Role of Toll-like receptors in the development of sepsis

The outcome of sepsis and septic shock has not significantly improved in recent decades despite the development of numerous drugs and supportive care therapies. To reduce sepsis-related mortality, a better understanding of molecular mechanism(s) associated with the development of sepsis and sepsis-related organ injury is essential. There is increasing evidence that Toll-like receptors (TLRs) play a key role in the mediation of systemic responses to invading pathogens during sepsis. However, the role of TLRs in the development of sepsis and in sepsis-related organ injury remains debatable. In this review, we focus on the biological significance of TLRs during sepsis. Medline was searched for pertinent publications relating to TLRs, with emphasis on their clinical and pathophysiological importance in sepsis. In addition, a summary of the authors' own experimental data from this field was set in the context of current knowledge regarding TLRs. In both animal models and human sepsis, TLRs are highly expressed on monocytes/macrophages, and this TLR expression may not simply be a ligand-specific response in such an environment. The fact that TLR signaling enables TLRs to recognize harmful mediators induced by invading pathogens may be associated with a positive feedback loop for the inflammatory response among different cell populations. This mechanism(s) may contribute to the organ dysfunction and mortality that occurs in sepsis. A better understanding of TLR biology may unveil novel therapeutic approaches for sepsis.