Correlation between cytotoxicity induced by Pseudomonas aeruginosa clinical isolates from acute infections and IL-1 beta secretion in a model of human THP-1 monocytes

摘要

abstract_textpType III secretion system (T3SS) in Pseudomonas aeruginosa is associated with poor clinical outcome in acute infections. T3SS allows for injection of bacterial exotoxins (e. g. ExoU or ExoS) into the host cell, causing cytotoxicity. It also activates the cytosolic NLRC4 inflammasome, activating caspase-1, inducing cytotoxicity and release of mature IL-1 beta, which impairs bacterial clearance. In addition, flagellum-mediated motility has been suggested to also modulate inflammasome response and IL-1 beta release. Yet the capacity of clinical isolates to induce IL-1 beta release and its relation with cytotoxicity have never been investigated. Using 20 clinical isolates from acute infections with variable T3SS expression levels and human monocytes, our aim was to correlate IL-1 beta release with toxin expression, flagellar motility and cytotoxicity. ExoU-producing isolates caused massive cell death but minimal release of IL-1 beta, while those expressing T3SS but not ExoU (i. e. expressing ExoS or no toxins) induced caspase-1 activation and IL-1 beta release, the level of which was correlated with cytotoxicity. Botheffects were prevented by a specific caspase-1 inhibitor. Flagellar motility was not correlated with cytotoxicity or IL-1 beta release. No apoptosis was detected. Thus, T3SS cytotoxicity is accompanied by a modification in cytokine balance for P. aeruginosa clinical isolates that do not express ExoU./p/abstract_text