Class II MHC/peptide complexes are released from APC and are acquired by T cell responders during specific antigen recognition.

T cell expression of class II MHC/peptide complexes may be important for maintenance of peripheral self-tolerance, but mechanisms underlying the genesis of class II MHC glycoproteins on T cells are not well resolved. T cell APC (T-APC) used herein were transformed IL-2-dependent clones that constitutively synthesized class II MHC glycoproteins. When pulsed with myelin basic protein (MBP) and injected into Lewis rats, these T-APC reduced the severity of experimental autoimmune encephalomyelitis, whereas unpulsed T-APC were without activity. Normal MBP-reactive clones cultured without APC did not express class II MHC even when activated with mitogens and exposed to IFN-gamma. However, during a 4-h culture with T-APC or macrophage APC, recognition of MBP or mitogenic activation of responder T cells elicited high levels of I-A and I-E expression on responders. Acquisition of class II MHC glycoproteins by responders was resistant to the protein synthesis inhibitor cycloheximide, coincided with transfer of a PKH26 lipophilic dye from APC to responders, and resulted in the expression of syngeneic and allogeneic MHC glycoproteins on responders. Unlike rested I-A- T cell clones, rat thymic and splenic T cells expressed readily detectable levels of class II MHC glycoproteins. When preactivated with mitogens, naive T cells acquired APC-derived MHC class II molecules and other membrane-associated proteins when cultured with xenogeneic APC in the absence of Ag. In conclusion, this study provides evidence that APC donate membrane-bound peptide/MHC complexes to Ag-specific T cell responders by a mechanism associated with the induction of tolerance.     

Cutting edge: in vitro-generated tolerogenic APC induce CD8+ T regulatory cells that can suppress ongoing experimental autoimmune encephalomyelitis

APC exposed to TGFbeta2 and Ag (tolerogenic APC) promote peripheral Ag-specific tolerance via the induction of CD8(+) T regulatory cells capable of suppressing Th1 and Th2 immunity. We postulated that tolerogenic APC might reinstate tolerance toward self-neuronal Ags and ameliorate ongoing experimental autoimmune encephalomyelitis (EAE). Seven days after immunization with myelin basic protein (MBP), mice received MBP-specific tolerogenic APC, and EAE was evaluated clinically. To test for the presence and the phenotype of T regulatory cells, CD4 and/or CD8 T cells from tolerogenic APC-treated mice were transferred to naive mice before their immunization with MBP. The MBP-specific tolerogenic APC decreased both the severity and incidence of ongoing EAE. Tolerance to self-neuronal Ags was induced in naive recipient mice via adoptive transfer of CD8(+), but not CD4(+) T cells. Rational use of in vitro-generated tolerogenic APC may lead to novel therapy for autoimmune disease.     

Peripheral tolerance induction using ethylenecarbodiimide-fixed APCs uses both direct and indirect mechanisms of antigen presentation for prevention of experimental autoimmune encephalomyelitis

MHC class II (MHC II)-restricted T cell responses are a common driving force of autoimmune disease. Accordingly, numerous therapeutic strategies target CD4(+) T cells with the hope of attenuating autoimmune responses and restoring self-tolerance. We have previously reported that i.v. treatment with Ag-pulsed, ethylenecarbodiimide (ECDI)-fixed splenocytes (Ag-SPs) is an efficient protocol to induce Ag-specific tolerance for prevention and treatment of experimental autoimmune encephalomyelitis (EAE). Ag-SPs coupled with peptide can directly present peptide:MHC II complexes to target CD4(+) T cells in the absence of costimulation to induce anergy. However, Ag-SPs coupled with whole protein also efficiently attenuates Ag-specific T cell responses suggesting the potential contribution of alternative indirect mechanisms/interactions between the Ag-SPs and target CD4(+) T cells. Thus, we investigated whether MHC II compatibility was essential to the underlying mechanisms by which Ag-SP induces tolerance during autoimmune disease. Using MHC-deficient, allogeneic, and/or syngeneic donor Ag-SPs, we show that MHC compatibility between the Ag-SP donor and the host is not required for tolerance induction. Interestingly, we found that ECDI treatment induces apoptosis of the donor cell population which promotes uptake and reprocessing of donor cell peptides by host APCs resulting in the apparent MHC II-independent induction of tolerance. However, syngeneic donor cells are more efficient at inducing tolerance, suggesting that Ag-SPs induce functional Ag-SP tolerance via both direct and indirect (cross-tolerance) mechanisms leading to prevention and effective treatment of autoimmune disease.     

