SERPINB1 is a member of the serpin family and Ov-serpin subfamily. As protease inhibitors, serpins have an array of functions including regulating blood coagulation, fibrinolysis, the complement pathway, angiogenesis, inflammation, tumor suppression, extracellular matrix remodeling, and cell motility. SERPINB1 regulates the activity of the neutrophil proteases elastase, cathepsin G, proteinase-3, chymase, chymotrypsin, and kallikrein-3. Reactive bond 1 of SerpinB1 is specific for reaction with chymotrypsin-like protease such as cathepsin G, chymotrypsin or chymase. Reactive bond 2 of SerpinB1 is specific for reaction with elastase-like protease such as neutrophyl elastase, proteinase-3, pancreatic elastase or PSA. In addition, SERPINB1 also functions as a potent intracellular inhibitor of granzyme H.