Neutrophil elastase (NE) is a serine proteinase in the same family as chymotrypsin and has broad substrate specificity. In humans, neutrophil elastase is encoded by the ELANE gene, which resides on chromosome 19. Secreted by neutrophils and macrophages during inflammation, it destroys bacteria and host tissue. Elastases form a subfamily of serine proteases that hydrolyze many proteins in addition to elastin.  Neutrophil elastase may play a role in degenerative and inflammatory diseases by its proteolysis of collagen-IV and elastin of the extracellular matrix. Neutrophil elastase is an important protease enzyme that when expressed aberrantly can cause emphysema or emphysematous changes. This involves breakdown of the lung structure and increased airspaces. Mutations of the ELANE gene cause severe congenital neutropenia, which is a failure of neutrophils to mature.

Neutrophil elastase  is expressed in developing granulocytes in the bone marrow, stored in the azurophilic  granules of mature neutrophils and released upon neutrophil activation or disintegration. Despite the fact that neutrophils carry large amount of NE, and are capable of synthesizing a variety of proteins, the NE gene is not expressed in mature neutrophils. Also, NE can be used as an additional marker to differentiate the involvement of neutrophilic myeloid cells. This marker is useful for differentiating leukemic infiltrates of myeloproliferative processes in lymph nodes and other organs from undifferentiated carcinomas and/or histiocytic sarcomas or large cell lymphomas. Neutrophil elastase is a useful aid for classification of acute myeloid leukemia and extramedullary myeloid cell tumors.