Table 1.

Neutrophil granules and their anti-microbial properties.

Protein Name	Function
Azurophil (primary) neutrophil granules
Azurocidin	Antibacterial activity (in particular, specific to Gram-bacteria) [16,18]
Neutrophil defensins	Antibacterial, fungicidal, and antiviral activities [19]
Myeloblastin	Serine protease; facilitates transendothelial neutrophil migration [16]
CD63 antigen	Cell surface receptor for TIMP1; activates cellular signalling cascades [20]
Cathepsin G	Serine protease, cleaves complement C3 and has antibacterial activity [21]
Neutrophil elastase (NE)	Modifies the functions of NK cells, monocytes, and granulocytes; inhibits C5a-dependent neutrophil enzyme release and chemotaxis [16,22]
Myeloperoxidase (MPO)	Microbicidal activity against a wide range of organisms [23]
Cap57	Antibacterial activity (Specific to Gram-bacteria) [16]
Specific (secondary) neutrophil granules
Chitinase-3-like protein 1	Important for inflammation [18]
Lipocalin 2	Iron-trafficking; involved in apoptosis, innate immunity, and renal development; limits bacterial proliferation [24]
Lactoferrin	Antimicrobial activity; stimulates TLR4 signalling, binds heparin [16]
Gelatinase (tertiary) neutrophil granules
Matrix metalloproteinase-9 (MMP-9)	Cleaves gelatin types I and V and collagen types IV and V; important roles in leukocyte migration [25]
Ficolin-1	Anti-microbial pattern-recognition receptor
Cathelicidin antimicrobial peptide	Antibacterial activity; cleaved into 2 antimicrobial peptides FALL-39 and LL-37 [26]
Neutrophil collagenase	Degrades fibrillar collagens (type I, II, and III) [27]