sCD14-ST is a 13k Da fragment derived from cleavage of CD14, a glycoprotein of 55k Da anchored to the membrane of monocytes, macrophages and polymorphic neutrophils. CD14 acts as a receptor for lipopolysaccharide (LPS) complexes and the specific LPS binding protein (LBP) (Fig.1).
It can bind to peptidoglycans and other surface structures present in both Gram-Positive and Gram-Negative bacteria. Once bound to the LPS-LBP complex, it activates the intracellular inflammatory response of the Toll-Like receptor 4 (TLR4)/MD2-complex, triggering the host’s inflammatory cascade against the infectious pathogenic agent. Phagocytosis and activity of plasma proteases (lysosomal enzymes, cathepsin D) result in the formation of the fragment sCD14 subtype, in particular the 13 kDa fragment of sCD14-ST, known as Presepsin.