Serpin peptidase inhibitor, clade B (ovalbumin), member 9 (SERPINB9)

Serpin peptidase inhibitor, clade B (ovalbumin), member 9 (SERPINB9 or Serpin B9) is an intracellular serine protease inhibitor predominantly known for inhibiting granzyme B, a key cytotoxic molecule released by cytotoxic T lymphocytes and natural killer cells to induce apoptosis in target cells[1][2][3][6]. SERPINB9 acts as a cellular safeguard in immune and non-immune cells, including cytotoxic lymphocytes, dendritic cells, and tissues such as placenta, by binding and inactivating granzyme B, thereby preventing self-inflicted or bystander cell death during immune responses[1][2][3][6]. It is widely implicated in cancer progression, immune evasion, inflammation, viral infection, autoimmune disorders, cardiovascular conditions, and transplantation biology[1][2][6]. While its inhibition of granzyme B confers cellular protection, aberrant expression can allow tumor cells and pathogens to evade the immune system, making SERPINB9 a molecule of interest in immuno-oncology, autoimmunity, and transplantation research[1][2]. No direct small molecule drugs are currently in clinical use to modulate SERPINB9, but its role and expression level can impact response to immunotherapies and is actively being studied as a potential biomarker in several clinical settings[1][2].

Other names

Serpin B9PI-9PI9CAP-3CAP3Cytoplasmic antiproteinase 3Peptidase inhibitor 9Protease inhibitor 9 (ovalbumin type)Testicular tissue protein Li 180

Inhibits granzyme B by forming a covalent inhibitory complex, blocking its proteolytic activity and preventing granzyme B–induced apoptosis in target cells[1][2][3][5][6]. Weakly inhibits other proteases, including caspase-1 and, to a lesser extent, caspase-4, caspase-8, subtilisin A, and neutrophil elastase[2].