TLR4 and serum lipopolysaccharide activity: Endotoxemia, an experimental model in which healthy volunteers are intravenously administered a form of endotoxin (lipopolysaccharide, LPS, a major component of Gram-negative bacteria outer membrane and a Toll-like receptor 4 (TLR4) agonist) [9], has served as a valuable experimental venue for more than six decades [10-12].