[Human beta-defensin 1: from defence to offence].

The human gut is colonised by about one kilogram of commensal bacteria. These microorganisms are a potential threat, thus an efficient defence system is crucial in preventing bacterial translocation and infection. Besides other mechanisms of protection humans produce antimicrobial peptides (AMPs) that are able to kill a broad range of microorganisms. The human beta-defensin 1 (hBD-1) plays a major role because it is produced constitutively by all human epithelia and some immune cells. In contrast to other AMPs, however, the biological function of hBD-1 has remained unclear since the antibiotic activity of hBD-1 in vitro was only marginal. But still, several diseases have been associated with genetic polymorphisms in the hBD-1 encoding gene. Herein we discuss why the biological role of hBD-1 has been overlooked and how hBD-1 can be activated by chemical reduction. We elaborate on the biological significance of this activation and its importance for inflammatory bowel disease. © Georg Thieme Verlag KG Stuttgart · New York.