B cells of multiple sclerosis patients induce autoreactive proinflammatory T cell responses

•B cells of MS patients showed increased costimulatory CD80 and CD86 expression.•Immunomodulatory treatment restored B cell CD80 and CD86 expression in MS patients.•B cells of MS patients induced MBP-specific proinflammatory T cell responses.•B cell induced T cell responses were reduced in MS patients under treatment.

Antibody-independent B cell functions play an important role in multiple sclerosis (MS) pathogenesis. In this study, B cell antigen presentation and costimulation in MS were studied. Peripheral blood B cells of MS patients showed increased expression of costimulatory CD86 and CD80 molecules compared with healthy controls (HC). In MS cerebrospinal fluid (CSF), 12-fold and 2-fold increases in CD86+ and CD80+ B cells, respectively, were evidenced compared with peripheral blood. Further, B cells from MS patients induced proinflammatory T cells in response to myelin basic protein (MBP). Immunomodulatory treatment restored B cell costimulatory molecule expression and caused significantly reduced B cell induced T cell responses. Together, these results demonstrate the potential of B cells from MS patients to induce autoreactive proinflammatory T cell responses. Immunomodulatory therapy abrogated this effect, emphasizing the importance of B cell antigen presentation and costimulation in MS pathology.