Defensins are small cation proteins found in animals and plants. They are host defence peptides. They work against bacteria, fungi and many viruses.
Defensins have 18-45 amino acids including six to eight conserved cysteine residues. Cells of the immune system have these peptides to help kill phagocytosed bacteria. Those cells include neutrophil granulocytes and almost all epithelial cells. Most defensins work by binding to the microbial cell membrane. Once there, they make tiny holes in the membrane which allow vital ions and nutrients to leak out.