While the pathology of multiple sclerosis implicates a role for B cells and antibodies in the disease process, results from animal models have yielded conflicting results. To further characterize the role of B cells in experimental allergic encephalomyelitis (EAE), wild-type and B cell-deficient C57BL/6 mice were immunized with either a recombinant form of myelin oligodendrocyte glycoprotein (MOG) or with the encephalitogenic MOG(35-55) peptide. B cell-deficient mice did not develop EAE when immunized with MOG, although they were susceptible to MOG(35-55)-induced disease. In contrast, wild-type mice were fully susceptible to both MOG and MOG(35-55)-induced EAE. B cell-deficient mice immunized with MOG were primed to the encephalitogenic MOG(35- 55) epitope, as their spleen cells responded with Th1 cytokine production in a fashion similar to WT cells when challenged in vitro with MOG protein or MOG(35-55) peptide. These results demonstrate that the form of inducing antigen (protein vs. peptide) plays a role in the pathogenesis of EAE and may be relevant when applying results from the EAE model to multiple sclerosis.