Amelioration of established experimental autoimmune encephalomyelitis by an MHC anchor-substituted variant of proteolipid protein 139-151

Murine experimental autoimmune encephalomyelitis (EAE) is a CD4+ T cell-mediated autoimmune disorder directed against myelin proteins within the CNS. We propose that variant peptides containing amino acid substitutions at MHC anchor residues will provide a unique means to controlling the polyclonal autoimmune T cell response. In this study, we have identified an MHC variant of proteolipid protein (PLP) 139-151 (145D) that renders PLP(139-151)-specific T cell lines anergic in vitro, as defined by a significant reduction in proliferation and IL-2 production following challenge with wild-type peptide. In vivo administration of 145D before challenge with PLP(139-151) results in a significant reduction in disease severity and incidence. Importantly, we demonstrate the ability of an MHC variant peptide to ameliorate established EAE. An advantage to this treatment is that the MHC variant peptide does not induce an acute hypersensitivity reaction. This is in contrast to previous work in the PLP(139-151) model demonstrating that anaphylactic shock resulting in death occurs upon rechallenge with the encephalitogenic peptide. Taken together, these data demonstrate the effectiveness of MHC anchor-substituted peptides in the treatment of EAE and suggest their utility in the treatment of other autoimmune disorders.     

The role of the MHC class II transactivator in class II expression and antigen presentation by astrocytes and in susceptibility to central nervous system autoimmune disease

The role of the MHC class II transactivator (CIITA) in Ag presentation by astrocytes and susceptibility to experimental autoimmune encephalomyelitis (EAE) was examined using CIITA-deficient mice and newly created transgenic mice that used the glial fibrillary acidic protein promoter to target CIITA expression in astrocytes. CIITA was required for class II expression on astrocytes. Like class II-deficient mice, CIITA-deficient mice were resistant to EAE by immunization with CNS autoantigen, although T cells from immunized CIITA-deficient, but not class II-deficient, mice proliferated and secreted Th1 cytokines. CIITA-deficient splenic APC presented encephalitogenic peptide to purified wild-type encephalitogenic CD4(+) T cells, indicating that CIITA-independent mechanisms can be used for class II-restricted Ag presentation in lymphoid tissue. CIITA-deficient mice were also resistant to EAE by adoptive transfer of encephalitogenic class II-restricted CD4(+) Th1 cells, indicating that CIITA-dependent class II expression was required for CNS Ag presentation. Despite constitutive CIITA-driven class II expression on astrocytes in vivo, glial fibrillary acidic protein-CIITA transgenic mice were no more susceptible to EAE than controls. CIITA-transfected astrocytes presented peptide Ag, but in contrast to IFN-gamma-activated astrocytes, they could not process and present native Ag. CIITA-transfected astrocytes did not express cathepsin S without IFN-gamma activation, indicating that CIITA does not regulate other elements that may be required for Ag processing by astrocytes. Although our results demonstrate that CIITA-directed class II expression is required for EAE induction, CIITA-directed class II expression by astrocytes does not appear to increase EAE susceptibility. These results do not support the role of astrocytes as APC for class II-restricted Ag presentation during the induction phase of EAE.     

