Caspase inhibitor. Acts as a regulator of procaspase-1/CASP1 activation implicated in the regulation of the proteolytic maturation of pro-interleukin-1 beta (IL1B) and its release during inflammation. Inhibits the release of IL1B in response to LPS in monocytes. Also induces NF-kappa-B activation during the pro-inflammatory cytokine response. Also able to inhibit CASP1-mediated neuronal cell death, TNF-alpha, hypoxia-, UV-, and staurosporine-mediated cell death but not ER stress-mediated cell death. Acts by preventing activation of caspases CASP1 and CASP4, possibly by preventing the interaction between CASP1 and RIPK2. Homooligomer. Interacts with CASP1, CASP4, CARD8 and RIPK2. Widely expressed. Expressed at higher level in placenta, spleen, lymph node and bone marrow. Weakly or not expressed in thymus. Down-regulated in patients suffering of Huntington disease.