Susceptible MHC alleles, not background genes, select an autoimmune T cell reactivity

Identification of T cell antigens in the 21st century, as difficult as ever

Identifying antigens recognized by T cells is still challenging, particularly for innate like T cells that do not recognize peptides but small metabolites or lipids in the context of MHC-like molecules or see non-MHC restricted antigens. The fundamental reason for this situation is the low affinity of T cell receptors for their ligands coupled with a level of degeneracy that makes them bind to similar surfaces on antigen presenting cells. Herein we will describe non-exhaustively some of the methods that were used to identify peptide antigens and briefly mention the high throughput methods more recently proposed for that purpose. We will then present how the molecules recognized by innate like T cells (NKT, MAIT and γδ T cells) were discovered. We will show that serendipity was instrumental in many cases.

Tolerance induction by liposomes targeting a single CD8 epitope IGRP206-214 in a model of type 1 diabetes is impeded by co-targeting a CD4+ islet epitope

The autoimmune disease type 1 diabetes is predominantly mediated by CD8⁺ cytotoxic T-cell destruction of islet beta cells, of which islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP)_206-214 is a dominant target antigen specificity. Previously, we found that a liposome-based antigen-specific immunotherapy encapsulating the CD4⁺ T-cell islet epitope 2.5_mim together with the nuclear factor-κB inhibitor calcitriol induced regulatory T cells and protected from diabetes in NOD mice. Here we investigated whether the same system delivering IGRP_206-214 could induce antigen-specific CD8⁺ T-cell-targeted immune regulation and delay diabetes. Subcutaneous administration of IGRP_206-214 /calcitriol liposomes transiently activated and expanded IGRP-specific T-cell receptor transgenic 8.3 CD8⁺ T cells. Liposomal co-delivery of calcitriol was required to optimally suppress endogenous IGRP-specific CD8⁺ T-cell interferon-γ production and cytotoxicity. Concordantly, a short course of IGRP_206-214 /calcitriol liposomes delayed diabetes progression and reduced insulitis. However, when IGRP_206-214 /calcitriol liposomes were delivered together with 2.5_mim /calcitriol liposomes, disease protection was not observed and the regulatory effect of 2.5_mim /calcitriol liposomes was abrogated. Thus, tolerogenic liposomes that target either a dominant CD8⁺ or a CD4⁺ T-cell islet epitope can delay diabetes progression but combining multiple epitopes does not enhance protection.

MHC class II tetramers engineered for enhanced binding to CD4 improve detection of antigen-specific T cells

The ability to identify T cells that recognize specific peptide antigens bound to major histocompatibility complex (MHC) molecules has enabled enumeration and molecular characterization of the lymphocytes responsible for cell-mediated immunity. Fluorophore-labeled peptide:MHC class I (p:MHCI) tetramers are well-established reagents for identifying antigen-specific CD8+ T cells by flow cytometry, but efforts to extend the approach to CD4+ T cells have been less successful, perhaps owing to lower binding strength between CD4 and MHC class II (MHCII) molecules. Here we show that p:MHCII tetramers engineered by directed evolution for enhanced CD4 binding outperform conventional tetramers for the detection of cognate T cells. Using the engineered tetramers, we identified about twice as many antigen-specific CD4+ T cells in mice immunized against multiple peptides than when using traditional tetramers. CD4 affinity-enhanced p:MHCII tetramers, therefore, allow direct sampling of antigen-specific CD4+ T cells that cannot be accessed with conventional p:MHCII tetramer technology. These new reagents could provide a deeper understanding of the T cell repertoire.

A Hybrid Insulin Epitope Maintains High 2D Affinity for Diabetogenic T Cells in the Periphery

β-Cell antigen recognition by autoreactive T cells is essential in type 1 diabetes (T1D) pathogenesis. Recently, insulin hybrid peptides (HIPs) were identified as strong agonists for CD4 diabetogenic T cells. Here, using BDC2.5 transgenic and NOD mice, we investigated T-cell recognition of the HIP2.5 epitope, which is a fusion of insulin C-peptide and chromogranin A (ChgA) fragments, and compared it with the WE14 and ChgA_{29 -42} epitopes. We measured in situ two-dimensional affinity on individual live T cells from thymus, spleen, pancreatic lymph nodes, and islets before and after diabetes. Although preselection BDC2.5 thymocytes possess higher affinity than splenic BDC2.5 T cells for all three epitopes, peripheral splenic T cells maintained high affinity only to the HIP2.5 epitope. In polyclonal NOD mice, a high frequency (∼40%) of HIP2.5-specific islet T cells were identified at both prediabetic and diabetic stages comprising two distinct high- and low-affinity populations that differed in affinity by 100-fold. This high frequency of high- and low-affinity HIP2.5 T cells in the islets potentially represents a major risk factor in diabetes pathogenesis.

Detection of Antigen-Specific T Cells Using In Situ MHC Tetramer Staining

The development of in situ major histocompatibility complex (MHC) tetramer (IST) staining to detect antigen (Ag)-specific T cells in tissues has radically revolutionized our knowledge of the local cellular immune response to viral and bacterial infections, cancers, and autoimmunity. IST combined with immunohistochemistry (IHC) enables determination of the location, abundance, and phenotype of T cells, as well as the characterization of Ag-specific T cells in a 3-dimensional space with respect to neighboring cells and specific tissue locations. In this review, we discuss the history of the development of IST combined with IHC. We describe various methods used for IST staining, including direct and indirect IST and IST performed on fresh, lightly fixed, frozen, and fresh then frozen tissue. We also describe current applications for IST in viral and bacterial infections, cancer, and autoimmunity. IST combined with IHC provides a valuable tool for studying and tracking the Ag-specific T cell immune response in tissues.

Position β57 of I-Ag7 controls early anti-insulin responses in NOD mice, linking an MHC susceptibility allele to type 1 diabetes onset

The class II region of the major histocompatibility complex (MHC) locus is the main contributor to the genetic susceptibility to type 1 diabetes (T1D). The loss of an aspartic acid at position 57 of diabetogenic HLA-DQβ chains supports this association; this single amino acid change influences how TCRs recognize peptides in the context of HLA-DQ8 and I-Ag7 using a mechanism termed the P9 switch. Here, we built register-specific insulin peptide MHC tetramers to examine CD4+ T cell responses to Ins12-20 and Ins13-21 peptides during the early prediabetic phase of disease in nonobese diabetic (NOD) mice. A single-cell analysis of anti-insulin CD4+ T cells performed in 6- and 12-week-old NOD mice revealed tissue-specific gene expression signatures. TCR signaling and clonal expansion were found only in the islets of Langerhans and produced either classical TH1 differentiation or an unusual Treg phenotype, independent of TCR usage. The early phase of the anti-insulin response was dominated by T cells specific for Ins12-20, the register that supports a P9 switch mode of recognition. The presence of the P9 switch was demonstrated by TCR sequencing, reexpression, mutagenesis, and functional testing of TCRαβ pairs in vitro. Genetic correction of the I-Aβ57 mutation in NOD mice resulted in the disappearance of D/E residues in the CDR3β of anti-Ins12-20 T cells. These results provide a mechanistic molecular explanation that links the characteristic MHC class II polymorphism of T1D with the recognition of islet autoantigens and disease onset.

Rapid CLIP dissociation from MHC II promotes an unusual antigen presentation pathway in autoimmunity

Spontaneous CLIP dissociation from an autoimmunity-associated MHC II protein enhances presentation of peptides released by insulin-producing β cells. Presentation of such extracellular peptides does not require endosomal antigen processing and augments islet infiltration by CD4 T cells.

