초록/요약

Streptococcus pneumoniae, also called pneumococcus, is a major cause of infectious disease in human. Pneumococcus resides in the nasopharynx as an upper respiratory commensal, and most of pneumococcal colonizations are asymptomatic in immunocompetent individuals. When nasopharyngeal mucosal homeostasis is disrupted, pneumococcus migrates into middle ear and lower respiratory tract and causes detrimental colonization. In this regard, the epithelial cells of middle ear and lung act as first line of defense against pneumococcus to prevent invasive pneumococcal diseases. Respiratory epithelial cells express various cell-surface and intra-cellular receptors sensing microbial pathogens and respond to sensed pathogens by triggering intra-cellular signaling pathways and inducing pathogen-specific innate immune responses. Various epithelial cell-surface and intra-cellular receptors, such as Toll-like receptors (TLRs), Nod-like receptors (NLRs), intracellular DNA sensing receptors, and scavenger receptors (SRs), participate in sensing of pneumococcus, and the activation of these receptors by pneumococcal components induces anti-pneumococcal innate immune responses including epithelial apoptosis and inflammatory cytokine/chemokine expressions. Epithelial sensing of pneumococcus is a critical step for setting an early defense against pneumococcal infection, and also is required to recruit and activate innate immune cells and trigger adaptive immunity.