TLR4 and bacterial infectious disease: In bacterial infection, lipopolysaccharide (LPS) has been shown to interact with toll-like receptor 4 (TLR4) of dendritic cells (DCs) and induce NKT cell activation in the absence of an activating bacterial antigen, but is dependent on the secretion of IL-12 by DC (Brigl et al., 2003; Mattner et al., 2005).