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Study Confirms Gut Health Affects the Immune System

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Key Takeaways

  • Researchers found that the concentration of various types of immune cells in the blood changes based on the different bacterial strains in the gut.
  • Previous studies about the gut microbiome and the immune system have mostly been done on animals, but this new research looks specifically at the human body.
  • This data may be instrumental in furthering treatments for conditions such as cancer, autoimmune issues, and infectious diseases.

New research provides more insight into the relationship between having a healthy gut microbiome and our immune system.

Researchers found that the concentration of various types of immune cells in the blood changed based on the different bacterial strains in the gut. Their study, published in the journal Nature in November, was based on more than 10 years of data from more than 2,000 patients.

The scientific community already believes that the gut microbiota plays an important role in immune system health. But the data supporting that notion was based on animal studies, Joao Xavier, PhD, co-senior author and biologist at Sloan Kettering Institute in New York, said in a statement.

“The study proves what has been said by functional medicine for decades but now even more
evidence that our microbiome is so important in shaping our immune system,” Jennifer Kessmann, MD, a functional medicine doctor in Dallas, Texas, who was not affiliated with the study, tells Verywell. "It shows that the immune system can be modulated by the types and numbers of bacteria in the gut. When the gut microbiome is diversified, meaning many different types of healthy bacteria, the immune reactions can be more balanced.”

She says the findings are “revolutionary to further the concept of just how important the microbiome is to our health.”

What This Means For You

There's still plenty to learn about how gut health impacts your immune system, but researchers believe learning more can lead to new treatments in the future.

Evaluating Gut and Immune Health

For the study, researchers gathered data from cancer patients who underwent allogeneic stem cell and bone marrow transplants (BMTs). Patients undergo this procedure, where they receive stem cells from a donor, after chemotherapy and radiation destroy cancerous cells in the blood.

Because their immune systems and microbiota are damaged and restored with a BMT, the team took it as a chance to evaluate both parts of the body, the researchers say.

After a BMT, patients are vulnerable to infection and go on antibiotics to ensure the donor’s blood cells are established. Antibiotics destroy healthy microbiota in the gut until the patient stops taking them. Afterward, the gut microbiota re-establishes itself.

Blood and fecal samples were collected during the process, sometimes daily in many of the patients, which gave doctors a detailed look at the rapid changes in the patients’ microbiome and immune
systems.

The team’s previous research in the New England Journal of Medicine assessed how gut microbiota impacted patients’ health during the BMT process. That study found that greater intestinal microbiota diversity was linked with a lower risk of death after a BMT. Having a lower diversity prior to BMT was tied to a higher incidence of graft-versus-host disease, which is a complication that occurs when immune cells from a donor attack healthy tissue.

The team thinks their research, along with more closely monitoring a patient’s microbiota, can help them determine how to make BMTs safer.

“Because we have so much data collected over a period of time when the immune system of patients as well as the microbiome shift dramatically, we can start to see patterns," Jonas Schluter, PhD, a member of the team and an assistant professor at NYU Langone Health, said in a statement. "This gives us a good start toward understanding the forces that the microbiota exerts on the rebuilding of the immune system."

Xavier notes that the purpose of the work wasn’t to determine if certain microbes were good or bad, though he wants to focus on that in the future.

“The subtypes of immune cells we would want to increase or decrease vary from day to day, depending on what else is going on in the body. What’s important is that now we have a way to study this complex
ecosystem,” he said.

The researchers say they also plan to apply their data to study the immune system of patients receiving other cancer treatments.

A Research Stepping Stone

Schluter tells Verywell these findings were a “significant step for the microbiome field.” They were a stepping stone, he says.

“Much of what we know about the relationships between gut microbes and immunity comes from experiments in animals," he says. "Microbiome research has been somewhat under fire recently for its lack of human data. Our work fills this important gap, it consolidates several previous studies, and it demonstrates a link between gut microbes and immune system directly in humans."

The findings suggest that some bacteria influence the concentration of circulatory immune cell counts. Their work reveals the best bacteria candidates to test to determine if microbiota-targeted therapies that aim to modulate immune system function are feasible. This could then be used to support therapies that rely on the activity of the immune system, such as cancer immunotherapies, Schluter says.

“Our work focuses on estimating how the abundances of bacteria in the gut influence immune cell dynamics,” Schluter adds. He believes the relationship is bidirectional.

“We found some evidence for a reverse-direction association, but the potential effect of circulatory immune cell counts on bacterial populations was largely drowned out by the overwhelming effect of antibiotics that are given to our patients,” he says.

“For certain, the microbiota can change immune system cell lines (which can be either good or
bad), but also, when our immune system is dysfunctional from other toxic inputs, our gut microbiota seems to respond with dysbiosis [microbial imbalance] from immune dysfunction,” Kessmann adds.

The knowledge of how immune cell lines change in relation to specific bacteria in the gut is now evidence of how the microbiome is intricately connected to our immune system, Kessmann says, and certain cell lines are crucial to fighting off diseases. The data may be instrumental in furthering treatment ideas for conditions such as cancer, autoimmune issues, and infectious diseases.

What's Next

There’s still much to study about the link between gut bacteria and immune health, Schluter says. That’s why he thinks the scientific community is entering a new phase of microbiome research he likes to call “microbiome 2.0.”

Hopefully, that next stage of research will focus on “rational engineering of the microbiome, and develop it as a novel therapeutic target,” he says.

“Our work provides first candidates to manipulate if we want to influence immune health, but this will have to be tested in dedicated experiments, something we and many others are now working towards," he says.

The team doesn’t yet know the mechanisms underlying the links they observed, Schluter notes. “Once we understand those, we may learn what it is that microbes do to support or harm our immune system,” he says.

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  1. Schluter J, Peled JU, Taylor BP, et al. The gut microbiota is associated with immune cell dynamics in humans. Nature. 2020. doi:10.1038/s41586-020-2971-8

  2. Memorial Sloan Kettering Cancer Center. MSK Study Is the First to Link Microbiota to Dynamics of the Human Immune System. Nov. 25, 2020. 

  3. Memorial Sloan Kettering Cancer Center. Allogeneic Transplantation.

  4. Peled J, Gomes ALC, Devlin SM, et al. Microbiota as predictor of mortality in allogeneic hematopoietic-cell transplantation. N Engl J Med. 2020;382:822-834. doi: 10.1056/NEJMoa1900623