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Defensins (alpha and beta) are cationic peptides with a broad spectrum of antimicrobial activity that comprise an important arm of the innate immune system.  The α-defensins are distinguished from the β-defensins by the pairing of their three disulfide bonds.  To date, six human β-defensins have been identified; BD-1, BD-2, BD-3, BD-4, BD-5 and BD-6.  β-defensins are expressed on some leukocytes and at epithelial surfaces.  In addition to their direct antimicrobial activities, they can act as chemoattractants towards immature dendritic cells and memory T cells.  The β-defensin proteins are expressed as the C-terminal portion of precursors, and are released by proteolytic cleavage of a signal sequence and, in some cases, a propeptide sequence.  β-defensins contain a six-cysteine motif that forms three intra-molecular disulfide bonds.  Recombinant Human BD-2 is a 4.3 kDa protein containing 41 amino acid residues.