Tolerance In Experimental Autoimmune Encephalomyelitis Research Articles

Targeting transmembrane-domain-less MOG expression to platelets prevents disease development in experimental autoimmune encephalomyelitis.

Multiple sclerosis (MS) is a chronic inflammatory autoimmune disease of the central nervous system with no cure yet. Here, we report genetic engineering of hematopoietic stem cells (HSCs) to express myelin oligodendrocyte glycoprotein (MOG), specifically in platelets, as a means of intervention to induce immune tolerance in experimental autoimmune encephalomyelitis (EAE), the mouse model of MS. The platelet-specific αIIb promoter was used to drive either a full-length or truncated MOG expression cassette. Platelet-MOG expression was introduced by lentivirus transduction of HSCs followed by transplantation. MOG protein was detected on the cell surface of platelets only in full-length MOG-transduced recipients, but MOG was detected in transmembrane-domain-less MOG1-157-transduced platelets intracellularly. We found that targeting MOG expression to platelets could prevent EAE development and attenuate disease severity, including the loss of bladder control in transduced recipients. Elimination of the transmembrane domains of MOG significantly enhanced the clinical efficacy in preventing the onset and development of the disease and induced CD4+Foxp3+ Treg cells in the EAE model. Together, our data demonstrated that targeting transmembrane domain-deleted MOG expression to platelets is an effective strategy to induce immune tolerance in EAE, which could be a promising approach for the treatment of patients with MS autoimmune disease.

Mechanistic contributions of Kupffer cells and liver sinusoidal endothelial cells in nanoparticle-induced antigen-specific immune tolerance

The intravenous delivery of disease-relevant antigens (Ag) by polymeric nanoparticles (NP-Ags) has demonstrated Ag-specific immune tolerance in autoimmune and allergic disorders as well as allogeneic transplant rejection. NP-Ags are observed to distribute to the spleen, which has an established role in the induction of immune tolerance. However, studies have shown that the spleen is dispensable for NP-Ag-induced tolerance, suggesting significant contributions from other immunological sites. Here, we investigated the tolerogenic contributions of Kupffer cells (KCs) and liver sinusoidal endothelial cells (LSECs) to NP-Ag-induced tolerance in a mouse model of multiple sclerosis, experimental autoimmune encephalomyelitis (EAE). Intravenously delivered Ag-conjugated poly(lactide-co-glycolide) NPs (PLG-Ag) distributed largely to the liver, where they associated with both KCs and LSECs. This distribution was accompanied by CD4 T cell accumulation, clonal deletion, and PD-L1 expression by KCs and LSECs. Ex vivo co-cultures of PLG-Ag-treated KCs or LSECs with Ag-specific CD4 T cells resulted in PGE2 and IL-10 or PGE2 secretion, respectively. KC depletion and adoptive transfer experiments demonstrated that KCs were sufficient, but not necessary, to mediate PLG-Ag-induced tolerance in EAE. The durability of PLG-Ag-induced tolerance in the absence of KCs may be attributed to the distribution of PLG-Ags to LSECs, which demonstrated similar levels of PD-L1, PGE2, and T cell stimulatory ability. Collectively, these studies provide mechanistic support for the role of liver KCs and LSECs in Ag-specific tolerance for a biomaterial platform that is currently being evaluated in clinical trials.

JAK1 signaling in dendritic cells promotes peripheral tolerance in autoimmunity through PD-L1-mediated regulatory Tcell induction.

