Antimicrobial Peptides in the Gut

Abstract

The gut represents a unique interface toward our environment. It not only facilitates digestion and resorption but also battles ingested pathogens, while also controlling an immense community of commensal microorganisms. To aid with the latter, it produces a wide range of innate immune mediators, such as antimicrobial peptides (AMPs), which can combat viruses, bacteria, and fungi. Gut AMPs have differing activity ranges and modes of action, so their expression varies depending on the present conditions and threats. The most famous examples for site-specific AMPs are probably the two α-defensins HD5 and HD6. In a homeostatic state, they are exclusive to the Paneth cells of the small intestine. Since the importance of gut microbiota has become more and more evident, research on AMPs has also increased. This is particularly obvious in the case of inflammatory bowel diseases, but also noticeable in other disorders. Defects in the AMP machinery have been linked to increased susceptibility to infections, chronic inflammation, and disturbances in commensal composition. Recently, even a role in colon cancer has been proposed. The gut provides a complex and challenging environment for the study of interactions between AMPs and microbes; and while we are now widely aware of their crucial role in keeping us healthy, more research is needed to fully uncover the involved multi-level crosstalk of their actions. Such investigations might one day help us in fully understanding the mechanisms of various diseases. Even more, they might aid in developing new anti-infectious, antiinflammatory, and maybe even antitumorigenic drugs.