Gut microbiome changes linked to multiple sclerosis, study finds

The gut microbiome comprises the trillions of bacteria and other microorganisms that live in our digestive tracts, and it has been increasingly connected to human health and disease. A new Yale study reveals significant differences between the gut microbiomes of individuals recently diagnosed with multiple sclerosis (MS)—an autoimmune disease that impacts the central nervous system—and healthy individuals.

The study, published recently in Neurology Neuroimmunology & Neuroinflammation, identified gut bacteria that had significantly different levels of abundance in patients with MS. It also found that, compared to healthy individuals, those with MS had a smaller number of bacteria coated in an antibody known as host immunoglobulin A (IgA).

These antibodies are pumped into the gut by immune cells that live in the mucosa—the soft tissue that lines the intestines—and they bind to specific groups of bacteria, triggering their removal.

“The fact that fewer bacteria were coated with IgA in patients with MS suggests that there is perhaps a fundamental disconnect going on with the host-microbe interactions,” says Erin Longbrake, MD, Ph.D., associate professor of neurology and the study’s principal investigator.

Scientists still haven’t discovered the cause of MS, but emerging research suggests that environmental risk factors that stem from outside the body, such as poor diet and smoking, can contribute to the development of the disease. This makes the microbiome an intriguing area of study to learn how multiple sclerosis develops.

“The microbiome interfaces with the environment as well as the immune system,” says Longbrake. “Theoretically, the environmental risk factors could predispose people to MS because they change the bugs that are in the gut.”

MS associated with a smaller proportion of IgA-coated bacteria

The researchers recruited 43 people who were newly diagnosed with MS and had not started any sort of immune therapy to treat the disorder, as well as 42 healthy controls, all of whom gave stool samples. The researchers first isolated the bacteria from these samples. They then divided the bacteria into those bound with IgA and those that were not and measured the abundance of the various bacteria species.

The researchers found that patients who had been recently diagnosed with MS had a significantly smaller proportion of gut bacteria coated in IgA. They also identified differences in the specific bacteria that populated the gut in these patients. Some of these bacteria had been identified in prior research. For example, the researchers observed that species of Faecalibacterium were less abundant in patients with MS, which was in line with previous findings. They also discovered new differences, such as a species of Monoglobus that was more abundant in untreated MS patients.

Of the 43 people with MS, 19 gave the researchers an additional stool sample six months after starting B-cell depletion therapy—a treatment that destroys immune cells that contribute to autoimmune diseases. The gut microbiomes of these patients, the research team found, more closely resembled the microbiomes of healthy controls than they had pre-treatment. “This gives us some clues into the mechanisms underlying how this type of drug works to treat MS,” Longbrake says.

The findings might help explain why some people develop MS, but not others. Scientists could also potentially one day use patterns of microbes in the gut as biomarkers for predicting who is most at risk. “We’re still analyzing what our results mean and how we can use this information to improve care,” says Longbrake. “These are areas to investigate in the future.”