TNF and infection: Three days post-infection, the E. coli challenge significantly increased the expression of nuclear factor-κB (NF-κB), peroxisome proliferator-activated receptor-γ (PPAR-γ), toll-like receptor 4 (TLR4), IL-1β, and IL-6 (P < 0.05) and tended to increase the expression of TNF-α (P = 0.052).