Toll-Like Receptor 4 Protects Against Infection in Mice.

Toll-like receptor 4 (TLR4) has been reported to protect against Gram-negative bacteria by acting as a pathogen recognition receptor that senses mainly lipopolysaccharide (LPS) from Gram-negative bacteria. However, the role of TLR4 in Gram-positive bacterial infection is less well understood. type A is a Gram-positive bacterium that causes gas gangrene characterized by severe myonecrosis. It was previously demonstrated that θ-toxin is a TLR4 agonist, but the role of TLR4 in infection is unclear. Here, TLR4-defective C3H/HeJ mice infected with showed a remarkable decrease in survival rate, an increase in viable bacterial counts, and accelerated destruction of myofibrils at the infection site compared with wild-type C3H/HeN mice. These results demonstrate that TLR4 plays an important role in the elimination of . Remarkable increases in levels of inflammatory cytokines, such as interleukin-1β (IL-1β), interleukin-6 (IL-6), and granulocyte colony-stimulating factor (G-CSF), were observed in -infected C3H/HeN mice, whereas the increases were limited in C3H/HeJ mice. Generally, increased G-CSF accelerates granulopoiesis in the bone marrow and the spleen to exacerbate neutrophil production, resulting in elimination of bacteria. The number of neutrophils in the spleen was increased in -infected C3H/HeN mice compared with non-infected mice, while the increase was lower in -infected C3H/HeJ mice. Furthermore, DNA microarray analysis revealed that the mutation in TLR4 partially affects host gene expression during infection. Together, our results illustrate that TLR4 is crucial for the innate ability to eliminate .