Inflammation plays an important role in ischemic stroke and in humans IL-10 may have a beneficial effect in stroke. We mucosally administered myelin oligodendrocyte glycoprotein (MOG) 35-55 peptide to C57BL/6 mice before middle cerebral artery occlusion (MCAO) to induce an anti-inflammatory T cell response directed at CNS myelin. Nasal and oral administration of MOG(35-55) peptide decreased ischemic infarct size at 24 and 72 h after MCAO surgery. Nasal MOG(35-55) peptide was most efficacious and reduced infarct size by 70% at 24 h and by 50% at 72 h (p <or= 0.0001 vs control) and also improved behavior score. Immunohistochemistry demonstrated increased IL-10 and reduced IFN-gamma in the area surrounding the ischemic infarct following nasal treatment. Nasal MOG did not reduce infarct size in IL-10-deficient mice. Adoptive transfer of CD4(+) T cells to untreated mice from nasally tolerized mice before MCAO surgery decreased stroke size (p < 0.001 vs control), whereas, CD4(+) T cells from nasally tolerized IL-10-deficient mice had no effect. Our results demonstrate that IL-10-secreting CD4(+) T cells induced by nasal MOG reduce injury following stroke. In addition, we observed a dramatic reduction of CD11b(+) cells in nasal MOG-treated animals. CD11b(+) cells may contribute to secondary infarct expansion by enhancing NO synthesis that may be reduced by elevated IL-10 levels. Modulation of cerebral inflammation by nasal vaccination with myelin Ags that increase IL-10 in the brain may improve outcome after stroke and enhance mechanisms of recovery.