Dendritic cells (DCs) induce peripheral Tcell tolerance, but cell-intrinsic signaling cascades governing their stable tolerogenesis remain poorly defined. Janus Kinase 1 (JAK1) transduces cytokine-receptor signaling, and JAK inhibitors (Jakinibs), including JAK1-specific filgotinib, break inflammatory cycles in autoimmunity. Here, we report in heterogeneous DC populations of multiple secondary lymphoid organs that JAK1 promotes peripheral Tcell tolerance during experimental autoimmune encephalomyelitis (EAE). Mice harboring DC-specific JAK1 deletion exhibit elevated peripheral CD4+ Tcell expansion, less regulatory Tcells (Tregs), and worse EAE outcomes, whereas adoptive DC transfer ameliorates EAE pathogenesis by inducing peripheral Tregs, programmed cell death ligand 1 (PD-L1) dependently. This tolerogenic program is substantially reduced upon the transfer of JAK1-deficient DCs. DC-intrinsic IFN-γ-JAK1-STAT1 signaling induces PD-L1, which is required for DCs to convert CD4+ Tcells into Tregs invitro and attenuated upon JAK1 deficiency and filgotinib treatment. Thus, DC-intrinsic JAK1 promotes peripheral tolerance, suggesting potential unwarranted DC-mediated effects of Jakinibs in autoimmune diseases.

Prevention of EAE by tolerogenic vaccination with PEGylated antigenic peptides.

Background:Therapeutic treatment options for chronic autoimmune disorders such as multiple sclerosis (MS) rely largely on the use of non-specific immunosuppressive drugs, which are not able to cure the disease. Presently, approaches to induce antigen-specific tolerance as a therapeutic approach; for example, by peptide-based tolerogenic ‘inverse’ vaccines have regained great interest. We have previously shown that coupling of peptides to carriers can enhance their capacity to induce regulatory T cells in vivo.Method:In this present study, we investigated whether the tolerogenic potential of immunodominant myelin T-cell epitopes can be improved by conjugation to the synthetic carrier polyethylene glycol (PEG) in an experimental autoimmune encephalomyelitis (EAE) mouse model for chronic MS (MOG C57BL/6).Results:Preventive administration of the PEGylated antigenic peptide could strongly suppress the development of EAE, accompanied by reduced immune cell infiltration in the central nervous system (CNS). Depletion of regulatory T cells (Tregs) abrogated the protective effect indicating that Tregs play a crucial role in induction of antigen-specific tolerance in EAE. Treatment during the acute phase of disease was safe and did not induce immune activation. However, treatment at the peak of disease did not affect the disease course, suggesting that either induction of Tregs does not occur in the highly inflamed situation, or that the immune system is refractory to regulation in this condition.Conclusion:PEGylation of antigenic peptides is an effective and feasible strategy to improve tolerogenic (Treg-inducing) peptide-based vaccines, but application for immunotherapy of overt disease might require modifications or combination therapies that simultaneously suppress effector mechanisms.

Intravenous tolerance induces T cell anergy/apoptosis via IFN-γ/IL-27/PD-L1 axis

Abstract The induction of peripheral tolerance by intravenous injection (i.v.) of auto-Ags has shown to suppress experimental autoimmune encephalomyelitis (EAE), a mouse model of Multiple Sclerosis, by eliciting tolerogenic APCs, Tregs, and suppressing self-reactive T cells. The programmed cell death protein (PD)-1 and its ligands, PD-L1 and PD-L2, regulate the balance between T cell activation and immune tolerance. Although PD-L1 and PD-L2 are expressed on a variety of cell types, however, the mechanisms related to peripheral tolerance that induce these molecules are still unclear. Here we show that PD-L1, but not PD-L2, is critical for inducing peripheral tolerance in EAE, and that PD-L1-dependent tolerance relies on both IFN-γ and IL-27. I.v. administration of auto-Ag(s) attenuates the progression of EAE, by inducing PD-L1 expression in monocyte-derived DCs (moDCs) in the CNS, via IFN-γ/ IL-27-dependent mechanism. Indeed, when PD-L1 is blocked, autoantigen(s)/i.v treatment becomes ineffective. Following IFN-γ−/− CD4+ T cell transfer into Rag1−/− mice, i.v. tolerance treatment failed to suppress EAE. Moreover, loss of IFN-γR signaling in classical DCs type I (cDCs I) compromised IL-27 production and consequent PD-L1 expression by moDCs. We also show that IL-27 stimulates moDCs to over-express PD-L1, in a STAT-3-dependent way. Indeed, in CCR2−/−/WSX−/− (CD45.2) → CD45.1 radiation-induced bone marrow chimera mice, auto-Ag(s)/i.v. treatment failed to suppress EAE. Similarly, EAE mice that expressed mutant STAT-3 (muSTAT-3) in CCR2+ cells were also insensitive to i.v. tolerance induction. Our data reveal a mechanism whereby IFN-γ and IL-27 are the key factors in PD-L1 induction and subsequent peripheral tolerance restoration.

