The role of B cells and antibody in the pathogenesis of experimental autoimmune encephalomyelitis (EAE) remains controversial. We previously demonstrated that B cells are required for EAE to be induced by the 120-amino acid extracellular domain of myelin oligodendrocyte glycoprotein (MOG). In the present study, the role of B cells in MOG-induced EAE was further characterized. Passive transfer of activated B cells or serum from MOG-primed wild-type (WT) mice was found to reconstitute the ability for clinical and histological EAE to be induced in MOG-immunized B cell-deficient mice. MOG-induced EAE did not occur with transfer of B cells that had been nonspecifically activated by lipopolysaccharide or isolated from naïve or myelin basic protein (MBP)-primed WT mice. Likewise, MOG-primed serum, but not naive serum or serum from MBP-, Hen egg lysozyme-, or MOG(35-55)-primed mice, led to EAE in B cell-/- animals. While both MOG-primed B cells and serum reconstituted the ability for disease induction, MOG-primed serum was much more efficient, leading to clinical and histological EAE similar to that seen in the WT. Injection of MOG serum into healthy B cell-/- mice 30 days after MOG immunization led to rapid appearance of clinical signs and CNS inflammation, indicating that an antigen-specific factor is necessary for initiation of CNS inflammation,and not just demyelination. These data strongly suggest that MOG-specific antibody is critical to the initiation of MOG-induced murine EAE.