Autophagy regulates the therapeutic potential of mesenchymal stem cells in experimental autoimmune encephalomyelitis

Mesenchymal stem cell (MSC)-based therapy is a promising approach to treat various inflammatory disorders including multiple sclerosis. However, the fate of MSCs in the inflammatory microenvironment is largely unknown. Experimental autoimmune encephalomyelitis (EAE) is a well-studied animal model of multiple sclerosis. We demonstrated that autophagy occurred in MSCs during their application for EAE treatment. Inflammatory cytokines, e.g., interferon gamma and tumor necrosis factor, induced autophagy in MSCs synergistically by inducing expression of BECN1/Beclin 1. Inhibition of autophagy by knockdown of Becn1 significantly improved the therapeutic effects of MSCs on EAE, which was mainly attributable to enhanced suppression upon activation and expansion of CD4⁺ T cells. Mechanistically, inhibition of autophagy increased reactive oxygen species generation and mitogen-activated protein kinase 1/3 activation in MSCs, which were essential for PTGS2 (prostaglandin-endoperoxide synthase 2 [prostaglandin G/H synthase and cyclooxygenase]) and downstream prostaglandin E2 expression to exert immunoregulatory function. Furthermore, pharmacological treatment of MSCs to inhibit autophagy increased their immunosuppressive effects on T cell-mediated EAE. Our findings indicate that inflammatory microenvironment-induced autophagy downregulates the immunosuppressive function of MSCs. Therefore, modulation of autophagy in MSCs would provide a novel strategy to improve MSC-based immunotherapy.     

T cell apoptosis and induction of foxp3+ regulatory T cells underlie the therapeutic efficacy of CD4 blockade in experimental autoimmune encephalomyelitis

The pathogenesis of multiple sclerosis requires the participation of effector neuroantigen-specific T cells. Thus, T cell targeting has been proposed as a promising therapeutic strategy. However, the mechanism underlying effective disease prevention following T cell targeting remains incompletely known. We found, using several TCR-transgenic strains, that CD4 blockade is effective in preventing experimental autoimmune encephalopathy and in treating mice after the disease onset. The mechanism does not rely on direct T cell depletion, but the anti-CD4 mAb prevents the proliferation of naive neuroantigen-specific T cells, as well as acquisition of effector Th1 and Th17 phenotypes. Simultaneously, the mAb favors peripheral conversion of Foxp3(+) regulatory T cells. Pre-existing effector cells, or neuroantigen-specific cells that undergo cell division despite the presence of anti-CD4, are committed to apoptosis. Therefore, protection from experimental autoimmune encephalopathy relies on a combination of dominant mechanisms grounded on regulatory T cell induction and recessive mechanisms based on apoptosis of neuropathogenic cells. We anticipate that the same mechanisms may be implicated in other T cell-mediated autoimmune diseases that can be treated or prevented with Abs targeting T cell molecules, such as CD4 or CD3.     

Liposomal encapsulation of glucocorticoids alters their mode of action in the treatment of experimental autoimmune encephalomyelitis

Glucocorticoids (GCs) are widely used to treat acute relapses of multiple sclerosis (MS). In this study, we demonstrate that liposomal encapsulation augments the therapeutic potency of GCs as they ameliorate experimental autoimmune encephalomyelitis (EAE) to the same extent as free GC, but at strongly reduced dosage and application frequency. Importantly, this is accompanied by an altered mode of action. Unlike free GCs, which mainly target T lymphocytes during EAE therapy, liposomal GCs only marginally affect T cell apoptosis and function. In contrast, liposomal GCs efficiently repress proinflammatory macrophage functions and upregulate anti-inflammatory genes associated with the alternatively activated M2 phenotype. The GC receptor (GR) per se is indispensable for the therapeutic efficacy of liposomal GC. In contrast to free GCs, however, the individual deletion of the GR either in T cells or myeloid cells has little effect on the efficacy of liposomal GCs in the treatment of EAE. Only the combined deletion of the GR in both cellular compartments markedly compromises the therapeutic effect of liposomal GCs on disease progression. In conclusion, encapsulation of GC does not only enhance their efficacy in the treatment of EAE but also alters their target cell specificity and their mode of action compared with free GCs.     

