The immune system in your gut
Your gut does more than just digest food!
You might think that your skin is your body’s largest surface to the outside world. However, in terms of surface area, it’s actually the lining of your gut. The gut lining, or ‘mucosa’, is constantly exposed to substances called ‘antigens’ from your food and the bacteria living in your gut. These antigens could potentially trigger an immune response.1 To cope with all these antigens, 70% of the body’s entire immune system is actually located in the gut.2
The gut mucosal immune system needs to be able to tell the difference between something that is a threat to your health and something that is not. For example, it wouldn’t be helpful for your immune system to react to the food you eat or to the healthy bacteria that live in the gut. However, you do want the immune system to protect you against harmful bacteria or viruses.3 Therefore, the intestinal mucosa is constantly being monitored by your immune system.
Three specific parts of the gut lining are involved in your immune system
There are three important structures in the gut lining that make up the intestinal immune system: 4
- Peyer’s patches, which are relatively large lymphoid structures scattered along the intestines. They contain lots of different types of immune cells3
- The lamina propria, which is a thin layer of connective tissue just under the epithelium that also contains numerous immune cells
- The epithelium, which is the name for the cells forming the outer layer of the gut lining. These cells are at the frontline and connect to the immune system
Within these structures, immune cells send messages, to help defend your bodyFirstly, special immune cells called ‘dendritic cells’ are able to look out for antigens. There are lots of dendritic cells in Peyer’s patches. Dendritic cells are also able to squeeze through tight gaps between the cells making up the epithelium to reach inside the intestine and check for antigens.5 When a dendritic cell finds an antigen, it becomes activated and tells another type of immune cell, ‘T-helper cells’, about the antigen.
Depending on the message the dendritic cell gives, the T-helper cells either help the body to build up tolerance to a non-threatening antigen or to start defensive tactics to protect the body against a harmful antigen. Defensive tactics can lead to inflammation, which you may feel as symptoms like fever, aches and pains when your body is fighting an infection.6,7
When T-helper cells are given a message from the dendritic cells, they start sending out chemicals called ‘cytokines’ that give instructions to either ‘turn down’ (anti-inflammatory) or ‘turn up’ (pro-inflammatory) the level of inflammation.
An example of an important anti-inflammatory cytokine is interleukin-10 (IL-10). IL-10 is important for ‘turning down’ the immune system and reducing the inflammatory response.1,8 Other cytokines such as IL-1β, IL-6, and TNF-α are important for activating the immune system.9
When a harmful antigen is detected, dendritic cells send out cytokines that boost the number of particular pro-inflammatory T-helper cells called Th1, Th2, or Th17.10,11 These in turn attract other types of immune cells to join in to fight the infection.12,13 The fact that many different cells are involved means that the immune system is well equipped to protect us from many pathogenic microorganisms which may be present in the gut.14
Inflammation can be ‘acute’ or ‘chronic’As noted earlier, inflammation is a result of the immune system fighting an infection. Sometimes, inflammation starts quickly and goes away quickly. This is called ‘acute’ inflammation.15,16 Inflammation that lasts longer or doesn’t completely go away, often because the intestinal barrier is not functioning well, is called ‘chronic’ inflammation.17 Low-level chronic inflammation is an underlying factor in a range of diseases, such as inflammatory bowel disease (IBD),18 atherosclerosis,19 arthritis,20 and neurodegenerative diseases such as Alzheimer’s disease.21
The effects of probiotics on the immune system and how they work varies between different probiotic strains.11 Studies suggest that Lactobacillus rhamnosus, LGG®, Lactobacillus paracasei, L. CASEI 431® and Bifidobacterium, BB-12® probiotic strains may support the immune system, and have been shown to reduce the occurrence, duration and severity of respiratory issues in children and adults.22-26 Data suggest that these strains support the immune system by helping Th1 cells to mature and stimulating them to send out the important cytokines that make your body produce antibodies to fight invading pathogens.27-32
LGG®, L. CASEI 431®, 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.