Impact of B cell-depletion on plasma cells in a pre-clinical model of meningeal inflammation and subpial demyelination

Abstract Anti-CD20 B cell depletion therapy has provided evidence for the pathogenic roles of B cells in multiple sclerosis (MS). Terminally differentiated plasma cells (PCs) are spared by anti-CD20, and our lab has previously shown that during experimental autoimmune encephalomyelitis (EAE), IgA+ PCs mediate protection against neuroinflammation. One hypothesis is that in addition to depleting pro-inflammatory B cells, anti-CD20 also removes the major consumers of BAFF (i.e. B cells) thus promoting a favourable niche for regulatory PCs and may represent an additional mechanism by which anti-CD20 therapy confers protection. Adoptive transfer EAE of PLP-primed Th17 cells into SJL/J mice leads to ascending paralysis and meningeal inflammation which parallels brain pathology seen in human MS. Mice were prophylactically treated with anti-CD20 (10mg/kg) or isotype control antibodies which we re-administered throughout the course of the experiment and monitored daily for clinical symptoms. We find that anti-CD20 treatment effectively depleted B cells (but not T cells) in the periphery; within the central nervous system, meningeal immune clusters formed in both anti-CD20 and isotype control treated mice, with the former being devoid of B220+ B cells. Compared to control treated mice, anti-CD20 treated mice showed limited subpial demyelination and pathology adjacent to B cell-less meningeal immune clusters, and is accompanied by a reduction in clinical score. In the serum, anti-CD20 treatment elevated levels of BAFF and IgA, which inversely correlated with disease severity. We thus propose that anti-CD20 exerts its protective effects by providing a favourable niche for suppressive IgA+ PCs.