Selective depletion of CD11c+ CD11b+ dendritic cells partially abrogates tolerogenic effects of intravenous MOG in murine EAE.

Intravenous (i.v.) injection of a soluble myelin antigen can induce tolerance, which effectively ameliorates experimental autoimmune encephalomyelitis (EAE). We have previously shown that i.v. myelin oligodendrocyte glycoprotein (MOG) induces tolerance in EAE and expands a subpopulation of tolerogenic CD11c+ CD11b+ dendritic cells (DCs) with an immature phenotype having low expression of IA and co-stimulatory molecules CD40, CD86, and CD80. Here, we further investigate the role of tolerogenic DCs in i.v. tolerance by injecting clodronate-loaded liposomes, which selectively deplete CD11c+ CD11b+ and immature DCs, but not CD11c+ CD8+ DCs and mature DCs. I.v. MOG-induced suppression of EAE was partially, yet significantly, blocked by CD11c+ CD11b+ DC depletion. While i.v. MOG inhibited IA, CD40, CD80, CD86 expression and induced TGF-β, IL-27, IL-10 production in CD11c+ CD11b+ DCs, these effects were abrogated after injection of clodronate-loaded liposomes. Depletion of CD11c+ CD11b+ DCs also precluded i.v. autoantigen-induced T-cell tolerance, such as decreased production of IL-2, IFN-γ, IL-17 and numbers of IL-2+ , IFN-γ+ , and IL-17+ CD4+ T cells, as well as an increased proportion of CD4+ CD25+ Foxp3+ regulatory T cells and CD4+ IL-10+ Foxp3- Tr1 cells. CD11c+ CD11b+ DCs, through low expression of IA and costimulatory molecules as well as high expression of TGF-β, IL-27, and IL-10, play an important role in i.v. tolerance-induced EAE suppression.

Galectin-1 is essential for the induction of MOG35-55 -based intravenous tolerance in experimental autoimmune encephalomyelitis.

In experimental autoimmune encephalomyelitis (EAE), intravenous (i.v.) injection of the antigen, myelin oligodendrocyte glycoprotein-derived peptide, MOG35-55 , suppresses disease development, a phenomenon called i.v. tolerance. Galectin-1, an endogenous glycan-binding protein, is upregulated during autoimmune neuroinflammation and plays immunoregulatory roles by inducing tolerogenic dendritic cells (DCs) and IL-10 producing regulatory type 1 T (Tr1) cells. To examine the role of galectin-1 in i.v. tolerance, we administered MOG35-55 -i.v. to wild-type (WT) and galectin-1 deficient (Lgals1(-/-) ) mice with ongoing EAE. MOG35-55 suppressed disease in the WT, but not in the Lgals1(-/-) mice. The numbers of Tr1 cells and Treg cells were increased in the CNS and periphery of tolerized WT mice. In contrast, Lgals1(-/-) MOG-i.v. mice had reduced numbers of Tr1 cells and Treg cells in the CNS and periphery, and reduced IL-27, IL-10, and TGF-β1 expression in DCs in the periphery. DCs derived from i.v.-tolerized WT mice suppressed disease when adoptively transferred into mice with ongoing EAE, whereas DCs from Lgals1(-/-) MOG-i.v. mice were not suppressive. These findings demonstrate that galectin-1 is required for i.v. tolerance induction, likely via induction of tolerogenic DCs leading to enhanced development of Tr1 cells, Treg cells, and downregulation of proinflammatory responses.

