1. Intestinal structure  Structure Crimpy structure to facilitate the contacts between nutrients and absorptive cells Extends surface area to 300 m 2  Functions Lined by a single layer of enterocytes Efficient structure for absorption of nutrients Not an effective structure for barrier function To effectively block pathogens Barrier system Gut-associated immune system (Illustration: courtesy of the University of Waikato)

2. Intestinal structure Capillaries leading to portal veins underneath the single layer of enterocytes Any damage in enterocytes will open up primary barrier function and pigs will be exposed to infections (photo: courtesy of Southern Illinois University, School of Medicine)

3. Intestinal immune system – antigen uptake as a surveillance system Nature Reviews Immunology, Mowat et al., 2003 Antigen sampling through M cell Preparing possible open up of intestinal barrier and pathogen invasion Require energy and protein Perform less efficiently in a dirty environment

4. Physical barriers in the monolayer of enterocytes Loose tight junction causes “leaky gut” Groschwitz and Hogan, 2009 Paracellular permeability is directly related to pathogen translocation into the body system and TJ plays a key role