Priming of CTLs by lymphocytic choriomeningitis virus depends on dendritic cells

Appropriate activation of naive CD8(+) T cells depends on the coordinated interaction of these cells with professional APC that present antigenic peptides in the context of MHC class I molecules. It is accepted that dendritic cells (DC) are efficient in activating naive T cells and are unique in their capacity to prime CD8(+) T cell responses against exogenous cell-associated Ags. Nevertheless, it is unclear whether epitopes, derived from endogenously synthesized proteins and presented by MHC class I molecules on the surface of other APC including B cells and macrophages, can activate naive CD8(+) T cells in vivo. By infecting transgenic CD11c-DTR/GFP mice that allow conditional depletion of DC with lymphocytic choriomeningitis virus (LCMV), which infects all types of APC and elicits a vigorous CTL response, we unambiguously show that priming of LCMV-specific CD8(+) T cells is crucially dependent on DC, despite ample presence of LCMV-infected macrophages and B cells in secondary lymphoid organs.     

Dimeric MHC-peptides inserted into an immunoglobulin scaffold as new immunotherapeutic agents

The interactions of the T cell receptor (TCR) with cognate MHC-peptide and co-stimulatory molecules expressed at surface of antigen presenting cells (APC) leads to activation or tolerance of T cells. The development of molecular biological tools allowed for the preparation of soluble MHC-peptide molecules as surrogate for the APC. A decade ago a monomeric class II MHC molecule in which the peptide was covalently linked to β-chain of class II molecule was generated. This type of molecule had a low-binding affinity and did not cause the multimerization of TCR. The requirement of multimerization of TCR led to development of a new class of reagents, chimeric peptides covalently linked to MHC that was dimerized via Fc fragment of an immunoglobulin and linked to 3' end of the β-chain of MHC class II molecule. These soluble dimerized MHC-peptide chimeric molecules display high affinity for the TCR and caused multimerization of TCR without processing by an APC. Because dimeric molecules are devoid of co-stimulatory molecules interacting with CD28, a second signal, they induce anergy rather the activation of T cells. In this review, we compare the human and murine dimerized MHC class II-peptides and their effect on CD4(+) T cells, particularly the generation of T regulatory cells, which make these chimeric molecules an appealing approach for the treatment of autoimmune diseases.     

Acquisition of MHC:Peptide Complexes by Dendritic Cells Contributes to the Generation of Antiviral CD8+ T Cell Immunity In Vivo

There is an increasing body of evidence suggesting that the transfer of preformed MHC class I:peptide complexes between a virus-infected cell and an uninfected APC, termed cross-dressing, represents an important mechanism of Ag presentation to CD8(+) T cells in host defense. However, although it has been shown that memory CD8(+) T cells can be activated by uninfected dendritic cells (DCs) cross-dressed by Ag from virus-infected parenchymal cells, it is unknown whether conditions exist during virus infection in which naive CD8(+) T cells are primed and differentiate to cytolytic effectors through cross-dressing, and indeed which DC subset would be responsible. In this study, we determine whether the transfer of MHC class I:peptide complexes between infected and uninfected murine DC plays a role in CD8(+) T cell priming to viral Ags in vivo. We show that MHC class I:peptide complexes from peptide-pulsed or virus-infected DCs are indeed acquired by splenic CD8α(-) DCs in vivo. Furthermore, the acquired MHC class I:peptide complexes are functional in that they induced Ag-specific CD8(+) T cell effectors with cytolytic function. As CD8α(-) DCs are poor cross-presenters, this may represent the main mechanism by which CD8α(-) DCs present exogenously encountered Ag to CD8(+) T cells. The sharing of Ag as preformed MHC class I:peptide complexes between infected and uninfected DCs without the restraints of Ag processing may have evolved to accurately amplify the response and also engage multiple DC subsets critical in the generation of strong antiviral immunity.     

