Inflammasome activation via intracellular NLRs triggered by bacterial infection

Members of the nucleotide-binding, oligomerization domain (NOD)-like receptor (NLR) proteins assemble into a multiprotein platform, known as the inflammasome, to induce caspase-1 activation followed by the subsequent secretion of IL-1β and IL-18. In this review, we focus on the role of NLRs in inflammasome activation as part of the host defence against bacterial pathogens. One of activators of the NLRC4 inflammasome is bacterial flagellin secreted through type III or IV secretion systems, which are important for the pathogenicity of many Gram-negative bacteria. The NLRP3 inflammasome is mainly activated by a large number of bacterial pore-forming toxins. Despite our knowledge of inflammasome activation upon bacterial infection, the function of antibacterial defence under in vivo conditions remains to be elucidated. Further understanding of NLR function should provide new insights into the mechanisms of host pro-inflammatory responses and the pathogenesis of bacterial infections.