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. Author manuscript; available in PMC: 2016 Jan 31.
Published in final edited form as: Curr Opin Immunol. 2015 Jan 24;0:84–89. doi: 10.1016/j.coi.2015.01.010

Figure 1. Specific detection of bacterial ligands by NAIPs.

Figure 1

The needle or rod components of bacterial type III secretion systems (T3SS) are detected in the host cell cytosol by mouse NAIP1 or mouse NAIP2, respectively. Flagellin, the main structural protein comprising the flagellum, is detected by mouse NAIP5 or NAIP6. Human NAIP (hNAIP) detects the T3SS needle only and does not detect flagellin. Once NAIPs are activated in the presence of their cognate ligands, they co-assemble with NLRC4 to form an inflammasome that recruits and activates Caspase-1 (CASP1). The precise mechanism by which the needle and rod proteins access the host cell cytosol remains to be determined and may not involve direct secretion via the T3SS as shown.