口服卡介菌治疗实验性自身免疫性脑脊髓炎的研究

目的:观察口服卡介菌对实验性变态反应性脑脊髓炎(EAE)的治疗效果。方法:制备EAE大鼠模型,随机分为BCG高、中、低剂量组和PBS对照组,每组各15只,对大鼠治疗后的临床症状及病理组织学进行评估,提取脾脏淋巴细胞,流式细胞术检测T淋巴细胞亚群,3H-TdR掺入法检测淋巴细胞增殖能力。结果:BCG组EAE大鼠与对照组相比,临床症状减轻,发病时间延迟,炎性细胞浸润数减少;急性期,口服BCG各组CD4+、CD8+T细胞的数量随剂量增加而增加,缓解期CD4+、CD8+T细胞数量减少;口服BCG可促进EAE大鼠T淋巴细胞增殖能力;高、中剂量组上述变化均较其它分组明显。结论:口服BCG可很好的诱导免疫耐受,延迟EAE发病,减轻炎症反应,改善临床症状。     

口服卡介菌治疗实验性自身免疫性脑脊髓炎的研究

目的：观察口服卡介菌对实验性变态反应性脑脊髓炎（EAE）的治疗效果。方法：制备EAE大鼠模型,随机分为BCG高、中、低剂量组和PBS对照组,每组各15只,对大鼠治疗后的临床症状及病理组织学进行评估,提取脾脏淋巴细胞,流式细胞术检测T淋巴细胞亚群,3H—TdR掺入法检测淋巴细胞增殖能力。结果：BCG组EAE大鼠与对照组相比,临床症状减轻,发病时间延迟,炎性细胞浸润数减少;急性期,口服BCG各组CD4^＋、CD8^＋T细胞的数量随剂量增加而增加,缓解期CD4^＋、CD8^＋T细胞数量减少;口服BCG可促进EAE大鼠T淋巴细胞增殖能力;高、中剂量组上述变化均较其它分组明显。结论：口服BCG可很好的诱导免疫耐受,延迟EAE发病,减轻炎症反应,改善临床症状。     

CD8+ T cells specific for cryptic apoptosis-associated epitopes exacerbate experimental autoimmune encephalomyelitis

The autoimmune immunopathology occurring in multiple sclerosis (MS) is sustained by myelin-specific and -nonspecific CD8⁺ T cells. We have previously shown that, in MS, activated T cells undergoing apoptosis induce a CD8⁺ T cell response directed against antigens that are unveiled during the apoptotic process, namely caspase-cleaved structural proteins such as non-muscle myosin and vimentin. Here, we have explored in vivo the development and the function of the immune responses to cryptic apoptosis-associated epitopes (AEs) in a well-established mouse model of MS, experimental autoimmune encephalomyelitis (EAE), through a combination of immunization approaches, multiparametric flow cytometry, and functional assays. First, we confirmed that this model recapitulated the main findings observed in MS patients, namely that apoptotic T cells and effector/memory AE-specific CD8⁺ T cells accumulate in the central nervous system of mice with EAE, positively correlating with disease severity. Interestingly, we found that AE-specific CD8⁺ T cells were present also in the lymphoid organs of unprimed mice, proliferated under peptide stimulation in vitro, but failed to respond to peptide immunization in vivo, suggesting a physiological control of this response. However, when mice were immunized with AEs along with EAE induction, AE-specific CD8⁺ T cells with an effector/memory phenotype accumulated in the central nervous system, and the disease severity was exacerbated. In conclusion, we demonstrate that AE-specific autoimmunity may contribute to immunopathology in neuroinflammation.Subject terms: Cell death and immune response, Immunological disorders     

Functional heterogeneity among CD4+ encephalitogenic T cells in recruitment of CD8+ T cells in experimental autoimmune encephalomyelitis

Inoculation of Lewis rats with live or attenuated (irradiated or paraformaldehyde-fixed) CD4+ encephalitogenic T cells (S1 line) protects the recipients from transferred experimental autoimmune encephalomyelitis (tEAE) induced by S1 cells. A CD8+ T lymphocyte population specifically activated against the EAE-inducing S1 cells can be readily isolated from the lymphoid organs of pretreated animals. We show, in the present study, that encephalitogenic T cell lines derived from Lewis rats differ in their ability to induce resistance against tEAE in vivo and to stimulate CD8+ cell proliferation in vitro. We also demonstrate that the S19 line of encephalitogenic T cells, in combination with myelin basic protein (MBP), can stimulate CD8+ cell proliferation in vitro. The CD8+ cells generated in this way strongly suppress MBP-specific T cell proliferation in vitro. This combined effect of T cells and MBP was also evident in vivo. Neither S19 cells nor MBP alone induced resistance against S19-mediated tEAE, rather coinjection of these cells and MBP was required. Our results suggest that resistance to EAE is mediated by distinct populations of encephalitogenic T cells that activate Ts cells through different mechanisms. In some instances, both autoreactive T cells and their relevant autoantigen(s) may be needed to activate Ts cells in vivo.     

