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An international research team led by UCSF scientists has shown, for the first time, that gut immune cells travel to the brain during multiple sclerosis (MS) flare-ups in patients. These gut cells seem to be playing a protective role, helping drive MS symptoms back into remission.

Scientists know that in MS, other types of immune cells go haywire and attack myelin, crucial insulation material that helps nerve cells communicate with one another quickly and reliably. The resulting damage leads to periodic MS attacks that can leave patients struggling with vision loss, memory problems, pain and other symptoms. These "relapse" symptoms often subside on their own after days or weeks, but medical experts still don't have a good understanding of what flips the switch from flare-up to remission and back again.

The new findings, published November 20, 2020 in Science Immunology, suggest that an unexpected new player might help bring flare-ups under control: immune cells from the gut that express a type of antibody called IgA. In the gut, these cells serve as a critical first line of defense against foreign invaders and, scientists think, help keep the teeming bacteria of our gut microbiome from growing out of control. Recently, a UCSF-led international research team made the surprising discovery that, in animal models of MS, these gut immune cells leave the digestive system and travel to the brain where they appear to help cut inflammation.

"It was a very new idea," said Sergio Baranzini, Ph.D., a professor of neurology and member of the UCSF Weill Institute for Neurosciences, lead author on the new study. "Nobody thought to look for this type of immune cell."