Human neutrophil alpha-defensins (Human Neutrophil Peptides, HNP) belong to the family of cationictrisulfide-containing microbicidal peptides. Three highly homologous human defensins stored inazurophilic granules of polymorphonuclear leukocytes (PMN), HNP 1-3, account for about 5% of totalPMN protein and comprise about 99% of the total defensin content of the neutrophils with traces ofHNP-4.HNP-1, HNP-2 and HNP-3 are encoded by two genes DEFA1 and DEFA3 localized to chromosome 8.Number of gene copies substantially varies between individuals with complete lack of the DEFA3 allelein 10% subjects. DEFA1 and DEFA3 encode identical peptides except the conversion of the first aminoacid from alanine in HNP-1 to aspartic acid in HNP-3; HNP-2 represent N-terminally truncated iso-formlacking the first amino acid.HNP 1-3 are capable to kill and/or inactivate a broad spectrum of bacteria, fungi or some envelopedviruses and have recently been shown to exert the anti-HIV activity produced by CD8+ T cells of HIVnonprogressors.HNP 1-3 have the potential to modulate immune response and inflammation byinducing the chemokine interleukin-8 (IL-8) in epithelial cells and modulating cytokine expression inseveral cell types and causing chemotaxis to monocytes, T cells and immature dendritic cells.Defensins are relatively resistant to proteolysis, low pH and boiling. Activation of neutrophils leads torapid release of HNP. HNP can be measured in plasma and other body fluids during infection andinflammation. Micromolar concentrations of HNP are described in septic blood, while in normal plasmavery low levels of HNP are present. (HNP 1-3 can be measured using Human Neutrophil Defensin 1-3(HNP 1-3) ELISA, Cat. # HK317).