A number of autoimmunity-associated MHC class II proteins interact only weakly with the invariant chain–derived class II–associated invariant chain peptide (CLIP). CLIP dissociates rapidly from I-A^g7 even in the absence of DM, and this property is related to the type 1 diabetes–associated β57 polymorphism. We generated knock-in non-obese diabetic (NOD) mice with a single amino acid change in the CLIP segment of the invariant chain in order to moderately slow CLIP dissociation from I-A^g7. These knock-in mice had a significantly reduced incidence of spontaneous type 1 diabetes and diminished islet infiltration by CD4 T cells, in particular T cells specific for fusion peptides generated by covalent linkage of proteolytic fragments within β cell secretory granules. Rapid CLIP dissociation enhanced the presentation of such extracellular peptides, thus bypassing the conventional MHC class II antigen-processing pathway. Autoimmunity-associated MHC class II polymorphisms therefore not only modify binding of self-peptides, but also alter the biochemistry of peptide acquisition.

Treatment of T1D via optimized expansion of antigen-specific Tregs induced by IL-2/anti-IL-2 monoclonal antibody complexes and peptide/MHC tetramers

Type 1 diabetes can be overcome by regulatory T cells (Treg) in NOD mice yet an efficient method to generate and maintain antigen-specific Treg is difficult to come by. Here, we devised a combination therapy of peptide/MHC tetramers and IL-2/anti-IL-2 monoclonal antibody complexes to generate antigen-specific Treg and maintain them over extended time periods. We first optimized treatment protocols conceived to obtain an improved islet-specific Treg/effector T cell ratio that led to the in vivo expansion and activation of these Treg as well as to an improved suppressor function. Optimized protocols were applied to treatment for testing diabetes prevention in NOD mice as well as in an accelerated T cell transfer model of T1D. The combined treatment led to robust protection against diabetes, and in the NOD model, to a close to complete prevention of insulitis. Treatment was accompanied with increased secretion of IL-10, detectable in total splenocytes and in Foxp3⁻ CD4 T cells. Our data suggest that a dual protection mechanism takes place by the collaboration of Foxp3⁺ and Foxp3⁻ regulatory cells. We conclude that antigen-specific Treg are an important target to improve current clinical interventions against this disease.

MHC-mismatched mixed chimerism restores peripheral tolerance of noncross-reactive autoreactive T cells in NOD mice

Mixed chimerism has shown good potential to cure some autoimmune diseases and prevent tissue rejection. It is known that MHC-mismatched but not -matched mixed chimerism effectively tolerizes autoreactive T cells, even those noncross-reactive T cells that do not directly recognize donor-type antigen presenting cells [i.e., dendritic cells (DCs)]. How this is accomplished remains unknown. These studies have shown that tolerizing peripheral residual host-type noncross-reactive autoreactive T cells requires engraftment of donor-type DCs and involves a host-type DC-mediated increase in donor-type Treg cells, which associates with restoration of tolerogenic features of host-type plasmacytoid DCs and expansion of host-type Treg cells. This study suggests a previously unrecognized tolerance network among donor- and host-type DCs and Treg cells in MHC-mismatched mixed chimeras.

Autoimmune type 1 diabetes (T1D) and other autoimmune diseases are associated with particular MHC haplotypes and expansion of autoreactive T cells. Induction of MHC-mismatched but not -matched mixed chimerism by hematopoietic cell transplantation effectively reverses autoimmunity in diabetic nonobese diabetic (NOD) mice, even those with established diabetes. As expected, MHC-mismatched mixed chimerism mediates deletion in the thymus of host-type autoreactive T cells that have T-cell receptor (TCR) recognizing (cross-reacting with) donor-type antigen presenting cells (APCs), which have come to reside in the thymus. However, how MHC-mismatched mixed chimerism tolerizes host autoreactive T cells that recognize only self-MHC–peptide complexes remains unknown. Here, using NOD.Rag1^−/−.BDC2.5 or NOD.Rag1^−/−.BDC12-4.1 mice that have only noncross-reactive transgenic autoreactive T cells, we show that induction of MHC-mismatched but not -matched mixed chimerism restores immune tolerance of peripheral noncross-reactive autoreactive T cells. MHC-mismatched mixed chimerism results in increased percentages of both donor- and host-type Foxp3⁺ Treg cells and up-regulated expression of programmed death-ligand 1 (PD-L1) by host-type plasmacytoid dendritic cells (pDCs). Furthermore, adoptive transfer experiments showed that engraftment of donor-type dendritic cells (DCs) and expansion of donor-type Treg cells are required for tolerizing the noncross-reactive autoreactive T cells in the periphery, which are in association with up-regulation of host-type DC expression of PD-L1 and increased percentage of host-type Treg cells. Thus, induction of MHC-mismatched mixed chimerism may establish a peripheral tolerogenic DC and Treg network that actively tolerizes autoreactive T cells, even those with no TCR recognition of the donor APCs.

Maintenance of peripheral tolerance to islet antigens

Reestablishment of immune tolerance to the insulin-producing beta cells is the desired goal for type 1 diabetes (T1D) treatment and prevention. Immune tolerance to multiple islet antigens is defective in individuals with T1D, but the mechanisms involved are multifaceted and may involve loss of thymic and peripheral tolerance. In this review we discuss our current understanding of the varied mechanisms by which peripheral tolerance to islet antigens is maintained in healthy individuals where genetic protection from T1D is present and how this fails in those with genetic susceptibility to disease. Novel findings in regards to expression of neo-islet antigens, non-classical regulatory cell subsets and the impact of specific genetic variants on tolerance induction are discussed.

Pathogenic CD4 T cells in type 1 diabetes recognize epitopes formed by peptide fusion

T cell-mediated destruction of insulin-producing β cells in the pancreas causes type 1 diabetes (T1D). CD4 T cell responses play a central role in β cell destruction, but the identity of the epitopes recognized by pathogenic CD4 T cells remains unknown. We found that diabetes-inducing CD4 T cell clones isolated from nonobese diabetic mice recognize epitopes formed by covalent cross-linking of proinsulin peptides to other peptides present in β cell secretory granules. These hybrid insulin peptides (HIPs) are antigenic for CD4 T cells and can be detected by mass spectrometry in β cells. CD4 T cells from the residual pancreatic islets of two organ donors who had T1D also recognize HIPs. Autoreactive T cells targeting hybrid peptides may explain how immune tolerance is broken in T1D.

Expanding antigen-specific regulatory networks to treat autoimmunity

Regulatory T cells hold promise as targets for therapeutic intervention in autoimmunity, but approaches capable of expanding antigen-specific regulatory T cells in vivo are currently not available. Here we show that systemic delivery of nanoparticles coated with autoimmune-disease-relevant peptides bound to major histocompatibility complex class II (pMHCII) molecules triggers the generation and expansion of antigen-specific regulatory CD4(+) T cell type 1 (TR1)-like cells in different mouse models, including mice humanized with lymphocytes from patients, leading to resolution of established autoimmune phenomena. Ten pMHCII-based nanomedicines show similar biological effects, regardless of genetic background, prevalence of the cognate T-cell population or MHC restriction. These nanomedicines promote the differentiation of disease-primed autoreactive T cells into TR1-like cells, which in turn suppress autoantigen-loaded antigen-presenting cells and drive the differentiation of cognate B cells into disease-suppressing regulatory B cells, without compromising systemic immunity. pMHCII-based nanomedicines thus represent a new class of drugs, potentially useful for treating a broad spectrum of autoimmune conditions in a disease-specific manner.

Imbalanced signal transduction in regulatory T cells expressing the transcription factor FoxP3

FoxP3(+) T regulatory (Treg) cells have a fundamental role in immunological tolerance, with transcriptional and functional phenotypes that demarcate them from conventional CD4(+) T cells (Tconv). Differences between these two lineages in the signaling downstream of T-cell receptor-triggered activation have been reported, and there are different requirements for some signaling factors. Seeking a comprehensive view, we found that Treg cells have a broadly dampened activation of several pathways and signaling nodes upon TCR-mediated activation, with low phosphorylation of CD3ζ, SLP76, Erk1/2, AKT, or S6 and lower calcium flux. In contrast, STAT phosphorylation triggered by interferons, IL2 or IL6, showed variations between Treg and Tconv in magnitude or choice of preferential STAT activation but no general Treg signaling defect. Much, but not all, of the Treg/Tconv difference in TCR-triggered responses could be attributed to lower responsiveness of antigen-experienced cells with CD44(hi) or CD62L(lo) phenotypes, which form a greater proportion of the Treg pool. Candidate regulators were tested, but the Treg/Tconv differential could not be explained by overexpression in Treg cells of the signaling modulator CD5, the coinhibitors PD-1 and CTLA4, or the regulatory phosphatase DUSP4. However, transcriptome profiling in Dusp4-deficient mice showed that DUSP4 enhances the expression of a segment of the canonical Treg transcriptional signature, which partially overlaps with the TCR-dependent Treg gene set. Thus, Treg cells, likely because of their intrinsically higher reactivity to self, tune down TCR signals but seem comparatively more attuned to cytokines or other intercellular signals.

