Future long-term studies are needed to verify the avirulence of the S. Typhimurium LT2 strain ∆rfa mutants and their potential usefulness in modulation of the TLR2 and TLR4 signaling pathways for the protection of immunocompromised gnotobiotic piglets against subsequent infection with the virulent wild-type S. Typhimurium LT2 strain. Here, TLR4 is linked to infection.