IDO upregulates regulatory T cells via tryptophan catabolite and suppresses encephalitogenic T cell responses in experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is a Th1 and Th17 cell-mediated autoimmune disease of the CNS. IDO and tryptophan metabolites have inhibitory effects on Th1 cells in EAE. For Th17 cells, IDO-mediated tryptophan deprivation and small molecule halofuginone-induced amino acid starvation response were shown to activate general control nonrepressed 2 (GCN2) kinase that directly or indirectly inhibits Th17 cell differentiation. However, it remains unclear whether IDO and tryptophan metabolites impact the Th17 cell response by mechanisms other than the GCN2 kinase pathway. In this article, we show that IDO-deficient mice develop exacerbated EAE with enhanced encephalitogenic Th1 and Th17 cell responses and reduced regulatory T cell (Treg) responses. Administration of the downstream tryptophan metabolite 3-hydroxyanthranillic acid (3-HAA) enhanced the percentage of Tregs, inhibited Th1 and Th17 cells, and ameliorated EAE. We further demonstrate that Th17 cells are less sensitive to direct suppression by 3-HAA than are Th1 cells. 3-HAA treatment in vitro reduced IL-6 production by activated spleen cells and increased expression of TGF-β in dendritic cells (DCs), which correlated with enhanced levels of Tregs, suggesting that 3-HAA-induced Tregs contribute to inhibition of Th17 cells. By using a DC-T cell coculture, we found that 3-HAA-treated DCs expressed higher levels of TGF-β and had properties to induce generation of Tregs from anti-CD3/anti-CD28-stimulated naive CD4(+) T cells. Thus, our data support the hypothesis that IDO induces the generation of Tregs via tryptophan metabolites, such as 3-HAA, which enhances TGF-β expression from DCs and promotes Treg differentiation.     

IL-13 production by regulatory T cells protects against experimental autoimmune encephalomyelitis independently of autoantigen

Treatment with an anti-inflammatory Salmonella vaccine expressing enterotoxigenic Escherichia coli colonization factor Ag 1 (CFA/I) proved effective in stimulating protective, potent CD25(+)CD4(+) regulatory T (T(reg)) cells in susceptible mice challenged with experimental autoimmune encephalomyelitis (EAE). Because the Salmonella vector was considerably less protective, we questioned whether altering fimbrial subunit expression to resemble conventional Salmonella expression may impact T(reg) cell potency. The Salmonella-CFA/I vaccine was modified to limit fimbrial subunit expression to the intracellular compartment (Salmonella-CFA/I(IC)). SJL mice were challenged with proteolipid protein peptide 139-151 to induce EAE and orally treated with one of three Salmonella vaccines 6 days postchallenge. Treatment with Salmonella-CFA/I(IC) greatly reduced clinical disease, similarly as Salmonella-CFA/I, by subduing IL-17 and IL-21; however, mechanisms of protection differed as evident by increased IL-13 and IFN-gamma but diminished TGF-beta production by T(reg) cells from Salmonella-CFA/I(IC)-treated mice. Adoptive transfer of T(reg) cells from both CFA/I-expressing constructs was equivalent in protecting against EAE, showing minimal disease. Although not as potent in its protection, CD25(-)CD4(+) T cells from Salmonella-CFA/I(IC) showed minimal Th2 cells, but vaccination did prime these Th2 cells rendering partial protection against EAE challenge. In vivo IL-13 but not IFN-gamma neutralization compromised protection conferred by adoptive transfer with Salmonella-CFA/I(IC)-induced T(reg) cells. Thus, the Salmonella-CFA/I(IC) vaccine elicits T(reg) cells with attributes from both the Salmonella vector and Salmonella-CFA/I vaccines. Importantly, these T(reg) cells can be induced to high potency by simply vaccinating against irrelevant Ags, offering a novel approach to treat autoimmune diseases independently of the autoantigen.     

