Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system, in which the body's own immune cells attack the fatty, insulating myelin sheath surrounding nerve fibers. The regeneration of intact myelin sheaths is a necessary prerequisite for patients to recover from MS relapses. Nevertheless, the body's ability to regenerate myelin decreases with age. A team led by Prof. Mikael Simons from the Technical University of Munich (TUM) has now found a possible explanation. Fat derived from myelin, which is not carried away rapidly enough by phagocytes, can trigger chronic inflammation that, in turn, impedes regeneration. Furthermore, in a second publication, Simons' team describes the discovery of novel cell type, which appears only when a myelin sheath is being created. The myelin sheath plays a decisive role in the function of the central nervous system. It is a specialized membrane enriched in lipids, which insulates nerve fibers so that electrical signals can be passed on quickly and efficiently.