The connection between the gut and autoimmune diseases
When I see clients with autoimmune conditions and I start asking questions about their digestion, they often look a little confused as they cannot grasp what their digestion has to do with their immune system; until I explain to them that there is a connection.
So what is the connection between the gut and autoimmune conditions?
First let’s have a look at some of the gut functions.
The first thing that comes to mind about the gut is digestion and absorption, but another important function that is often overlooked is that the gut also forms a physical barrier that separates our internal environment from the outside world.
The main job of this barrier is to let nutrients from our food into the body while preventing foreign particles, such as toxins and microorganisms, from entering our blood stream. If this barrier function is compromised, then something called ‘leaky gut’ or ‘increased intestinal permeability’ ensues (see diagram below).
It is this impaired intestinal barrier function that has been associated with autoimmune conditions. (1).
Source: https://commons.wikimedia.org/wiki/File:Increased_intestinal_permeability.png
Before going further, let’s also have a look at autoimmune mechanisms.
Autoimmune diseases develop when a person’s immune system loses the ability to recognise its own tissue and mounts an immune response against it, leading to tissue damage.
The question is then why would this happen?
What triggers the body to attack its own tissue?
Although there are a few theories on what might lead to the development of autoimmune diseases, such as genetics, viruses and bacterial infections, in recent years leaky gut has received much attention as a potential trigger of autoimmune diseases (1, 2).
Adapted with modification from Campbell AW (2014). Autoimmunity and gut. Autoimmune Dis. 2014:152428. doi: 10.1155/2014/152428
So what is the mechanism behind the gut-autoimmunity connection?
As mentioned above, the gut provides a barrier between the internal and external environments. It does this through a single layer of cells, called epithelial cells. As can be seen in the diagram below, in a healthy state these cells are interconnected by tight junctions. The transfer of molecules between the inside of the gut (the intestinal lumen) and the blood stream can be either through individual epithelial cells (transcellular transport) or via these tight junctions (paracellular transport). The transfer of molecules is regulated by many factors, including the size of molecules. If a molecule is too large then the tight junctions will not allow it to be transferred across.
Source: https://commons.wikimedia.org/wiki/File:Selective_permeability_routes_in_epithelium.svg
Under different circumstances, theses tight junctions could be impaired and thus ‘opened’ to foreign particles leading to an immune cascade.
Behind this layer of epithelial cells reside 80% of our immune cells ready to attack anything that tries to cross this barrier (3) (see diagram 4). If this barrier is impaired (i.e. the tight junctions are ‘opened’), then the intestinal immune cells will be activated and ready to put up a line of defence. Unfortunately, in some cases, this immune response could lead to unintended autoimmune consequences. When a foreign particle crosses the barrier, the immune cells will attack and form memory cells to recognise these invaders if they are found in the body again. Put very simple, the immune cells learn that whenever they see this ‘antigen’ they should attack it. However, with this new learning they can mistakenly identify tissue in the body as one of these antigens and attack it.
The gut-autoimmune connection is much more complex then presented here, obviously, but I tried to keep it simple.
Nevertheless, I hope this sheds some light on why a practitioner might ask you questions regarding your digestion even though you came in for the management of an autoimmune condition.
