Defensins are cationic peptides. It is an important ingredient of the innate immune system. β-defensins are expressed on some leukocytes and epithelial surfaces. Four human β-Defensins have been identified to date: BD-1, BD-2, BD-3 and BD-4. β-defensins contain a six-cysteine motif, they forms three intra-molecular disulfide bonds. β-defensins are also chemoattractant towards immature dendritic cells and memory T cells. The β-defensin proteins are expressed as the C-terminal portion of precursors; they are released by proteolytic cleavage of a signal sequence.