Galectin-1 plays an essential role in intravenous tolerance in experimental autoimmune encephalomyelitis (BA4P.139)

Abstract Multiple sclerosis and its animal model, experimental autoimmune encephalomyelitis (EAE), are inflammatory demyelinating diseases of the central nervous system (CNS). EAE can be induced by immunizing mice with myelin oligodendrocyte glycoprotein-derived peptide, MOG35-55, in adjuvant. It has been previously demonstrated that intravenous (i.v.) injection of MOG35-55 post immunization induction suppresses disease development, a phenomenon called i.v. tolerance. The glycan-binding protein galectin-1, produced primarily by regulatory T cells plays an immunoregulatory role in EAE by inducing tolerogenic DCs and IL-10-producing regulatory type 1 T cells (Tr1). To examine the role of galectin-1 in i.v. tolerance, we administered MOG35-55 peptide i.v. to wild-type (WT) and galectin-1-/- (Gal1-/-) mice with ongoing EAE. MOG35-55 rapidly suppressed disease in the WT, but not in the Gal1-/- mice. Expression of pro-inflammatory cytokines IFN-gamma and IL-17A were reduced in the CNS and periphery of tolerized WT mice, while the number of Tr1 cells increased in the periphery. In contrast, i.v. MOG35-55 significantly increased IFN-gamma and IL-17A in the CNS and periphery of Gal1-/-mice and these mice had markedly fewer Tr1 cells in the periphery. Our data suggest that galectin-1 mediated i.v. tolerance induction is dependent on the downregulation of Th1 and Th17 pro-inflammatory responses, and enhanced development of Tr1 cells.

C-kit plays a critical role in induction of intravenous tolerance in experimental autoimmune encephalomyelitis.

c-kit (CD117) is a tyrosine kinase receptor found in various types of immune cells. It has been shown that c-kit plays a role in the pathogenesis of multiple sclerosis, an inflammatory demyelinating disorder of the CNS. Recent data have suggested an immunoregulatory effect of c-kit. We therefore examined the role of c-kit in autoantigen-induced i.v. tolerance in experimental autoimmune encephalomyelitis (EAE), an animal model of MS. Our results show that induction of intravenous tolerance against EAE in B6 mice is characterized by increased numbers of CD117(+) cells and altered mast cell-associated molecules in the periphery and in the CNS. W(-sh) (c-kit-deficient) mice were resistant to i.v autoantigen-induced tolerance, with increased proinflammatory cytokine production in the periphery. I.v. autoantigen in WT mice suppressed the production of proinflammatory cytokines IFN-γ and IL-6 and up-regulated the expression of FoxP3, a transcription factor of Tregs; however, in W(-sh) mice, IFN-γ and IL-6 were increased with a failure of FoxP3 induction upon i.v. autoantigen injection and is thus a mechanism for resistance to i.v. tolerance induction in these mice. We conclude that c-kit signaling has a regulatory role in i.v. tolerance and could be a target for potential immunotherapy in autoimmune disorders.

Mechanism of induction of immune tolerance in experimental autoimmune encephalomyelitis by combination treatment with fingolimod plus pathogenic autoantigen

AbstractObjectiveWe previously reported that relapse of experimental autoimmune encephalomyelitis (EAE) occurred approximately 1 week after discontinuation of fingolimod (FTY720), but combination treatment with FTY720 plus pathogenic autoantigen significantly suppressed occurrence of relapse. Here, we investigated the mechanism of this suppression.MethodsEAE mice were treated from onset with FTY720 alone or in combination with an autoantigenic peptide of myelin oligodendrocyte glycoprotein 35(MEVGWYRSPFSRVVHLYRNGK)55 (MOG35‐55). Antigen‐specific T cell activity and T cell subpopulations were analyzed by using flow cytometric analysis. Spinal cords were excised and examined immunohistochemically.ResultsAfter treatment with FTY720 alone, CD4+ T cells from inguinal lymph nodes (LN) maintained activity towards pathogenic autoantigen. The percentage of CD4+CD44highCD62Llow (effector memory) T cells in inguinal LN was significantly increased. At day 8 after discontinuation, infiltration of CD3+ and CD4+ cells in spinal cords was significantly increased, and the absolute number of CD4+ T cells in inguinal LN was decreased. However, in the case of combination treatment, the absolute number of CD4+ T cells in inguinal LN remained unchanged, and infiltration of CD3+ and CD4+ cells was significantly suppressed.ConclusionsAs the number of CD4+ T cells in inguinal LN was unchanged in the FTY720 plus MOG35‐55 group, the combination treatment might inhibit relapse by decreasing the ability of pathogenic T cells to migrate from peripheral tissues to the central nervous system. The combination treatment might become a breakthrough remission‐induction treatment for MS.

