experimental allergic encephalomyelitis (EAE), a roleascribed essentially to IFN-γ and IL-17, the signaturecytokines that respectively define these T cell subsets.But in spite of the extensive amount of studies investigat-ing the specific roles of IFN-γ and IL-17, to date, little isknown regarding the possible collaborative interplaybetween these two cytokines, especially at the single celllevel. We thus sought to evaluate the frequency of IFN-γ-expressing TH17 lymphocytes in MS and EAE, and studytheir recruitment into the central nervous system (CNS).We show that in response to a polyclonal stimulation withIL-23, human CD4+CD45RO+memory lymphocytes expandinto a TH17-like phenotype with a subpopulation of cellssimultaneously expressing IL-17 and IFN-γ. We note anincreased percentage of this particular subpopulation ofdual producers in TH17 cell lines expanded from theperipheral blood of acutely relapsing MS patients ascompared to healthy controls and remitting MS patients.We identify numerous IL-17-IFN-γ co-producing CD4+Tlymphocytes in frozen brain tissue of MS patients. Wefurther provide in vitro and in vivo evidence that IFN-γ-expressing TH17 lymphocytes preferentially cross thehuman blood-brain barrier and accumulate in the CNS ofmice during the effector phase of EAE. Our data underscorethe involvement of IL-17-IFN-γ co-producing CD4+T lym-phocytes in the pathology of MS and EAE and theirpreferential recruitment into the CNS during inflammatoryevents.

doi:10.1016/j.clim.2009.03.068

OR.57. IL-4 Inhibits TGF-β-induced Foxp3+T Cellsand, Together with TGF-β, Generates IL-9+IL-10+Foxp3-Effector T CellsAmit Awasthi1, Valerie Dardalhon2, George Galileos1,Wenda Gao2, Terry Strom 2, Raymond Sobel3, I Cheng Ho1,Mohamed Oukka1, Vijay Kuchroo1. 1 Brigham and Women'sHospital, Boston, MA; 2 Beth Israel Hospital, Boston, MA;3 Stanford University School of Medicine, Palo Alto, CA

Transcription factor Foxp3 is critical for generatingregulatory T cells (Treg cells). Transforming growth factor-β (TGF-β) induces Foxp3 and suppressive Treg cells fromnaive T cells, whereas interleukin 6 (IL-6) inhibits thegeneration of inducible Treg cells. Here we show that IL-4blocked the generation of TGF-β-induced Foxp3+Treg cellsand instead induced a population of T helper cells thatproduced IL-9 and IL-10. The IL-9+IL-10+Tcells demonstratedno regulatory properties despite producing abundant IL-10.Adoptive transfer of IL-9+IL-10+T cells into recombination-activating gene 1-deficient mice induced colitis and periphe-ral neuritis, the severity of which was aggravated if the IL-9+IL-10+Tcells were transferred with CD45RBhi CD4+effector Tcells. Thus IL-9+IL-10+T cells lack suppressive function andconstitute a distinct population of helper-effector T cellsthat promote tissue inflammation.

doi:10.1016/j.clim.2009.03.069

OR.58. Expression of the Orphan Nuclear ReceptorNR4A2 is Required for IL-17 Production by Th17 CellsBen Raveney, Shinji Oki, Takashi Yamamura. NationalInstitute of Neuroscience, NCNP, Tokyo, Japan

We have previously reported that NR4A2, an orphannuclear receptor, is upregulated in peripheral blood cellsduring the human autoimmune disease multiple sclerosis(MS). NR4A2 upregulation was also observed during experi-mental autoimmune encecephalomyelitis (EAE), the murinemodel of MS, amongst peripheral blood cells and leukocytesinfiltrating the central nervous system (CNS). The pathologyof MS and EAE is mediated by infiltration of Th1 and Th17cells into the CNS. NR4A2 was shown to influence thefunction of both of such Th subsets: NR4A2 overexpressionled to enhanced IL-17 and IFN-γ production, whilst NR4A2siRNA-treated splenocytes elaborated reduced levels of IL-17and IFN-γ following polyclonal stimulation. Furthermore,NR4A2 siRNA-treated encephalitogenic Tcells were unable totransfer passive EAE. We now show that the upregulation ofNR4A2 observed in CNS-infiltrating leukocytes is mostapparent amongst IL-17-secreting CD4+T cells. Therefore,we examined the role of NR4A2 in the differentiation ofthese Th17 cells. Transfection of naïve T cells with NR4A2siRNA precludes IL-17 secretion when cultured under Th17polarising conditions. However, such cells do proliferate andupregulate RORγt to the same extent as functional Th17cells. Surprisingly, NR4A2 inhibition also reduced theexpression of foxp3. Thus, NR4A2 controls IL-17 productionby mechanisms independent of both RORγt upregulation andfoxp3-mediated regulation of RORγt. Our findings indicatethat NR4A2 may play a critical role in Th17 cell function andis therefore an attractive therapeutic target in the treat-ment of Th17-mediated autoimmune diseases.

doi:10.1016/j.clim.2009.03.070

OR.59. Investigating the Role of Skin HomingVγ9Vδ2 T Cells as Novel Pathogenic Cellsin PsoriasisUte Laggner, Paola Di Meglio, Christian Hundhausen,Gayathri Perera, Elisabetta Botti, Adrian Hayday, FrankNestle. King's College London, London, UK

Psoriasis is a common autoimmune disease of the skincharacterized by infiltration of CD4 and CD8 Tcells into dermisand epidermis. The pathogenic Tcell in psoriasis has not beenidentified yet. γδ T cells are key players in immunologicaleffectors in mouse skin while little is known about theirfunction in human skin during tissue homeostasis andinflammation. In this study we aimed to investigate the roleof Vγ9Vδ2 T cells in psoriasis. PBMCs of psoriasis patients andcontrols were assessed by flow cytometry for γδ Tcell and skinhoming receptors. Vγ9Vδ2 Tcells in skin were investigated byimmunohistochemical and immunofluorescence analysis.Vγ9Vδ2 T cell lines and clones from skin and blood were usedfor functional studies. Vγ9Vδ2 T cells were significantlyreduced in peripheral blood of psoriasis patients comparedto controls. This decrease was correlated with enhanceddisease severity.We identified a novel subset of peripheral skin

S25Abstracts