Cutting edge: Immunosuppressant as adjuvant for tolerogenic immunization

Vaccination for autoimmune and alloimmune diseases has long been an attractive idea. Yet, there is no suitable adjuvant to forcefully steer the immune response toward tolerance. In this study we show that dexamethasone, a potent glucocorticoid immunosuppressant, can function as a tolerogenic adjuvant when applied together with peptide immunogen. BALB/c mice with pre-established delayed-type hypersensitivity to hen OVA were immunized with an OVA-derived, MHC II-restricted peptide (OVA(323-339)) in the presence of dexamethasone. The treatment caused long-term desensitization in treated animals to hen OVA via a dexamethasone-dependent tolerogenic mechanism that blocks maturation of dendritic cells and expands OVA(323-339)-specific CD4(+)CD25(+)Foxp3(+) regulatory T cells in vivo. Similar treatment of NOD mice using dexamethasone and an insulin-derived, MHC II-restricted peptide (B:9-23) prevented predisposed spontaneous diabetes. Remarkably, in both models, dexamethasone-augmented immunization induced long-term persistent, Ag-specific regulatory T cells responsive to recall Ags. These results reveal for the first time the potential usefulness of immunosuppressants as tolerogenic adjuvants.     

Cutting edge: link between innate and adaptive immunity: Toll-like receptor 2 internalizes antigen for presentation to CD4+ T cells and could be an efficient vaccine target

An ideal vaccine for induction of CD4(+) T cell responses should induce local inflammation, maturation of APC, and peptide loading of MHC class II molecules. Ligation of Toll-like receptor (TLR) 2 provides the first two of these three criteria. We have studied whether targeting of TLR2 results in loading of MHC class II molecules and enhancement of CD4(+) T cell responses. To dissociate MHC class II presentation from APC maturation, we have used an antagonistic, mouse anti-human TLR2 mAb (TL2.1) as ligand and measured proliferation of a mouse Ckappa-specific human CD4(+) T cell clone. TL2.1 mAb was 100-1000 times more efficiently presented by APC compared with isotype-matched control mAb. Moreover, TL2.1 mAb was internalized into endosomes and processed by the conventional MHC class II pathway. This novel function of TLR2 represents a link between innate and adaptive immunity and indicates that TLR2 could be a promising target for vaccines.     

Thiopalmitoylation of myelin proteolipid protein epitopes enhances immunogenicity and encephalitogenicity

Proteolipid protein (PLP) is the most abundant protein of CNS myelin, and is posttranslationally acylated by covalent attachment of long chain fatty acids to cysteine residues via a thioester linkage. Two of the acylation sites are within epitopes of PLP that are encephalitogenic in SJL/J mice (PLP(104-117) and PLP(139-151)) and against which increased immune responses have been detected in some multiple sclerosis patients. It is known that attachment of certain types of lipid side chains to peptides can result in their enhanced immunogenicity. The aim of this study was to determine whether thioacylated PLP peptides, as occur in the native protein, are more immunogenic than their nonacylated counterparts, and whether thioacylation influences the development of autoreactivity and experimental autoimmune encephalomyelitis. The results show that in comparison with nonacylated peptides, thioacylated PLP lipopeptides can induce greater T cell and Ab responses to both the acylated and nonacylated peptides. They also enhanced the development and chronicity of experimental autoimmune encephalomyelitis. Synthetic peptides in which the fatty acid was attached via an amide linkage at the N terminus were not encephalitogenic, and they induced greater proportions of CD8+ cells in initial in vitro stimulation. Therefore, the lability and the site of the linkage between the peptide and fatty acid may be important for induction of encephalitogenic CD4+ T cells. These results suggest that immune responses induced by endogenous thioacylated lipopeptides may contribute to the immunopathogenesis of chronic experimental demyelinating diseases and multiple sclerosis.     

Parental MHC molecule haplotype expression in (SJL/J x SWR)F1 mice with acute experimental allergic encephalomyelitis induced with two different synthetic peptides of myelin proteolipid protein.

