MHC class II–dependent B cell APC function is required for induction of CNS autoimmunity independent of myelin-specific antibodies

Abstract

Whether B cells serve as antigen-presenting cells (APCs) for activation of pathogenic T cells in the multiple sclerosis model experimental autoimmune encephalomyelitis (EAE) is unclear. To evaluate their role as APCs, we engineered mice selectively deficient in MHC II on B cells (B–MHC II−/−), and to distinguish this function from antibody production, we created transgenic (Tg) mice that express the myelin oligodendrocyte glycoprotein (MOG)–specific B cell receptor (BCR; IgHMOG-mem) but cannot secrete antibodies. B–MHC II−/− mice were resistant to EAE induced by recombinant human MOG (rhMOG), a T cell– and B cell–dependent autoantigen, and exhibited diminished Th1 and Th17 responses, suggesting a role for B cell APC function. In comparison, selective B cell IL-6 deficiency reduced EAE susceptibility and Th17 responses alone. Administration of MOG-specific antibodies only partially restored EAE susceptibility in B–MHC II−/− mice. In the absence of antibodies, IgHMOG-mem mice, but not mice expressing a BCR of irrelevant specificity, were fully susceptible to acute rhMOG-induced EAE, also demonstrating the importance of BCR specificity. Spontaneous opticospinal EAE and meningeal follicle–like structures were observed in IgHMOG-mem mice crossed with MOG-specific TCR Tg mice. Thus, B cells provide a critical cellular function in pathogenesis of central nervous system autoimmunity independent of their humoral involvement, findings which may be relevant to B cell–targeted therapies.