The messenger molecule interleukin 17 (IL-17) does not contribute directly to the development of multiple sclerosis (MS) in the central nervous system (CNS). However, IL-17 does influence the development of experimental autoimmune encephalomyelitis (EAE), the animal model for MS, through the gut microbiome. Current therapies against chronic-inflammatory autoimmune diseases, which target the biological function of IL-17, must therefore be considered with caution due to potential long-term adverse effects on intestinal health. Scientists of the University Medical Center Mainz have now published these important findings in the current issue of the renowned journal “Science Immunology”.