Human epithelia are permanently challenged by microorganisms. In the gut, the fraction of strict anaerobic bacteria increases from proximal to distal, reaching 99% of bacterial species in the colon. Moreover, microbial metabolism causes a reduction of the environment to a low redox potential of only –200 mV to –300 mV. Defensins, characterised by three intramolecular disulfide-bridges, are key eff ...