Defensins are endogenous peptides with cysteine-rich antimicrobial ability that 
contribute to host defence against bacterial, fungal and viral infections. There 
are three subfamilies of defensins in primates: α, β and θ-defensins. 
α-defensins are most present in neutrophils and Paneth cells; β-defensins are 
involved in protecting the skin and the mucous membranes of the respiratory, 
genitourinary and gastrointestinal tracts; and θ-defensins are physically 
distinguished as the only known fully-cyclic peptides of animal origin, which 
are first isolated from rhesus macaques. All three kinds of defensins have six 
conserved cysteines, three intramolecular disulfide bonds, a net positive 
charge, and β-sheet regions. α and θ-defensins are closely related, comparative 
amino acid sequences showed that the difference between them is that θ-defensins 
have an additional stop codon limits the initial defensin domain peptides to 12 
residues. Humans, chimpanzees and gorillas do not produce θ-defensin peptides 
due to a premature stop codon present in the signal sequence of all θ-defensin 
pseudogenes. By using comprehensive computational searches, here we report the 
discovery of complete repertoires of the α and θ-defensin gene family in ten 
primate species. Consistent with previous studies, our phylogenetic analyses 
showed all primate θ-defensins evident formed one distinct clusters evolved from 
α-defensins. β-defensins are ancestors of both α and θ-defensins. Human has two 
copies of DEFA1 and DEFT1P, and two extra DEFA3 and DEFA10P genes compared with 
gorilla. As different primates inhabit in quite different ecological niches, the 
production of species-specific α and θ-defensins and these highly evolved 
θ-defensins in old world monkeys would presumably allow them to better respond 
to the specific microbial challenges that they face.