Multiple sclerosis is an inflammatory disease of the central nervous system (CNS) mediated by autoimmune T- and B-lymphocytes. The role of B cells is largely unknown. A recent study showed that brain resident cells (astrocytes) produce a factor, named BAFF, which promotes the survival of B-lymphocytes. While BAFF is present in the healthy brain, its production is highly elevated in inflammatory brain lesions of MS patients. Thereby the CNS seems to provide a “B cell friendly” environment which promotes the survival of inflammatory cells inside of the CNS of MS patients.