Regulates the activity of the neutrophil proteases. Forms only a stable complex with CTSG/Cathepsin G (PubMed:12189154). During inflammation, limits the activity of inflammatory caspases CASP1 and CASP4 by suppressing their caspase-recruitment domain (CARD) oligomerization and enzymatic activation (PubMed:30692621). Monomer. Interacts (via C-terminus) with CASP1 and CASP4 (via CARD domain); these interactions regulate the activity of inflammatory caspases. Expressed in brain with lower expression in lung, spleen and testis. Belongs to the serpin family. Ov-serpin subfamily.