Researchers have designed a probiotic to suppress autoimmunity in the brain. In a new study, researchers demonstrated the treatment’s potential using a preclinical model of multiple sclerosis. The findings suggest the technique offers a more precise way to target brain inflammation with reduced negative side effects compared to standard therapies.

Autoimmune diseases that affect the brain, such as MS, are particularly challenging to treat because of their location – many pharmacological therapies can’t effectively access the brain because of the blood-brain barrier, a protective mechanism that separates the brain from the circulatory system.

To look for new ways to treat autoimmune diseases, the researchers from Brigham and Women’s Hospital studied dendritic cells, a type of immune cell that is abundant in the gastrointestinal tract and in the spaces around the brain. These cells help control the rest of the immune system, but scientists don’t yet know their role in autoimmune diseases. By analyzing dendritic cells in the central nervous system of mice, they were able to identify a biochemical pathway that dendritic cells use to stop other immune cells from attacking the body.

The researchers found that this biochemical pathway can be activated with lactate, a molecule involved in many metabolic processes. The researchers were then able to genetically engineer probiotic bacteria to produce lactate.

They tested their probiotic in mice with a disease closely resembling MS. They found that even though the bacteria live in the gut, they were able to reduce the effects of the disease in the brain. They did not find the bacteria in the bloodstream of the mice, suggesting that the effect they observed was a result of biochemical signaling between cells in the gut and in the brain.

Results of animal model studies sometimes do not translate to humans and may be years away from providing a marketable treatment. However, the researchers are optimistic that the approach could be readily translated into the clinic because the strain of bacteria they used to create their probiotic has already been tested in humans.

The results are published in the journal Nature.