Cutting Edge: Nonobese Diabetic Mice Deficient in Chromogranin A Are Protected from Autoimmune Diabetes

T cells reactive to β cell Ags are critical players in the development of autoimmune type 1 diabetes. Using a panel of diabetogenic CD4 T cell clones derived from the NOD mouse, we recently identified the β cell secretory granule protein, chromogranin A (ChgA), as a new autoantigen in type 1 diabetes. CD4 T cells reactive to ChgA are pathogenic and rapidly transfer diabetes into young NOD recipients. We report in this article that NOD.ChgA(-/-) mice do not develop diabetes and show little evidence of autoimmunity in the pancreatic islets. Using tetramer analysis, we demonstrate that ChgA-reactive T cells are present in these mice but remain naive. In contrast, in NOD.ChgA(+/+) mice, a majority of the ChgA-reactive T cells are Ag experienced. Our results suggest that the presence of ChgA and subsequent activation of ChgA-reactive T cells are essential for the initiation and development of autoimmune diabetes in NOD mice.

Use of autoantigen-loaded phosphatidylserine-liposomes to arrest autoimmunity in type 1 diabetes

Introduction

The development of new therapies to induce self-tolerance has been an important medical health challenge in type 1 diabetes. An ideal immunotherapy should inhibit the autoimmune attack, avoid systemic side effects and allow β-cell regeneration. Based on the immunomodulatory effects of apoptosis, we hypothesized that apoptotic mimicry can help to restore tolerance lost in autoimmune diabetes.

Objective

To generate a synthetic antigen-specific immunotherapy based on apoptosis features to specifically reestablish tolerance to β-cells in type 1 diabetes.

Methods

A central event on the surface of apoptotic cells is the exposure of phosphatidylserine, which provides the main signal for efferocytosis. Therefore, phosphatidylserine-liposomes loaded with insulin peptides were generated to simulate apoptotic cells recognition by antigen presenting cells. The effect of antigen-specific phosphatidylserine-liposomes in the reestablishment of peripheral tolerance was assessed in NOD mice, the spontaneous model of autoimmune diabetes. MHC class II-peptide tetramers were used to analyze the T cell specific response after treatment with phosphatidylserine-liposomes loaded with peptides.

Results

We have shown that phosphatidylserine-liposomes loaded with insulin peptides induce tolerogenic dendritic cells and impair autoreactive T cell proliferation. When administered to NOD mice, liposome signal was detected in the pancreas and draining lymph nodes. This immunotherapy arrests the autoimmune aggression, reduces the severity of insulitis and prevents type 1 diabetes by apoptotic mimicry. MHC class II tetramer analysis showed that peptide-loaded phosphatidylserine-liposomes expand antigen-specific CD4⁺ T cells in vivo. The administration of phosphatidylserine-free liposomes emphasizes the importance of phosphatidylserine in the modulation of antigen-specific CD4⁺ T cell expansion.

Conclusions

We conclude that this innovative immunotherapy based on the use of liposomes constitutes a promising strategy for autoimmune diseases.

Population dynamics of islet-infiltrating cells in autoimmune diabetes

Type-1 diabetes in the nonobese diabetic (NOD) mouse starts with an insulitis stage, wherein a mixed population of leukocytes invades the pancreas, followed by overt diabetes once enough insulin-producing β-cells are destroyed by invading immunocytes. Little is known of the dynamics of lymphocyte movement into the pancreas during disease progression. We used the Kaede transgenic mouse, whose photoconvertible fluorescent reporter permits noninvasive labeling and subsequent tracking of immunocytes, to investigate pancreatic infiltrate dynamics and the requirement for antigen specificity during progression of autoimmune diabetes in the unmanipulated NOD mouse. Our results indicate that the insulitic lesion is very open with constant cell influx and active turnover, predominantly of B and T lymphocytes, but also CD11b(+)c(+) myeloid cells. Both naïve- and memory-phenotype lymphocytes trafficked to the insulitis, but Foxp3(+) regulatory T cells circulated less than their conventional CD4(+) counterparts. Receptor specificity for pancreatic antigens seemed irrelevant for this homing, because similar kinetics were observed in polyclonal and antigen-specific transgenic contexts. This "open" configuration was also observed after reversal of overt diabetes by anti-CD3 treatment. These results portray insulitis as a dynamic lesion at all stages of disease, continuously fed by a mixed influx of immunocytes, and thus susceptible to evolve over time in response to immunologic or environmental influences.

In vivo detection of peripherin-specific autoreactive B cells during type 1 diabetes pathogenesis

Autoreactive B cells are essential for the pathogenesis of type 1 diabetes. The genesis and dynamics of autoreactive B cells remain unknown. In this study, we analyzed the immune response in the NOD mouse model to the neuronal protein peripherin (PRPH), a target Ag of islet-infiltrating B cells. PRPH autoreactive B cells recognized a single linear epitope of this protein, in contrast to the multiple epitope recognition commonly observed during autoreactive B cell responses. Autoantibodies to this epitope were also detected in the disease-resistant NOR and C57BL/6 strains. To specifically detect the accumulation of these B cells, we developed a novel approach, octameric peptide display, to follow the dynamics and localization of anti-PRPH B cells during disease progression. Before extended insulitis was established, anti-PRPH B cells preferentially accumulated in the peritoneum. Anti-PRPH B cells were likewise detected in C57BL/6 mice, albeit at lower frequencies. As disease unfolded in NOD mice, anti-PRPH B cells invaded the islets and increased in number at the peritoneum of diabetic but not prediabetic mice. Isotype-switched B cells were only detected in the peritoneum. Anti-PRPH B cells represent a heterogeneous population composed of both B1 and B2 subsets. In the spleen, anti-PRPH B cell were predominantly in the follicular subset. Therefore, anti-PRPH B cells represent a heterogeneous population that is generated early in life but proliferates as diabetes is established. These findings on the temporal and spatial progression of autoreactive B cells should be relevant for our understanding of B cell function in diabetes pathogenesis.

B6.g7 mice reconstituted with BDC2·5 non-obese diabetic (BDC2·5NOD) stem cells do not develop autoimmune diabetes

In BDC2·5 non-obese diabetic (BDC2·5NOD) mice, a spontaneous model of type 1 diabetes, CD4(+) T cells express a transgene-encoded T cell receptor (TCR) with reactivity against a pancreatic antigen, chromogranin. This leads to massive infiltration and destruction of the pancreatic islets and subsequent diabetes. When we reconstituted lethally irradiated, lymphocyte-deficient B6.g7 (I-A(g7+)) Rag(-/-) mice with BDC2·5NOD haematopoietic stem and progenitor cells (HSPC; ckit(+)Lin(-)Sca-1(hi)), the recipients exhibited hyperglycaemia and succumbed to diabetes. Surprisingly, lymphocyte-sufficient B6.g7 mice reconstituted with BDC2·5NOD HSPCs were protected from diabetes. In this study, we investigated the factors responsible for attenuation of diabetes in the B6.g7 recipients. Analysis of chimerism in the B6.g7 recipients showed that, although B cells and myeloid cells were 98% donor-derived, the CD4(+) T cell compartment contained ∼50% host-derived cells. These host-derived CD4(+) T cells were enriched for conventional regulatory T cells (Tregs ) (CD25(+) forkhead box protein 3 (FoxP3)(+)] and also for host- derived CD4(+)CD25(-)FoxP3(-) T cells that express markers of suppressive function, CD73, FR4 and CD39. Although negative selection did not eliminate donor-derived CD4(+) T cells in the B6.g7 recipients, these cells were functionally suppressed. Thus, host-derived CD4(+) T cells that emerge in mice following myeloablation exhibit a regulatory phenoytpe and probably attenuate autoimmune diabetes. These cells may provide new therapeutic strategies to suppress autoimmunity.

