Caspase-1 activation by NLRP3 inflammasome dampens IL-33-dependent house dust mite-induced allergic lung inflammation

The cysteine protease caspase-1(Casp-1)contributes to innate immunity through the assembly of NLRP3,NLRC4,AIM2,and NLRP6 inflammasomes.Here we ask whether caspase-1 activation plays a regulatory role in house dust mite(HDM)-induced experimental allergic airway inflammation.We report enhanced airway inflammation in caspase-1-deficient mice exposed toHDMwith a marked eosinophil recruitment,increased expression of IL-4,IL-5,IL-13,aswell as full-length and bioactive IL-33.Furthermore,mice deficient for NLRP3 failed to control eosinophil influx in the airways and displayed augmented Th2 cytokine and chemokine levels,suggesting that the NLPR3 inflammasome complex controls HDM-induced inflammation.IL-33 neutralization by administration of soluble ST2 receptor inhibited the enhanced allergic inflammation,while administration of recombinant IL-33 during challenge phase enhanced allergic inflammation in caspase-1-deficient mice.Therefore,we show that caspase-1,NLRP3,and ASC,but not NLRC4,contribute to the upregulation of allergic lung inflammation.Moreover,we cannot exclude an effect of caspase-11,because caspase-1-deficient mice are deficient for both caspases.Mechanistically,absence of caspase-1 is associated with increased expression of IL-33,uric acid,and spleen tyrosine kinase(Syk)production.This study highlights acritical role of caspase-1 activation andNLPR3/ASCinflammasomecomplex in the down-modulation of IL-33 in vivo and in vitro,thereby regulating Th2 response in HDM-induced allergic lung inflammation.

Inflammasome-IL-1-Th17 response in allergic lung inflammation

Allergic asthma has increased dramatically in prevalence and severity over the last three decades.Both clinical and experimental data support an important role of Th2 cell response in the allergic response.Recent investigations revealed that airway exposure to allergen in sensitized individuals causes the release of ATP and uric acid,activating the NLRP3 inflammasome complex and cleaving pro-IL-1b to mature IL-1b through caspase-1.The production of pro-IL-1b requires a toll-like receptor(TLR)4 signal which is provided by the allergen.IL-1b creates a pro-inflammatory milieu with the production of IL-6 and chemokines which mobilize neutrophils and enhance Th17 cell differentiation in the lung.Here,we review our results showing that NLRP3 inflammasome activation is required to develop allergic airway inflammation in mice and that IL-17 and IL-22 production by Th17 cells plays a critical role in established asthma.Therefore,inflammasome activation leading to IL-1b production contributes to the control of allergic asthma by enhancing Th17 cell differentiation.