Vaccinelike and Prophylactic Treatments of EAE with Novel I-Domain Antigen Conjugates (IDAC): Targeting Multiple Antigenic Peptides to APC

The objective of this work is to utilize novel I-domain antigenic-peptide conjugates (IDAC) for targeting antigenic peptides to antigen-presenting cells (APC) to simulate tolerance in experimental autoimmune encephalomyelitis (EAE). IDAC-1 and IDAC-3 molecules are conjugates between the I-domain protein and PLP-Cys and Ac-PLP-Cys-NH(2) peptides, respectively, tethered to N-terminus and Lys residues on the I-domain. The hypothesis is that the I-domain protein binds to ICAM-1 and PLP peptide binds to MHC-II on the surface of APC; this binding event inhibits the formation of the immunological synapse at the APC-T-cell interface to alter T-cell differentiation from inflammatory to regulatory phenotypes. Conjugation of peptides to the I-domain did not change the secondary structure of IDAC molecules as determined by circular dichroism spectroscopy. The efficacies of IDAC-1 and -3 were evaluated in EAE mice by administering iv or sc injections of IDAC in a prophylactic or a vaccinelike dosing schedule. IDAC-3 was better than IDAC-1 in suppressing and delaying the onset of EAE when delivered in prophylactic and vaccinelike manners. IDAC-3 also suppressed subsequent relapse of the disease. The production of IL-17 was lowered in the IDAC-3-treated mice compared to those treated with PBS. In contrast, the production of IL-10 was increased, suggesting that there is a shift from inflammatory to regulatory T-cell populations in IDAC-3-treated mice. In conclusion, the I-domain can effectively deliver antigenic peptides in a vaccinelike or prophylactic manner for inducing immunotolerance in the EAE mouse model.

Intravenous tolerance effectively overcomes enhanced pro-inflammatory responses and experimental autoimmune encephalomyelitis severity in the absence of IL-12 receptor signaling

Intravenous (i.v.) administration of autoantigen effectively induces Ag-specific tolerance against experimental autoimmune encephalomyelitis (EAE). We and others have shown enhanced EAE severity in mice lacking IL-12 or its receptor, strongly suggesting an immunoregulatory effect of IL-12 signaling. To examine the role of IL-12 responsiveness in autoantigen-induced tolerance in EAE, we administered autoantigen i.v. in two distinct treatment regimes to wildtype and IL-12Rβ2−/− mice, immunized to develop EAE. Administration at the induction phase suppressed EAE in wildtype and IL-12Rβ2−/− mice however the effect was somewhat less potent in the absence of IL-12Rβ2. Expression of pro-inflammatory cytokines such as IFN-γ, IL-17 and IL-2, was inhibited in wild-type tolerized mice but less so in IL-12Rβ2−/− mice. I.v. antigen was also effective in suppressing disease in both genotypes when given during the clinical phase of disease with similar CNS inflammation, demyelination and peripheral inflammatory cytokine profiles observed in both genotypes. There was however a mild impact of a lack of IL-12 signaling on Treg induction during tolerance induction compared to WT mice in this treatment regime. These findings show that the enhanced severity of EAE that occurs in the absence of IL-12 signaling can be effectively overcome by i.v. autoantigen, indicating that this therapeutic effect is not primarily mediated by IL-12 and that i.v. tolerance could be a powerful approach in suppressing severe and aggressive MS.