Cutting edge: type 1 diabetes occurs despite robust anergy among endogenous insulin-specific CD4 T cells in NOD mice

Insulin-specific CD4(+) T cells are required for type 1 diabetes. How these cells are regulated and how tolerance breaks down are poorly understood because of a lack of reagents. Therefore, we used an enrichment method and tetramer reagents to track insulin-specific CD4(+) T cells in diabetes-susceptible NOD and resistant B6 mice expressing I-A(g7). Insulin-specific cells were detected in both strains, but they only became activated, produced IFN-γ, and infiltrated the pancreas in NOD mice. Unexpectedly, the majority of Ag-experienced cells in NOD mice displayed an anergic phenotype, but this population decreased with age as tolerance was lost. B6 mice expressing I-A(g7) were protected because insulin-specific cells did not become effector or anergic T cells but remained naive. These data suggest that NOD mice promote tolerance through anergy induction, but a small proportion of autoreactive T cells escape anergy to provoke type 1 diabetes.

CD8+ dendritic cell-mediated tolerance of autoreactive CD4+ T cells is deficient in NOD mice and can be corrected by blocking CD40L

DCs are important mediators of peripheral tolerance for the prevention of autoimmunity. Chimeric αDEC-205 antibodies with attached antigens allow in vivo antigen-specific stimulation of T cells by CD8(+) DCs, resulting in tolerance in nonautoimmune mice. However, it is not clear whether DC-mediated tolerance induction occurs in the context of ongoing autoimmunity. We assessed the role of CD8(+) DCs in stimulation of autoreactive CD4(+) T cells in the NOD mouse model of type 1 diabetes. Targeting of antigen to CD8(+) DCs via αDEC-205 led to proliferation and expansion of β-cell specific BDC2.5 T cells. These T cells also produced IL-2 and IFN-γ and did not up-regulate FoxP3, consistent with an activated rather than tolerant phenotype. Similarly, endogenous BDC peptide-reactive T cells, identified with I-A(g7) tetramers, did not become tolerant after antigen delivery via αDEC-205: no deletion or Treg induction was observed. We observed that CD8(+) DCs from NOD mice expressed higher surface levels of CD40 than CD8(+) DCs from C57BL/6 mice. Blockade of CD40-CD40L interactions reduced the number of BDC2.5 T cells remaining in mice, 10 days after antigen targeting to CD8 DCs, and blocked IFN-γ production by BDC2.5 T cells. These data indicate that the ability of autoreactive CD4(+) T cells to undergo tolerance mediated by CD8(+) DCs is defective in NOD mice and that blocking CD40-CD40L interactions can restore tolerance induction.

Cutting edge: CD4 T cells reactive to an islet amyloid polypeptide peptide accumulate in the pancreas and contribute to disease pathogenesis in nonobese diabetic mice

We previously reported a peptide KS20 from islet amyloid polypeptide (IAPP) to be the target Ag for a highly diabetogenic CD4 T cell clone BDC-5.2.9. To track IAPP-reactive T cells in NOD mice and determine how they contribute to the pathogenesis of type 1 diabetes, we designed a new I-Ag7 tetramer with high affinity for BDC-5.2.9 that contains the peptide KS20. We found that significant numbers of KS20 tetramer(+) CD4 T cells can be detected in the pancreas of prediabetic and diabetic NOD mice. To verify pathogenicity of IAPP-reactive cells, we sorted KS20 tetramer(+) cells and cloned them from uncloned T cell lines isolated from spleen and lymph nodes of diabetic mice. We isolated a new KS20-reactive Th1 CD4 T cell clone that rapidly transfers diabetes. Our results suggest that IAPP triggers a broad autoimmune response by CD4 T cells in NOD mice.

Cholera toxin subunit B peptide fusion proteins reveal impaired oral tolerance induction in diabetes-prone but not in diabetes-resistant mice

The cholera toxin B subunit (CTB) has been used as adjuvant to improve oral vaccine delivery in type 1 diabetes. The effect of CTB/peptide formulations on Ag-specific CD4(+) T cells has remained largely unexplored. Here, using tetramer analysis, we investigated how oral delivery of CTB fused to two CD4(+) T-cell epitopes, the BDC-2.5 T-cell 2.5 mi mimotope and glutamic acid decarboxylase (GAD) 286-300, affected diabetogenic CD4(+) T cells in nonobese diabetic (NOD) mice. When administered i.p., CTB-2.5 mi activated 2.5 mi(+) T cells and following intragastric delivery generated Ag-specific Foxp3(+) Treg and Th2 cells. While 2.5 mi(+) and GAD-specific T cells were tolerized in diabetes-resistant NODxB6.Foxp3(EGFP) F1 and nonobese resistant (NOR) mice, this did not occur in NOD mice. This indicated that NOD mice had a recessive genetic resistance to induce oral tolerance to both CTB-fused epitopes. In contrast to NODxB6.Foxp3(EGFP) F1 mice, oral treatment in NOD mice lead to strong 2.5 mi(+) T-cell activation and the sequestration of these cells to the effector-memory pool. Oral treatment of NOD mice with CTB-2.5 mi failed to prevent diabetes. These findings underline the importance of investigating the effect of oral vaccine formulations on diabetogenic T cells as in selected cases they may have counterproductive consequences in human patients.

Destabilization of peptide:MHC interaction induces IL-2 resistant anergy in diabetogenic T cells

Autoreactive T cells are responsible for inducing several autoimmune diseases, including type 1 diabetes. We have developed a strategy to induce unresponsiveness in these cells by destabilizing the peptide:MHC ligand recognized by the T cell receptor. By introducing amino acid substitutions into the immunogenic peptide at residues that bind to the MHC, the half life of the peptide:MHC complex is severely reduced, thereby resulting in abortive T cell activation and anergy. By treating a monoclonal diabetogenic T cell population with an MHC variant peptide, the cells are rendered unresponsive to the wild type ligand, as measured by both proliferation and IL-2 production. Stimulation of T cells with MHC variant peptides results in minimal Erk1/2 phosphorylation or cell division. Variant peptide stimulation effectively initiates a signaling program dominated by sustained tyrosine phosphatase activity, including elevated SHP-1 activity. These negative signaling events result in an anergic phenotype in which the T cells are not competent to signal through the IL-2 receptor, as evidenced by a lack of phospho-Stat5 upregulation and proliferation, despite high expression of the IL-2 receptor. This unique negative signaling profile provides a novel means to shut down the anti-self response.

Novel autoantigens for diabetogenic CD4 T cells in autoimmune diabetes

Autoreactive CD4 T cells play a central role in the development of type 1 diabetes. The BDC panel of diabetogenic T cell clones was originally isolated from non-obese diabetic mice and has been used to study the role of autoreactive CD4 T cells and T cell autoantigens in the development of diabetes. Recent studies by our group have led to the identification of two new target antigens for clones of this panel. This review describes the proteomic strategy used for antigen identification, the antigens identified, and the potential contribution of post-translational modification to autoantigen generation. In addition, we compare peptide epitopes for the T cell clones and discuss their potential applications in investigating the role of T cell autoantigens in the pathogenesis and regulation of disease.

Host-derived CD4+ T cells attenuate stem cell-mediated transfer of autoimmune arthritis in lethally irradiated C57BL/6.g7 mice

OBJECTIVE

In the K/BxN mouse model of inflammatory arthritis, T cells carrying a transgenic T cell receptor initiate disease by helping B cells to produce arthritogenic anti-glucose-6-phosphate isomerase (anti-GPI) autoantibodies. We found that lethally- irradiated lymphocyte-deficient C57BL/6 (B6).g7 (I-A(g7) +) recombinase-activating gene-deficient (Rag(-/-)) mice reconstituted with K/BxN hematopoietic stem and progenitor cells exhibit arthritis by week 4. In contrast, healthy B6.g7 recipients of K/BxN hematopoietic stem and progenitor cells show only mild arthritis, with limited extent and duration. The objective of this study was to investigate the factors responsible for the attenuation of arthritis in B6.g7 recipients.