Key metalloproteinases are expressed by specific cell types in experimental autoimmune encephalomyelitis

Metalloproteinases (MPs) include matrix metalloproteinases (MMPs) and metalloproteinase-disintegrins (ADAMs). Their physiological inhibitors are tissue inhibitor of metalloproteinases (TIMPs). MPs are thought to be mediators of cellular infiltration in the pathogenesis of multiple sclerosis and its animal model, experimental autoimmune encephalomyelitis (EAE). We used real-time RT-PCR to profile the expression of all 22 known mouse MMPs, seven ADAMs, and all four known TIMPs in spinal cord from SJL/J mice and mice with adoptively transferred myelin basic protein (MBP)-specific EAE. A significant and >3-fold alteration in expression was observed for MMP-8, MMP-10, MMP-12, ADAM-12, and TIMP-1, which were up-regulated, and for MMP-15, which was down-regulated. Expression levels correlated with disease course, with all but ADAM-12 returning toward control levels in remission. To examine potential cellular sources of these strongly affected proteins in the inflamed CNS, we isolated macrophages, granulocytes, microglia, and T cells by cell sorting from the CNS of mice with EAE and analyzed their expression by real-time RT-PCR. This identified macrophages as a major source of MMP-12 and TIMP-1. Granulocytes were a major source of MMP-8. ADAM-12 was expressed primarily by T cells. Cellular localization of MMP-10, TIMP-1, and ADAM-12 in perivascular infiltrates was confirmed by immunostaining or in situ hybridization. Microglia from control mice expressed strong signal for MMP-15. Strikingly, the expression of MMP-15 by microglia was significantly down-regulated in EAE, which was confirmed by immunostaining. Our study identifies the cellular sources of key MPs in CNS inflammation.     

Alterations in the spinal cord T cell repertoire during relapsing experimental autoimmune encephalomyelitis

The CNS T cell repertoire was analyzed by RT-PCR, spectratyping, and nucleotide sequencing of the amplified products at different times following adoptive transfer of a CD4+, Th1, VB2+ encephalitogenic SJL/J proteolipid protein peptide 139-151-specific T cell clone. The third complementarity-determining region of TCR B chains in the spinal cord was used as an indicator of T cell heterogeneity. Spectratypic analysis revealed that a single peak corresponding to the third complementarity-determining region of the initiating T cell clone predominated during the acute phase. During recovery and relapse the complexity of the spectratype increased. DNA sequence analysis revealed that the donor clone predominated at the acute phase. By the first relapse the donor clone, although represented most frequently, was a minority of the total. Spectratypic analysis of the same samples for several other VB families revealed their presence during acute disease or relapses but, with the exception of VB17, their absence during the recovery stage.     

Costimulation-dependent modulation of experimental autoimmune encephalomyelitis by ligand stimulation of V alpha 14 NK T cells

Experimental autoimmune encephalomyelitis (EAE) is a Th1 cell-mediated autoimmune disease that can be protected against by stimulating regulatory cells. Here we examined whether EAE can be purposefully modulated by stimulating Valpha14 NK T cells with the CD1d-restricted ligand alpha-galactosylceramide (alpha-GC). EAE induced in wild-type C57BL/6 (B6) mice was not appreciably altered by injection of alpha-GC. However, EAE induced in IL-4 knockout mice and IFN-gamma knockout mice was enhanced or suppressed by alpha-GC, respectively. This indicates that the IL-4 and IFN-gamma triggered by alpha-GC may play an inhibitory or enhancing role in the regulation of EAE. We next studied whether NK T cells of wild-type mice may switch their Th0-like phenotype toward Th1 or Th2. Notably, in the presence of blocking B7.2 (CD86) mAb, alpha-GC stimulation could bias the cytokine profile of NK T cells toward Th2, whereas presentation of alpha-GC by CD40-activated APC induced a Th1 shift of NK T cells. Furthermore, transfer of the alpha-GC-pulsed APC preparations suppressed or enhanced EAE according to their ability to polarize NK T cells toward Th2 or Th1 in vitro. These results have important implications for understanding the role of NK T cells in autoimmunity and for designing a therapeutic strategy targeting NK T cells.     