Viral vector mediated tolerance induction in experimental autoimmune encephalomyelitis by dendritic cell targeted expression of a self-antigen (115.2)

Abstract Multiple sclerosis (MS) is an autoimmune disease characterized by the presence of self-reactive T cells that target myelin components. Immunization of susceptible animals with myelin antigens induces experimental autoimmune encephalomyelitis (EAE), an animal model for MS. The aim of this project was to induce permanent, antigen-specific tolerance in EAE/MS and to address the mechanisms that would contribute to tolerance. The strategy includes the ex vivo modification of autologous hematopoietic stem cells (HSC) with lentiviral vectors that express myelin oligodendrocyte glycoprotein (MOG) under the control of a dendritic cell (DC) specific promoter. After re-infusion, the modified HSC will give rise to antigen expressing DCs. We demonstrated the effectiveness of this strategy for inducing MOG-specific tolerance in EAE, as 100% of the mice that received BM cells transduced with MOG-lentivector were protected. In addition, we show depletion of MOG specific T cells and generation of Foxp3+ regulatory T cells in chimeras that received HSC transduced with MOG-lentivector. As apposed to the protected animals, the diseased control mice showed high levels of IL-1, INF-γ and IL-17. The strategy presented here is particularly promising for clinical applications and important for addressing fundamental questions in immunity and tolerance.

A GMCSF-neuroantigen (NAg) fusion protein targets NAg to dendritic cells (DC) and is an effective therapy for experimental autoimmune encephalomyelitis (EAE) (50.10)

Abstract The GM-CSF and M-CSF cytokines were tested as domains in cytokine-NAg fusion proteins to assess targeting of NAg to different APC subsets. Fusion proteins were designed with a cytokine N-terminal domain and the encephalitogenic peptide 69-88 of guinea pig myelin basic protein (MBP) as the C-terminal domain. Studies measuring T-cell activation in vitro, prevention of EAE, and treatment of EAE showed that GMCSF-NAg was the most potent fusion protein, represented by the following rank order of activity (GMCSF-NAg > MCSF-NAg > GP69-88). GMCSF-NAg was 1000-fold more potent than GP69-88 in stimulating MBP-specific T-cell proliferation. The mechanism by which GMCSF-NAg promoted T-cell activation involved cytokine receptor-mediated uptake of NAg by antigen presenting cells (APC), because free GM-CSF inhibited the GMCSF-NAg potentiated response. GMCSF-NAg potently targeted NAg to dendritic cells and macrophages in vitro, but not to B or T cell APC. Covalent linkage between GM-CSF and NAg was required for enhanced potency of GMCSF-NAg in vitro and for the prevention and treatment of EAE in vivo. In conclusion, GMCSF-NAg potently targeted self-antigen to myeloid APC subsets and caused profound antigen-specific tolerance in EAE. This study was supported by research grants from the National Multiple Sclerosis Society and the Brody Brothers Endowment Fund.

IL‐17 Eliminates the Therapeutic Effects of Myelin Basic Protein‐Induced Nasal Tolerance in Experimental Autoimmune Encephalomyelitis by Activating IL‐6

Interleukin (IL)-17 is a proinflammatory cytokine primarily secreted by Th17 cells, which are a CD4(+) T-cell subset. Th17 cells and IL-17 are important in the pathogenesis of multiple sclerosis and in its established animal model, experimental autoimmune encephalomyelitis (EAE). However, it is unclear whether IL-17 contributes to EAE immune tolerance. We used the myelin basic protein (MBP) peptide MBP 68-86 to induce nasal tolerance to EAE, and simultaneously interfered with the tolerance by treatment with different doses of IL-17. We found that IL-17 dramatically interfered with MBP 68-86-induced immune tolerance. IL-17 administration increased IL-6 release, skewing T cell differentiation towards Th17 cells and decreasing the number of Treg cells. This led to an imbalance between Treg cells and Th17 cells and spurred the development of EAE.

Modulation of established murine collagen-induced arthritis by a single inoculation of short-term lipopolysaccharide-stimulated dendritic cells

Background:The use of regulatory or immature dendritic cells (DCs) as tools for modulating experimental rheumatoid arthritis is very recent. Tumour necrosis factor (TNF)-stimulated DCs have been shown to restore tolerance...

