[3][4] Azurophil granules, specialized lysosomes of the neutrophil, contain at least 10 proteins implicated in the killing of microorganisms.

[5] The genes encoding this protein, neutrophil elastase 2, and proteinase 3 are in a cluster located at chromosome 19pter.

All 3 genes are expressed coordinately and their protein products are packaged together into azurophil granules during neutrophil differentiation.

[4] This encoded protein is a member of the PA clan of proteases but it is not a serine proteinase, because the active site serine and histidine residues are replaced, making it a pseudoenzyme.

[6] In patients with fever, high plasma levels of HBP indicates that the patient is at high risk of developing sepsis with circulatory collapse.