Spontaneous development of a pancreatic exocrine disease in CD28-deficient NOD mice

Cracking the type 1 diabetes code: Genes, microbes, immunity, and the early life environment

Type 1 diabetes (T1D) results from a complex interplay of genetic predisposition, immunological dysregulation, and environmental triggers, that culminate in the destruction of insulin-secreting pancreatic β cells. This review provides a comprehensive examination of the multiple factors underpinning T1D pathogenesis, to elucidate key mechanisms and potential therapeutic targets. Beginning with an exploration of genetic risk factors, we dissect the roles of human leukocyte antigen (HLA) haplotypes and non-HLA gene variants associated with T1D susceptibility. Mechanistic insights gleaned from the NOD mouse model provide valuable parallels to the human disease, particularly immunological intricacies underlying β cell-directed autoimmunity. Immunological drivers of T1D pathogenesis are examined, highlighting the pivotal contributions of both effector and regulatory T cells and the multiple functions of B cells and autoantibodies in β-cell destruction. Furthermore, the impact of environmental risk factors, notably modulation of host immune development by the intestinal microbiome, is examined. Lastly, the review probes human longitudinal studies, unveiling the dynamic interplay between mucosal immunity, systemic antimicrobial antibody responses, and the trajectories of T1D development. Insights garnered from these interconnected factors pave the way for targeted interventions and the identification of biomarkers to enhance T1D management and prevention strategies.

PD-1/PDL1 Blockade Exacerbates Pancreatic Damage and Immune Response in a Mouse Model of Acute Pancreatitis

Programmed necrosis factor 1 (PD-1) is significantly overexpressed in lymphocytes, neutrophils, and macrophages and has been studied in depth in tumors. As a member of the negative costimulatory family of immune regulatory molecules, expression of PD-1 and its primary regulatory pathway are related to immune cells. Recently, PD-1 was demonstrated to be clinically important in inflammatory diseases, such as multiple sclerosis, glomerulonephritis, and inflammatory bowel disease. PD-1, a negative regulator molecule, was recently found to protect tissues from the inflammatory response and inflammatory cell infiltration. Conversely, PD-1 deficiency may contribute to the occurrence of a diverse array of inflammatory diseases. However, whether PD-1 regulates the pathogenesis of acute pancreatitis (AP) is unclear. AP is a noninfectious inflammatory disease with primary pathological manifestations that include edema, inflammatory cell infiltration, and acinar cell necrosis. Among these features, costimulatory molecules including PD-1/PDL1 play a critical role in the regulation of immune response and immune activation. Here, we first found that PD-1 is notably upregulated in neutrophils and macrophages in peripheral blood and pancreatic injury tissue in AP mice. PD-1 gene deficiency exacerbated pancreatic injury in an experimental mouse model of AP. We observed more severe pancreatic injury in PD-1-deficient mice than in control mice, including increased pancreatic edema, inflammatory cells, infiltration, and acinar cell necrosis. We also found that PD-1-deficient mice exhibited higher levels of serum enzymology and inflammatory factors in AP. Furthermore, PD-1/PDL1 neutralizing antibodies significantly aggravated pancreatic and lung injury and increased serum inflammatory cytokine levels. These findings were consistent with those in PD-1-deficient mice. In summary, PD-1 may protect against AP in mice and act as a potential target for the prevention of AP in the future.

Possible involvement of autoimmunity in fulminant type 1 diabetes

Fulminant type 1 diabetes (FT1D) is characterized by a relatively low HbA1c level at the onset, despite the abrupt occurrence of marked hyperglycemia with ketosis or ketoacidosis. The initial symptoms/findings are flu-like, absence of islet-associated autoantibodies, and a drastic decrease in β-cells and α-cells, which strongly suggest the involvement of a viral infection. In fact, we successfully demonstrated that a FT1D-like phenotype can be reproduced in encephalomyocarditis virus-induced diabetes murine model. However, there is a discussion on the possible involvement of autoimmunity rather than viral infection as the underlying cause of FT1D. For example, HLA-DRB1*04:05, a susceptible antigen of type 1A diabetes, is reportedly associated with FT1D in Japan. Moreover, anti-glutamic acid decarboxylase antibody is reportedly detected in ~ 5% of the patients. Additionally, half of the patients with anti-programmed cell death-1 therapy-related type 1 diabetes fulfilled the criteria of the disease. These findings suggest that islet-associated autoimmunity can partially contribute to the development of FT1D. Furthermore, using nonobese diabetic mice with reduced regulatory T-cell (Treg) numbers, we found that a human FT1D-like phenotype can be induced by islet-associated autoimmunity through collaboration between innate immunity (macrophages and/or natural killer cells) and acquired immunity (predominantly cytotoxic CD8⁺ T cells) in genetically predisposed individuals of autoimmune type 1 diabetes with low Tregs or Treg dysfunction. To clarify greater details regarding the association of autoimmunity in the pathogenesis of FT1D, further studies using suitable animal models and accumulation of the relevant patients are required.

LatY136F knock-in mouse model for human IgG4-related disease

Background

The adaptor protein Linker for activation of T cell (LAT) is a key signaling hub used by the T cell antigen receptor. Mutant mice expressing loss-of-function mutations affecting LAT and including a mutation in which tyrosine 136 is replaced by a phenylalanine (Lat^Y136F) develop lymphoproliferative disorder involving T helper type 2 effector cells capable of triggering a massive polyclonal B cell activation that leads to hypergammaglobulinemia G1 and E and to non-resolving inflammation and autoimmunity. The purpose of this study was to evaluate whether the phenotypes of Lat^Y136F knock-in mice resemble the immunohistopathological features of immunoglobulin G4-related disease (IgG4-RD).

