Figure 1

From: Human Intestinal Barrier Function in Health and Disease

Figure 1

Schematic figure of the intestinal barrier and affecting factors. The intestinal barrier is composed of several layers providing protection against microbial invasion. The intestinal lumen contains anti-microbial peptides (AMPs), secreted immunoglobulin A (IgA), and commensal bacteria, which inhibit the colonization of pathogens by competitive inhibition and by production of, e.g., butyrate, which has barrier-protective properties. A mucus layer covers the intestinal surface providing a physical barrier. The epithelial layer consists of a single layer of epithelial cells that are sealed by tight junction proteins such as occludin, claudin, and zonulin-1 preventing paracellular passage. This layer also harbors intraepithelial lymphocytes, M cells (overlying Peyer’s patches and lymphoid follicles), mucus-producing Goblet cells and bacteriocin-producing Paneth cells (not shown). The lamina propria contains a large amount of immune cells, both of the innate immune system (e.g., macrophages, dendritic cells, mast cells) and the adaptive immune system (e.g., T cells, IgA producing plasma cells). In addition, cells of the central and enteric nervous system innervate in the lamina propria (not shown). Factors affecting the intestinal barrier function include pathogenic bacteria such as enteropathogenic E. coli, high-fat diet, lipopolysaccharides (LPS), drugs such as non-steroidal anti-inflammatory drugs (NSAIDs), and proton pump inhibitors (PPIs), as well as various food allergens and the gluten component gliadin.