The role of endosomal toll-like receptors in bacterial recognition

BACKGROUND: Infections caused by extracellular Gram positive bacteria are still a major health problems. Better understanding of the mechanisms underlying immune responses to these organisms is key to develop pharmacological agents, including vaccines, to control these infections. OBJECTIVE AND PERSPECTIVES: The objective of this review is to highlight the importance of nucleic acid-sensing, intracellular Toll-like receptors in innate immune recognition and in host defenses against extracellular bacteria. CONCLUSIONS: Toll-like receptors 7 and 9 have a major role in inducing host-protective type I interferon responses in conventional dendritic cells in response to streptococci and other extracellular gram positive bacteria. Moreover an as yet unidentified MyD88-dependent receptor is likely responsible for proinflammatory cytokine induction in response to these pathogens.