Multiple Functions of Neutrophil Proteinases and their Inhibitor Complexes

During inflammatory episodes neutrophils are recruited to the site of injury where they function as scavengers by killing bacteria and ingesting and degrading foreign and damaged human proteins. As a consequence of these processes significant quantities of neutrophil proteins are released extracellularly, both through cell leakage and cell death. This places a heavy burden on normal, healthy tissues which may now become susceptible to attack by neutrophil-derived oxidizing agents (myeloperoxidase-derived) and proteinases [primarily elastase (HNE) and cathepsin G (cat G)]. It is not clear as to how the body regulates the activity of myeloperoxidase, although it is likely that this involves the use of catalase in order to reduce H2O2 levels; however, to offset the possibility of protei-nase damage the body offers a series of inhibitors, primarily plasma derived, which function to specifically inactivate these enzymes. In particular, it is now known that human plasma α1 proteinase inhibitor (α1PI) regulates the activity of HNE while cat G is controlled by α1 antichymotrypsin (α1Achy).2