Understanding the Gut-Immune System Connection

At a glance

A healthy immune system is essential to ward off viruses, infections, and other threats. A significant share of the immune system lives in the gut, and the two are intricately linked. A healthy gut supports a healthy immune system, and gut imbalances can impair immune function. 

The gut microbiome, the diverse collection of bacteria living in our intestines, influences immune function in a number of different ways. 

Gut bacteria help regulate immune responses and inflammation, maintain a healthy gut lining to keep pathogens from escaping into the bloodstream, and produce antibodies and immune cells. 

A healthy gut lining is also essential for optimal immune function. If the lining of the gut becomes too permeable (known as "leaky gut"), it can lead to chronic inflammation and the development of autoimmune conditions, in which the immune system attacks the body's cells and tissues. 

Research has shown that healthy gut bacteria can help identify, prevent, and fight viruses like influenza and infections like pneumonia. Healthy gut bacteria may also help prevent autoimmune disease and improve immunotherapy treatments for certain kinds of cancer. 

Supporting a healthy immune system requires supporting a healthy gut. High-quality probiotic supplements, a nutrient-dense diet, and avoiding dysbiosis triggers can help. 

The gut microbiome and the immune system

The gut microbiome, made up of trillions of microbes, influences health in many different ways. A diverse and balanced microbiome where beneficial bacteria are plentiful is essential for a healthy immune system and overall wellness.

Because so much of the immune system is housed in the gut, the microbiome plays a crucial role in regulating immune response, inflammatory processes, and disease and infection. 

To some extent, we can see this in action through research on sterile lab mice who are born germ-free (without any bacteria). Under these conditions, mice are missing critical immune cells. Once introduced to bacteria, their immune systems grow more robust and offer better immune support. 

The relationship between the microbiome and the immune system is a two-way street. The immune system learns to defend against pathogenic strains of bacteria to protect beneficial strains in the gut. In this sense, a healthy immune system helps to build or maintain a healthy gut microbiome. A healthy gut microbiome, in turn, helps to produce immune cells and regulate immune function. 

Another one of the many jobs our beneficial microbes hold is maintaining the integrity of the gut lining. If there is an imbalance within the gut microbiome (known as dysbiosis), increased intestinal permeability, chronic inflammation, and immune system dysfunction can result.

Microbes as teachers

An individual's immune system and gut microbiome develop and adapt together over the course of a lifetime, beginning at birth. 

You probably think about the immune system for its role in defending us against things we know to be harmful, like viruses and infections. However, the immune system is equally responsible for knowing when not to react. 

A healthy immune response involves prompting inflammation to alert guards (i.e., white blood cells) to an invader (i.e., pathogen) that needs to be attacked. But throughout the day, you're exposed to all kinds of things that don't need to be attacked—from new foods to dust or pollen in the air. If the immune system mounted an attack every time anything foreign entered the body, you'd remain in a dangerous state of constant inflammation.

This is one of the most critical ways in which your gut bacteria influence your immune system. Healthy microbes teach immune cells that some microbes should be tolerated instead of attacked. Essentially, gut bacteria teach the immune system what to do and when to act. 

If the gut is in a state of dysbiosis, inflammation and immune system dysfunction are more likely to occur. A hyperactive immune system hinders our ability to fight off real threats and increases our risk of getting sick. 

Fighting viruses and infections with gut bacteria 

Gut microbes play a key role in helping the immune system identify and fight viruses. The sooner your immune system can identify a virus that has entered the body, the better chance your body has of fighting it off. 

Research has shown that helpful gut bacteria are involved in this process. For example, effective communication between gut microbes and the immune system can lead to more rapid identification of influenza virus that has entered the lungs and play a preventive role. 

Healthy gut bacteria also help protect against infections, including pneumonia. 

Zeroing in on beneficial bacteria

Understanding the general role that gut bacteria play in immune function is only one piece of the puzzle. Researchers are now zeroing in on which bacterial strains play which roles and how that might influence the development or progression of specific diseases. 

One example is a recent study on gut bacteria and immunotherapy for certain kinds of cancer. 

Immunotherapy, a type of cancer treatment that involves strengthening the immune system, is useful for some, but not all, patients. It was previously unknown why some patients responded to this type of therapy while others did not. 

This study pinpointed not only the role the microbiome plays in battling cancerous tumors, but specifically which bacteria assist the immune system in these attacks and how. Although more research is still needed, this may mean that providing specific strains of bacteria to cancer patients can improve the efficacy of immunotherapy treatments. 

The leaky gut and autoimmunity connection

Increased intestinal permeability, or leaky gut, may be one of the leading factors in developing autoimmune diseases. Similarly, healing the gut may be essential for treating, managing, or reversing autoimmune diseases. 

What is an autoimmune disease? 

