Neutrophils, also known as neutrophilic polymorphonuclear leukocytes, are the major class of white blood cell in human peripheral blood. They, have a multilobed nucleus and neutrophilic granules, and are phagocytes and have an important role in engulfing and killing extracellular pathogens.

The neutrophil form of elastase is 218 amino acids long, with two asparagine-linked carbohydrate chains. Current studies show that both Cathepsin G and Neutrophil Elastase are key enzymes for tissue injury caused by activated neutrophils, such as occurs in Acute Lung injury.