B cells from patients with multiple sclerosis have a pathogenic phenotype and increased LTα and TGFβ1 response

The contribution of B cells to the pathogenesis of relapsing-remitting multiple sclerosis (RRMS) is currently of great interest due to the positive outcomes of treatment with B cell-depleting monoclonal antibodies. In this exploratory study we examined the phenotype and cytokine response of B cells from untreated patients with RRMS and healthy controls. The CNS migration potential of the individual blood B cell subpopulations was evaluated according to the expression of CD49d, ALCAM, CXCR3, and CCR7, and cerebrospinal fluid (CSF) samples were analyzed to establish the phenotype of migrated B cells. The frequency of the individual blood B cell subsets expressing CD5, CD43, CD69, CD80, CD83, DC-SIGN and CD138 was similar in patients with RRMS and healthy controls. However, a higher percentage of CD27^-IgD^-IgM⁺ memory B cells were found in the blood of patients with RRMS, a population also identified in the CSF samples. We also observed an increased percentage of B cells producing LTα and a higher level of TGFβ1 in patients with RRMS. Altogether, we found that patients with RRMS have an increased frequency of blood CD27^-IgD^-IgM⁺ memory B cells that are recruited to the CSF together with other memory B cell populations. Furthermore, we report an increased B cell production of LTα and TGFβ1 in patients with RRMS.