Regulatory T cell vaccination without autoantigen protects against experimental autoimmune encephalomyelitis

Regulatory T (T(reg)) cells show promise for treating autoimmune diseases, but their induction to elevated potency has been problematic when the most optimally derived cells are from diseased animals. To circumvent reliance on autoantigen-reactive T(reg) cells, stimulation to myelin-independent Ags may offer a viable alternative while maintaining potency to treat experimental autoimmune encephalomyelitis (EAE). The experimental Salmonella vaccine expressing colonization factor Ag I possesses anti-inflammatory properties and, when applied therapeutically, reduces further development of EAE in SJL mice. To ascertain T(reg) cell dependency, a kinetic analysis was performed showing increased levels of FoxP3(+)CD25(+)CD4(+) T cells. Inactivation of these T(reg) cells resulted in loss of protection. Adoptive transfer of the vaccine-induced T(reg) cells protected mice against EAE with greater potency than naive or Salmonella vector-induced T(reg) cells, and cytokine analysis revealed enhanced production of TGF-beta, not IL-10. The development of these T(reg) cells in conjunction with immune deviation by Th2 cells optimally induced protective T(reg) cells when compared those induced in the absence of Th2 cells. These data show that T(reg) cells can be induced to high potency to non-disease-inducing Ags using a bacterial vaccine.     

Protein kinase Ctheta controls Th1 cells in experimental autoimmune encephalomyelitis

Molecules that regulate encephalitogenic T cells are of interest for multiple sclerosis. In this study we show that protein kinase Ctheta (PKCtheta) is critical for the development of Ag-specific Th1 cells in experimental allergic encephalomyelitis (EAE), a model of multiple sclerosis. PKCtheta-deficient mice immunized with myelin oligodendrocyte glycoprotein failed to develop cell infiltrates and Th1 cytokines in the CNS and were resistant to the development of clinical EAE. CD4 T cells became primed and accumulated in secondary lymphoid organs in the absence of PKCtheta, but had severely diminished IFN-gamma, TNF, and IL-17 production. Increasing Ag exposure and inflammatory conditions failed to induce EAE in PKCtheta-deficient mice, showing a profound defect in the myelin oligodendrocyte glycoprotein-reactive T cell population. These data provide evidence of a pivotal role for PKCtheta in the generation and effector function of autoimmune Th1 cells.     

BAFF promotes Th17 cells and aggravates experimental autoimmune encephalomyelitis

Background

BAFF, in addition to promoting B cell survival and differentiation, may affect T cells. The objective of this study was to determine the effect of BAFF on Th17 cell generation and its ramifications for the Th17 cell-driven disease, EAE.

Methodology/Principal Findings

Th17 cells were increased in BAFF-Tg B6 (B6.BTg) mice and decreased in B6.Baff^−/− mice. Th17 cells in B6.Baff^−/− mice bearing a BAFF Tg (B6.Baff^−/−.BTg mice) were identical to those in B6.BTg mice, indicating that membrane BAFF is dispensable for Th17 cell generation as long as soluble BAFF is plentiful. In T + non-T cell criss-cross co-cultures, Th17 cell generation was greatest in cultures containing B6.BTg T cells and lowest in cultures containing B6.Baff^−/− T cells, regardless of the source of non-T cells. In cultures containing only T cells, Th17 cell generation followed an identical pattern. CD4⁺ cell expression of CD126 (IL-6R α chain) was increased in B6.BTg mice and decreased in B6.Baff^−/− mice, and activation of STAT3 following stimulation with IL-6 + TGF-β was also greatest in B6.BTg cells and lowest in B6.Baff^−/− cells. EAE was clinically and pathologically most severe in B6.BTg mice and least severe in B6.Baff^−/− mice and correlated with MOG_35–55 peptide-induced Th17 cell responses.

Conclusions/Significance

Collectively, these findings document a contribution of BAFF to pathogenic Th17 cell responses and suggest that BAFF antagonism may be efficacious in Th17 cell-driven diseases.     

Essential role of CD8+CD122+ regulatory T cells in the recovery from experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is one of the best-documented animal models of autoimmune disease. We examined the role of CD8+CD122+ regulatory T cells, which we previously identified as naturally occurring regulatory T cells that effectively regulate CD8+ T cells, in EAE. Depletion of CD8+CD122+ regulatory T cells by in vivo administration of anti-CD122 mAb resulted in persistent EAE symptoms. Transfer of CD8+CD122+ regulatory T cells into EAE mice at the peak EAE score clearly improved symptoms, indicating an important role of CD8+CD122+ regulatory T cells in the recovery phase of EAE. This was further confirmed by an increase and a decrease in the number of infiltrating T cells in the CNS and T cell cytokine production in mice that were depleted of or complemented with CD8+CD122+ cells. Furthermore, transfer of preactivated CD8+CD122+ regulatory T cells resulted in diminished EAE symptoms, especially in the recovery phase of EAE. These results elucidate the essential role of CD8+CD122+ regulatory T cells in the recovery phase of EAE and suggest the preventive effect of preactivated CD8+CD122+ regulatory T cells for EAE.     