METHODS

Antibody responses were measured by enzyme-linked immunosorbent assay. Fluorescence-activated cell sorting analyses were performed for testing chimerism, expression of markers of activation and suppression, tetramer binding, and intracellular cytokines in CD4+ T cells. Suppressive activity of CD4+ T cells was studied by adoptive transfer.

RESULTS

Titers of anti-GPI antibodies in reconstituted B6.g7 mice were ∼60-fold lower than in reconstituted B6.g7 Rag(-/-) mice. Examination of chimerism in the reconstituted B6.g7 mice showed that B cells and myeloid cells in these mice were donor derived, but CD4+ T cells were primarily host derived and enriched for cells expressing the conventional regulatory markers CD25 and FoxP3. Notably, CD4+CD25-FoxP3- T cells expressed markers of suppressive function (CD73 and folate receptor 4), and delayed disease after adoptive transfer. Activation of donor-derived CD4+ T cells was reduced, and thymic deletion of these cells appeared increased.

CONCLUSION

Despite myeloablation, host CD4+ T cells having a regulatory phenotype emerge in these mice and attenuate autoimmunity.

Antidiabetogenic MHC class II promotes the differentiation of MHC-promiscuous autoreactive T cells into FOXP3+ regulatory T cells

Polymorphisms in MHC class II molecules, in particular around β-chain position-57 (β57), afford susceptibility/resistance to multiple autoimmune diseases, including type 1 diabetes, through obscure mechanisms. Here, we show that the antidiabetogenic MHC class II molecule I-A(b) affords diabetes resistance by promoting the differentiation of MHC-promiscuous autoreactive CD4(+) T cells into disease-suppressing natural regulatory T cells, in a β56-67-regulated manner. We compared the tolerogenic and antidiabetogenic properties of CD11c promoter-driven transgenes encoding I-A(b) or a form of I-A(b) carrying residues 56-67 of I-Aβ(g7) (I-A(b-g7)) in wild-type nonobese diabetic (NOD) mice, as well as NOD mice coexpressing a diabetogenic and I-A(g7)-restricted, but MHC-promiscuous T-cell receptor (4.1). Both I-A transgenes protected NOD and 4.1-NOD mice from diabetes. However, whereas I-A(b) induced 4.1-CD4(+) thymocyte deletion and 4.1-CD4(+)Foxp3(+) regulatory T-cell development, I-A(b-g7) promoted 4.1-CD4(+)Foxp3(+) Treg development without inducing clonal deletion. Furthermore, non-T-cell receptor transgenic NOD.CD11cP-I-A(b) and NOD.CD11cP-IA(b-g7) mice both exported regulatory T cells with superior antidiabetogenic properties than wild-type NOD mice. We propose that I-A(b), and possibly other protective MHC class II molecules, afford disease resistance by engaging a naturally occurring constellation of MHC-promiscuous autoreactive T-cell clonotypes, promoting their deviation into autoregulatory T cells.

The influence of the microbiota on type-1 diabetes: on the threshold of a leap forward in our understanding

The last several years have seen breakthroughs in techniques to track the symbiont communities that normally colonize mammals (the microbiota) and in cataloguing the universe of the genes they carry (the microbiome). Applying these methods to human patients and corresponding murine models should allow us to decipher just how the microbiota impacts type-1 diabetes, i.e. which particular microbes are responsible and the cellular and molecular processes that are involved. Here, at its threshold, we set the stage for what promises to be an exciting rejuvenated area of investigation.

Loss of intra-islet CD20 expression may complicate efficacy of B-cell-directed type 1 diabetes therapies

OBJECTIVE

Consistent with studies in NOD mice, early clinical trials addressing whether depletion of B cells by the Rituximab CD20-specific antibody provides an effective means for type 1 diabetes reversal have produced promising results. However, to improve therapeutic efficacy, additional B-cell-depleting agents, as well as attempts seeking diabetes prevention, are being considered.

RESEARCH DESIGN AND METHODS

Autoantibodies, including those against insulin (IAAs), are used to identify at-risk subjects for inclusion in diabetes prevention trials. Therefore, we tested the ability of anti-CD20 to prevent diabetes in NOD mice when administered either before or after IAA onset.

RESULTS

The murine CD20-specific 18B12 antibody that like Rituximab, depletes the follicular (FO) but not marginal zone subset of B cells, efficiently inhibited diabetes development in NOD mice in a likely regulatory T-cell-dependent manner only when treatment was initiated before IAA detection. One implication of these results is that the FO subset of B cells preferentially contributes to early diabetes initiation events. However, most important, the inefficient ability of anti-CD20 treatment to exert late-stage diabetes prevention was found to be attributable to downregulation of CD20 expression upon B cell entry into pancreatic islets.

CONCLUSIONS

These findings provide important guidance for designing strategies targeting B cells as a potential means of diabetes intervention.

Cutting edge: accelerated autoimmune diabetes in the absence of LAG-3

Lymphocyte activation gene-3 (LAG-3; CD223) is a CD4 homolog that is required for maximal regulatory T cell function and for the control of CD4(+) and CD8(+) T cell homeostasis. Lag3(-)(/)(-) NOD mice developed substantially accelerated diabetes with 100% incidence. Adoptive transfer experiments revealed that LAG-3 was primarily responsible for limiting the pathogenic potential of CD4(+) T cells and, to a lesser extent, CD8(+) T cells. Lag3(-)(/)(-) mice exhibited accelerated, invasive insulitis, corresponding to increased CD4(+) and CD8(+) T cell islet infiltration and intraislet proliferation. The frequencies of islet Ag-reactive chromogranin A-specific CD4(+) T cells and islet specific glucose-6-phosphatase-specific CD8(+) T cells were significantly increased in the islets of Lag3(-)(/)(-) mice, suggesting an early expansion of pathogenic clones that is normally restrained by LAG-3. We conclude that LAG-3 is necessary for regulating CD4(+) and CD8(+) T cell function during autoimmune diabetes, and thus may contribute to limiting autoimmunity in disease-prone environments.

Induction of mixed chimerism with MHC-mismatched but not matched bone marrow transplants results in thymic deletion of host-type autoreactive T-cells in NOD mice

OBJECTIVE

Induction of mixed or complete chimerism via hematopoietic cell transplantation (HCT) from nonautoimmune donors could prevent or reverse type 1 diabetes (T1D). In clinical settings, HLA-matched HCT is preferred to facilitate engraftment and reduce the risk for graft versus host disease (GVHD). Yet autoimmune T1D susceptibility is associated with certain HLA types. Therefore, we tested whether induction of mixed chimerism with major histocompatibility complex (MHC)-matched donors could reverse autoimmunity in the NOD mouse model of T1D.

RESEARCH DESIGN AND METHODS

Prediabetic wild-type or transgenic BDC2.5 NOD mice were conditioned with a radiation-free GVHD preventative anti-CD3/CD8 conditioning regimen and transplanted with bone marrow (BM) from MHC-matched or mismatched donors to induce mixed or complete chimerism. T1D development and thymic deletion of host-type autoreactive T-cells in the chimeric recipients were evaluated.

RESULTS

Induction of mixed chimerism with MHC-matched nonautoimmune donor BM transplants did not prevent T1D in wild-type NOD mice, although induction of complete chimerism did prevent the disease. However, induction of either mixed or complete chimerism with MHC-mismatched BM transplants prevented T1D in such mice. Furthermore, induction of mixed chimerism in transgenic BDC2.5-NOD mice with MHC-matched or -mismatched MHC II(-/-) BM transplants failed to induce thymic deletion of de novo developed host-type autoreactive T-cells, whereas induction of mixed chimerism with mismatched BM transplants did.

