INCREASED EXPRESSION OF B7-1 COSTIMULATORY MOLECULE ON CEREBROSPINAL-FLUID CELLS OF PATIENTS WITH MULTIPLE-SCLEROSIS AND INFECTIOUS CENTRAL-NERVOUS-SYSTEM DISEASE

The expression of the costimulatory molecule B7-1 (BB-1; CD80) and its ligand CD28 was investigated on peripheral blood (PB) and cerebrospin al fluid (CSF) T and B lymphocytes and monocytes in 11 patients with r elapsing-remitting multiple sclerosis (MS), 21 age-matched healthy con trols and 10 patients with central nervous system (CNS) infectious dis ease (CID). Three channel flow cytometry was used with a novel gating technique in order to unambiguously identify the low numbers of B lymp hocytes present in normal CSF. There was a significantly higher fracti on of B7-1(+) B lymphocytes in the CSF of patients with MS (72%) and C ID (69%) when compared with healthy individuals (53%; p < 0.0001 and p < 0.002, respectively). Furthermore, two patients with a clinical pic ture of encephalitis showed a profoundly increased B7-1 expression on CSF monocytes. Comparison of absolute numbers of B7-1(+) B lymphocytes /mL CSF between MS patients and healthy controls revealed a highly inc reased frequency of these cells among MS patients (235 cells/mL in MS patients versus 3.9 cells/mL in controls; p < 0.0001) with no overlap between the groups, which was otherwise seen for all other analyzed ce ll populations. We therefore hypothesize that activated B lymphocytes expressing high levels of B7-1 may be of pathogenetic importance in th e development and maintenance of the MS disease.