Functional characterization of IgD^-CD27^- double negative B cells in multiple sclerosis pathology

Abstract

Recently, our research group showed an increased population of IgD-CD27- double negative (DN) B cells with pro-inflammatory characteristics in about 20% of multiple sclerosis (MS) patients. However, their exact function in MS remains unknown. Additionally, novel findings in mouse models suggested a role for T-bet+ B cells, with similar characteristics as DN B cells, in autoimmune responses. Therefore, we hypothesized that DN B cells contribute to neuroinflammation in MS patients through autoreactive and pro-inflammatory functions regulated via T-bet expression. Using flow cytometry, we showed that DN B cells of untreated MS patients express the transcription factor T-bet, whereby their expression levels were the highest and significantly increased compared to naive and NCSM B cells, indicating their possible involvement in autoimmune diseases. Additionally, DN B cells of untreated MS patients expressed the chemokine receptors CXCR3 and CXCR5. By performing an in vitro chemotaxis assay, we demonstrated the in vitro migration capacity of DN B cells of untreated MS patients towards CXCL13 and CXCL10, which are involved in B cell recruitment into the CNS of MS patients. Furthermore DN B cells were strongly activated following CpG2006 stimulation, indicating that they are no unresponsive, terminally differentiated cells. Future research into DN B cells will result in better insights into MS pathogenesis and discovery of new therapeutic targets.