CONCLUSIONS

Induction of mixed chimerism with MHC-mismatched, but not matched, donor BM transplants re-establishes thymic deletion of host-type autoreactive T-cells and prevents T1D, with donor antigen-presenting cell expression of mismatched MHC II molecules being required.

MHC-peptide tetramers for the analysis of antigen-specific T cells

The development of the fluorescently labeled tetrameric MHC-peptide complex has enabled the direct visualization, quantification and phenotypic characterization of antigen-specific T cells using flow cytometry and has transformed our understanding of cellular immune responses. The combination of this technology with functional assays provides many new insights into these cells, allowing investigation into their lifecycle, manner of death and effector function. In this article, we hope to provide an overview of the techniques used in the construction of these tetramers, the problems and solutions associated with them, and the methods used in the study of antigen-specific T cells. Understanding how the antigen-specific cells develop and function in different circumstances and with different pathogens will be key to understanding natural host defense, as well as vaccine design and assessment.

Peripherin-reactive antibodies in mouse, rabbit, and human blood

Type 1 diabetes (T1D) is an autoimmune disorder that results from the destruction of insulin-producing beta-cells in the islets of Langerhans. To date, autoimmune T-cell response and antibody reactivity to more than 20 autoantigens have been linked to this disease. Some studies have described the intermediate filament protein peripherin (PRPH) as an autoantigen associated with T1D in non-obese diabetic (NOD) mice. We evaluated immune reactivity of mouse and rabbit sera and human plasma to a 58 kDa protein expressed in RIN-m5F rat insulinoma cells. The protein was isolated using 2-DE and identified by mass spectrometry as PRPH. Antibodies from healthy humans and T1D patients, CD-1 mice, C57BL/6 mice, NOR (non-obese diabetes resistant) mice, and NOD mice reacted with PRPH on Western blots. However, antibody response to PRPH was stronger in NOD than non-autoimmune prone C57BL/6 mice. We conclude that immune reactivity to PRPH is not exclusively associated with NOD mice or human patients with T1D. Furthermore, the frequent occurrence of PRPH-reactive antibodies in mouse and human blood suggests that binding may be non-specific or could reflect the presence of natural autoantibodies against PRPH. These findings point to the need for a re-evaluation of PRPH as a T1D autoantigen in NOD mice and raise the question of the physiological relevance of such widespread immune reactivity against this peripheral nervous system protein.

The diabetogenic mouse MHC class II molecule I-Ag7 is endowed with a switch that modulates TCR affinity

Genetic susceptibility to autoimmunity is frequently associated with specific MHC alleles. Diabetogenic MHC class II molecules, such as human HLA-DQ8 and mouse I-Ag7, typically have a small, uncharged amino acid residue at position 57 of their beta chain (beta57); this results in the absence of a salt bridge between beta57 and Argalpha76, which is adjacent to the P9 pocket of the peptide-binding groove. However, the influence of Argalpha76 on the selection of the TCR repertoire remains unknown, particularly when the MHC molecule binds a peptide with a neutral amino acid residue at position P9. Here, we have shown that diabetogenic MHC class II molecules bound to a peptide with a neutral P9 residue primarily selected and expanded cells expressing TCRs bearing a negatively charged residue in the first segment of their complementarity determining region 3beta. The crystal structure of one such TCR in complex with I-Ag7 bound to a peptide containing a neutral P9 residue revealed that a network of favorable long-range (greater than 4 A) electrostatic interactions existed among Argalpha76, the neutral P9 residue, and TCR, which supported the substantially increased TCR/peptide-MHC affinity. This network could be modulated or switched to a lower affinity interaction by the introduction of a negative charge at position P9 of the peptide. Our results support the existence of a switch at residue beta57 of the I-Ag7 and HLA-DQ8 class II molecules and potentially link normal thymic TCR selection with abnormal peripheral behavior.

Mouse Models for Type 1 Diabetes

Our understanding of the genetics, aetiology and pathogenesis of Type 1 Diabetes (T1D) was propelled by the discovery of animal models of T1D in the late 1970s and early 1980s, particularly the non-obese diabetic (NOD) mouse. Since then, transgenic and gene-targeting technologies allowed the generation of many models with reduced genetic and pathogenic complexity. These models allowed researchers to zoom in on specific aspects of this complex disease. In this review, we provide an overview of currently available mouse models for T1D.

Idd9/11 genetic locus regulates diabetogenic activity of CD4 T-cells in nonobese diabetic (NOD) mice

OBJECTIVE

Although the H2(g7) major histocompatibility complex (MHC) provides the primary pathogenic component, the development of T-cell-mediated autoimmune type 1 diabetes in NOD mice also requires contributions from other susceptibility (Idd) genes. Despite sharing the H2(g7) MHC, the closely NOD-related NOR strain remains type 1 diabetes resistant because of contributions of protective Idd5.2, Idd9/11, and Idd13 region alleles. To aid their eventual identification, we evaluated cell types in which non-MHC Idd resistance genes in NOR mice exert disease-protective effects.

RESEARCH DESIGN AND METHODS

Adoptive transfer and bone marrow chimerism approaches tested the diabetogenic activity of CD4 and CD8 T-cells from NOR mice and NOD stocks congenic for NOR-derived Idd resistance loci. Tetramer staining and mimotope stimulation tested the frequency and proliferative capacity of CD4 BDC2.5-like cells. Regulatory T-cells (Tregs) were identified by Foxp3 staining and functionally assessed by in vitro suppression assays.

RESULTS

NOR CD4 T-cells were less diabetogenic than those from NOD mice. The failure of NOR CD4 T-cells to induce type 1 diabetes was not due to decreased proliferative capacity of BDC2.5 clonotypic-like cells. The frequency and function of Tregs in NOD and NOR mice were also equivalent. However, bone marrow chimerism experiments demonstrated that intrinsic factors inhibited the pathogenic activity of NOR CD4 T-cells. The NOR Idd9/11 resistance region on chromosome 4 was found to diminish the diabetogenic activity of CD4 but not CD8 T-cells.

CONCLUSIONS

In conclusion, we demonstrated that a gene(s) within the Idd9/11 region regulates the diabetogenic activity of CD4 T-cells.

Delineating the role of the HLA-DR4 "shared epitope" in susceptibility versus resistance to develop arthritis

In humans, HLA-DR alleles sharing amino acids at the third hypervariable region with DRB1*0401(shared epitope) are associated with a predisposition to rheumatoid arthritis, whereas DRB1*0402 is not associated with such a predisposition. Both DRB1*0402 and DRB1*0401 occur in linkage with DQ8 (DQB1*0302). We have previously shown that transgenic (Tg) mice expressing HLA-DRB1*0401 develop collagen-induced arthritis. To delineate the role of "shared epitope" and gene complementation between DR and DQ in arthritis, we generated DRB1*0402, DRB1*0401.DQ8, and DRB1*0402.DQ8 Tg mice lacking endogenous class II molecules, AE(o). DRB1*0402 mice are resistant to develop arthritis. In double-Tg mice, the DRB1*0401 gene contributes to the development of collagen-induced arthritis, whereas DRB1*0402 prevents the disease. Humoral response to type II collagen is not defective in resistant mice, although cellular response to type II collagen is lower in *0402 mice compared with *0401 mice. *0402 mice have lower numbers of T cells in thymus compared with *0401 mice, suggesting that the protective effect could be due to deletion of autoreactive T cells. Additionally, DRB1*0402 mice have a higher number of regulatory T cells and show increased activation-induced cell death, which might contribute toward protection. In DRB1*0401.DQ8 mice, activated CD4(+) T cells express class II genes and can present DR4- and DQ8-restricted peptides in vitro, suggesting a role of class II(+) CD4 T cells locally in the joints. The data suggest that polymorphism in DRB1 genes determines predisposition to develop arthritis by shaping the T cell repertoire in thymus and activating autoreactive or regulatory T cells.

