In contrast, IL-17−IFN-γ+ cells were more numerous than IL-17+IFN-γ− cells among the WT donor population in both the periphery and the CNS. Spleens of RAG2−/− mice that received T-bet−/− donor cells were disproportionately

enlarged, primarily due to a local expansion of myeloid cells (Fig. 3G, right panel). There was no difference in the absolute numbers of CD4+CD3+ T cells, granulocytes or monocytes infiltrating the spinal cords of T-bet−/− or WT hosts (Fig. 3G, left panel). MS is a heterogeneous disease characterized by diversity in both the clinical course and in responsiveness Ku-0059436 manufacturer to individual therapeutic agents. At present, no biomarkers have been identified that can guide the selection of an optimal disease Z-VAD-FMK in vitro modifying regimen. Strategies to manage MS are complicated by the observation that distinct myelin-reactive Th-cell subsets can induce inflammatory demyelination via independent cellular and molecular pathways [1]. Therefore it is not surprising that signature Th1 and Th17 cytokines are dispensable for the manifestation of EAE [3-5]. The identification of a molecule

that is critical for encephalitogenicity, irrespective of Th effector phenotype, would serve as an ideal therapeutic target. The transcription factor T-bet has been proposed as a candidate therapeutic target in MS, based on its nonredundant roles in Th1 differentiation and in Th17 plasticity. However, in the current study we show that IL-23 polarized myelin-reactive Th17 cells can mediate autoimmune demyelination without expressing Ureohydrolase T-bet or converting into Th1 (“ex-Th17”) cells. Consistent with our findings, Duhen et al. [20] recently reported that T-bet deficiency confined to CD4+ T cells does not confer resistance

against EAE induced by active immunization with MOG peptide emulsified in CFA. We found that stable T-bet−/− Th17 cells maintain the capacity to produce GM-CSF, and induce augmented production of CXCL2, each of which has been implicated in EAE pathogenesis [21-24]. In ongoing studies we are investigating whether compensatory upregulation of these factors drives the accumulation of myeloid cells (Ly6G+ granulocytes in particular) in the spleens of the recipients of T-bet−/− Th17 donor cells. Engagement of alternative chemokine/cytokine pathways could underlie the preserved encephalitogenicity of myelin-reactive T-bet−/− Th17 cells. We consistently found that MOG-specific T-bet−/− Th17 cells induce a milder course of EAE than their WT counterparts. This could be due to reduced production of the pro-inflammatory factor GM-CSF, as we observed in primary cultures of T-bet−/− and WT CD4+ T cells (Fig. 2A). However, we detected similar frequencies of GM-CSF+ cells among T-bet−/− and WT donor cells harvested from the CNS and peripheral lymphoid tissues of adoptive transfer recipients with EAE (Fig. 3F and data not shown).