Defensins are 2-6 kDa, cationic, antimicrobial peptides active against many Gram-negative and Gram-positive bacteria, fungi, and enveloped viruses,[2] containing three pairs of intramolecular disulfide bonds.

On the basis of their size and pattern of disulfide bonding, mammalian defensins are classified into alpha, beta and theta categories.

Alpha-defensins, which have been identified in humans, monkeys and several rodent species, are particularly abundant in neutrophils, certain macrophage populations and Paneth cells of the small intestine.

The topology that arises from this structure is an amphipathic globular form in which the termini are paired opposite a pole including a cluster of cationic residues.

[4] Sequences of major human α-defensins:[5] Genes encoding cryptdins are located on the proximal arm of mouse chromosome 8.

[6] Biosynthesized as precursors possessing an anionic, N-terminal proregion, cryptdins are packaged into the apically directed secretory granules of Paneth cells.

[7] With the ability to kill gram-positive and gram-negative bacteria, fungi, spirochetes and some enveloped viruses, cryptdins are classified as broad-spectrum antimicrobial peptides.

There, cryptdins, along with other antimicrobial peptides expressed by Paneth cells, contribute to enteric mucosal innate immunity by clearing the intestinal crypt of potential invading pathogens.

This might be further reinforced by the capacity of some human and rabbit alpha-defensins to inhibit the production of immunosuppressive glucocorticoids by competing for the binding of adrenocorticotropic hormone to its receptor.

[11] The Virtual Colony Count antibacterial assay was originally developed to measure the activity of all six human alpha defensins on the same microplate.

Cryptdins are the protein products of a related family of highly polymorphic genes that are specifically expressed by mouse Paneth cells at the base of intestinal crypts.