CD14 is a membrane-associated glycosylphosphatidylinositol-linked protein expressed at the surface of cells, especially macrophages. CD14 was the first described pattern recognition receptor. CD14 acts as a co-receptor (along with the Toll- like receptor TLR 4 and MD-2) for the detection of bacterial lipopolysaccharide. Soluble CD14 (sCD14), a 55-kDa glycoprotein found in plasma, has been shown to act as a shuttle for bacterial LPS and phospholipids, transporting LPS and phospholipid monomers from LPS aggregates or liposomes to high density lipoprotein particles. sCD14 has also been shown to mediate the transport of LPS and phosphatidylinositol into cells.