Autoimmune disease occurs when the immune system, which we rely on to protect us against viruses, infections, and other threats, attacks the body's own tissues. Common examples of autoimmune conditions include Rheumatoid Arthritis, Hashimoto's Thyroiditis, Inflammatory Bowel Disease (IBD), and psoriasis. 

While autoimmune conditions may look different on the outside based on their symptoms, what underlies them all is a problem with the immune system. 

What is leaky gut? 

The intestinal wall, or gut lining, is a complex and dynamic system of cells, molecules, and other substances. The intestinal lining functions as a barrier and as a guard, selectively allowing those who knock to pass through. When you eat, the nutrients you're consuming need to pass through the intestinal lining and enter the bloodstream, where the body can make proper use of them. 

Conversely, when larger food particles, toxins, and harmful bacteria knock at the door, the intestinal lining is responsible for keeping them out. 

Problems occur when the intestinal barrier loosens and becomes more permeable, allowing larger and potentially harmful particles and substances to slip through into the bloodstream. This condition of increased intestinal permeability is often referred to as "leaky gut." 

A number of factors can stress the gut and intestinal lining, contributing to increased permeability. These factors include inflammatory foods, chronic or excessive stress, infections, and certain medications. 

Leaky gut, inflammation, and autoimmunity

The intestinal lining can be thought of as the first line of defense against toxins, viruses, and pathogenic (harmful) bacteria. Once these particles have escaped into the bloodstream, the rest of the immune system steps in to attack and diffuse any threats.  

The immune system fights foreign cells by generating an inflammatory response, which alerts other components of the immune system to where the threat is. However, if foreign cells become more common due to a leaky gut, inflammation can become chronic and excessive. 

An overstressed and overactive immune system can lead to autoimmunity, in which the immune system inadvertently attacks the body's own tissues. 

Adaptive immunity and molecular mimicry 

Adaptive immunity, also referred to as acquired immunity, is a subsystem of the immune system responsible for responding to and attacking specific pathogens. 

When the adaptive immune system identifies a new guest, it creates antibodies specifically designed to attack it. If the same foreign body returns, the immune system will have learned which antibodies to produce and will get to work right away. 

This immunological memory is an impressive feature of the immune system, but it can also become problematic for those with increased intestinal permeability. 

Some of the foreign substances that leak into the bloodstream may, structurally, resemble the body's own cells and tissues. When overburdened, the immune system may begin to attack the body's cells, mistaking them for foreign invaders. 

This occurrence, referred to as molecular mimicry, explains why undigested or partially digested food particles that leak through the gut lining can be so problematic. Certain proteins found in foods, particularly those containing gluten or casein (milk protein), are notorious for their molecular similarity to cells within the body.  

How to support gut and immune system health

Building and maintaining a healthy immune system means supporting the health of your gut. Fortunately, there are many ways to support both of these systems. 

Maintaining a healthy gut microbiome mainly involves making conscious diet and lifestyle choices. Certain things like sugar, hyper-processed foods, chronic stress, and certain medications can disrupt the delicate balance between good and bad bacteria in the gut. 

Eating a healthy Mediterranean diet has been shown to help support a healthy gut and reduce inflammation. This diet incorporates a variety of fresh, healthy fruits and vegetables and healthy fats such as olive oil, nuts, and certain kinds of fish.

Generally, foods high in antioxidants and phytochemicals have been shown to support the immune system as well as the gut. 

To support your gut further, engage in regular physical activity and consider supplementing with probiotics. Research has demonstrated the potential of probiotics for supporting immune health, boosting the production of antibodies and immune cells.

There are many other health benefits associated with taking probiotics, and they may be taken daily as a preventive measure to help maintain overall wellness.  

In summary

To stay healthy, fight off viruses and infections, and reduce your risk of chronic inflammation, it's critical to prioritize the health of your immune system. The majority of the immune system resides within the gut, and these intricate systems remain in constant communication. 

If gut issues are present, immune system function may suffer, too. Common gut issues that can affect immune function include dysbiosis (an imbalance between beneficial and harmful bacteria in the gut microbiome) or increased intestinal permeability ("leaky gut"). 

A healthy gut microbiome, encompassing a diverse range of trillions of microbes, plays a significant role in sustaining balance throughout the body and the immune system. 

When it comes to immune function, gut bacteria help produce immune cells and antibodies in response to threats, regulate inflammation, and preserve a healthy gut lining. 

Beneficial gut microbes can help identify viruses, infections, and other threats early on. They can also help fight these threats if they take hold. A healthy gut can also help prevent autoimmune diseases and may enhance the effects of immunotherapy treatments for cancer patients. 

To support a healthy gut and a healthy immune system, prioritize a nutrient-dense diet, stress management, and supplementing with a high-quality probiotic when necessary. 

Ellie Ellias - Contributing Writer, Physician's Choice 

Up next: Understanding the Gut-Brain Connection