Methods

Lat^Y136F knock-in mice were sacrificed at 4–20 weeks of age, and pancreas, kidney, salivary gland and lung were obtained. All organs were stained with hematoxylin-eosin and with Azan for estimation of collagen in fibrosis, and the severity scores of inflammation and fibrosis were evaluated. Immunostainings were performed to analyze the types of infiltrating cells. In addition, the effects of corticosteroid treatment on the development of tissue lesions and serum levels of IgG1 were assessed.

Results

Tissue lesions characterized by inflammatory mononuclear cell infiltration and fibrosis were detected in pancreas, kidney, and salivary gland starting from 6 weeks of age. Immunostainings showed pronounced infiltration of plasma cells, CD4-positive T cells, and macrophages. Infiltrating plasma cells predominantly expressed IgG1. The extent of inflammation in pancreas and salivary glands was markedly reduced by corticosteroid treatment.

Conclusions

Lat^Y136F knock-in mice displayed increased production of Th2-type IgG1 (a homologue of human IgG4) and developed multiple organ tissue lesions reminiscent of those seen in patients with IgG4-RD. Moreover, the development of these tissue lesions was highly sensitive to corticosteroid treatment like in IgG4-RD. For these reasons we consider the Lat^Y136F knock-in mouse strain to represent a promising model for human IgG4-RD.

NOD mice, susceptible to pancreatic autoimmunity, demonstrate delayed growth of pancreatic cancer

Pancreatic cancer is a high mortality form of cancer, with a median survival only six months. There are multiple associated risk factors associated, most importantly type 2 diabetes, obesity, pancreatitis and smoking. The relative rarity of the disease, however, has made it difficult to dissect causative risk factors, especially with related risk factors. A major unanswered question with important therapeutic implications is the effect of immunological responses on pancreatic cancer formation, with data from other cancers suggesting the potential for local immunological responses to either increase cancer development or increase cancer elimination. Due to the rarity and late diagnosis of pancreatic cancer direct epidemiological evidence is lacking, thus necessitating a reliance on animal models. Here we investigated the relationship between pancreatic autoimmunity and cancer by backcrossing the well characterised Ela1-Tag transgenic model of pancreatic cancer onto the pancreatic autoimmune susceptible NOD mouse strain. Through longitudinal magnetic resonance imaging we found that the NOD genetic background delayed the onset of pancreatic tumours and substantially slowed the growth rate of tumours after development. These results suggest that elevated autoimmune surveillance of the pancreas limits tumour formation and growth, identifying pancreatic cancer as a promising target for immune checkpoint blockade therapies that unleash latent autoimmunity.

Aire-deficient mice provide a model of corneal and lacrimal gland neuropathy in Sjögren's syndrome

Sjögren's syndrome (SS) is a chronic, autoimmune exocrinopathy that leads to severe dryness of the mouth and eyes. Exocrine function is highly regulated by neuronal mechanisms but little is known about the link between chronic inflammation, innervation and altered exocrine function in the diseased eyes and exocrine glands of SS patients. To gain a better understanding of neuronal regulation in the immunopathogenesis of autoimmune exocrinopathy, we profiled a mouse model of spontaneous, autoimmune exocrinopathy that possess key characteristics of peripheral neuropathy experienced by SS patients. Mice deficient in the autoimmune regulator (Aire) gene developed spontaneous, CD4+ T cell-mediated exocrinopathy and aqueous-deficient dry eye that were associated with loss of nerves innervating the cornea and lacrimal gland. Changes in innervation and tear secretion were accompanied by increased proliferation of corneal epithelial basal cells, limbal expansion of KRT19-positive progenitor cells, increased vascularization of the peripheral cornea and reduced nerve function in the lacrimal gland. In addition, we found extensive loss of MIST1+ secretory acinar cells in the Aire -/- lacrimal gland suggesting that acinar cells are a primary target of the disease, Finally, topical application of ophthalmic steroid effectively restored corneal innervation in Aire -/- mice thereby functionally linking nerve loss with local inflammation in the aqueous-deficient dry eye. These data provide important insight regarding the relationship between chronic inflammation and neuropathic changes in autoimmune-mediated dry eye. Peripheral neuropathies characteristic of SS appear to be tightly linked with the underlying immunopathological mechanism and Aire -/- mice provide an excellent tool to explore the interplay between SS-associated immunopathology and peripheral neuropathy.

Impact of Immune-Modulatory Drugs on Regulatory T Cell

Immunosuppression strategies that selectively inhibit effector T cells while preserving and even enhancing CD4FOXP3 regulatory T cells (Treg) permit immune self-regulation and may allow minimization of immunosuppression and associated toxicities. Many immunosuppressive drugs were developed before the identity and function of Treg were appreciated. A good understanding of the interactions between Treg and immunosuppressive agents will be valuable to the effective design of more tolerable immunosuppression regimens. This review will discuss preclinical and clinical evidence regarding the influence of current and emerging immunosuppressive drugs on Treg homeostasis, stability, and function as a guideline for the selection and development of Treg-friendly immunosuppressive regimens.

New Murine Model of Early Onset Autoimmune Thyroid Disease/Hypothyroidism and Autoimmune Exocrinopathy of the Salivary Gland

