Toll-like receptors in human infectious diseases

Toll-like receptors (TLRs) have emerged as critical players in immunity. They are capable of sensing organisms ranging from protozoa to bacteria, fungi or viruses upon detection of the pathogen as well as recognizing endogenous ligands, and triggering transduction pathways. Following activation of the innate immune system, strong inflammatory signals are generated inducing inflammation and activation of the adaptive immune response. However, the deregulation of TLRs signaling pathways may be conducive to the pathogenesis of many infectious diseases. Therefore, innate and adaptive immunity are not simply sequential and complementary mechanisms of resistance to pathogen, they regulate each other through cellular contacts and the secretion of soluble mediators. Herein, we summarize recent findings on TLRs signaling in infectious diseases and how pathogens have developed strategies to evade these pathways. In this context, a potential modulation of the innate immune response could have therapeutic benefit through the development of new drugs as well as vaccination strategies to be employed in infectious diseases.