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, an international research team led by scientists from University of California – San Francisco (UCSF) suggests.

In MS, other types of immune cells go haywire and attack myelin. 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.

IgA: An Unexpected Player

In Science Immunology, the researchers 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, a media release from UCSF explains.

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 the gut microbiome from growing out of control. 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, the researchers suggest.

“It was a very new idea. Nobody thought to look for this type of immune cell.”

— Sergio Baranzini, PhD, a professor of neurology and member of the UCSF Weill Institute for Neurosciences, lead author on the new study

Now the team, including scientists in Canada, Germany, Sweden, and Switzerland, has gone a step further, finding traces of the IgA antibody in the cerebrospinal fluid of MS patients during flare-ups, but not when episodes are in remission. They also found signs of IgA-producing immune cells in donated postmortem brain tissue that had been damaged during MS attacks. The findings suggest that gut immune cells are involved in MS relapses in humans.

“Only at the time of an attack was there an increase in these cells and the antibodies they produce. That really caught our attention.”

Why Are They in the Brain?

In the hopes of determining what these gut immune cells were doing in the brain, the team then looked to see what kinds of molecules the IgA antibody reacted to. Recent research has provided evidence that an unhealthy gut microbiome plays a role in MS, when certain potentially damaging species of bacteria proliferate. While the team found that IgA did not bind to myelin protein, it did bind to some of these harmful bacteria species, suggesting that, unlike other immune cells, which are known to cause damage in MS, IgA-expressing immune cells play a protective role, possibly chasing these harmful bacteria to the brain and mounting a defense against them there, the release continues.

“This opens up a whole new line of research. I think it has huge potential for therapeutics.”

— Anne-Katrin Pröbstel, MD, a former UCSF postdoctoral researcher, now at the University of Basel in Switzerland and first author on the paper

[Source(s): University of California – San Francisco, EurekAlert]

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