B cells expressing CD5 are increased in cerebrospinal fluid of patients with multiple sclerosis.

By two-colour flow cytometric analysis, we found increased numbers of B cells co-expressing the pan-T cell marker CD5 and the B cell marker CD19 in cerebrospinal fluid (CSF) of 21 patients with multiple sclerosis (MS), compared with 17 control subjects with muscular tension headache. Only one patient with MS, but nine controls lacked CD5+ B cells in CSF. This difference was not observed in peripheral blood. Numbers of CD5+19+ B cells were increased in CSF compared with blood in MS, but not in the controls. In both groups, CD5+19+ B cells were not restricted to small resting lymphocytes, but were also found among larger-sized lymphocytes. The relative density of CD5 molecules and of CD19 molecules was lower in CD5+19+ than in CD5-19+ B cells and CD5+19- T cells. CD5+ B cells are assumed to be responsible for autoantibody production, and our results suggest a pathogenetic role of such cells, predominantly within the central nervous system, in MS.