Lipopolysaccharide is a component of Gram-negative bacteria which strongly activates macrophages inducing production of pro-inflammatory cytokines, like TNF-. This reaction is initiated by Toll-like receptor 4 (TLR4) associated with MD-2, and aims at combating bacterial infection by the immune system. An exaggerated inflammatory reaction evokes sepsis. One of mechanisms protecting an organism against sepsis is an uptake of LPS by macrophages and its intracellular detoxification. The goal of our studies was to reveal an involvement of CD14 protein of the macrophage plasma membrane in reaction to various chemotypes of LPS in a wide range of concentrations from low (1 ng/ml) to high (1000 ng/ml). Cells were exposed to “smooth” or “rough” LPS which vary in the presence of the O-specific chain polysaccharide, thus have different physico-chemical properties. We found that participation of CD14 is crucial for binding and internalization of LPS. In these events CD14 collaborates with macrophage scavenger receptor A (SR-A). On the other hand, in the presence of high LPS doses participation of CD14 in activation of TLR4 leading to cytokine production can be omitted. Among the two forms of LPS, ”rough” LPS-induced TNF- production was less CD14-dependent which suggest that this chemotype of LPS can directly activate TLR4/MD-2. Taken together the data indicate that CD14 mediates recognition and binding of high doses of LPS but is dispensable for TNF- production.

http://www.hindawi.com/journals/mi/2013/824919/