Acid-stable proteinase inhibitor with strong affinities for trypsin, chymotrypsin, elastase, and cathepsin G (PubMed:9126337). Modulates the innate immune response after bacterial infection (PubMed:12615907). Contributes to regulate the inflammatory and immune responses to the intracellular parasite L.major (PubMed:25030421). Down-regulates responses to bacterial lipopolysaccharide (LPS) (PubMed:9039268, PubMed:12615907, PubMed:25030421). Plays a role in regulating the activation of NF-kappa-B and inflammatory responses (PubMed:11017147, PubMed:12615907). Has antimicrobial activity against mycobacteria, but not against salmonella (PubMed:18322212). Contributes to normal resistance against infection by M.tuberculosis (PubMed:18322212). Required for normal resistance to L.major (PubMed:25030421). Required for normal wound healing, probably by preventing tissue damage by limiting protease activity (PubMed:11017147, PubMed:25030421). Together with ELANE, required for normal differentiation and proliferation of bone marrow myeloid cells (By similarity). Interacts with GRN; interaction protects progranulin from proteolysis. Detected in bronchial epithelial cells (PubMed:18322212). Detected in bronchoalveolar fluid after infection with M.tuberculosis (at protein level) (PubMed:18322212). Highest expression in lung, spleen, intestine and epididymis with lower levels in liver and seminal vesicle. No expression in brain, heart, kidney and muscle. Up-regulated by bacterial lipopolysaccharide (PubMed:9039268, PubMed:25030421). Up-regulated in lung after infection with M.tuberculosis (PubMed:18322212). Down-regulated by IFNG (PubMed:9039268). Up-regulated in lung in response to bacterial pneumonia (PubMed:9351627). Up-regulated in macrophages after exposure to L.major (PubMed:25030421). Not up-regulated in spleen in response to bacterial pneumonia (PubMed:9351627). Up-regulated in wounded skin (PubMed:11017147). Mutant mice show delayed epithelial wound healing and an increased inflammatory response at the site of wounding, possibly due to increased elastase activity (PubMed:11017147, PubMed:25030421). Mutant mice show an increased tendency to die from toxic shock after exposure to bacterial lipopolysaccharide (LPS) (PubMed:12615907). Mutant mice are highly susceptible to M.tuberculosis; all die within 50 days after infection (PubMed:18322212). Mutant mice are highly susceptible infection by L.major. Contrary to what is observed with wild-type, the parasites are not restricted to the initial site of infection, but spread to spleen, liver and bone morrow. The skin lesions at the initial site of infection do not heal normally, but become bigger over time, in parallel with the spread of the parasites. The inflammatory response at the site of infection is more intense and persists longer than normal. Increased protease activity is observed in these lesions and may be the cause of the extensive tissue damage and necrosis (PubMed:25030421).