Bacterial triggering of inflammation by intracellular sensors

Recognition of bacterial infection is the first key step to the initiation of an inflammatory response and host defense. Transmembrane proteins of the Toll-like receptor family have long been recognized as key detectors of the extracellular presence of pathogens. Recently, much research has identified a variety of intracellular detectors that also mediate innate immune responses following bacterial infection. These cannot only recognize bacteria that invade the cell cytoplasm, but also a variety of bacterial products that are introduced into cells by specialized secretion systems or are secreted toxins. This article will focus on these intracellular detectors and the bacterial components that they recognize. These detectors are particularly well adapted to recognize the presence of pathogenic bacteria as opposed to commensal organisms. Their growing importance suggests that targeting such intracellular pathways may be important in the future for manipulating the immune response to infection as an aid to augmenting host defense and providing more effective vaccines.