The term defensin relates to a set of host defense peptides (HDPs)in vertebrates, invertebrates, plants, and
molds that display structural similarities based on a cystine stabilized antiparallel bet-sheetcore, with an
alpha-helical stretch also present in some membrers, Defensins of different origins exhibit structural and
functional similarities, with phylogenetic relationships between invertebrate and plant defensins, and
between different types of vertebrate defensisn, and a possible common bacterl ancestor. Most defensins
demonstrate a direct anbtimicrobial action in vitro with varyiing activity spectra. This requires
interaction with components of the microbial cell wall, and often involves membrane permeabilization,
although the mode of action differes markedly for defensins both within and from different families.
Defensins also play important regulatory roles in the immune system of animals and plants,acting as a bridge
between innate and adaptive immunity in vertebrates. Roles outside host defense have also been reported.
