HNP-1

Where it comes from

Made in

Neutrophils, which store it in their azurophilic granules; some in natural killer and T cells and in monocytes

Sent out by

When the neutrophil swallows a microbe or dies at a site of infection

Acts on

• Bacteria, fungi and enveloped viruses
• Immune cells (chemotaxis)
• Host cells at high concentration

What it does

• Kills microbes inside the phagosome
• Blocks bacterial toxins (anthrax lethal factor, diphtheria toxin) by binding them
• Attracts T cells and immature dendritic cells
• Toxic to the body’s own cells at high levels, as in inflamed lungs

In medicine

• Measured in research as a marker of neutrophil activation; high in the sputum of cystic fibrosis and in sepsis
• No medicine. Its gene sits in a tandem array of four to eleven copies per person, and the proportions of HNP-1 and HNP-3 follow the copies ³

Beyond the body’s own use

• Defensins inspired many antimicrobial peptide drugs; none built on HNP-1 has reached approval
• It binds and neutralises anthrax lethal toxin, and protected mice against a lethal dose of it, which is studied as a way to blunt toxin-driven disease ²
• Copy number of the gene array is studied as a risk factor in infection; what it does to the total amount of defensin a person makes is not settled ³