The recent research provides evidence as to why stress is one of the factors of autoimmune diseases. This new study proves that continues social stress can negatively affect the gut microbiota or the microorganisms which then triggers different harmful immune responses.
A person develops an autoimmune disease when its own immune system starts attacking the body’s tissues, organs, and cells. The immune system at that time considers them as a foreign particle for example bacteria and viruses. “Many studies support the notion that stressful life events play a role in the etiopathogenesis of autoimmune disorders,” the author says.
According to the information given by the National Institute of Allergy and Infectious Diseases, there are approximately 80 autoimmune diseases which can easily attack anyone including type 1 diabetes, lupus, and rheumatoid arthritis. Type 1 diabetes is the most common autoimmune disease affecting 1.25 million people in America. While autoimmune diseases are found in 5% of the population worldwide.
Researchers while working on this disease found stress as a possible risk factor, however, the mechanism involved in this is still unclear.
A group of researchers from the Bar Ilan University in Israel found that mice under social stress-related conditions increase the production of effector T helper cells. These are a type of immune cells which performs the function of autoimmunity in the body.
Findings of the research paper “Social-Stress-Responsive Microbiota Induces Stimulation of Self-Reactive Effector T Helper Cells” are published in the journal mSystems.
“We know that there’s strong crosstalk between the immune system and the microbiota,” said lead study author and immunologist Orly Avni, Ph.D. Avni with her team worked on this project and found that continuous stress does not only pose a threat to genes expression of the gut bacteria in the mice but also changes their composition.
She explains, “And the consequent immune response to that threat jeopardized the tolerance to self.”
All the autoimmune disease patients would face different symptoms
As per the statistics of the American Autoimmune Related Diseases Association around 50 million people in the United States are going through some type of autoimmune disease.
There are many diseases which develop more frequently in women than men, and researchers are unaware of the causes of most of these diseases.
Researchers firmly believe that other than inheritance there are many other risk factors too for autoimmune diseases out of which one of them is the complex interaction between the genes and its surroundings.
The researchers found the study on the cause of the autoimmune diseases challenging because of the severeness of the manifestations and its varied nature. This variation is not only observed across the different conditions but within them too.
For instance, if a patient develops multiple sclerosis (MS), he may have unpredictable manifestations from being relatively benign to devastating. Multiple sclerosis could even limit one’s movements, senses or activities.
It is a disease in which the person’s immune system attacks its own myelin sheath which is a protective protein layer on the nerve fibers in the central nervous system. Myelin sheath also serves for insulation of the nerves. The symptoms of the disease begin with eyesight issues and then slowly progresses to weakness and poor balance and coordination.
In comparison, in a rare and disabling disease called scleroderma, there is an overproduction of collagen and other proteins forming abnormal connective tissues. This type of autoimmunity induces a condition called fibrosis.
This disease can affect different parts of a human body for example skin, various internal organs, and blood vessels. Variety exists in this type of disease from fibrosis being localized or systemic.
Persistent stress transforms the genes of gut bacteria in mice
For the conduction of the study, researchers set two groups of mice; one had mice going through some social stress while the other one was a control group. The mice of the social stress set were forced to face other hostile dominant mice. On the other hand, the control group was kept far away from any type of possible social stress.
Researchers explain that in order “to determine whether social stress increases the risk for autoimmunity in genetically susceptible mice, myelin oligodendrocyte glycoprotein (MOG)-specific T cell receptor transgenic (2D2) mice, of which 30% develop spontaneous autoimmune optic neuritis within their first year of life (20), were subjected to chronic social defeat (SD).”
“SD is an established model for social stress and depression, wherein an intruder is repeatedly exposed to attacks and threats from a dominant resident.”
On analyzing the gut microbiota of mice of both the sets, they found that the social stress group developed more Bilophila and Dehalobacterium than the controls. Researchers also find a similar type of bacteria in high concentration in patients with multiple sclerosis.
According to the research paper, “The stress-influenced microbiota increased the presence of effector T helper cells in the mesenteric lymph nodes, including myelin-autoreactive cells. Inhibition of the bacterial quorum sensor QseC, which is also responsive to norepinephrine, diminished the presence of effector T helper cells and bacteria such as Acinetobacter in the mesenteric lymph nodes, without remarkably affecting the gut microbial composition.”
The further research led cleared that it is stress which alters some of the important genes of the gut microbiota in mice. The important changes which need to be noted include the gene changes which trigger the bacterial growth and their movement. These changes help the gut microbes in relaying signals to the host and vice versa.
The change in the expression of these genes can increase the chances of the gut microbes to travel outside the gut. The microbes travel to the nearby lymph nodes where they initiate immune responses. The mice of the stress group had increased concentration of pathogenic bacteria as well as effector T cells. This included the “including myelin-autoreactive cells.”
The research suggests that these progressive changes due to stress in the gut bacteria and the immune cells increase the risk of an autoimmune attack. Avni still alerts that it might appear that gut bacteria and stress have a close relationship, there a dire need to research how these events play their role in the longer term.
Researchers believe that by understanding this complex and deep connection between gut microbiota and stress one day they will be able to discover various gut microbe treatments for autoimmune diseases which are triggered by stress.
“It’s not enough to study the composition or the increase or decrease of a species. We also have to understand how the microbiota senses us and how they change their ‘behavior’ accordingly,” says Orly Avni, Ph.D.