TLR4 and infection: Our findings showed that TQN protected rabbits against P. multocida experimental challenge as evidenced by reducing P. multocida counts in rabbits’ lungs, downregulating the transcription levels of P. multocida virulence-related genes (ptfA, toxA and nanB) at 48 and 96 h post-infection and ameliorating the expression levels of cytokines-related genes (IL-1β, IL-10, IL-8, IL-6, DEFB1, TNF-α, TLR-4 and TLR-2) at 96 h post-infection.