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The intestinal mucus layer

The intestines are lined with a layer of mucus which acts as a physical barrier to separate the intestinal contents, such as bacteria, from the human body. The epithelium in the small intestine is covered by a single, thin mucus layer that allows uptake of nutrients. In the stomach and colon mucus is stratified into two layers and offers stronger protection of the underlying epithelium. The inner mucus layer is impermeable to bacteria.1, 2 The mucus layer is continuously and rapidly replenished by secretion from mucus-producing goblet cells creating a flow of mucus away from the epithelium.3 Host defense molecules and secreted antibodies are concentrated in the mucus layer and further reinforce the mucus barrier.4

Some gastro-intestinal pathogenic bacteria that can cause infections, such as Helicobacter pylori and Clostridioides difficile, have developed mechanisms that inhibit mucus secretion as part of their pathogenesis.5 By reducing the thickness of the mucus layer, pathogens decrease their proximity to epithelial cells. In intestinal inflammatory diseases a reduced or structurally modified mucus layer has been found5, 6, 7, 8 and the degree of reduced mucus thickness correlates with disease severity.9

Rodent studies have suggested that lifestyle factors such as diet,10, 11, 12, 13 alcohol consumption,14 psychological stress,15, 16, 17 and ageing18 may affect the intestinal mucus layer and its barrier function. Additionally, the composition of the microbiome influences mucus barrier function.19, 20 Limited information is available from human studies, but a recent study showed that a thinner colonic mucus layer was associated with red meat and whole-grain intake.21

Some probiotics may stimulate mucus production and support the mucus barrier. Sticky, hair-like structures extend from the surface of Lactobacillus rhamnosus, LGG®. These pili mediates adhesion of LGG® to intestinal mucus and epithelial cells ensuring close contact to the epithelium.22, 23 Studies have shown that LGG® is able to stimulate mucus production in epithelial cells through secretion of a specific protein, p40.24, 25
Increased intestinal secretion of defensins and antibodies associated with enhanced normal mucosal barrier function was observed in humans after treatment with Bifidobacterium, BB-12®.26, 27

LGG®, and BB-12® are registered trademarks of Chr. Hansen A/S.

The article is provided for informational purposes regarding probiotics and is not meant to suggest that any substance referenced in the article is intended to diagnose, cure, mitigate, treat, or prevent any disease.

 

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References Open Close

  1. Johansson MEV, et al. The two mucus layers of colon are organized by the MUC2 mucin, whereas the outer layer is a legislator of host-microbial interactions. Proc Natl Acad Sci U S A. 2011;108(Suppl 1):4659–4665. (PubMed)
  2. Johansson MEV, et al. The gastrointestinal mucus system in health and disease. Nat Rev Gastroenterol Hepatol. 2013;10(6):352–361. (PubMed)
  3. Johansson MEV. Fast renewal of the distal colonic mucus layers by the surface goblet cells as measured by in vivo labeling of mucin glycoproteins. PLoS One. 2012;7(7):e41009. (PubMed)
  4. Johansson MEV, Hansson GC. Immunological aspects of intestinal mucus and mucins. Nat Rev Immunol. 2016;16(10):639–649. (PubMed)
  5. Cornick S, et al. Roles and regulation of the mucus barrier in the gut. Tissue Barriers. 2015;3(1-2):e982426. (PubMed)
  6. Capaldo CT, et al. Layered defense: how mucus and tight junctions seal the intestinal barrier. J Mol Med (Berl). 2017;95(9):927-934. (PubMed)
  7. Strugala V, et al. Thickness and continuity of the adherent colonic mucus barrier in active and quiescent ulcerative colitis and Crohn’s disease. Int J Clin Pract. 2008;62(5):762–769. (PubMed)
  8. Johansson MEV, et al. Bacteria penetrate the normally impenetrable inner colon mucus layer in both murine colitis models and patients with ulcerative colitis. Gut. 2014;63(2):281–291. (PubMed)
  9. Schroeder BO. Fight them or feed them: How the intestinal mucus layer manages the gut microbiota. Gastroenterol Rep (Oxf). 2019;7(1):3–12. (PubMed)
  10. Schroeder BO, et al. Bifidobacteria or Fiber Protects against Diet-Induced Microbiota-Mediated Colonic Mucus Deterioration. Cell Host Microbe. 2018;23(1):27-40.e7. (PubMed)
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  14. Kirpich IA, et al. Ethanol and Dietary Unsaturated Fat (Corn Oil/Linoleic Acid Enriched) Cause Intestinal Inflammation and Impaired Intestinal Barrier Defense in Mice Chronically Fed Alcohol. Alcohol. 2013;47(3):257–264. (PubMed)
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  16. Söderholm JD, et al. Chronic Stress Induces Mast Cell-Dependent Bacterial Adherence and Initiates Mucosal Inflammation in Rat Intestine. Gastroenterology. 2002;123(4):1099-1108. (PubMed)
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