Toll-Like Receptor 2 Deficiency Increases Resistance to Pseudomonas aeruginosa Pneumonia in the Setting of Sepsis-Induced Immune Dysfunction

Background. Sepsis is characterized by a dysregulated inflammatory response followed by immunosuppression that favors the development of secondary infections. Toll-like receptors (TLRs) are major regulators of the host's response to infections. How variability in TLR signaling may impact the development of sepsis-induced immune dysfunction has not been established. We sought to establish the role of TLR2, TLR4, and TLR5 in postseptic mice with Pseudomonas aeruginosa pneumonia. Methods. We used an experimental model of sublethal polymicrobial sepsis induced by cecal ligation and puncture (CLP). Wild-type, tlr2(-/-), tlr4(-/-), tlr5(-/-), tlr2 x 4(-/-) mice that underwent CLP were secondarily subjected to P. aeruginosa pulmonary infection. Results. Postseptic wild-type and tlr4(-/-) and tlr5(-/-) mice displayed high susceptibility to P. aeruginosa pneumonia. In contrast, TLR2-deficient mice, either tlr2(-/-)or tlr2 x 4(-/-), that underwent CLP were resistant to the secondary pulmonary infection. As compared to wild-type mice, tlr2(-/-) mice displayed improvement in bacterial clearance, decreased bacteremic dissemination, and attenuated lung damage. Furthermore, tlr2(-/-) mice exhibited a pulmonary proinflammatory cytokine balance, with increased production of tumor necrosis factor alpha and decreased release of interleukin 10. Conclusions. In a model of secondary P. aeruginosa pneumonia in postseptic mice, TLR2 deficiency improves survival by promoting efficient bacterial clearance and restoring a proinflammatory cytokine balance in the lung.