B Cells Drive MHC Class I-Restricted CD4 T Cells to Induce Spontaneous Central Nervous System Autoimmunity.

Multiple sclerosis (MS) is an inflammatory, demyelinating CNS disease believed to be mediated by CD4 T cells specific for CNS self-antigens. CD8 T cells are also implicated in MS but their function is not well understood. MS lesions are heterogeneous and may reflect variation in the contribution of different types of lymphocytes. Understanding how lymphocytes with different effector functions contribute to MS is essential to develop effective therapies. We investigated how T cells expressing an MHC class I-restricted transgenic TCR specific for myelin basic protein (MBP) contribute to CNS autoimmunity using the mouse model of MS, experimental autoimmune encephalomyelitis. Virus infection triggered cytotoxic TCR-transgenic CD8 T cells to initiate acute experimental autoimmune encephalomyelitis in an IFN-γ- and perforin-dependent manner. Unexpectedly, spontaneous CNS autoimmunity developed in the TCR-transgenic mice that was accelerated by IFN-γ-deficiency. Spontaneous disease was associated with CD4 T cells that develop via endogenous TCR rearrangements but retain specificity for the MHC class I-restricted MBP epitope. The CD4 T cells produced TNF-α without other inflammatory cytokines and caused lesions with striking similarity to active MS lesions. Surprisingly, B cells were the predominant cell type that cross-presented MBP, and their depletion halted disease progression. This work provides a new model of spontaneous CNS autoimmunity with unique similarities to MS that is mediated by T cells with a distinct effector phenotype.