Sixty to seventy percent of IFN-γ(-/-) NOD.H-2h4 mice given sodium iodide (NaI)-supplemented water develop a slow onset autoimmune thyroid disease, characterized by thyrocyte epithelial cell (TEC) hyperplasia and proliferation (H/P). TEC H/P develops much earlier in CD28(-/-) mice and nearly 100% (both sexes) have severe TEC H/P at 4 mo of age. Without NaI supplementation, 50% of 5- to 6-mo-old CD28(-/-)IFN-γ(-/-) mice develop severe TEC H/P, and 2-3 wk of NaI is sufficient for optimal development of severe TEC H/P. Mice with severe TEC H/P are hypothyroid, and normalization of serum thyroxine levels does not reduce TEC H/P. Activated CD4(+) T cells are sufficient to transfer TEC H/P to SCID recipients. Thyroids of mice with TEC H/P have infiltrating T cells and expanded numbers of proliferating thyrocytes that highly express CD40. CD40 facilitates, but is not required for, development of severe TEC H/P, as CD40(-/-)IFN-γ(-/-)CD28(-/-) mice develop severe TEC H/P. Accelerated development of TEC H/P in IFN-γ(-/-)CD28(-/-) mice is a result of reduced regulatory T cell (Treg) numbers, as CD28(-/-) mice have significantly fewer Tregs, and transfer of CD28(+) Tregs inhibits TEC H/P. Essentially all female IFN-γ(-/-)CD28(-/-) NOD.H-2h4 mice have substantial lymphocytic infiltration of salivary glands and reduced salivary flow by 6 mo of age, thereby providing an excellent new model of autoimmune exocrinopathy of the salivary gland. This is one of very few models where autoimmune thyroid disease and hypothyroidism develop in most mice by 4 mo of age. This model will be useful for studying the effects of hypothyroidism on multiple organ systems.

Co-stimulate or Co-inhibit Regulatory T Cells, Which Side to Go?

Co-stimulatory and co-inhibitory molecules direct the "second signal," which largely determines the outcome of the "first signal" generated by the interaction of T cell receptor (TCR) with cognate MHC-peptide complex. The co-stimulatory and co-inhibitory signals are key mechanistic contributors to the regulation of adaptive immunity, especially the T cell-mediated immune response. Regulatory T cells (Tregs) are a special population of T cells, which unlike other T cells function as "attenuators" to suppress T cell immunity. Dysregulation of either the "second signal" or Tregs leads to an unbalanced immune system, which can result in a range of immune-related disorders, including autoimmune diseases, chronic infections, and tumors. In contrast, precise manipulation of these two systems offers tremendous clinical opportunities to treat these same diseases. Co-stimulatory and co-inhibitory molecules modulate immunity at molecular level, whereas Tregs delicately control the immune response at cellular level. Accumulating evidence has demonstrated that these two regulatory strategies converge and synergize with each other. This review discusses recent progress on the roles of co-stimulatory and co-inhibitory signals in the context of Tregs.

Possible involvement of Toll-like receptor 7 in the development of type 1 autoimmune pancreatitis

BACKGROUND

High serum immunoglobulin G4 (IgG4) levels and IgG4-positive plasma cell infiltration are characteristic of type 1 autoimmune pancreatitis (AIP). It is unclear whether innate immunity is a cause of type 1 AIP; the possible involvement of microbial infection has been suggested in its pathogenesis. To clarify the pathogenesis of type 1 AIP, we investigated Toll-like receptors (TLRs) in type 1 AIP patients.

METHODS

We studied nine cases of type 1 AIP with ten cases of alcoholic chronic pancreatitis (ACP) and three of the samples from non-tumorous lesion of neuroendocrine tumor (NET) as control subjects. We counted the number of TLR1-11-positive cells immunohistochemically stained with anti-TLR1-11 antibodies. To identify TLR-positive cells in pancreata from type 1 AIP patients, we used a double-immunofluorescence method and counted the numbers of identifiable CD68-, CD163-, CD123-, and CD20-positive cells.

RESULTS

In type 1 AIP, TLR7 (8.815 ± 1.755), TLR8 (3.852 ± 1.489), and TLR10 (3.852 ± 0.921) were highly expressed. Only the ratio of TLR7 per monocyte was significantly higher in type 1 AIP (0.053 ± 0.012) than in ACP (0.007 ± 0.004; p < 0.01) and non-tumorous lesion of NET (0.000 ± 0.000; p < 0.01). In type 1 AIP, the CD163 to TLR7 ratio (0.789 ± 0.031) was significantly higher both than that of CD123 to TLR7 ratio (0.034 ± 0.006; p < 0.001) and CD20 to TLR7 ratio (0.029 ± 0.010; p < 0.001).

CONCLUSIONS

TLR7 might be key pattern-recognition receptors involved in the development of type 1 AIP.

Exploiting apoptosis for therapeutic tolerance induction

Immune tolerance remains the most promising yet elusive strategy for treating immune-mediated diseases. An experimental strategy showing promise in phase 1 clinical studies is the delivery of Ag cross-linked to apoptotic leukocytes using ethylene carbodiimide. This approach originated from demonstration of the profound tolerance-inducing ability of i.v. administered Ag-coupled splenocytes (Ag-SP) in mice, which has been demonstrated to treat T cell-mediated disorders including autoimmunity, allergy, and transplant rejection. Recent studies have defined the intricate interplay between the innate and adaptive immune systems in Ag-SP tolerance induction. Innate mechanisms include scavenger receptor-mediated uptake of Ag-SP by host APCs, Ag representation, and the required upregulation of PD-L1 expression and IL-10 production by splenic marginal zone macrophages leading to Ag-specific T cell regulation via the combined effects of cell-intrinsic anergy and regulatory T cell induction. In this paper, we discuss the history, advantages, current mechanistic understanding, and clinical potential of tolerance induction using apoptotic Ag-coupled apoptotic leukocytes.

Regulatory T-cell therapy in transplantation: moving to the clinic

Regulatory T cells (Tregs) are essential to transplantation tolerance and their therapeutic efficacy is well documented in animal models. Moreover, human Tregs can be identified, isolated, and expanded in short-term ex vivo cultures so that a therapeutic product can be manufactured at relevant doses. Treg therapy is being planned at multiple transplant centers around the world. In this article, we review topics critical to effective implementation of Treg therapy in transplantation. We will address issues such as Treg dose, antigen specificity, and adjunct therapies required for transplant tolerance induction. We will summarize technical advances in Treg manufacturing and provide guidelines for identity and purity assurance of Treg products. Clinical trial designs and Treg manufacturing plans that incorporate the most up-to-date scientific understanding in Treg biology will be essential for harnessing the tolerogenic potential of Treg therapy in transplantation.

