Rhesus macaque θ-defensin isoforms: expression, antimicrobial activities, and demonstration of a prominent role in neutrophil granule microbicidal activities

Mammalian defensins are cationic, antimicrobial peptides that play a central role in innate immunity. The peptides are composed of three structural subfamilies: alpha-, beta-, and theta-defensins. theta-Defensins are macrocyclic octadecapeptides expressed only in Old World monkeys and Orangutans and are produced by the pair-wise, head-to-tail splicing of nonapeptides derived from their respective precursors. The existence of three active theta-defensin genes predicts that six different RTDs (1-6) are produced in this species. In this study, we isolated and quantified RTDs 1-6 from the neutrophils of 10 rhesus monkeys. RTD-1 was the most abundant theta-defensin, constituting similar to 50% of the RTD content; total RTD content varied by as much as threefold between animals. All peptides tested were microbicidal at similar to 1 mu M concentrations. The contribution of theta-defensins to macaque neutrophil antimicrobial activity was assessed by analyzing the microbicidal properties of neutrophil granule extracts after neutralizing theta-defensin content with a specific antibody. theta-Defensin neutralization markedly reduced microbicidal activities of the corresponding extracts. Macaque neutrophil granule extracts had significantly greater microbicidal activity than those of human neutrophils, which lack theta-defensins. Supplementation of human granule extracts with RTD-1 markedly increased the microbicidal activity of these preparations, further demonstrating a prominent microbicidal role for theta-defensins. J. Leukoc. Biol. 89: 283-290; 2011.