Two new papers have linked multiple sclerosis to the certain bacteria in the gut microbiome, a term for the trillions of bacteria than inhabit human intestines. Multiple sclerosis, or MS, is an autoimmune disorder that affects 2.5 million people globally. By damaging the protective covers of nerve cells, MS can cause blindness, muscle weakness, and can even prove fatal.
The new studies shed light on exactly how the activity of the gut microbiome may cause the immune system to attack nerve cells, knowledge that could pave the way to drugs based on microbial byproducts, which could help patients fighting the effects of the disease.
While prior studies have identified certain bacteria that are present in higher levels in MS patients, scientists have relatively little understanding about what specifically causes MS. The new studies go further in identifying how these bacteria lead to the condition.
One paper, by UC San Francisco geneticist Sergio Baranzini and colleagues, investigated the gut microbiomes of 71 people with MS and 71 healthy people. The study found two groups of bacteria at levels four time higher in the MS patients: Acinetobacter and Akkermansia. A third group, Parabacteroides, was found to be four times as abundant in the healthy individuals.
The team took “naïve immune cells” from healthy people, then exposing them to bacteria from the intestines of MS patients. These cells transform in response to pathogens they encounter in the body. When they encountered Acinetobacter and Akkermansia, they transformed into a type of T helper cell that triggers inflammation, assisting the immune system in fighting off invaders and killing infected cells. However, Acinetobacter also lowered the production of regulatory T cells, which help to avoid autoimmune diseases by diminishing the autoimmune response.
When they implanted MS gut bacteria to germ-free mice, within 20 days, the mice developed severe brain inflammation.
“But when we transferred the gut microbes from healthy people, the mice didn’t get nearly as sick,” according to Baranzini.
In another study published recently in the journal Proceedings of the National Academy of Sciences, a team of immunologists led by Gurumoorthy Krishnamoorthy and Hartmut Wekerle from the Max Planck Institute of Neurobiology analyzed the gut microbiomes of 34 sets of identical twins, in which only one of the two twins had MS. The team found that Akkermansia was present in significantly higher amounts in the MS patients than in their twins. Transferring microbes from the MS patients to mice predisposed to develop a condition similar to MS, they found that in 12 weeks, brain inflammation was three times as common in the mice with MS bacteria as in mice with microbes from disease-free donors.
The microbes from MS patients also apparently blocked the production of molecules that fight inflammation.
Together, these studies suggest that certain intestinal bacteria may block important anti-inflammatory molecules, leading to MS, alongside environmental and genetic factors. These findings could someday help researchers develop treatments involving drugs or even anti-inflammatory bacteria. But the authors of both studies admit there is much more research to be done before this can become a reality.
According to Baranzini: “Therapeutic applications are in everyone’s mind. But it’s still too early to think about that.”