Reevaluation of P-selectin and alpha 4 integrin as targets for the treatment of experimental autoimmune encephalomyelitis

There has been a great deal of interest in adhesion molecules as targets for the treatment of multiple sclerosis and other inflammatory diseases. In this study, we systematically evaluate alpha(4) integrin and P-selectin as targets for therapy in murine models of multiple sclerosis-for the first time directly measuring the ability of their blockade to inhibit recruitment and relate this to clinical efficacy. Experimental autoimmune encephalomyelitis was induced in C57BL/6 or SJL/J mice and intravital microscopy was used to quantify leukocyte interactions within the CNS microvasculature. In both strains, pretreatment with blocking Abs to either alpha(4) integrin or P-selectin reduced firm adhesion to a similar extent, but did not block it completely. The combination of the Abs was more effective than either Ab alone, although the degree of improvement was more evident in SJL/J mice. Similarly, dual blockade was much more effective at preventing the subsequent accumulation of fluorescently labeled leukocytes in the tissue in both strains. Despite evidence of blockade of leukocyte recruitment mechanisms, no clinical benefit was observed with anti-adhesion molecule treatments or genetic deletion of P-selectin in the C57BL/6 model, or in a pertussis toxin-modified model in SJL/J mice. In contrast, Abs to alpha(4) integrin resulted in a significant delay in the onset of clinical signs of disease in the standard SJL/J model. Despite evidence of a similar ability to block firm adhesion, Abs to P-selectin had no effect. Importantly, combined blockade of both adhesion molecules resulted in significantly better clinical outcome than anti-alpha(4) integrin alone.     

Impaired autoimmune T helper 17 cell responses following DNA vaccination against rat experimental autoimmune encephalomyelitis

Background

We have previously shown that vaccination with DNA encoding the encephalitogenic peptide myelin oligodendrocyte glycoprotein (MOG)_91–108 (pMOG) suppresses MOG_91–108-induced rat Experimental Autoimmune Encephalomyelitis (EAE), a model for human Multiple Sclerosis (MS). The suppressive effect of pMOG is dependent on inclusion of CpG DNA in the plasmid backbone and is associated with early induction of Interferon (IFN)-β.

Principal Findings

In this study we examined the mechanisms underlying pMOG-induced protection. We found that in the DNA vaccinated cohort proinflammatory Interleukin (IL)-17 and IL-21 responses were dramatically reduced compared to in the control group, but that the expression of Foxp3 and Tumor Growth Factor (TGF)-β1, which are associated with regulatory T cells, was not enhanced. Moreover, genes associated with Type I IFNs were upregulated. To delineate the role of IFN-β in the protective mechanism we employed short interfering RNA (siRNA) to IFN-β in the DNA vaccine. SiRNA to IFN-β completely abrogated the protective effects of the vaccine, demonstrating that a local early elaboration of IFN-β is important for EAE protection. IL-17 responses comparable to those in control rats developed in rats injected with the IFN-β-silencing DNA vaccine.

Conclusions

We herein demonstrate that DNA vaccination protects from proinflammatory Th17 cell responses during induction of EAE. The mechanism involves IFN-β as IL-17 responses are rescued by silencing of IFN-β during DNA vaccination.     

GM-CSF production by autoreactive T cells is required for the activation of microglial cells and the onset of experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is a CNS autoimmune disease believed to be triggered by T cells secreting Th1-specific proinflammatory cytokines, such as GM-CSF. In the animal model of MS, experimental autoimmune encephalomyelitis (EAE), Th1 but not Th2 cells have been shown to induce disease; however, to date, no single encephalitogenic T cell-derived cytokine has been shown to be required for EAE onset. Because GM-CSF-deficient mice have been shown to be resistant to EAE following immunization with myelin self-Ag, we investigated the cellular source of the required GM-CSF and found that GM-CSF production by encephalitogenic T cells, but not CNS resident or other peripheral cells, was required for EAE induction. Furthermore, we showed that microglial cell activation, but not peripheral macrophage activation, was a GM-CSF-dependent process. Activation of microglial cells by the injection of LPS abrogated the GM-CSF requirement for EAE induction, suggesting that microglial cell activation is required for EAE onset. These data also demonstrate that GM-CSF is a critical Th1 cell-derived cytokine required for the initiation of CNS inflammation associated with EAE, and likely MS.