In contrast, some studies show that TLR4 may play a key role in host resistance to Mtb infection in vivo.28,29 TLR4 mutant C3H/HeJ mice have reduced capacity to eliminate mycobacteria from the lungs and increased spreading of infection to spleen and liver, with 10–100 times higher bacteria burden levels than the wild-type mice.28 This evidence concerns the gene TLR4 and infection.