Stress can have a detrimental effect on our health, and appears to contribute to the development of autoimmune diseases. Scientists have not known much about the physiology underlying that link, however. New research suggests that the bacteria that live in our gut, our gut microbiome, may be involved. Reporting in mSystems, researchers found that in a mouse model, stress-induced changes in intestinal bacteria, triggered activity in immune cells, and raised the likelihood that the body would be attacked by its own immune system.
"We know that there's strong crosstalk between the immune system and the microbiota," said immunologist Orly Avni, Ph.D. of Bar Ilan University. There are millions of microbes in our gastrointestinal tract, which carry their own genomes. Knowing how bacterial genes are working can help us understand how autoimmunity is connected to stress, noted Avni. In this work, the researchers found that stress altered the composition of the microbiome as well as how microbial genes were being expressed. "And the consequent immune response to that threat jeopardized the tolerance to self," she added.
Autoimmune conditions are highly variable among affected individuals, and teasing out the causes can be very challenging. Researchers think that genetics and the environment are both at work in most autoimmune disease patients.
For this study, the scientists were especially interested in environmental influences on autoimmunity as they might also be easily used to treat the disease. Two groups of mice were utilized in the research; one had to deal with an aggressive mouse, and thus experienced stress, while the other did not. After ten days, the microbiomes of the stressed mice were different from the unstressed mice; they exhibited high levels of certain bacterial strains including two, Bilophila and Dehalobacterium, which have also been found in high amounts in multiple sclerosis patients.
The scientists also found that some of the microbial genes that were activated might be related to virulence, like motility and growth, in those bacteria. The microbes in the stressed mice might have the potential to move to other parts of the body, like the lymph nodes, where they can stimulate an immune response. An analysis of the stressed mice seemed to support this idea; they had high levels of an immune cell type, effector T cells, that are linked to autoimmunity.
This work has suggested a potential causal link between stress and illness, but much more work will be needed to both confirm causality as well as replicate the findings in humans.
Avni wants to know more about how the bacterial stress response impacts their hosts. "It's not enough to study the composition or the increase or decrease of a species," she said. "We also have to understand how the microbiota sense us, and how they change their 'behavior' accordingly." If we have that information, we might be able to create therapeutic microbial interventions.
Learn more about how a gut microbe can cause illness when it migrates to another part of the body from the video above.