Reduced effectiveness of CD4+Foxp3+ regulatory T cells in CD28-deficient NOD.H-2h4 mice leads to increased severity of spontaneous autoimmune thyroiditis

NOD.H-2h4 mice given NaI in their drinking water develop iodine-accelerated spontaneous autoimmune thyroiditis (ISAT) with chronic inflammation of the thyroid by T and B cells and production of anti-mouse thyroglobulin (MTg) autoantibody. CD28(-/-) NOD.H-2h4 mice, which have reduced numbers of CD4(+)Foxp3(+) regulatory T cells (Tregs), were developed to examine the role of Tregs in ISAT development. CD28(-/-) NOD.H2-h4 mice develop more severe ISAT than do wild-type (WT) mice, with collagen deposition (fibrosis) and low serum T4. CD28(-/-) mice have increased expression of proinflammatory cytokines IFN-γ and IL-6, consistent with increased mononuclear cell infiltration and tissue destruction in thyroids. Importantly, transferring purified CD4(+)Foxp3(+) Tregs from WT mice reduces ISAT severity in CD28(-/-) mice without increasing the total number of Tregs, suggesting that endogenous Tregs in CD28(-/-) mice are functionally ineffective. Endogenous CD28(-/-) Tregs have reduced surface expression of CD27, TNFR2 p75, and glucocorticoid-induced TNFR-related protein compared with transferred CD28(+/+) Tregs. Although anti-MTg autoantibody levels generally correlate with ISAT severity scores in WT mice, CD28(-/-) mice have lower anti-MTg autoantibody responses than do WT mice. The percentages of follicular B cells are decreased and those of marginal zone B cells are increased in spleens of CD28(-/-) mice, and they have fewer thyroid-infiltrating B cells than do WT mice. This suggests that CD28 deficiency has direct and indirect effects on the B cell compartment. B cell-deficient (B(-/-)) NOD.H-2h4 mice are resistant to ISAT, but CD28(-/-)B(-/-) mice develop ISAT comparable to WT mice and have reduced numbers of Tregs compared with WT B(-/-) mice.

Breakdown in peripheral tolerance in type 1 diabetes in mice and humans

Type 1 Diabetes (T1D), also called juvenile diabetes because of its classically early onset, is considered an autoimmune disease targeting the insulin-producing β cells in the pancreatic islets of Langerhans. T1D reflects a loss of tolerance to tissue self-antigens caused by defects in both central tolerance, which aims at eliminating potentially autoreactive lymphocytes developing in the thymus, and peripheral tolerance, which normally controls autoreactive T cells that escaped the thymus. Like in other autoimmune diseases, the mechanisms leading to T1D are multifactorial and depend on a complex combination of genetic, epigenetic, molecular, and cellular elements that result in the breakdown of peripheral tolerance. In this article, we discuss the contribution of these factors in the development of the autoimmune response targeting pancreatic islets in T1D and the therapeutic strategies currently being explored to correct these defects.

The B7-independent isoform of CTLA-4 functions to regulate autoimmune diabetes

The critical role of CTLA-4 in inhibiting Ag-driven T cell responses upon engagement with its ligands, B7-1 and B7-2 and its importance for peripheral T cell tolerance and T cell homeostasis has been studied intensively. The CTLA-4 splice variant ligand-independent (li)-CTLA-4 is expressed in naive and activated T cells and can actively alter T cell signaling despite its lack of a B7 binding domain. To study the effect of li-CTLA-4 in regulating T cell responses in the context of autoimmunity, we engineered a B6.CTLA-4 (floxed-Exon2)-BAC-transgene, resulting in selective expression of li-CTLA-4 upon Cre-mediated deletion of Exon 2. Introducing the B6.BAC into the NOD background, which is genetically deficient for li-CTLA-4, restores mRNA levels of li-CTLA-4 to those observed in C57BL/6 mice. Furthermore, re-expressing this ligand nonbinding isoform in NOD mice reduced IFN-γ production in T effector cells accompanied by a significant decrease in insulitis and type 1 diabetes frequency. However, selective expression of li-CTLA-4 could not fully rescue the CTLA-4 knockout disease phenotype when bred onto NOD.BDC2.5.CTLA-4 knockout background because of the requirement of the full-length, B7-binding CTLA-4 molecule on T effector cells. Thus, the li-CTLA-4 form, when expressed at physiologic levels in the CTLA-4-sufficient NOD background can suppress autoimmunity; however, the functionality of the li-CTLA-4 isoform depends on the presence of the full-length molecule to alter effector T cell signaling.

Lymphotoxin β receptor signaling promotes development of autoimmune pancreatitis

BACKGROUND & AIMS

Little is known about the pathogenic mechanisms of autoimmune pancreatitis (AIP), an increasingly recognized, immune-mediated form of chronic pancreatitis. Current treatment options are limited and disease relapse is frequent. We investigated factors that contribute to the development of AIP and new therapeutic strategies.

METHODS

We used quantitative polymerase chain reaction, immunohistochemical, and enzyme-linked immunosorbent analyses to measure the expression of cytokines and chemokines in tissue and serum samples from patients with and without AIP. We created a mouse model of human AIP by overexpressing lymphotoxin (LT)α and β specifically in acinar cells (Ela1-LTab mice).

