Neutrophil elastase, also known as Elastase-2, Bone marrow serine protease, Medullasin, ELANE, and ELA2, is a serine proteinase in the same family as chymotrypsin and has broad substrate specificity. Secreted by neutrophils during inflammation, it destroys bacteria and host tissue. As with other serine proteinases, ELANE / ELA2 contains a charge relay system composed of the catalytic triad of histidine, aspartate, and serine residues that are dispersed throughout the primary sequence of the polypeptide but that are brought together in the three dimension conformation of the folded protein.ELANE / ELA2 is an important protease enzyme that when expressed aberrantly can causeemphysemaor emphysematous changes. This involves breakdown of the lung structure and increased airspaces. Elastases form a subfamily of serine proteases that hydrolyze many proteins in addition to elastin. ELANE / ELA2 hydrolyzes proteins within specialized neutrophil lysosomes, called azurophil granules, as well as proteins of the extracellular matrix following the protein's release from activated neutrophils. ELANE / ELA2 may play a role in degenerative and inflammatory diseases by its proteolysis of collagen-IV and elastin of the extracellular matrix. ELANE / ELA2 degrades the outer membrane protein A (OmpA) of E. coli as well as the virulence factors of such bacteria as Shigella, Salmonella and Yersinia. Defects in ELANE are a cause of cyclic haematopoiesis (CH), also known as cyclic neutropenia. CH is an autosomal dominant disease in which blood-cell production from the bone marrow oscillates with 21-day periodicity. Defects in ELANE are also the cause of autosomal dominant severe congenital neutropenia type 1 (SCN1) which is a heterogeneous disorder of hematopoiesis.