To determine if the Ag that induces an autoimmune disease influences parental MHC haplotype molecule expression in situ in MHC heterozygotes, acute experimental allergic encephalomyelitis (EAE) was induced with different encephalitogenic peptides in (SJL/J x SWR)F1 mice. The mice were sensitized with either a synthetic peptide corresponding to mouse myelin proteolipid protein (PLP) residues 103-116 YKTTICGKGLSATV which induces EAE in SWR (H-2q), but not SJL/J (H-2s) mice or a synthetic peptide corresponding to PLP residues 139-151 HCLGKWLGHPDKF which is encephalitogenic in SJL/J but not SWR mice. Mice were killed when they were moribund or at 30 days after sensitization. Twelve of 18 F1 mice given PLP peptide 103-116 and 12 of 17 mice given PLP peptide 139-151 developed EAE within 2 to 3 wk after sensitization. Cryostat sections of brain samples from F1 and parental mice were immunostained with a panel of mAb identifying H-2s and H-2q class I and II MHC molecules. In brains of controls, class I MHC molecules were expressed on choroid plexus, endothelial cells, and microglia whereas class II MHC molecules were absent. In EAE lesions, class I and II MHC molecules were present on inflammatory and parenchymal cells, but the degree of parental haplotype molecule expression did not vary with the different peptide Ag tested. Thus, in (SJL/J x SWR)F1 mice, myelin PLP peptides 103-116 and 139-151 are co-dominant Ag with respect to clinical and histologic disease and parental haplotype MHC molecule expression. We propose a unifying hypothesis consistent with these results and previous observations of differential Ia expression in (responder x non-responder)F1 guinea pigs. We suggest that MHC molecules may bind locally derived peptide Ag in inflammatory sites and that these interactions influence levels of MHC haplotype molecules on APC.     

Cysteinylation of MHC class II ligands: peptide endocytosis and reduction within APC influences T cell recognition

Peptides bind cell surface MHC class II proteins to yield complexes capable of activating CD4(+) T cells. By contrast, protein Ags require internalization and processing by APC before functional presentation. Here, T cell recognition of a short peptide in the context of class II proteins occurred only after delivery of this ligand to mature endosomal/lysosomal compartments within APC. Functional and biochemical studies revealed that a central cysteine within the peptide was cysteinylated, perturbing T cell recognition of this epitope. Internalization and processing of the modified epitope by APC, was required to restore T cell recognition. Peptide cysteinylation and reduction could occur rapidly and reversibly before MHC binding. Cysteinylation did not disrupt peptide binding to class II molecules, rather the modified peptide displayed an enhanced affinity for MHC at neutral pH. However, once the peptide was bound to class II proteins, oxidation or reduction of cysteine residues was severely limited. Cysteinylation has been shown to radically influence T cell responses to MHC class I ligands. The ability of professional APC to reductively cleave this peptide modification presumably evolved to circumvent a similar problem in MHC class II ligand recognition.     

Cutting edge: CNS CD11c+ cells from mice with encephalomyelitis polarize Th17 cells and support CD25+CD4+ T cell-mediated immunosuppression, suggesting dual roles in the disease process

CD11c(+) dendritic cells (DCs) are a prominent component of CNS infiltrates in mice with experimental autoimmune encephalomyelitis. However, their role in immunopathogenesis is controversial. In this study, we report that they originate from peripheral hemopoietic cells and exhibit diverse functions that change during the course of acute disease. CNS DCs stimulate naive T cells to proliferate and polarize Th(17) responses when harvested shortly following disease onset but are relatively inefficient APC by the time of peak disability. Conversely, they can support CD4(+)CD25(+) T cell-mediated immunosuppression early during experimental autoimmune encephalomyelitis. Such paradoxical functions might reflect dual roles of CNS DCs in promoting local inflammation while setting the stage for remission.     