RESULTS

Messenger RNA levels of LTα and β were increased in pancreatic tissues from patients with AIP, compared with controls, and expression of chemokines (CXCL13, CCL19, CCL21, CCL1, and B-cell-activating factor) was increased in pancreatic and serum samples from patients. Up-regulation of these factors was not affected by corticosteroid treatment. Acinar-specific overexpression of LTαβ (Ela1-LTαβ) in mice led to an autoimmune disorder with various features of AIP. Chronic inflammation developed only in the pancreas but was sufficient to cause systemic autoimmunity. Acinar-specific overexpression of LTαβ did not cause autoimmunity in mice without lymphocytes (Ela1-LTab/Rag1(-/-)); moreover, lack of proinflammatory monocytes (Ela1-LTab/Ccr2(-/-)) failed to prevent AIP but prevented early pancreatic tissue damage. Administration of corticosteroids reduced pancreatitis but did not affect production of autoantibodies, such as antipancreatic secretory trypsin inhibitor in Ela1-LTab mice. In contrast, inhibition of LTβR signaling reduced chemokine expression, renal immune-complex deposition, and features of AIP in Ela1-LTab mice.

CONCLUSIONS

Overexpression of LTαβ specifically in acinar cells of mice causes features of AIP. Reagents that neutralize LTβR ligands might be used to treat patients with AIP.

Comparative study on experimental autoimmune pancreatitis and its extrapancreatic involvement in mice

OBJECTIVE

The objective of the study was to study the relationship between autoimmune pancreatitis (AIP) and colitis in C57BL/6 interleukin 10-deficient (IL-10KO) mice and to compare the extrapancreatic involvement of AIP between IL-10KO and MRL/Mp mice that developed pancreatitis.

METHODS

Six-week-old female IL-10KO and MRL/Mp mice were injected intraperitoneally with polyinosinic polycytidylic acid (poly I:C) twice weekly for 8 or 12 weeks, respectively. The mice were killed, and the severity of inflammation in the pancreas, colon, liver, bile duct, and salivary gland was assessed using histological scoring systems. T-cell subsets derived from IL-10KO mice with pancreatitis were adoptively transferred into recombination activating gene 2-deficient mice.

RESULTS

Administration of poly I:C induced pancreatitis and accelerated the development of colitis in IL-10KO mice. Pancreatitis was characterized by specific destruction of exocrine glands and the production of various autoantibodies. Involvement of the liver and bile duct was observed in both IL-10KO and MRL/Mp mice, but sialadenitis was present only in MRL/Mp mice. Adoptive transfer of CD4(+) T cells from AIP mice induced pancreatitis in recipient mice.

CONCLUSIONS

Pancreatitis in IL-10KO mice resembles human type 1 AIP and is not associated with colitis. Genetic background may affect susceptibility to extrapancreatic involvement in type 1 AIP.

Nuclear export of histone deacetylase 7 during thymic selection is required for immune self-tolerance

Histone deacetylase 7 (HDAC7) is a T-cell receptor (TCR) signal-dependent regulator of differentiation that is highly expressed in CD4/CD8 double-positive (DP) thymocytes. Here, we examine the effect of blocking TCR-dependent nuclear export of HDAC7 during thymic selection, through expression of a signal-resistant mutant of HDAC7 (HDAC7-ΔP) in thymocytes. We find that HDAC7-ΔP transgenic thymocytes exhibit a profound block in negative thymic selection, but can still undergo positive selection, resulting in the escape of autoreactive T cells into the periphery. Gene expression profiling reveals a comprehensive suppression of the negative selection-associated gene expression programme in DP thymocytes, associated with a defect in the activation of MAP kinase pathways by TCR signals. The consequence of this block in vivo is a lethal autoimmune syndrome involving the exocrine pancreas and other abdominal organs. These experiments establish a novel molecular model of autoimmunity and cast new light on the relationship between thymic selection and immune self-tolerance.

Autoantibodies in autoimmune pancreatitis

Autoimmune pancreatitis (AIP) was first used to describe cases of pancreatitis with narrowing of the pancreatic duct, enlargement of the pancreas, hyper-γ-globulinaemia, and antinuclear antibody (ANA) positivity serologically. The main differential diagnosis, is pancreatic cancer, which can be ruled out through radiological, serological, and histological investigations. The targets of ANA in patients with autoimmune pancreatitis do not appear to be similar to those found in other rheumatological diseases, as dsDNA, SS-A, and SS-B are not frequently recognized by AIP-related ANA. Other disease-specific autoantibodies, such as, antimitochondrial, antineutrophil cytoplasmic antibodies or diabetes-specific autoantibodies are virtually absent. Further studies have focused on the identification of pancreas-specific autoantigens and reported significant reactivity to lactoferrin, carbonic anhydrase, pancreas secretory trypsin inhibitor, amylase-alpha, heat-shock protein, and plasminogen-binding protein. This paper discusses the findings of these investigations and their relevance to the diagnosis, management, and pathogenesis of autoimmune pancreatitis.

Commensal Flora, is it an Unwelcomed Companion as a Triggering Factor of Autoimmune Pancreatitis?

The etiopathogenesis of many autoimmune disorders has not been identified. The aim of this paper is to focus on the involvement of bacterial exposure, as an environmental factor, in the pathogenesis of autoimmune pancreatitis (AIP), which is broadly categorized as autoimmune disorders involving pancreatic lesions. Avirulent and/or commensal bacteria, which may have an important role(s) as initiating/progressing factors in the pathogenesis of autoimmune disorder AIP, will be emphasized.

B7-H4 Treatment of T Cells Inhibits ERK, JNK, p38, and AKT Activation

B7-H4 is a newly identified B7 homolog that plays an important role in maintaining T-cell homeostasis by inhibiting T-cell proliferation and lymphokine-secretion. In this study, we investigated the signal transduction pathways inhibited by B7-H4 engagement in mouse T cells. We found that treatment of CD3(+) T cells with a B7-H4.Ig fusion protein inhibits anti-CD3 elicited T-cell receptor (TCR)/CD28 signaling events, including phosphorylation of the MAP kinases, ERK, p38, and JNK. B7-H4.Ig treatment also inhibited the phosphorylation of AKT kinase and impaired its kinase activity as assessed by the phosphorylation of its endogenous substrate GSK-3. Expression of IL-2 is also reduced by B7-H4. In contrast, the phosphorylation state of the TCR proximal tyrosine kinases ZAP70 and lymphocyte-specific protein tyrosine kinase (LCK) are not affected by B7-H4 ligation. These results indicate that B7-H4 inhibits T-cell proliferation and IL-2 production through interfering with activation of ERK, JNK, and AKT, but not of ZAP70 or LCK.

