How the immune system maintains the balance between intestinal bacteria – healing practice

Intestinal bacteria are specifically regulated by the immune system

Our intestines contain billions of intestinal bacteria, fungi and other microorganisms. A healthy balance between up to 1000 different bacterial strains is an important basic requirement for our overall health. If the intestinal flora is out of balance, numerous diseases can arise. A research team has now shown that the immune system plays a key role in maintaining the balance in the intestines.

Researchers from the Department of BioMedical Research (DBMR) at the University of Bern, the Inselspital, Universitätsspital Bern and the German Cancer Research Center have documented how antibodies in the intestine keep bacteria of the intestinal flora in check. The research results were recently published in the renowned specialist journal “Nature” presents.

Gut microbiome is important to our health

Around 500 to 1000 different types of intestinal bacteria populate the intestine, according to the working group. They make up the majority of the so-called intestinal microbiome. Studies over the last few years have shown that this microbiome has a decisive influence on our health and even on it Gut-brain axis communicates with the brain. The intestinal flora plays a central role in digestion and in preventing infections.

The immune system as a guardian of the intestinal flora

Gut bacteria are usually tolerated by the immune system. In contrast to pathogens, antibodies normally do not attack the intestinal bacteria. So until now it was unclear how the human immune system manages to maintain the balance in the intestine. The research group around Dr. Tim Rollenske and Professor Andrew Macpherson were now able to show in a mouse model how certain cells of the immune system, known as IgA antibodies, fine-tune the microbial balance in the intestine.

“We were able to show that the immune system specifically recognizes these bacteria and restricts both growth and activity,” explains first author of the study, Dr. Tim Rollenske. As the researchers explain, IgA antibodies are the most common antibodies in the human immune system. They are secreted by specialized cells in the mucous membranes and make up two thirds of human immunoglobulins (antibodies circulating in the blood).

Breakthrough in research into the intestinal flora

It was already known that some IgA antibodies produced by the immune system were also directed against benign intestinal bacteria. Without these antibodies, certain strains of bacteria could spread excessively and thus become pathogenic. How the immune system succeeds in regulating it has so far been considered insufficiently understood, as studies of IgA antibodies in their natural form in animal models have so far only been possible to a limited extent.

The working group was now able to overcome this hurdle in its experiments. The researchers succeeded in producing a sufficient number of IgA antibodies that were specifically directed against a type of Escherichia coli bacteria, a typical intestinal bacterium. The study team reports that the antibodies recognized and bound a building block on the shell of the microorganisms.

IgA antibodies as supervisors in the intestine

Over a period of three years, the researchers observed the effects of IgA antibodies on intestinal bacteria. It was shown that the antibodies specifically limit the fitness of the intestinal bacteria. For example, the mobility or the uptake of sugar building blocks for the metabolism of the bacteria was limited by the IgA antibodies.

According to the working group, the effect was dependent on which surface building block was specifically recognized. “The immune system apparently has the possibility of influencing the benign intestinal bacteria in different ways at the same time,” adds study co-author Hedda Wardemann from the German Cancer Research Center. The effect is therefore called “IgA parallelism”.

Some questions still remain open

How exactly the IgA antibodies succeed in restricting benign intestinal bacteria, but immediately and effectively killing pathogenic invaders, could not be conclusively clarified within the scope of the study. “Our experiment shows, however, that IgA antibodies can fine-tune the balance between the human organism and the intestinal flora,” emphasizes Professor Macpherson.

What is the significance of the findings

According to the researchers, the new findings expand the basic understanding of the immune system in the intestine. This could, for example, help improve vaccine development. “If we understand how and where exactly the antibodies recognize the microorganisms in the intestine, we can also design vaccines against pathogenic organisms in a more targeted manner,” sums up Dr. Rollenske. (vb)

Author and source information

This text complies with the requirements of specialist medical literature, medical guidelines and current studies and has been checked by medical professionals.


Diploma-Editor (FH) Volker Blasek


  • Tim Rollenske, Hedda Wardemann, Andrew J. Macpherson, et al.: Parallelism of intestinal secretory IgA shapes functional microbial fitness; in: Nature, 2021,
  • University of Bern: Immune system keeps intestinal flora in balance (published: October 13, 2021),

Important NOTE:
This article is for general guidance only and is not intended to be used for self-diagnosis or self-treatment. He can not substitute a visit at the doctor.


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