A Symbiotic Relationship: Your Gut and the Immune System

Not long ago, we held the belief that bacteria had little to do with our well-being and considered it a separate entity that just assisted the digestion of certain foods. More recently, it has become a fact that humans possess as many bacterial cells as human cells – with over 10,000 species and trillions of microorganisms present in our gut!

The Gut Microbiota

It has been estimated that the human gut houses 100 trillion microbial cells (collectively referred to as the gut microbiota), which is 10 times the number of human cells. We are more bacteria than we are human.

Over time, the body has evolved with bacteria in a symbiotic relationship. Human cells and bacteria live in close proximities and have a mutually advantageous relationship.

Researchers are only starting to see how large the influence of bacteria is on our health. In fact, the gut microbiota impacts many physiological processes. These include mood, level of concentration, memory, weight, digestion, and more.

Some food allergens like soy, dairy and GMO corn can disturb the delicate intestinal lining of your gut while others like probiotics can support strengthening the tight junctions of the epithelial cells lining the gut.

Though the organisms in the microbiome impact so many of our body functions (e.g. cognitive function and more); they are mostly located in our digestive tract, gut, genitals, mouth and nose. Bacteria are also found on the outer surface of our skin and on every surface we come into contact with.

Maintaining a balanced ratio of good to bad bacteria is crucial for our health. The more good guys that are on your side, the better chance your immune system and gut have a chance to protect the body from the destructive bad bacteria.

The Immune System’s Task

The immune system has a vital role in the body and that is to protect it from foreign and harmful invaders. It consists of a group of cells, proteins and organs that work together to protect the body from germs, viruses, fungi, and pathogens. Immune cells act as your body’s first line of defence – they recognize, identify and neutralize any harmful substances (environmental or pathogenic) that have found their way into the body.

When the immune system is working optimally, it goes unnoticed. However, when it doesn’t work adequately or when you are run down, your defences become too weak to fight. Opportunistic bacteria and viruses swoop in and are more likely to make you ill.

What Activates The Immune System?

When our body doesn’t recognize something as our own, the immune system gets into gear, ready to fight back. We refer to the ‘attackers’ of the immune system as antigens. Some of them are proteins found on the surface viruses, bacteria and fungi. The way this works is as they enter the body and bind to immune cell receptors, this activates a sequence of events.

Immune cells have the powerful capacity to remember germs they encounter. Once an antigen has been identified, they record its information and the way to neutralize it for future reference. That way, next time the germ reappears, immune cells will know how to fight it more effectively.

How Gut Bacteria Affects the Immune System

The role of the immune system is to protect the body from illness and fend off unwanted pathogens and bacteria. But what about gut bacteria, how do these come into play?

In the last few decades, there has been a huge shift in our comprehension of human-microbe connections. A new concept of “holobiont” has been introduced – which refers to an ecosystem composed of a host, i.e. us, surrounded with other species living together.

We now understand how human cells and microbial units have co-evolved together in symbiosis, through the introduction of prokaryotic cells (bacteria) into eukaryotic cells (human and animal). The immune system is particularly interconnected with gut bacteria.

As we know, most of the human microbiota resides in the gut, and as it turns out, so does 70-80% of the body’s immune system. The relationship between the two is symbiotic, whereby they’ve evolved together to ensure that the body is protected and is eliminating any harmful pathogens that it comes into contact with. The interaction between the two begins at birth, which is the moment the body encounters bacteria for the first time –as the birth canal contains large numbers of bacteria.

In time, the immune system forms the diversity of the microbiome and the gut influences the strength and development of the immune system. Throughout life, other factors also shape the composition of the gut flora, i.e. diet, environment and lifestyle habits.

The gut and the immune system support one another to promote a healthy body. For instance, the gut microbiome acts as a gatekeeper and a trainer. It teaches immune cells called T-cells to distinguish foreign entities from our own tissue. When antibodies cannot access certain pathogens that have managed to attack our cells, T-cells mediate the situation and destroy infected cells – this process is referred to as cell-mediated immunity.

We see the importance of maintaining a powerful immune system and proper communication with the gut.When everything is running smoothly, the gut sends signals for the development of healthy immune function modulating immune responses. In exchange, the immune system helps to populate the microbiome with health-promoting microbes.

When these two are in good relations, the body is equipped to respond to pathogens and to tolerate harmless bacteria, preventing an autoimmune response and ensuring overall well-being. Because the immune system is intricately related to the gut microbiota, if the body is exposed to bacteria-stripping factors (i.e. poor diet, antibiotics, surgeries, heavy metals, chemotherapy), this lowers your intestinal flora, which can snowball into reduced immunity.

The intestinal lining of your gut is delicate, and when it is weakened, you are more vulnerable in the face of new harmful invaders. When your gut is out of balance, meaning not enough good friendly bacteria vs. the pathogenic, your whole body is affected. Luckily, the same way bad guys can overpopulate the gut, good guys can too.

Epigenetic research is finding that we have more control over our biodiversity than we think. Genes can be influenced. Changing the way you eat can change the expression of your genes by populating the microbiome with diverse microbial cells.

Improving your diet by cutting out processed foods and including more prebiotic fibre (vegetables and legumes) can increase biodiversity. If you are currently not eating a lot of fibre it is something to introduce very slowly as it can cause gastro upset. Also, having probiotic-rich foods such as kefir, sauerkraut, and probiotics may restore the composition and reintroduce strong microbes, allowing for a more efficient gut microbiome, immunity and cognitive abilities.

By Jess Wharton, Clinical Nutritionist