Human neutrophil defensins (alpha-defensins) belong to the family of cationic trisulfide-containingmicrobicidal peptides. Besides microbicidal, the peptides exert chemotactic, immunomodulating andcytotoxic activity and participate in host defense and inflammation. Defensins are important effectormolecules against enveloped viruses, bacteria, fungi and protozoa, and protein concentrationsranging from 0.5 to 5 μM were shown to kill a wide range of microbes in vitro. Defensins have theability to attack susceptible microorganisms and destroy the structure of target cell membranes and.Several members of each defensin family were shown to act as microbicides against distinct Gramnegativeand Gram-positive bacteria, as well as fungi and viruses in vitro.Azurophilic granules of neutrophils contain Human Neutrophil Peptide (HNP) 1-4, which are highlyhomologous. The three principal human defensins, HNP 1-3, are unique to neutrophils and accountfor about 99% of the total defensin content of these cells. Defensins HNP 1-3 are almost exclusivelyexpressed in neutrophils, therefore it is considered a neutrophil cell marker. Measured amount ofdefensins is 3-5 microgram per million human neutrophils. When treated with HNP the outermembrane of Escherichia coli becomes permeable. This permeabilization furthermore coincided withthe cessation of RNA, DNA and protein synthesis, and with a decreased bacterial viability Defensinsare relatively resistant to proteolysis, low pH and boiling. Activation of neutrophils leads to rapidrelease of HNP. HNP can be measured in plasma and other body fluids during infection andinflammation. In normal plasma very low levels of HNP are present. Activation of polymorphonuclearleukocytes (PMN) in plasma, as occurs during clotting of blood, leads to a rapid release of HNP.Anti HNP 1-3 antibody clone D21 recognizes natural HNP 1-3 in biological solutions by means ofELISA in tissue sections and leukocyte smears fixed with ethanol, methanol/acetone orparaformaldehyde, in flow cytometry analysis of human neutrophils stained by cell permeabilizationmethod and in Western-blotting (non-reduced). Furthermore the antibody is cross reactive withRhesus monkey and cynomolgous macaques HNP1-3.