A paradoxical role of APCs in the induction of intravenous tolerance in experimental autoimmune encephalomyelitis

The central role of T cells in the induction of tolerance to autoantigens has been well documented. However, the role of antigen-presenting cells (APCs) in this process is not yet fully understood. To better understand the contribution of APCs in tolerance, we studied the interaction of purified APCs and CD4 + T cells in a model of intravenous (i.v.) tolerance to experimental autoimmune encephalomyelitis (EAE). As expected, we found that T cells were tolerized to the autoantigen after i.v. injection. However, purified APCs obtained from MOG-i.v.-treated mice were paradoxically immuno-stimulatory, as they induced a non-specific Th1-type response both in vitro and in vivo. We conclude that blocking such APC activation would enhance the effectiveness of tolerance induction.

Cytokine shifts and tolerance in experimental autoimmune encephalomyelitis.

Cytokines play an important role in the pathogenesis of both multiple sclerosis and experimental autoimmune encephalomyelitis (EAE). Effective treatments for both diseases have been shown to alter cytokines in the central nervous system and in activated mononuclear cells. EAE is an animal model that mimics many aspects of multiple sclerosis, and has been widely used to study the mechanisms of disease and therapeutic approaches to multiple sclerosis. Cytokines play an important role in regulation of disease expression in EAE, and in tolerance to disease induction. In this review, we will summarize the current findings on the role of cytokine shifts in the induction of tolerance in EAE. In addition, we will discuss modulation of EAE by altered expression of members of the cytokineregulated Jak/STAT intracellular signaling pathway.

The Role of IL-12 in the Induction of Intravenous Tolerance in Experimental Autoimmune Encephalomyelitis

Intravenous administration of autoantigen is an effective method to induce Ag-specific tolerance against experimental autoimmune encephalomyelitis (EAE). IL-12 is a potent Th1 stimulator and an essential cytokine in the induction of EAE. The role of IL-12 in the induction of i.v. tolerance is not clear. In this study, we induced tolerance by i.v. administering myelin basic protein (MBP) peptide Ac1-11 (MBP1-11) in EAE. We observed significant suppression of IL-12 production by the lymph node cells of MBP1-11-injected mice. To see whether the low level of IL-12 is the cause or effect of tolerance, we administered IL-12 to the EAE mice at the time of i.v. MBP1-11 injection. Exogenous IL-12 abrogated the suppression of clinical and pathological EAE by i.v. tolerance. IL-12 blocked the suppressive effect of i.v. tolerance on the proliferative response to MBP1-11 and MBP1-11-induced production of IL-12 and IFN-gamma. Furthermore, IL-12 completely blocked the i.v. tolerance-induced type 1 T regulatory cell response. These data suggest that i.v. administration of autoantigen results in the suppression of endogenous IL-12 and the consequent switching of the immune response from an immunogenic to a tolerogenic form.

An autologous self-antigen differentially regulates expression of I-A glycoproteins and B7 costimulatory molecules on CD4- CD8- T helper cells.

During inflammation, T helper cells transiently express class II major histocompatibility complex (MHC) glycoproteins and present antigens to other T cells. To assess involvement of self-antigens in the generation of T cell antigen-presenting cell (T-APC) activity, rat (R) myelin basic protein (MBP) was used to stimulate a rat CD4-CD8- T cell clone. RMBP induced T cell surface expression of class II MHC glycoproteins and T-APC activity, although RMBP did not elicit interleukin (IL-2) production or proliferation. When added to culture with the strong agonist guinea pig (GP) MBP, RMBP acted as a partial antagonist and inhibited responses of IL-2 production, proliferation, and T cell expression of B7.1. RMBP did not, however, efficiently antagonize GPMBP-induced I-A expression on T cells. These findings indicate that the self-antigen RMBP specifically induces accumulation of I-A/peptide complexes at signaling thresholds that inhibit pathogenic autoimmune responses. Overall, this study suggests a role for self-antigens in the generation of B7-deficient T-APC activity as a mechanism of tolerance in experimental autoimmune encephalomyelitis.