THE ROLE OF PROTEGRINS AND OTHER ELASTASE-ACTIVATED POLYPEPTIDES IN THE BACTERICIDAL PROPERTIES OF PORCINE INFLAMMATORY FLUIDS

mammalian host response to infection includes the production and secre tion of antimicrobial peptides from phagocytes and epithelial cells. P rotegrins, a group of broadly microbicidal peptides isolated originall y from porcine neutrophil lysates, were found to he stored as inactive proforms in porcine neutrophil granules but could be activated extrac ellularly by neutrophil elastase, We assessed the biological role of p rotegrins and other elastase-activated polypeptides in the microbicida l activity of neutrophil secretions and inflammatory fluids. When stim ulated with phorbol myristate acetate (PMA), neutrophils generated sta ble microbicidal activity against both Escherichia coli and Listeria m onocytogenes under normal-salt conditions and in the presence of 0 to 10% serum. The generation of these antimicrobial substances was depend ent on neutrophil elastase, since it was inhibited by 1 mM N-methoxysu ccinyl-Ala-Ala-Pro-Val chloromethyl ketone when it was present during activation, but not when this inhibitor was added afterwards, However, elastase-dependent activation of proprotegrins to protegrins in PMA-s timulated neutrophils was not inhibited by the presence of 1 to 2% ser um. Porcine neutrophils also released antibacterial activity during ph agocytosis of latex beads, and this too was dependent in large part on elastase-activated polypeptides, including protegrins. Moreover, prot egrins were found at bactericidal concentrations in cell-free abscess fluid from naturally infected pigs, Taken together, these studies show that protegrins and other elastase-activated polypeptides are importa nt stable antibacterial factors in porcine neutrophil secretions, The potential host defense role of elastase as an activating enzyme for th e precursors of microbicidal peptides must be taken into account when therapeutic inhibitors of neutrophil elastase are evaluated for clinic al use as anti-inflammatory agents.