De novo central nervous system processing of myelin antigen is required for the initiation of experimental autoimmune encephalomyelitis

We demonstrate the absolute requirement for a functioning class II-restricted Ag processing pathway in the CNS for the initiation of experimental autoimmune encephalomyelitis (EAE). C57BL/6 (B6) mice deficient for the class II transactivator, which have defects in MHC class II, invariant chain (Ii), and H-2M (DM) expression, are resistant to initiation of myelin oligodendrocyte protein (MOG) peptide, MOG(35-55)-specific EAE by both priming and adoptive transfer of encephalitogenic T cells. However, class II transactivator-deficient mice can prime a suboptimal myelin-specific CD4(+) Th1 response. Further, B6 mice individually deficient for Ii and DM are also resistant to initiation of both active and adoptive EAE. Although both Ii-deficient and DM-deficient APCs can present MOG peptide to CD4(+) T cells, neither is capable of processing and presenting the encephalitogenic peptide of intact MOG protein. This phenotype is not Ag-specific, as DM- and Ii-deficient mice are also resistant to initiation of EAE by proteolipid protein peptide PLP(178-191). Remarkably, DM-deficient mice can prime a potent peripheral Th1 response to MOG(35-55), comparable to the response seen in wild-type mice, yet maintain resistance to EAE initiation. Most striking is the demonstration that T cells from MOG(35-55)-primed DM knockout mice can adoptively transfer EAE to wild-type, but not DM-deficient, mice. Together, these data demonstrate that the inability to process antigenic peptide from intact myelin protein results in resistance to EAE and that de novo processing and presentation of myelin Ags in the CNS is absolutely required for the initiation of autoimmune demyelinating disease.     

A fusion protein consisting of IL-16 and the encephalitogenic peptide of myelin basic protein constitutes an antigen-specific tolerogenic vaccine that inhibits experimental autoimmune encephalomyelitis

To test a novel concept for the generation of tolerogenic vaccines, fusion proteins were constructed encompassing a tolerogenic or biasing cytokine and the major encephalitogenic peptide of guinea pig myelin basic protein (GPMBP; i.e., neuroantigen or NAg). The cytokine domain was predicted to condition APC while simultaneously targeting the covalently linked encephalitogenic peptide to the MHC class II Ag processing pathway of those conditioned APC. Rats were given three s.c. injections of cytokine-NAg in saline 1-2 wk apart and then at least 1 wk later were challenged with NAg in CFA. The rank order of tolerogenic activity in the Lewis rat model of EAE was NAgIL16 > IL2NAg > IL1RA-NAg, IL13NAg >or= IL10NAg, GPMBP, GP69-88, and saline. NAgIL16 was also an effective inhibitor of experimental autoimmune encephalomyelitis when administered after an encephalitogenic challenge during the onset of clinical signs. Covalent linkage of the NAg and IL-16 was required for inhibition of experimental autoimmune encephalomyelitis. These data identify IL-16 as an optimal cytokine partner for the generation of tolerogenic vaccines and indicate that such vaccines may serve as Ag-specific tolerogens for the treatment of autoimmune disease.     

Loss of IFN-gamma enables the expansion of autoreactive CD4+ T cells to induce experimental autoimmune encephalomyelitis by a nonencephalitogenic myelin variant antigen

MHC variant peptides are analogues of immunogenic peptides involving alterations of the MHC-binding residues, thereby altering the affinity of the peptide for the MHC molecule. Recently, our laboratory demonstrated that immunization of WT B6 mice with 45D, a low-affinity MHC variant peptide of MOG(35-55), results in significantly attenuated experimental autoimmune encephalomyelitis (EAE), yet IFN-gamma production is comparable to myelin oligodendrocyte glycoprotein (MOG)(35-55)-immunized mice. In light of these findings, we asked whether IFN-gamma was required for the reduced encephalitogenicity of the weak ligand 45D in EAE. In this study, we report that immunization of mice deficient in IFN-gamma or its receptor with 45D exhibit significant EAE signs compared with 45D-immunized wild-type B6 mice. Moreover, 45D-immunized IFN-gamma(-/-) and IFN-gammaR(-/-) mice demonstrate MOG tetramer-positive CD4(+) T cells within the CNS and display substantial numbers of MOG-specific CD4(+) T cells in the periphery. In contrast, wild-type mice immunized with 45D exhibit reduced numbers of MOG-specific CD4(+) T cells in the periphery and lack MOG tetramer- positive CD4(+) T cells in the CNS. Importantly, the increased encephalitogenicity of 45D in mice lacking IFN-gamma or IFN-gammaR was not due to deviation toward an enhanced IL-17-secreting phenotype. These findings demonstrate that IFN-gamma significantly attenuates the encephalitogenicity of 45D and are the first to highlight the importance of IFN-gamma signaling in setting the threshold level of responsiveness of autoreactive CD4(+) T cells to weak ligands.     

