Cd14

Markers for: monocytes, macrophages, Langerhans cells, dendritic cells; also B cells and neutrophils.

Structure: Surface membrane protein (53-55 kDa)

Note: CD14 acts as an affinity receptor for the complex of lipopolysaccharides (LPS) and LPS binding protein (LBP).

Application: FACS, IHC (P) (G), IF

(see below) Cluster of differentiation

CD14 is a glycosylphosphatidylinositol-anchored protein that is mainly expressed on monocytes and macrophages. CD14 is also expressed on neutrophils and granulocytes, but to a much lesser extent. The corresponding human CD14 gene consists of two exons and is located on chromosome five. The corresponding encoded protein consists of 356 amino acids, mainly leucine repeats. A mutation of amino acids 39 to 44 inclusive leads to a loss of the ability to bind LPS. A proportion of 3-4 µg/ml of the CD14 receptors is present as a soluble, free proportion in the serum and is therefore able to bind LPS at an early stage, thus blocking cellular activation.

The CD14 receptor is a monocyte differentiation antigen that falls into the category of pattern recognition receptors. When the CD14 receptor was initially discovered, it was doubted that it could participate in an intracellular signaling cascade due to its lack of an intracellular component.

It was later recognized that CD14 is a co-receptor for the TLR4 signaling pathway. The CD14 receptor can therefore be regarded as a component of the innate immune response. Furthermore, CD14 together with the receptor protein TLR1 and TLR2 forms an activation cluster TLR2:TLR1:CD14 in response to triacylated lipopeptides. This cluster triggers signaling from the cell surface and is subsequently transmitted to the Golgi apparatus via a lipid-raft dependent pathway (Triantafilou M et al. 2006).

Furthermore, the receptor has also been reported as a transport protein of inflammatory lipids to initiate phagocytosis.

1. Hantschke M et al. (2016) Immunohistologic techniques. In: L. Cerroni et al. Histopathology of the skin. Springer Verlag Berlin-Heidelberg pp. 26-33.
2. Lancioni CL et al. (2011) Mycobacterium tuberculosis lipoproteins directly regulate human memory CD4(+) T cell activation via Toll-like receptors 1 and 2. Infect Immun 79:663-673.
3. Triantafilou M et al. (2006) Membrane sorting of toll-like receptor (TLR)-2/6 and TLR2/1 heterodimers at the cell surface determines heterotypic associations with CD36 and intracellular targeting. J Biol Chem 281:31002-31011.
4. Zhao H et al. (2019) Borrelia burgdorferi basic membrane protein A initiates proinflammatory chemokine storm in THP 1-derived macrophages via the receptors TLR1 and TLR2. Biomed Pharmacother 115:108874.