It was found that in COPD patients, PBMCs treated with combustion-generated ultrafine particles (UFPs) released caspase-4-dependent inflammasome compared with healthy subjects, besides, IL-18 and IL-33 released from PBMCs of unstable COPD patients were found correlated to caspase-4 release, instead of caspase-1 or caspase-8-dependent (176). Here, CASP1 is linked to chronic obstructive pulmonary disease.