Innate immunity and intestinal microbiota in the development of Type 1 diabetes

Type 1 diabetes (T1D) is a debilitating autoimmune disease that results from T-cell-mediated destruction of insulin-producing beta-cells. Its incidence has increased during the past several decades in developed countries, suggesting that changes in the environment (including the human microbial environment) may influence disease pathogenesis. The incidence of spontaneous T1D in non-obese diabetic (NOD) mice can be affected by the microbial environment in the animal housing facility or by exposure to microbial stimuli, such as injection with mycobacteria or various microbial products. Here we show that specific pathogen-free NOD mice lacking MyD88 protein (an adaptor for multiple innate immune receptors that recognize microbial stimuli) do not develop T1D. The effect is dependent on commensal microbes because germ-free MyD88-negative NOD mice develop robust diabetes, whereas colonization of these germ-free MyD88-negative NOD mice with a defined microbial consortium (representing bacterial phyla normally present in human gut) attenuates T1D. We also find that MyD88 deficiency changes the composition of the distal gut microbiota, and that exposure to the microbiota of specific pathogen-free MyD88-negative NOD donors attenuates T1D in germ-free NOD recipients. Together, these findings indicate that interaction of the intestinal microbes with the innate immune system is a critical epigenetic factor modifying T1D predisposition.

Impact of diabetes susceptibility loci on progression from pre-diabetes to diabetes in at-risk individuals of the diabetes prevention trial-type 1 (DPT-1)

OBJECTIVE

The unfolding of type 1 diabetes involves a number of steps: defective immunological tolerance, priming of anti-islet autoimmunity, and destruction of insulin-producing beta-cells. A number of genetic loci contribute to susceptibility to type 1 diabetes, but it is unclear which stages of the disease are influenced by the different loci. Here, we analyzed the frequency of type 1 diabetes-risk alleles among individuals from the Diabetes Prevention Trial-Type 1 (DPT-1) clinical trial, which tested a preventive effect of insulin in at-risk relatives of diabetic individuals, all of which presented with autoimmune manifestations but only one-third of which eventually progressed to diabetes.

RESEARCH DESIGN AND METHODS

In this study, 708 individuals randomized into DPT-1 were genotyped for 37 single nucleotide polymorphisms in diabetes susceptibility loci.

RESULTS

Susceptibility alleles at loci expected to influence immunoregulation (PTPN22, CTLA4, and IL2RA) did not differ between progressors and nonprogressors but were elevated in both groups relative to general population frequencies, as was the INS promoter variant. In contrast, HLA DQB1*0302 and DQB1*0301 differed significantly in progressors versus nonprogressors (DQB*0302, 42.6 vs. 34.7%, P = 0.0047; DQB*0301, 8.6 vs. 14.3%, P = 0.0026). Multivariate analysis of the factors contributing to progression demonstrated that initial titers of anti-insulin autoantibodies (IAAs) could account for some (P = 0.0016) but not all of this effect on progression (P = 0.00038 for the independent effect of the number of DQB*0302 alleles). The INS-23 genotype was most strongly associated with anti-IAAs (median IAA levels in TT individuals, 60 nU/ml; AT, 121; and AA, 192; P = 0.000037) and only suggestively to the outcome of oral insulin administration.

CONCLUSIONS

With the exception of HLA, most susceptibility loci tested condition the risk of autoimmunity rather than the risk of failed immunoregulation that results in islet destruction. Future clinical trials might consider genotyping INS-23 in addition to HLA alleles as disease/treatment response modifier.

Weak proinsulin peptide-major histocompatibility complexes are targeted in autoimmune diabetes in mice

OBJECTIVE

Weak major histocompatibility complex (MHC) binding of self-peptides has been proposed as a mechanism that may contribute to autoimmunity by allowing for escape of autoreactive T-cells from the thymus. We examined the relationship between the MHC-binding characteristics of a beta-cell antigen epitope and T-cell autoreactivity in a model of autoimmune diabetes.

RESEARCH DESIGN AND METHODS

The binding of a proinsulin epitope, proinsulin-1(47-64) (PI-1[47-64]), to the MHC class II molecules I-A(g7) and I-A(k) was measured using purified class II molecules. T-cell reactivity to the proinsulin epitope was examined in I-A(g7+) and I-A(k+) mice.

RESULTS

C-peptide epitopes bound very weakly to I-A(g7) molecules. However, C-peptide-reactive T-cells were induced after immunization in I-A(g7)-bearing mice (NOD and B6.g7) but not in I-A(k)-bearing mice (B10.BR and NOD.h4). T-cells reactive with the PI-1(47-64) peptide were found spontaneously in the peripancreatic lymph nodes of pre-diabetic NOD mice. These T-cells were activated by freshly isolated beta-cells in the presence of antigen-presenting cells and caused diabetes when transferred into NOD.scid mice.

CONCLUSIONS

These data demonstrate an inverse relationship between self-peptide-MHC binding and T-cell autoreactivity for the PI-1(47-64) epitope in autoimmune diabetes.

The genetics of multiple sclerosis: SNPs to pathways to pathogenesis

Multiple sclerosis (MS) is an autoimmune demyelinating disease and a common cause of neurological disability in young adults. The modest heritability of MS reflects complex genetic effects and multifaceted gene-environment interactions. The human leukocyte antigen (HLA) region is the strongest susceptibility locus for MS, but a genome-wide association study recently identified new susceptibility genes. Progress in high-throughput genotyping and sequencing technologies and a better understanding of the structural organization of the human genome, together with powerful brain-imaging techniques that refine the phenotype, suggest that the tools could finally exist to identify the full set of genes influencing the pathogenesis of MS.

Do the peptide-binding properties of diabetogenic class II molecules explain autoreactivity?

One seminal aspect in autoimmune diabetes is antigen presentation of beta cell antigens by the diabetes-propensity class II histocompatibility molecules. The binding properties of I-Ag7 molecules are reviewed here and an emphasis is placed on their selection of peptides with a highly specific sequence motif, in which one or more acidic amino acids are found at the carboxy end interacting at the P9 anchoring site of I-Ag7. The reasons for the central role of I-Ag7 in the autoimmune response are analyzed. The insulin B chain segment 9-23 is a hot spot for T cell selection and a striking example of a weak MHC binding peptide that triggers autoreactivity.

Spontaneous myocarditis mimicking human disease occurs in the presence of an appropriate MHC and non-MHC background in transgenic mice

Most individuals have viral infections at some point in their life, however, only few develop autoreactivity to cardiac myosin following infection resulting in myocarditis suggesting a genetic predisposition. Most mouse models of myocarditis are induced by viral infection or by immunization with cardiac myosin. We generated HLA-DR3.Abetao and HLA-DQ8.Abetao transgenic mice in NOD and HLA-DQ8.Abetao in B10 background to study spontaneous autoimmunity. A high mortality was observed in NOD.DQ8 female mice 16 weeks or older. Echocardiography showed marked systolic dysfunction. Histopathology of various organs revealed an enlarged heart with mononuclear infiltrate consisting of CD4 and Mac-1+ cells and myocyte necrosis. The autoimmunity was associated with the presence of spontaneous autoreactive T cells and antibodies to cardiac myosin. Serologically, mice were negative for all known mouse viruses. NOD.DR3.Abetao, the transgene negative littermates, NOD, and B10.DQ8 Abetao mice had no gross or microscopic cardiac pathology. Spontaneous cellular and humoral response to cardiac myosin suggests that NOD.DQ8 may harbor autoreactive cells that can lead to spontaneous myocarditis and dilated cardiomyopathy. HLA-DQ8 is required for the predisposition to the spontaneous autoreactivity while NOD background influences onset and progression of disease. This model of myocarditis occurs predominantly in female mice and may provide insight into the pathogenesis of heart disease in women.

