Acid-stable proteinase inhibitor with strong affinities for trypsin, chymotrypsin, elastase, and cathepsin G. Modulates the inflammatory and immune responses after bacterial infection, and after infection by the intracellular parasite L.major. Down-regulates responses to bacterial lipopolysaccharide (LPS). Plays a role in regulating the activation of NF-kappa-B and inflammatory responses. Has antimicrobial activity against mycobacteria, but not against salmonella. Contributes to normal resistance against infection by M.tuberculosis. Required for normal resistance to infection by L.major. Required for normal wound healing, probably by preventing tissue damage by limiting protease activity (By similarity). Together with ELANE, required for normal differentiation and proliferation of bone marrow myeloid cells (By similarity). Interacts with GRN; interaction protects progranulin from proteolysis. Found in pregnant endometrium and myometrium, placenta, allantoic fluids, fetal cord blood, and fetal liver. Also found in uterus and lung. Levels in endometrium, allantoic fluids, and fetal cord blood change with the stage of pregnancy. Maximal expression found at mid- and late gestation (at protein level). By estrogen and progesterone; in uterus.