B7-H4 Treatment of T Cells Inhibits ERK, JNK, p38, and AKT Activation

B7-H4 is a newly identified B7 homolog that plays an important role in maintaining T-cell homeostasis by inhibiting T-cell proliferation and lymphokine-secretion. In this study, we investigated the signal transduction pathways inhibited by B7-H4 engagement in mouse T cells. We found that treatment of CD3(+) T cells with a B7-H4.Ig fusion protein inhibits anti-CD3 elicited T-cell receptor (TCR)/CD28 signaling events, including phosphorylation of the MAP kinases, ERK, p38, and JNK. B7-H4.Ig treatment also inhibited the phosphorylation of AKT kinase and impaired its kinase activity as assessed by the phosphorylation of its endogenous substrate GSK-3. Expression of IL-2 is also reduced by B7-H4. In contrast, the phosphorylation state of the TCR proximal tyrosine kinases ZAP70 and lymphocyte-specific protein tyrosine kinase (LCK) are not affected by B7-H4 ligation. These results indicate that B7-H4 inhibits T-cell proliferation and IL-2 production through interfering with activation of ERK, JNK, and AKT, but not of ZAP70 or LCK.

A mimic of viral double-stranded RNA triggers fulminant type 1 diabetes-like syndrome in regulatory T cell-deficient autoimmune diabetic mouse

Human fulminant type 1 diabetes (FT1D) is an extremely aggressive disease. The delay of proper diagnosis results in high mortality. However, the pathophysiology of this disease remains unclear. We took advantage of CD28-deficient NOD (CD28(-/-) NOD) mice, which have limited numbers of regulatory T cells and develop aggressive autoimmune diabetes, to create a FT1D model that mimicked the disease in humans. Young CD28(-/-) NOD mice were injected with polyinosinic-polycytidylic acid to activate innate immunity in an effort to induce diabetes onset. In this model, innate immune cell activation precedes the onset of diabetes similar to ∼70% of FT1D patients. Eighty-three percent of CD28(-/-) NOD mice developed diabetes within 1-6 d after injection of polyinosinic-polycytidylic acid. Moreover, T cells infiltrated the pancreatic exocrine tissue and destroyed α cells, an observation characteristic of human FT1D. We conclude that an FT1D-like phenotype can be induced in the background of autoimmune diabetes by a mimic of viral dsRNA, and this model is useful for understanding human FT1D.

Are dysregulated inflammatory responses to commensal bacteria involved in the pathogenesis of hepatobiliary-pancreatic autoimmune disease? An analysis using mice models of primary biliary cirrhosis and autoimmune pancreatitis

The etiopathogenesis of many autoimmune disorders has not been identified. The aim of this paper is to focus on the involvement of bacterial exposure in the pathogenesis of primary biliary cirrhosis (PBC) and autoimmune pancreatitis (AIP), both of which are broadly categorized as autoimmune disorders involving hepatobiliary-pancreatic lesions. Avirulent and/or commensal bacteria, which may have important role(s) as initiating factors in the pathogenesis of autoimmune disorders such as PBC and AIP, will be emphasized.

The role of innate immunity in the pathogenesis of experimental autoimmune pancreatitis in mice

OBJECTIVE

To determine the role of innate immunity in the development of autoimmune pancreatitis in mice induced by toll-like receptor (TLR) stimulation.

METHODS

Six-week-old female MRL/Mp mice were injected intraperitoneally with polyinosinic polycytidylic acid (poly I:C) or lipopolysaccharide (LPS) at doses of 5 mg/kg body weight twice weekly for 12 weeks. The mice were killed, and the severity of pancreatitis was graded using a histological scoring system. Serum cytokine levels of mice with pancreatitis and mice that were given a single injection of TLR ligands were measured using enzyme-linked immunosorbent assays. The effect of TLR stimulation on the development of pancreatitis was also examined using C57BL/6 interleukin (IL)-10-deficient mice.

RESULTS

Administration of poly I:C accelerated the development of pancreatitis in MRL/Mp mice, but LPS did not. Serum levels of IL-10 and IL-12 were significantly elevated in mice with autoimmune pancreatitis. A single injection of LPS markedly increased serum levels of interferon-γ, tumor necrosis factor-α, IL-10, and IL-12 compared with those of poly I:C-treated mice. Treatment with not only poly I:C but also LPS induced pancreatitis in IL-10-deficient mice but not in wild-type mice.

CONCLUSION

Repeated stimulation of innate immunity induces autoimmunity in the pancreas of mice via an imbalance between proinflammatory and anti-inflammatory cytokines.

A critical role for regulatory T cell-mediated control of inflammation in the absence of commensal microbiota

Removal of regulatory T cells precipitates tissue inflammation and a systemic autoimmune lympho- and myeloproliferative syndrome, even in germ-free mice.

