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Abnormal B-Cell Cytokine Responses A Trigger of T-Cell–Mediated Disease in MS?

Objective: To study antibody-independent contributions of B cells to inflammatory disease activity, and the immune consequences of B-cell depletion with rituximab, in patients with multiple sclerosis (MS).Methods: B-Cell effector-cytokine responses were compared between MS patients and matched controls using a 3-signal model of activation. The effects of B-cell depletion on Th1/Th17 CD4 and CD8 T-cell responses in MS patients were assessed both ex vivo and in vivo, together with pharmacokinetic/pharmacodynamic studies as part of 2 rituximab clinical trials in relapsing–remitting MS.Results: B Cells of MS patients exhibited aberrant proinflammatory cytokine responses, including increased lymphotoxin (LT):interleukin-10 ratios and exaggerated LT and tumor necrosis factor (TNF) secretion, when activated in the context of the pathogen-associated TLR9-ligand CpG-DNA, or the Th1 cytokine interferon-y, respectively. B-Cell depletion, both ex vivo and in vivo, resulted in significantly diminished proinflammatory (Th1 and Th17) responses of both CD4 and CD8 T cells. Soluble products from activated B cells of untreated MS patients reconstituted the diminished T-cell responses observed following in vivo B-cell depletion in the same patients, and this effect appeared to be largely mediated by B-cell LT and TNF.Interpretation: We propose that episodic triggering of abnormal B-cell cytokine responses mediates ‘bystanderactivation’ of disease-relevant proinflammatory T cells, resulting in new relapsing MS disease activity. Our findings point to a plausible mechanism for the long-recognized association between infections and new MS relapses, and provide novel insights into B-cell roles in both health and disease, and into mechanisms contributing to therapeutic effects of B-cell depletion in human autoimmune diseases, including MS.

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