Induction of autoimmunity by expansion of autoreactive CD4+CD62Llow cells in vivo

The prerequisites of peripheral activation of self-specific CD4(+) T cells that determine the development of autoimmunity are incompletely understood. SJL mice immunized with myelin proteolipid protein (PLP) 139-151 developed experimental autoimmune encephalomyelitis (EAE) when pertussis toxin (PT) was injected at the time of immunization but not when injected 6 days later, indicating that PT-induced alterations of the peripheral immune response lead to the development of autoimmunity. Further analysis using IA(s)/PLP(139-151) tetramers revealed that PT did not change effector T cell activation or regulatory T cell numbers but enhanced IFN-gamma production by self-specific CD4(+) T cells. In addition, PT promoted the generation of CD4(+)CD62L(low) effector T cells in vivo. Upon adoptive transfer, these cells were more potent than CD4(+)CD62L(high) cells in inducing autoimmunity in recipient mice. The generation of this population was paralleled by higher expression of the costimulatory molecules CD80, CD86, and B7-DC, but not B7-RP, PD-1, and B7-H1 on CD11c(+)CD4(+) dendritic cells whereas CD11c(+)CD8alpha(+) dendritic cells were not altered. Collectively, these data demonstrate the induction of autoimmunity by specific in vivo expansion of CD4(+)CD62L(low) cells and indicate that CD4(+)CD62L(low) effector T cells and CD11c(+)CD4(+) dendritic cells may be attractive targets for immune interventions to treat autoimmune diseases.     

MHC variant peptide-mediated anergy of encephalitogenic T cells requires SHP-1

Our lab has demonstrated that encephalitogenic T cells can be effectively anergized by treatment with MHC variant peptides, which are analogues of immunogenic peptides containing an amino acid substitution at an MHC anchor residue. The MHC variant peptide of myelin oligodendrocyte glycoprotein (MOG)(35-55) proves an effective treatment as it does not induce symptoms of experimental autoimmune encephalomyelitis and fails to recruit macrophages or MOG(35-55)-specific T cells to the CNS. In this study, we sought to characterize the signaling pathways required for the induction of anergy by building upon the observations identifying the tyrosine phosphatase SHP-1 as a critical regulator of T cell responsiveness. Motheaten viable heterozygous mice, which contain a mutation in the SHP-1 gene resulting in a reduction in functional SHP-1, were challenged with MOG(35-55) or the MOG(35-55) MHC variant 45D. These mice display symptoms of experimental autoimmune encephalomyelitis upon immunization with MHC variant peptide and have significant CNS infiltration of tetramer-positive CD4(+) cells and macrophages, unlike B6 mice challenged with the variant peptide. The effects of SHP-1 are directly on the T cell as Motheaten viable heterozygous mice autoreactive T cells are not anergized in vitro. Lastly, we demonstrate no distinguishable difference in the initial interaction between the TCR and agonist or MHC variant. Rather, an unstable interaction between peptide and MHC attenuates the T cell response, seen in a decreased half-life relative to MOG(35-55). These results identify SHP-1 as a mediator of T cell anergy induced by destabilized peptide:MHC complexes.