Suppression mediated by regulatory T cells (T reg cells) represents a unique, cell-extrinsic mechanism of in-trans negative regulation that restrains multiple types of immune cells. The loss of T reg cells leads to fatal, highly aggressive, and widespread immune-mediated lesions. This severe autoimmunity may be driven by commensal microbiota, the largest source of non-self ligands activating the innate and adaptive immune systems. Alternatively, T reg cells may primarily restrain T cells with a diverse self–major histocompatibility complex (MHC)–restricted T cell receptor repertoire independently of commensal microbiota. In this study, we demonstrate that in germ-free (GF) mice, ablation of the otherwise fully functional T reg cells resulted in a systemic autoimmune lympho- and myeloproliferative syndrome and tissue inflammation comparable with those in T reg cell–ablated conventional mice. Importantly, there were two exceptions: in GF mice deprived of T reg cells, the inflammation in the small intestine was delayed, whereas exocrine pancreatitis was markedly accelerated compared with T reg cell–ablated conventional mice. These findings suggest that the main function of T reg cells is restraint of self-MHC–restricted T cell responsiveness, which, regardless of the presence of commensal microbiota, poses a threat of autoimmunity.

Cutting edge: Hematopoietic-derived APCs select regulatory T cells in thymus

Recognition of self-peptide-MHC complexes by high-affinity TCRs and CD28 signaling are critical for the development of forkhead-winged helix box transcription factor 3(+) regulatory T cells (Tregs) in thymus. However, the type of APCs that are responsible for selecting Tregs has remained unclear. To dissect the role of hematopoietic-derived APCs (HCs) and thymic epithelial cells (TECs) in Treg selection, we constructed bone marrow chimeras with disrupted CD28/B7 signaling in the HC or TEC compartment and analyzed the generation of Tregs in the thymus. We found that both HCs and TECs were independently able to fully reconstitute the Treg population in the thymus of bone marrow chimeras. In addition, Treg selection requires the TCR signal and CD28 costimulation presented in cis on the same APC type in vivo. This study demonstrates a new role, to our knowledge, for HCs in the development of Tregs in thymus.

Human risk allele HLA-DRB1*0405 predisposes class II transgenic Ab0 NOD mice to autoimmune pancreatitis

BACKGROUND & AIMS

Autoimmune pancreatitis (AIP) underlies 5%-11% of cases of chronic pancreatitis. An association between AIP and the human leukocyte antigen (HLA)-DRB1*0405/DQB1*0401 haplotype has been reported, but linkage disequilibrium has precluded the identification of predisposing HLA gene(s). We studied the role of single HLA genes in the development of AIP in transgenic mice.

METHODS

CD4(+) T-cell-negative I-Abeta chain(-/-) (Ab0) mice develop AIP spontaneously, likely due to dysregulation of CD8(+) T- cell responses. We generated Ab0 nonobese diabetic (NOD) mice transgenic for HLA-DR*0405, leading to rescue of CD4(+) T cells; we compared their susceptibility to AIP with HLA-DQ8 or HLA-DR*0401 (single) transgenic, or HLA-DR*0405/DQ8 (double) transgenic mice.

RESULTS

CD4(+) T-cell-competent HLA-DR*0405 transgenic Ab0 NOD mice develop AIP with high prevalence after sublethal irradiation and adoptive transfer of CD90(+) T cells, leading to complete pancreatic atrophy. HLA-DR*0405 transgenic mice can also develop unprovoked AIP, whereas HLA-DR*0401, HLA-DQ8, and HLA-DR*0405/DQ8 transgenic Ab0 NOD controls all remained normal, even after irradiation and adoptive transfer of CD90(+) T cells. Pancreas histology in HLA-DR*0405 transgenic mice was characterized by destructive infiltration of the exocrine tissue with CD4(+) and CD8(+) T cells, B cells, and macrophages. Mice with complete pancreatic atrophy lost weight, developed fat stools, and had reduced levels of serum lipase activity.

CONCLUSIONS

Because HLA-DR*0405 expression fails to protect mice from AIP, the HLA-DRB1*0405 allele appears to be an important risk factor for AIP on the HLA-DRB1*0405/DQB1*0401 haplotype. This humanized mouse model should be useful for studying immunopathogenesis, diagnostic markers, and therapy of human AIP.

Analysis of humoral immune response in experimental autoimmune pancreatitis in mice

OBJECTIVES

To study the autoimmune response in MRL/Mp mice, which spontaneously develop pancreatitis in the exocrine pancreatic tissue.

METHODS

Six-week-old female mice were injected intraperitoneally with polyinosinic polycytidylic acid at a dose of 5 mg/kg of body weight twice a week for up to 12 weeks. The mice were serially killed, and the severity of their pancreatitis was graded with a histological scoring system. Immunohistological examinations were performed, and the serum levels of autoantibodies were measured by enzyme-linked immunosorbent assay.

RESULTS

The administration of polyinosinic polycytidylic acid accelerated the development of pancreatitis, with abundant infiltration of B220 B cells and CD138 plasmacytes. Various autoantibodies directed against autoantigens, including carbonic anhydrase II and lactoferrin, were detected but none against glutamic acid decarboxylase. Of these, autoantibodies directed against the pancreatic secretory trypsin inhibitor (PSTI; 91.7%) were more prevalent than those against carbonic anhydrase II (33.3%) or lactoferrin (45.8%). Determination of the epitope of the anti-PSTI antibody showed that most immunoreactivity was directed at the site on PSTI that is active in the suppression of trypsin activity.

CONCLUSIONS

The autoimmune response to PSTI protein may induce a failure of PSTI activity, resulting in the activation of trypsinogen and the subsequent disease progression.

Immunology of beta-cell destruction

The pancreatic islet beta-cells are the target for an autoimmune process that eventually results in an inability to control blood glucose due to the lack of insulin. The different steps that eventually lead to the complete loss of the beta-cells are reviewed to include the very first step of a triggering event that initiates the development of beta-cell autoimmunity to the last step of appearance of islet-cell autoantibodies, which may mark that insulitis is about to form. The observations that the initial beta-cell destruction by virus or other environmental factors triggers islet autoimmunity not in the islets but in the draining pancreatic lymph nodes are reviewed along with possible basic mechanisms of loss of tolerance to islet autoantigens. Once islet autoimmunity is established the question is how beta-cells are progressively killed by autoreactive lymphocytes which eventually results in chronic insulitis. Many of these series of events have been dissected in spontaneously diabetic mice or rats, but controlled clinical trials have shown that rodent observations are not always translated into mechanisms in humans. Attempts are therefore needed to clarify the step 1 triggering mechanisms and the step to chronic autoimmune insulitis to develop evidence-based treatment approaches to prevent type 1 diabetes.

