CTSG (Cathepsin G) is a serine protease found in azurophil granules of neutrophilic polymorphonuclear leukocytes. It is thought to function in the remodeling of connective tissue at sites of inflammation. It is involved in neuroinflammation and may be important in neurodegenerative diseases including Alzheimer’s disease. CTSG also plays a role in killing and digesting engulfed pathogens and it is antimicrobial, with bacteriocidal activity against S. aureus and N. gonorrhoeae. CTSG is involved in the pathogenesis of a number of diseases, including chronic obstructive pulmonary disease, acute respiratory distress syndrome, cystic fibrosis, rheumatoid arthritis, coronary artery disease, periodontitis, ischemic reperfusion injury, and bone metastasis. Additionally, CTSG variants are correlated with a greater risk of chronic postsurgical pain. In immunohistochemistry, CSTG has cytoplasmic positivity in lymphoid and hematopoietic cells. References: J Immunol October 1, 2015, 195 (7) 3325-3333, DOI: 10.4049/jimmunol.1501012; Curr Opin Microbiol. 2015 Feb;23:42-8, PMID: 25461571; Current Opinion in Rheumatology. 19 (3): 289–95, PMID: 17414958; Anatolian Journal of Cardiology. 16 (1): 23–8, PMID: 26467359; Mediators of Inflammation. 2015: 1–10, PMID: 26185359; Anesthesiology. 123 (4): 838–50, PMID: 26270939; J Neuroinflammation. 2018 Aug 27;15(1):240, PMID: 30149799