Our gut microbiota and our immune system work together

The wildlife in our guts determines the strength of our immune system. This is how we can summarize in a few words the work of the researchers of the Memorial Sloan Kettering Cancer Center (United States). Gathered in a multidisciplinary team, they have shown that the gut microbiota and the concentration of different types of immune cells in our blood shape our immune system. The results of this study were published on November 25, 2020 in the journal Nature.

The intestinal microbiota, also called intestinal flora, represents all the bacteria, fungi and microorganisms that populate the interior of our digestive tract. All this fauna contributes to the good health of our body, because it is essential to guarantee functions such as digestion and the synthesis of essential elements for our body.

Studying the “rebirth” of immunity after cancer

“The scientific community had previously accepted the idea that the gut microbiota was important for the health of the human immune system, but the data used to make this hypothesis came from animal studies.says Joao Xavier, a systems biologist at the Sloan Kettering Institute and co-author of the study. In our laboratory, we have an amazing opportunity to follow how the composition of the microbiota changes in people treated for blood cancers.. “

To do this, the researchers used data collected from more than 2,000 patients who had participated in studies on the subject over the past decade. Their research has focused on the different types of immune cells found in the blood, as well as how they evolve, depending on whether or not there are bacterial strains in the gut.

The data used for this study comes from people who received an allogeneic stem cell and bone marrow transplant. When a patient is given chemotherapy and radiotherapy sessions to destroy cancerous blood cells, the cancer cells are replaced with donor stem cells to make new blood cells.

During the first few weeks, before donor blood cells, including the white blood cells that make up the immune system, are available to the body, patients remain vulnerable to infection. To protect them, antibiotics are given to strengthen them. However, these antibiotics can have unwanted side effects, including destroying part of the gut microbiota. During this time, some dangerous tensions for our body can settle to fill the void. When the patient’s immune system has recovered, the antibiotics are stopped and the gut microbiota can resume and take its place in the body.

A diverse microbiota, the key to good immunity

It is the concomitant phenomenon between our microbiota and our immunity that interests Jonas Schluter, assistant professor at Langore Health University Medical Center and co-author of the study. “The parallel recoveries of the immune system and the microbiota, both damaged and then restored, give us a unique opportunity to analyze the associations between these two systems.“

For years, researchers have been collecting and analyzing stool and blood samples from bone marrow transplant patients. The resulting database contains details on the types of microbes that live in the gut of patients at different times. The team then used machine learning algorithms to extract meaningful data from electronic health records. The data in these records included the types of immune cells present in the blood, information about the drugs given to patients, and the side effects they experienced.

A previous study published earlier this year had already shown that the presence of a great diversity of species in the gut microbiota was linked to a lower risk of death after a bone marrow transplant. Additionally, the presence of low microbiota diversity prior to transplantation has been found to lead to a higher likelihood of graft-versus-host disease, a life-threatening complication in which donor immune cells attack healthy tissues.