TLR4 and infection: To mimic this event in an infection-free environment, we administered lipopolysaccharide (LPS), a component of the cell wall of Gram-negative bacteria, to mice, which caused rapid B and T cell accumulation in lymph nodes (LNs) within 6 h after s.c injection, mediated by signaling through Toll-like receptor 4 (TLR4) and MyD88 (Figures 1A–1C).