The positive impact of the nutrient Zn on intestinal health is well known. Zn deficiency, a common condition, leads to numerous health complains. The molecular mechanism of the Zn effects however is not understood. Yet, Zn is important in prevention of disease and is used (in relatively high doses) by farmers to prevent weaned piglet diarrhea. Because of fear for environmental pollution, therapeutic doses of Zn will become forbidden in the European Union from 2022 on, leaving farmers without alternatives. We want to address this high need by studying the mechanism of the impact of Zn on intestinal homeostasis. Evidence points to a mechanism whereby Zn modulates the composition of the gut microbiota through communication of Zn with Paneth cells (PCs). These cells are found on the basis of the crypts in the ileum. They are specialized in fine-tuning the composition of the gut microbes, based on sensory signals, such as Zn, and by expressing, maturating and releasing antimicrobial peptides and proteins (AMPs). We will purify mouse and pig Paneth cells, and study their response to Zn on numerous levels (transcriptomics, proteomics, metabolomics) to understand the Zn-PC relation. We will generate immortalized PC lines and screen chemical component libraries to identify Zn-mimicking molecules that might be combined with Zn or replace Zn in animals. The use of such new molecules as therapeutics will be tested in mice and in pigs. The impact of Zn on the microbiota, will be studied by titrating Zn in mice and pig and by depleting PCs (in mice). Relations between blood Zn levels and microbiota will also be studied in cohorts of the Flemish Gut Flora Project. The development of the tools and the elucidation of the Zn-PCmicrobiome axis will also allow to identify blood- or stool-based biomarkers that reflect the activity of PCs. The impact of diseases such as arthritis, diabetes and aging on PC numbers and function will be studied in relation to the new biomarker.