD14 exists in two forms, one anchored to the membrane by a is_associated_with::glycosylphosphatidylinositol tail (mCD14), the other a soluble form (sCD14). Soluble CD14 either appears after shedding of mCD14 (48 is_associated_with::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 was the first described is_associated_with::pattern recognition receptor.

Function
CD14 acts as a co-receptor (along with the is_associated_with::Toll-like receptor is_associated_with::TLR 4 and MD-2) for the detection of bacterial is_associated_with::lipopolysaccharide (LPS). CD14 can bind LPS only in the presence of is_associated_with::lipopolysaccharide-binding protein (LBP). Although LPS is considered its main is_associated_with::ligand, CD14 also recognizes other pathogen-associated molecular patterns such as lipoteichoic acid.



Tissue distribution
CD14 is expressed mainly by is_associated_with::macrophages and (at 10-times lesser extent) by is_associated_with::neutrophils. It is also expressed by is_associated_with::dendritic cells. The soluble form of the receptor (sCD14) is secreted by the is_associated_with::liver and is_associated_with::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.

Differentiation
CD14+ is_associated_with::monocytes can differentiate into a host of different cells, including is_associated_with::dendritic cells, a differentiation pathway encouraged by is_associated_with::cytokines, including is_associated_with::GM-CSF and IL-4.

Interactions
CD14 has been shown to interact with lipopolysaccharide-binding protein.