Abstract
Detection of bacterial ligands is a pre-requisite for inflammasome activation. During Pseudomonas aeruginosa infection, flagellin which is secreted through the T3SS is detected by the NLRC4 inflammasome. Activation of the NLRC4 inflammasome is believed to contribute to high IL-1β production and pathogenicity in cystic fibrosis patients with chronic P. aeruginosa infection. Interestingly, the majority of P. aeruginosa isolated from cystic fibrosis patients with chronic airway infection are non-motile and T3SS-negative, suggesting that yet un-characterized inflammasome pathways regulate IL-1β production in cystic fibrosis patients. Here we demonstrate the role of guanylate-binding proteins (GBPs) in regulating bacterial proliferation and inflammasome activation in response to T3SS-negative P. aeruginosa. Bacterial ligands liberated by the action of GBP2 and IRGB10 activate caspase-11 and regulate non-canonical NLRP3 inflammasome activation and IL-1β release. Overall, our results reveal the role of caspase-11 in inhibiting bacterial proliferation and promoting IL-1β secretion during T3SS-negative P. aeruginosa infection. This study suggests that non canonical inflammasomes might have co-evolved to detect Gram-negative bacterial pathogens that have evolved to bypass detection by canonical NLRs.