The significant reduction in the expression of TNF by TLR2-deficient macrophages infected in vitro and the significant reduction of TNF expression in the lungs of TLR2−/− mice infected with LVS is striking and suggests that the increased susceptibility of TLR2-deficient mice to infection can perhaps be accounted for solely by the impairment of TNF expression in vivo early in the infection. This evidence concerns the gene TNF and infection.