Multiple sclerosis (MS) is an electrical disorder, or rather one of impaired myelin, a fatty, insulating substance that better allows electric current to bolt down our neurons and release the neurotransmitters that help run our bodies and brains. Researchers have speculated for some time that the myelin degradation seen in MS is due, at least in part, to autoimmune activity against the nervous system. Recent work presented at the MS Boston 2014 Meeting suggests that this aberrant immune response begins in the gut.
Eighty percent of the human immune system resides in the gastrointestinal tract. Alongside it are the trillions of symbiotic bacteria, fungi and other single-celled organisms that make up our guts’ microbiomes. Normally everyone wins: The microorganisms benefit from a home and a steady food supply; we enjoy the essential assistance they provide in various metabolic and digestive functions. Our microbiomes also help calibrate our immune systems, so our bodies recognize which co-inhabitants should be there and which should not. Yet mounting evidence suggests that when our resident biota are out of balance, they contribute to numerous diseases, including diabetes, rheumatoid arthritis, autism and, it appears, MS by inciting rogue immune activity that can spread throughout the body and brain.
One studypresented at the conference, out of Brigham and Women’s Hospital (BWH), reported a single-celled organism called methanobrevibacteriaceae that activates the immune system is enriched in the gastrointestinal tracts of MS patients whereas bacteria that suppress immune activity are depleted. Other work, which resulted from a collaboration among 10 academic researcher centers across the U.S. and Canada, reported significantly altered gut flora in pediatric MS patients while a group of Japanese researchers found that yeast consumption reduced the chances of mice developing an MS-like disease by altering gut flora.
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Sushrut Jangi, a staff physician at Beth Israel Deaconess Medical Center in Boston who co-authored the BWH study, thinks that regional dietary influences might even be at play. “The biomes of people living in different areas and who consume Western versus non-Western diets are demonstratively different,” he says. “People who emigrate from non-Western countries, including India, where MS rates are low, consequently develop a high risk of disease in the U.S. One idea to explain this is that the biome may shift from an Indian biome to an American biome,” although there is not yet data to support this theory.
The microbiome theory is gaining so much steam in academia that a coalition of four U.S. research centers called the MS Microbiome Consortium recently formed to investigate the role of gut microorganisms in the disease. The group presented data in Boston showing significantly different gastrointestinal bacterial populations in patients treated with the MS drug glatiramer acetate compared with untreated subjects. How exactly the drug suppresses MS activity is unknown but the findings suggest that perhaps it works in part by altering gut flora and, as a result, suppressing abnormal immune activity. “The gut is well-positioned for an important role in the development of autoimmune disease, including MS.,” says Ilana Katz Sand, an assistant professor of neurology at Mount Sinai Medical Center in New York City and member of the MS Microbiome Consortium. “But important questions remain, such as how MS medications affect the microbiome, how an individual’s microbiome may affect treatment responses, whether particular bacterial species are associated with more severe disease and ultimately whether we can manipulate the microbiome to benefit our patients.”
Katz Sand says that dietary and probiotic approaches to treating MS are worth pursuing, as is a less palatable approach: fecal transplantation. Yet answers in science and medicine are rarely simple, she added, pointing out that in all likelihood MS arises from a complicated confluence of genetic and environmental influences that might ultimately trigger autoimmune activity. Beyond just our gut flora well over 100 genetic variants—many related to immune function—are now known to contribute to the disease as are external factors including vitamin D deficiency (MS is more common at higher latitudes), smoking and increased salt intake.
Further confounding our ability to pinpoint root causes is that our genetic code influences how our bodies and brains respond to these external factors. It could be that both genes and environmental stimuli lead to pathologic microbiomes or that some unfortunate combination of these factors leads to a common autoimmunologic pathway that ravages myelin. “We know the microbiome shapes our immune system and that MS is an immune-mediated disease. We also know that genes influence our microbiomes and immune systems,” says David Hafler, professor of neurology and immunobiology at Yale University School of Medicine who was at the conference but not involved in the microbiome work presented. But there must be nongenetic factors contributing to the disease, too, given that the incidences of MS and other autoimmune disorders are increasing.
“Maybe it’s a lot of little factors like low vitamin D, increased body mass index and increased salt intake,” Hafler says, “but I wouldn’t be surprised if it was one big thing, much like how H. pylori was found to cause ulcers. No one’s identified a clear bug that’s driving MS but I think it’s important we keep looking.”