Human Neutrophil Elastase (HNE) belongs to the chymotrypsin family of serine proteases able to solubilize fibrous elastin, an important extracellular matrix protein that has the unique property of elastic recoil, and plays a major structural function in lungs, arteries, skin and ligaments. HNE is primarily located in the azurophil granules of polymorphonuclear leucocytes, but has also been detected in nuclear membrane, Golgi complex, ER and the mitochondria of these cells.  The enzyme is involved in tissue destruction and inflammation, and implicated in numerous diseases including emphysema, chronic obstructive pulmonary disease, cystic fibrosis, ischemic-reperfusion injury and rheumatoid arthritis.

NP57 is a useful tool for the differential diagnosis of acute leukaemia by APAAP labeling of cell smears.  It may also be of value for the histopathological  diagnosis of tumour deposits in myeloid leukaemia and for the detection ofn eutrophils in paraffin sections

Pulford KAF, Erber WN, Crick JA, Olsson I, Micklem KJ, Gatter KC, Mason DY (1988) Use of monoclonal antibody against human neutrophil elastase in normal and leukaemic myeloid cells. J Clin Pathol 41:853-860

Ralfkiaer E, Pulford KA, Lauritzen AF, Avnstrom S, Guldhammer B, Mason DY (1989) Diagnosis of acute myeloid leukaemia with the use of monoclonal anti-neutrophil elastase (NP57) reactive with routinely processed biopsy samples. Histopathology 14:637-643