Immunoglobulin sequencing in a spontaneous model of experimental autoimmune encephalomyelitis provides evidence of MOG-specific B cell recruitment and clonal expansion.

The key role of B cells in the pathophysiology of multiple sclerosis (MS) is primarily supported by the presence of oligoclonal bands in cerebrospinal fluid, the link between meningeal ectopic B cell follicles with demyelination, axonal loss and reduction astrocyte cells, as well as the high efficacy of B lymphocyte depletion in controlling inflammatory parameters of MS. Here we use a spontaneous model of experimental autoimmune encephalomyelitis (EAE) to study the clonality of the B cell response targeting myelin oligodendrocyte glycoprotein (MOG). In particular, 94% of SJL/j mice expressing an I-As: MOG92-106 specific transgenic T cell receptor (TCR1640) spontaneously develop a chronic paralytic EAE between the age of 60-500 days. The immune response is triggered by the microbiota in the gut associated lymphoid tissue, while the maturation of the autoimmune demyelinating response occurs in the cervical lymph nodes owing to local CNS drainage. Using MOG-tetramers we tracked the autoantigen-specific B cells and localized their enrichment to the deep cervical lymph nodes and among the brain immune infiltrate. MOG-specific IgG1 antibodies were detected in the serum of diseased TCR1640 mice and proved pathogenic upon adoptive transfer into disease prone recipients. The ontogeny of the MOG-specific humoral response preceded disease onset coherent with their contribution to EAE initiation. This humoral response was, however, not sufficient for disease induction as MOG-antibodies could be detected at the age of 7 weeks in a model with an average age of onset of 197 days. Questioning whether EAE onset would be accompanied by affinity maturation of the MOG-specific B cell response we electronically sorted MOG-tetramer binding cells and clonally expand them in vitro to sequence the paratopes of the IgG heavy chain and kappa light chains. Despite the fragility of clonally expanding MOG-tetramer binding effector B cells, our results indicate the selection of a common CDR-3 clonotype among the IgLk chains derived from both disease-free and diseased TCR1640 mice. Our study demonstrates the pre-clinical mobilization of the MOG-specific B cell response within the brain-draining cervical lymph nodes, and reiterate that pathogenic MOG antibodies are a poor biomarker of disease onset and progression.