Mycobacterial infection in MyD88-deficient mice

MyD88 is an adaptor protein that plays a major role in TLR/IL-1 receptor family signaling. To understand the role of MyD88 in the development of murine tuberculosis in vivo, MyD88 knockout (KO) mice aerially were infected with Mycobacterium tuberculosis. Infected MyD88 mice were not highly susceptible to M. tuberculosis infection, but they developed granulomatous pulmonary lesions with neutrophil infiltration which were larger than those in wild-type (WT) mice (P<0.01). The pulmonary tissue levels of mRNA for NOS and IL-18 were slightly lower, but levels of mRNA for IL-1beta, IL-2, IL-4, IL-6, IL-10, IFN-gamma, and TGF-beta were higher in MyD88 KO mice. IFN-gamma, TNF-alpha, IL-10, and IL-12 also were high in the sera of MyD88 KO mice. There were no statistically significant differences in the expression of TNF-alpha, IL-12, and ICAM-I mRNA between MyD88 KO and WT mice. Thus, MyD88 deficiency did not influence the development of murine tuberculosis. NF-kappaB activity was similar in the alveolar macrophages from the lung tissues of MyD88 KO and WT mice. Also, there may be a TLR2-specific, MyD88-independent IL-1 receptor/TLR-mediated pathway to activate NF-kappaB in the host defense against mycobacterial infection.