Multiple sclerosis: a link with the intestinal flora

Intestinal flora, also known as intestinal microflora or intestinal microbiota, is a set of microorganisms that live in the intestines. In recent years, scientists have become more and more interested in it. From his condition could depend chronic fatigue, intestinal worms or the effects of immunotherapies. And recently, scientists have even discovered a link between gut flora and central nervous system sites of inflammation in multiple sclerosis (MS). According to their study published on December 22 in the journal Science Immunology, a specific class of immune cells would play a central role in this gut-brain axis that has just been identified. Eventually, these results could make it possible to create new treatments for MS, an inflammatory and degenerative disease of the brain and spinal cord, which today affects 2.5 million people worldwide.

Currently, treatments for multiple sclerosis are based on the elimination of IgA-producing B cells (or IgA B) from the blood of patients. Immunoglobulin A (IgA) represents a class of antibodies specialized in the immune defense of the mucous membranes. However, a few years ago, an international team from the University of Basel and the University Hospital of Basel (Switzerland) discovered that it was better not to eliminate too many B cells at the risk of aggravating disease.

Today, by analyzing stool samples from patients with multiple sclerosis and from healthy people, the same researchers have observed that the patients have B cells that specifically target the bacteria typical of the disease. They then analyzed the role of these immune cells during acute attacks in 56 patients. They then discovered that IgA B cells accumulated in the cerebrospinal fluid and brain tissue of patients with sites of acute inflammation.

An anti-inflammatory effect

“Apparently, these immune cells migrate from the intestine to sites of inflammation in the central nervous system, where they release an anti-inflammatory messenger substanceexplains Dr. Anne-Katrin Pröbstel, who conducted the study. This could explain why the disease worsens if these immune cells are removed from the blood with drugs”, she continues. Thus, these cells would form a bridge between the intestinal flora and the sites of inflammation of the central nervous system, thus exerting an anti-inflammatory effect.

“We knew from previous studies that the composition of the gut flora plays a role in multiple sclerosis. But it was not yet known exactly how gut bacteria and immune cells influence each other.”, welcomes Dr. Pröbstel.

It remains to be understood what precisely activates IgA B cells as helpers against multiple sclerosis and triggers their migration from the intestine to the central nervous system. “If we find the trigger, we could use it to treat MS”, explains Dr. Pröbstel. Scientists could, for example, modify the composition of the intestinal flora of patients in a targeted manner in order to mobilize IgAB cells as helpers against inflammation in the nervous system.

Every case of MS is unique

Multiple sclerosis is an inflammatory disease that destroys myelin causing nerve fiber degeneration. Each case is unique: neither the number of relapses nor the age of diagnosis can predict the patient’s future. Some forms of the pathology lead to no physical difficulty while others can progress rapidly and become very debilitating. Finally, some people experience only one flare-up in their lifetime. Today, many treatments exist allowing patients to lead a fulfilling social, family and professional life. At the cost, however, of great fatigue.

But recently, other researchers have developed a treatment which could stop the progression of the disease while preserving the immune system, thanks to the antigens present in extracellular vesicles. Successfully tested on animals, the therapy may work well on humans too.