Serine protease with trypsin- and chymotrypsin-like specificity (PubMed:29652924, PubMed:8194606). Also displays antibacterial activity against Gram-negative and Gram-positive bacteria independent of its protease activity (PubMed:2116408, PubMed:2117044). Prefers Phe and Tyr residues in the P1 position of substrates but also cleaves efficiently after Trp and Leu (PubMed:29652924). Shows a preference for negatively charged amino acids in the P2' position and for aliphatic amino acids both upstream and downstream of the cleavage site (PubMed:29652924). Required for recruitment and activation of platelets which is mediated by the F2RL3/PAR4 platelet receptor (PubMed:10702240, PubMed:3390156). Binds reversibly to and stimulates B cells and CD4(+) and CD8(+) T cells (PubMed:7842483, PubMed:9000539). Also binds reversibly to natural killer (NK) cells and enhances NK cell cytotoxicity through its protease activity (PubMed:9000539, PubMed:9536127). Cleaves complement C3 (PubMed:1861080). Cleaves vimentin (By similarity). Cleaves thrombin receptor F2R/PAR1 and acts as either an agonist or an inhibitor, depending on the F2R cleavage site (PubMed:10702240, PubMed:7744748). Cleavage of F2R at '41-Arg-|- Ser-42' results in receptor activation while cleavage at '55-Phe-|-Trp- 56' results in inhibition of receptor activation (PubMed:7744748). Cleaves the synovial mucin-type protein PRG4/lubricin (PubMed:32144329). Cleaves and activates IL36G which promotes expression of chemokines CXCL1 and CXLC8 in keratinocytes (PubMed:30804664). Cleaves IL33 into mature forms which have greater activity than the unprocessed form (PubMed:22307629). Cleaves coagulation factor F8 to produce a partially activated form (PubMed:18217133). Also cleaves and activates coagulation factor F10 (PubMed:8920993). Cleaves leukocyte cell surface protein SPN/CD43 to release its extracellular domain and trigger its intramembrane proteolysis by gamma-secretase, releasing the CD43 cytoplasmic tail chain (CD43-ct) which translocates to the nucleus (PubMed:18586676). Cleaves CCL5/RANTES to produce RANTES(4-68) lacking the N-terminal three amino acids which exhibits reduced chemotactic and antiviral activities (PubMed:16963625). During apoptosis, cleaves SMARCA2/BRM to produce a 160 kDa cleavage product which localizes to the cytosol (PubMed:11259672). Cleaves myelin basic protein MBP in B cell lysosomes at '224-Phe-|-Lys-225' and '248-Phe-|-Ser-249', degrading the major immunogenic MBP epitope and preventing the activation of MBP-specific autoreactive T cells (PubMed:15100291). Cleaves annexin ANXA1 and antimicrobial peptide CAMP to produce peptides which act on neutrophil N-formyl peptide receptors to enhance the release of CXCL2 (PubMed:22879591). Acts as a ligand for the N-formyl peptide receptor FPR1, enhancing phagocyte chemotaxis (PubMed:15210802). Has antibacterial activity against the Gram-negative bacteria N.gonorrhoeae and P.aeruginosa (PubMed:1937776, PubMed:2116408). Likely to act against N.gonorrhoeae by interacting with N.gonorrhoeae penA/PBP2 (PubMed:2126324). Exhibits potent antimicrobial activity against the Gram-positive bacterium L.monocytogenes (PubMed:2117044). Has antibacterial activity against the Gram-positive bacterium S.aureus and degrades S.aureus biofilms, allowing polymorphonuclear leukocytes to penetrate the biofilm and phagocytose bacteria (PubMed:2117044, PubMed:32995850). Has antibacterial activity against M.tuberculosis (PubMed:15385470). Mediates CASP4 activation induced by the Td92 surface protein of the periodontal pathogen T.denticola, causing production and secretion of IL1A and leading to pyroptosis of gingival fibroblasts (PubMed:29077095). Induces platelet aggregation which is strongly potentiated in the presence of ELANE (PubMed:25211214, PubMed:9111081). {ECO:0000250|UniProtKB:P28293, ECO:0000269|PubMed:10702240, ECO:0000269|PubMed:11259672, ECO:0000269|PubMed:15100291, ECO:0000269|PubMed:15210802, ECO:0000269|PubMed:15385470, ECO:0000269|PubMed:16963625, ECO:0000269|PubMed:18217133, ECO:0000269|PubMed:18586676, ECO:0000269|PubMed:1861080, ECO:0000269|PubMed:1937776, ECO:0000269|PubMed:2116408, ECO:0000269|PubMed:2117044, ECO:0000269|PubMed:2126324, ECO:0000269|PubMed:22307629, ECO:0000269|PubMed:22879591, ECO:0000269|PubMed:25211214, ECO:0000269|PubMed:29077095, ECO:0000269|PubMed:29652924, ECO:0000269|PubMed:30804664, ECO:0000269|PubMed:32144329, ECO:0000269|PubMed:32995850, ECO:0000269|PubMed:3390156, ECO:0000269|PubMed:7744748, ECO:0000269|PubMed:7842483, ECO:0000269|PubMed:8194606, ECO:0000269|PubMed:8920993, ECO:0000269|PubMed:9000539, ECO:0000269|PubMed:9111081, ECO:0000269|PubMed:9536127}. (Microbial infection) Inhibited reversibly by S.aureus serine protease inhibitors Eap, EapH1 and EapH2, impairing microbicidal activity in neutrophils. {ECO:0000269|PubMed:25161283, ECO:0000269|PubMed:32303641, ECO:0000269|PubMed:36736422, ECO:0000269|PubMed:37269950, ECO:0000269|PubMed:39098536}. This is the function of ENSG00000100448 (CTSG, cathepsin G).