The K/BxN mouse model of inflammatory arthritis: theory and practice

Mice expressing the KRN T cell receptor transgene and the MHC class II molecule A(g7) (K/BxN mice) develop severe inflammatory arthritis, and serum from these mice causes similar arthritis in a wide range of mouse strains, owing to pathogenic autoantibodies to glucose-6-phosphate isomerase (GPI). This model has been useful for the investigation of the development of autoimmunity (K/BxN transgenic mice) and particularly of the mechanisms by which anti-GPI autoantibodies induce joint-specific imflammation (serum transfer model). In this chaper, after a summary of findings from this model system, we describe detailed methods for the maintenance of a K/BxN colony, crossing of the relevant TCR and MHC genes to other strain backgrounds, evaluation of KRN transgenic T cells, measurement of anti-GPI antibodies, induction of arthritis by serum transfer, and clinical and histological evaluation of arthritis.

Modulatory role of DR4- to DQ8-restricted CD4 T-cell responses and type 1 diabetes susceptibility

This study addressed an important biological question, namely how certain HLA molecules modulate the disease risk conferred by other HLA molecules. The HLA molecules under investigation were HLA-DQ8 and -DR4, the two most prevalent HLA class II alleles found in Caucasian type 1 diabetic patients. A panel of human GAD (hGAD65)-specific CD4 T-cell lines and hybridomas was generated to serve as detection reagents for evaluating the peptide occupancy of DQ8 and DR4. Results indicated that DQ8 and DR4 (0401) were able to bind the same hGAD65 peptides. The coexpression of DR4 (0401) diminished DQ8-restricted T-cell responses. In addition, we also demonstrated that the diminished T-cell response varied according to the specific DRB1*04 alleles. Taken together, this study provides evidence that DR4 is able to modulate DQ8-restricted T-cell responses, possibly by competing for peptides. Given that DQ8 is a primary genetic determinant of type 1 diabetes, the decreased DQ8-restricted CD4 T-cell activity due to peptide competition may be the mechanism explaining the modulation effect of DR4 to type 1 diabetes susceptibility.

The neurobiology of multiple sclerosis: genes, inflammation, and neurodegeneration

The autoimmune model of multiple sclerosis (MS) pathogenesis provided for many years a useful but incomplete conceptual framework for understanding the complex array of factors that lead to the loss of immune homeostasis, myelin and axonal injury, and progressive neurological symptoms. The availability of novel tools in molecular neurogenetics and increasingly sophisticated neuroimaging technologies, together with the revitalization of MS neuropathology, has created a new paradigm for the multidisciplinary study of this disease. This is reflected by the growing resolution of the MS genomic map, discovery of delicate inflammatory networks that are perturbed in MS, identification of mediators of demyelination, and recognition that cumulative axonal loss and neuronal injury are the histological correlates of neurological disability. Together, these advances have set the stage for the development of therapeutic approaches designed to target the demyelinating and neurodegenerative components of the disease and promote repair.

Altered susceptibility to EAE in congenic NOD mice: Altered processing of the encephalitogenic MOG35-55 peptide by NOR/LtJ mice

NOD mice (H-2 g7) naturally develop autoimmune diabetes, while the congenic NOR/LtJ mice (H-2 g7) are resistant. To determine if defective immune regulation renders NOD susceptible to autoimmune disease, we compared MOG35-55-induced EAE in NOD mice to that of NOR/LtJ. In two of three immunization protocols, the NOR/LtJ mice developed significantly reduced indices and severity of clinical disease, in spite of an exaggerated autoimmune response to MOG35-55. Characterization of the responding T cell repertoires revealed that V beta 8+ Th cells directed toward the MOG42-55 core epitope were dominant in both strains. Interestingly, CD8+ CTL were absent or significantly reduced in MOG35-55 lymphoblasts from NOR/LtJ mice, which poorly processed the MOG39-47 CTL epitope from MOG35-55. Thus, while particular MHC class II alleles may be associated with increased risk, molecules involved in the processing of key epitopes may be influential in the progression of autoimmune disease.

Heterogeneity at the HLA-DRB1 locus and risk for multiple sclerosis

Variation in major histocompatibility complex genes on chromosome 6p21.3, specifically the human leukocyte antigen HLA-DR2 or DRB1*1501-DQB1*0602 extended haplotype, confers risk for multiple sclerosis (MS). Previous studies of DRB1 variation and both MS susceptibility and phenotypic expression have lacked statistical power to detect modest genotypic influences, and have demonstrated conflicting results. Results derived from analyses of 1339 MS families indicate DRB1 variation influences MS susceptibility in a complex manner. DRB1*15 was strongly associated in families (P=7.8x10(-31)), and a dominant DRB1*15 dose effect was confirmed (OR=7.5, 95% CI=4.4-13.0, P<0.0001). A modest dose effect was also detected for DRB1*03; however, in contrast to DRB1*15, this risk was recessive (OR=1.8, 95% CI=1.1-2.9, P=0.03). Strong evidence for under-transmission of DRB1*14 (P=5.7x10(-6)) even after accounting for DRB1*15 (P=0.03) was present, confirming a protective effect. In addition, a high risk DRB1*15 genotype bearing DRB1*08 was identified (OR=7.7, 95% CI=4.1-14.4, P<0.0001), providing additional evidence for trans DRB1 allelic interactions in MS. Further, a significant DRB1*15 association observed in primary progressive MS families (P=0.0004), similar to relapsing-remitting MS families, suggests that DRB1-related mechanisms are contributing to both phenotypes. In contrast, results obtained from 2201 MS cases argue convincingly that DRB1*15 genotypes do not modulate age of onset, or significantly influence disease severity measured using expanded disease disability score and disease duration. These results contribute substantially to our understanding of the DRB1 locus and MS, and underscore the importance of using large sample sizes to detect modest genetic effects, particularly in studies of genotype-phenotype relationships.

Where CD4+CD25+ T reg cells impinge on autoimmune diabetes

Foxp3 is required for the generation and activity of CD4⁺CD25⁺ regulatory T (T reg) cells, which are important controllers of autoimmunity, including type-1 diabetes. To determine where T reg cells affect the diabetogenic cascade, we crossed the Foxp3 scurfy mutation, which eliminates T reg cells, with the BDC2.5 T cell receptor (TCR) transgenic mouse line. In this model, the absence of T reg cells did not augment the initial activation or phenotypic characteristics of effector T cells in the draining lymph nodes, nor accelerate the onset of T cell infiltration of the pancreatic islets. However, this insulitis was immediately destructive, causing a dramatic progression to overt diabetes. Microarray analysis revealed that T reg cells in the insulitic lesion adopted a gene expression program different from that in lymph nodes, whereas T reg cells in draining or irrelevant lymph nodes appeared very similar. Thus, T reg cells primarily impinge on autoimmune diabetes by reining in destructive T cells inside the islets, more than during the initial activation in the draining lymph nodes.

Soluble, dimeric HLA DR4-peptide chimeras: an approach for detection and immunoregulation of human type-1 diabetes

Still there are no effective methods to predict or cure type 1 diabetes (T1D) in humans. Soluble, dimeric MHC class II-peptide (DEF) chimeras have potential for both early diagnosis and immunospecific therapy. DEF chimeras prevent and reverse diabetes in mice by stimulating antigen-specific type 1 T regulatory cell (Tr1)-like cells. We also showed that diabetes could be predicted by changes in the phenotype of autoreactive CD4 T cells in peripheral blood. Herein, we demonstrated that human DEF (HLA-DR*0401/Fcgamma1) chimeras expressing peptides of beta-cell antigens stimulate Tr1-like cells in blood of patients with T1D, non-diabetic relatives, and controls. Furthermore, the specific and stable binding of DEF chimeras to cognate TCR and CD4 coreceptor allowed quantification and phenotyping of autoreactive CD4 T cells in non-stimulated blood by FACS. Our results indicate that (1) autoreactive CD4 T cells to GAD65 autoantigen are commonly present in humans expressing diabetes-susceptible HLA-DR*0401 molecules; (2) these autoreactive T cells undergo avidity maturation upon encountering the self antigen early in life; (3) the disease is associated with an imbalance between autoreactive CD4+CD25+ and CD4+CD69+ T cells specific for GAD65. Based on this, we propose a model to explain the kinetics of autoreactive CD4 T cells in blood during the natural history of T1D.