Defensins are a family of microbicidal and cytotoxic peptides thought to be involved in host defense. They are abundant in the granules of neutrophils and also found in the epithelia of mucosal surfaces such as those of the intestine, respiratory tract, urinary tract, and vagina. Members of the defensin family are highly similar in protein sequence and distinguished by a conserved cysteine motif. Several of the alpha defensin genes appear to be clustered on chromosome 8.

DEF5 is highly expressed in Paneth cells of the small intestine, making it the first example of an antimicrobial peptide gene expressed in human epithelial cells. Their data supported the hypothesis that epithelial defensins equip the human bowel with a defensive capability that augments other antimicrobial activities.