Changes in the gut microbiome alter the activity of immune cells in the brains of mice with an experimental form of multiple sclerosis (MS), reports a study published online this week in Nature. The work, which broadens our understanding of the interactions between gut and brain, could aid the development of new therapies for MS and other neurological disorders.

In MS, the brain’s normally quiescent immune system awakens and non-neuronal cells known as microglia and astrocytes become active. Francisco Quintana and colleagues show how metabolites of dietary tryptophan, which are produced by gut bacteria, dampen the pro-inflammatory activity of both cell types in a mouse model of MS. Additional studies on MS brain tissue suggest that a similar mechanism is at play in the human brain.

The activity of these immune cells becomes altered when metabolites of dietary tryptophan bind to a specific receptor on the cell surface. The same receptor also binds other naturally occurring compounds, including derivatives from plants such as broccoli. Therapies that target components of the related molecular pathway could one day prove useful in MS treatment, but the study also suggests that inflammatory brain diseases could be dampened indirectly via the gut.