Elsevier

Mucosal Immunology

Volume 8, Issue 3, May 2015, Pages 661-671
Mucosal Immunology

Article
Paneth cell α-defensin 6 (HD-6) is an antimicrobial peptide

https://doi.org/10.1038/mi.2014.100Get rights and content
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open access

Abstract

Defensins protect human barriers from commensal and pathogenic microorganisms. Human α-defensin 6 (HD-6) is produced exclusively by small intestinal Paneth cells but, in contrast to other antimicrobial peptides (AMPs) for HD-6, no direct antibacterial killing activity has been detected so far. Herein, we systematically tested how environmental factors, like pH and reducing conditions, affect antimicrobial activity of different defensins against anaerobic bacteria of the human intestinal microbiota. Remarkably, by mimicking the intestinal milieu we detected for the first time antibacterial activity of HD-6. Activity was observed against anaerobic gut commensals but not against some pathogenic strains. Antibiotic activity was attributable to the reduced peptide and independent of free cysteines or a conserved histidine residue. Furthermore, the oxidoreductase thioredoxin, which is also expressed in Paneth cells, is able to reduce a truncated physiological variant of HD-6. Ultrastructural analyses revealed that reduced HD-6 causes disintegration of cytoplasmic structures and alterations in the bacterial cell envelope, while maintaining extracellular net-like structures. We conclude that HD-6 is an antimicrobial peptide. Our data suggest two distinct antimicrobial mechanisms by one peptide: HD-6 kills specific microbes depending on the local environmental conditions, whereas known microbial trapping by extracellular net structures is independent of the reducing milieu.

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Published online: 5 November 2014

Author contributions B.O.S. performed antimicrobial activity assays, HPLC analyses, and MALDI-MS, reduction assays, was involved in sample preparation for electron microscopy analyses, designed and evaluated experiments, generated figures, and wrote the manuscript. D.E. performed antimicrobial activity assays, HPLC analyses, and MALDI-MS. J.C.P. performed and evaluated Q-TOF-MS analyses and was involved in generating figures and writing of the manuscript. P.A.C. assisted in and performed scanning microscopy analyses. R.K. tested antimicrobial activity against pathogenic microorganisms, J.B. performed scanning microscopy experiments and M.S. was in charge of transmission electron microscopy. E.F.S. was involved in data discussions and writing of the manuscript. J.W. was involved in data discussions, evaluation of experiments, writing of the manuscript, and design of the study. All authors were involved in data discussions and the final version of the manuscript.

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Supplementary information The online version of this article (doi:10.1038/mi.2014.100) contains supplementary material, which is available to authorized users.