EAE serves as an animal model for multiple sclerosis and is initiated by autoreactive T cells that infiltrate the CNS. Recognition of myelin-associatedAdditional supporting information may be found in the online version of this article at the publisher's web-site IntroductionMS is generally considered to be a chronic autoimmune disease of the CNS [1]. Nearly all of the 110 currently known genes contributing to the risk of MS development encode immunerelated molecules [2,3]. During the acute phase of MS, a variety of immune cells cross the blood-brain barrier and autoreactiveCorrespondence: Dr. Friederike Berberich-Siebelt e-mail: path230@mail.uni-wuerzburg.de T cells appear to play a dominant role [4]. Increased levels of Th1 cytokines are pronounced during MS relapses, whereas Th2 lymphokines, such as IL-4, have been associated with remission [5]. Nevertheless, genetic mouse models addressing different components of Th1 cells suggested that an imbalance of Th1/Th2 may not be sufficient for the human disease. Instead, critical pathogenic roles of Th17 cells and their hallmark cytokine IL-17 have been recognized as important drivers of autoimmunity. Similarly, Th17 cells are linked to the development of EAE, an animal model of MS [6]. However, not all Th17 cells are pathogenic, and Th17 cells comprise a wide range of effector phenotypes [7]. Broadly, Th17C 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.eji-journal.eu 1378 Lena Dietz et al. Eur. J. Immunol. 2015. 45: 1377-1389 cells are classified as either classical/nonpathogenic or alternative/pathogenic. Initially, differentiation depends on the cytokine milieu, that is, the dominance of TGF-β versus IL-23, and subsequently on transcription factor expression, which leads to various combinations of cytokine production and effector functions. Interestingly, the presence of Th1-inducing cytokines (IFN-γ in combination with IL-12) promotes an adaption of the classic Th17-cell type into pathogenic "Th1/17" cells [8]. In addition to the lineagedetermining RORγt and IL-17A/F, pathogenic Th17 cells are characterized by T-bet expression as well as IFN-γ, GM-CSF, and/or IL-22 production, whereas classical Th17 cells express c-Maf and secrete 9]. Previously, we observed an important role of the transcription factor NFAT2 for IL-17 expression [10]. The NFAT family comprises NFAT1/NFATc2, NFAT2/NFATc1, NFAT3/NFATc4, NFAT4/NFATc3, and the distantly related NFAT5 [11,12] Results NFAT is crucial for EAE pathogenesisTo actively induce EAE in Nfat1, and WT littermates, we treated mice with MOG 35-55 /CFA (where MOG is myelin oligodendrocyte glycoprotein). In line with the importance of NFAT for T-cell activation, DKO mice were completely protected against EAE (Fig. 1A). Accordingly, both Nfat1 and Nfat2 mRNA were upregulated in CD4 + T cells from EAEdiseased WT mice after in vitro restimulation with MOG 35-55 peptide (Fig. 1B). When we analyzed the immune cell infiltrates within the CNS of the DKO mice at the peak of disease, we found a strong relative reduction in CD45 ...

Neuromyelitis optica (NMO) is an autoimmune disorder of the central nervous system (CNS) mediated by antibodies to the water channel protein AQP4 expressed in astrocytes. The contribution of AQP4-specific T cells to the class switch recombination of pathogenic AQP4-specific antibodies and the inflammation of the blood–brain barrier is incompletely understood, as immunogenic naturally processed T-cell epitopes of AQP4 are unknown. By immunizing Aqp4−/− mice with full-length murine AQP4 protein followed by recall with overlapping peptides, we here identify AQP4(201-220) as the major immunogenic IAb-restricted epitope of AQP4. We show that WT mice do not harbor AQP4(201–220)-specific T-cell clones in their natural repertoire due to deletional tolerance. However, immunization with AQP4(201–220) of Rag1−/− mice reconstituted with the mature T-cell repertoire of Aqp4−/− mice elicits an encephalomyelitic syndrome. Similarly to the T-cell repertoire, the B-cell repertoire of WT mice is “purged” of AQP4-specific B cells, and robust serum responses to AQP4 are only mounted in Aqp4−/− mice. While AQP4 (201–220)-specific T cells alone induce encephalomyelitis, NMO-specific lesional patterns in the CNS and the retina only occur in the additional presence of anti-AQP4 antibodies. Thus, failure of deletional T-cell and B-cell tolerance against AQP4 is a prerequisite for clinically manifest NMO.