CTLA-4 suppresses the pathogenicity of self antigen-specific T cells by cell-intrinsic and cell-extrinsic mechanisms

The inhibitory immunoregulatory receptor CTLA-4 is critical in maintaining self-tolerance, but the mechanisms of its actions have remained controversial. Here we examined the antigen specificity of tissue-infiltrating CD4(+) T cells in Ctla4(-/-) mice. After adoptive transfer, T cells isolated from tissues of Ctla4(-/-) mice showed T cell antigen receptor (TCR)-dependent accumulation in the tissues from which they were derived, which suggested reactivity to tissue-specific antigens. We identified the pancreas-specific enzyme PDIA2 as an autoantigen in Ctla4(-/-) mice. CTLA-4 expressed either on PDIA2-specific effector cells or on regulatory T cells was sufficient to control tissue destruction mediated by PDIA2-specific T cells. Our results demonstrate that both cell-intrinsic and non-cell-autonomous actions of CTLA-4 operate to maintain T cell tolerance to a self antigen.

Levees of immunological tolerance

Immunological tolerance guards against spurious immune responses to body constituents. Tolerance encompasses a network of mechanisms: central and peripheral, cell-autonomous and cell-interactive. Our understanding of these mechanisms has improved greatly over recent years, often reflecting new insights into the processes underlying particular autoimmune diseases. Yet it is possible that important tolerance mechanisms remain to be discovered, perhaps an explanation for the so-far disappointing clinical translation to the prevention and cure of autoimmune diseases.

Diabetes associated with autoimmune pancreatitis: new insights into the mechanism of β-cell dysfunction

A high proportion of patients with autoimmune pancreatitis (AIP) have diabetes. The decreased β-cell function in active AIP, which leads to diabetes, can sometimes be reversed by corticosteroid treatment. However, the immunological mechanisms causing this β-cell dysfunction are largely unclear. Our recent studies on AIP complicated with diabetes, and data from other animal models of AIP, suggest the presence of distinct mechanisms responsible for β-cell damage in AIP. The presence of immunological cross-reactivity against antigens that are localized both in exocrine pancreatic tissue and β-cells may explain the concomitant occurrence of pancreatitis and β-cell damage in AIP.

Regulating the regulators: costimulatory signals control the homeostasis and function of regulatory T cells

SUMMARY

Costimulation is a concept that goes back to the early 1980s when Lafferty and others hypothesized that cell surface and soluble molecules must exist that are essential for initiating immune responses subsequent to antigen exposure. The explosion in this field of research ensued as over a dozen molecules have been identified to function as second signals following T-cell receptor engagement. By 1994, it seemed clear that the most prominent costimulatory pathway CD28 and functionally related costimulatory molecules, such as CD154, were the major drivers of a positive immune response. Then the immunology world turned upside down. CD28 knockout mice, which were, in most cases, immunodeficient, led to increased autoimmunity when bred into the non-obese diabetic background. Another CD28 family member, cytotoxic T-lymphocyte-associated protein 4, which was presumed to be a costimulatory molecule on activated T cells, turned out to be critical in downregulating immunity. These results, coupled with the vast suppressor cell literature which had been largely rebuked, suggested that the immune system was not poised for response but controlled in such a way that regulation was dominant. Over the last decade, we have learned that these costimulatory molecules play a key role in the now classical CD4(+)CD25(+)Foxp3(+) regulatory T cells (Tregs) that provide critical control of unwanted autoimmune responses. In this review, we discuss the connections between costimulation and Tregs that have changed the costimulation paradigm.

Identification of QTLs that modify peripheral neuropathy in NOD.H2b-Pdcd1-/- mice

The non-obese diabetic (NOD) mouse strain is prone to developing various autoimmune syndromes including type I diabetes mellitus (T1DM), sialadenitis, thyroiditis and pancreatitis. Although the genetic basis of T1DM has been extensively analyzed, genetic factors that modify the other autoimmune phenotypes are largely unknown. We have recently reported that NOD mice with anti-diabetogenic MHC haplotype (H-2(b)) and programmed cell death 1 (PD-1) deficiency (NOD.H2(b)-Pdcd1(-/-) mice) are protected from T1DM but develop various tissue-specific autoimmune diseases including peripheral neuropathy due to autoimmune neuritis, sialadenitis and gastritis. In the present study, we generated [(C57BL/6 x NOD.H2(b))(F1) x NOD-H2(b)](BC1)-Pdcd1(-/-) mice to screen non-MHC quantitative trait loci (QTLs) that modify autoimmune phenotypes other than T1DM. We identified seven QTLs for peripheral neuropathy and neuritis, one QTL for insulitis, four QTLs for gastritis, two QTLs for sialadenitis and seven QTLs for vasculitis throughout the genome and designated them as Annp loci for autoimmunity due to polymorphisms of non-MHC genes in NOD mice and PD-1 deficiency. Annp1, 5, 6 and 7 overlapped with reported loci for T1DM (Idd3, 9, 15 and 2, respectively), suggesting that these loci modify not only T1DM but also other autoimmune phenotypes. NOD allele was promotive at 9 of 14 Annp loci, while NOD allele was protective at the other loci. Half of Annp loci associated with a single phenotype, while the other seven loci associated with more than two phenotypes. These results indicate that NOD genetic background harbors various QTLs that modify autoimmune phenotypes either by organ-specific or by organ-non-specific manner.