Expression-ready ORF Clones

CD14 molecule.

Membrane-bound form

CD14 is a glycosylphosphatidylinositol (GPI)-anchored membrane protein which acts as a bacterial pattern recognition receptor [1]. CD14 is found on cells derived from the monocyte/macrophage lineage, as well as neutrophils and B lymphocytes. CD14 serves as a member of the heteromeric lipopolysaccharide (LPS) receptor complex that also contains TLR4 and MD2 [2]. CD14 binds LPS but is not capable of initiating a transmembrane activation signal since it does not contain a cytoplasmic domain. Upon LPS binding, CD14 physically associates with TLR4 which in turn transduces the signal. CD14 was also shown to interact with TLR2 in response to various microbial infections [3].

1. Pugin J. et al., 1994. CD14 is a pattern recognition receptor. Immunity, 1(6):509-16.
2. Da Silva Correia J. et al., 2001. Lipopolysaccharide is in close proximity to each of the proteins in its membrane receptor complex. transfer from CD14 to TLR4 and MD-2. J Biol Chem, 276(24): 21129-35.
3. Aderem A. & R.J. Ulevitch, 2000. Toll-like receptors in the induction of the innate immune response. Nature, 406(6797):782-7.

Soluble form

Many cell types do not express CD14 on the cell membrane. This is indeed the case of epithelial cells of tissues exposed to the external environment or endothelial cells. Therefore, they depend on a soluble form of CD14, found in plasma, to correctly recognize bacterial molecular patterns, such as LPS and peptidoglycan, through TLR4 and TLR2 respectively. Immunodepletion of sCD14 from serum prevents responses to LPS, and the responses are restored by addition of sCD14 [1]. Soluble CD14 can both potentiate and down-regulate responses to LPS [2,3].

Alias : CD14, sCD14

References:

1. Frey EA. et al., 1992. Soluble CD14 participates in the response of cells to lipopolysaccharide. J Exp Med. 176(6):1665-71.
2. Backhed F. et al., 2002. TLR4-dependent recognition of lipopolysaccharide by epithelial cells requires sCD14. Cell Microbiol, 4(8):493-501.
3. Kitchens RL. et al., 2001. Plasma CD14 decreases monocyte responses to LPS by transferring cell-bound LPS to plasma lipoproteins. J Clin Invest. 108(3):485-93.

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