Immunoregulatory pathways controlling progression of autoimmunity in NOD mice

The association of common autoimmune diseases with autoimmune thyroiditis: a two-sample Mendelian randomization study

Objective

Numerous observational and retrospective studies have demonstrated an association between Autoimmune Thyroiditis (AIT) and various systemic Autoimmune Diseases (AIDs). However, the causal relationship between them remains uncertain. This study aims to investigate the causal link between AIT and diverse types of AIDs utilizing the Mendelian Randomization (MR) method.

Method

We assessed the causal relationship between AIT and eight prevalent AIDs. Summary statistics from genome-wide association studies (GWAS) were sourced from the FinnGen biobank and IEU Open GWAS database. Two-sample MR analyses were conducted, with the primary statistical approach being the Inverse Variance Weighting (IVW) method. This was complemented by a series of sensitivity analyses, and the robustness of the findings was evaluated through the estimation of heterogeneity and pleiotropy.

Results

When AIT was considered as the outcome, MR evidence suggested an association between Rheumatoid arthritis (RA), Type 1 diabetes (T1D), and Systemic lupus erythematosus (SLE) with AIT. Utilizing the Inverse Variance Weighting (IVW) method, we observed an increased risk of AIT with exposure to RA (P = 0.024, OR=1.25; 95% CI = 1.03, 1.52), T1D (P < 0.001, OR=1.27 95% CI = 1.11,1.46), and SLE (P = 0.037, OR=1.14; 95% CI = 1.04,1.26). Conversely, no significant genetic causal relationship with AIT was found for Sjögren's syndrome (SS), Ankylosing Spondylitis (AS), Multiple sclerosis (MS), Crohn's disease (CD), and Ulcerative colitis (UC).

Conclusion

This study identified RA, T1D, and SLE as triggering factors for AIT. The incidence rate of AIT in patients with RA, T1D, and SLE may be higher than that in the general population. Therefore, individuals with these three diseases should undergo regular monitoring of thyroid-related indicators.

Immune checkpoint modulators in early clinical development for the treatment of type 1 diabetes

INTRODUCTION

Despite the improvements of insulin therapy, people with type 1 diabetes (T1D) still suffer from a decreased quality of life and life expectancy. The search toward a cure for T1D is therefore still a scorching open field of research.

AREAS COVERED

Tackling the immune checkpoint signaling pathways has gained importance in the field of cancer immunotherapy. The same pathways can be targeted in autoimmunity with an opposite principle: to dampen the exaggerated immune response. In this review, we report a comprehensive excursus on the cellular and molecular mechanisms that lead to loss of immunological tolerance, and recent evidence on the role of immune checkpoint molecules in the development of T1D and their potential application for the mitigation of autoimmune diabetes.

EXPERT OPINION

Contrasting results about the efficacy of immune checkpoint modulators for T1D have been published, with very few molecules from preclinical studies eligible for use in humans. The heterogeneous and complex pathophysiology of T1D may explain the conflicting evidence. Designing clinical trials that acknowledge the pathophysiological and clinical complexity of T1D and that forecast the need of simultaneously tackling different disease pathways will be crucial to enhance the benefits which may be gained by such compounds.

Current understanding of CTLA-4: from mechanism to autoimmune diseases

Autoimmune diseases (ADs) are characterized by the production of autoreactive lymphocytes, immune responses to self-antigens, and inflammation in related tissues and organs. Cytotoxic T-lymphocyte antigen 4 (CTLA-4) is majorly expressed in activated T cells and works as a critical regulator in the inflammatory response. In this review, we first describe the structure, expression, and how the signaling pathways of CTLA-4 participate in reducing effector T-cell activity and enhancing the immunomodulatory ability of regulatory T (Treg) cells to reduce immune response, maintain immune homeostasis, and maintain autoimmune silence. We then focused on the correlation between CTLA-4 and different ADs and how this molecule regulates the immune activity of the diseases and inhibits the onset, progression, and pathology of various ADs. Finally, we summarized the current progress of CTLA-4 as a therapeutic target for various ADs.

Understanding the Mechanism of Diabetes Mellitus in a LRBA-Deficient Patient

The scope of this study is to show that DM in a LRBA-deficient patient with a stop codon mutation (c.3999 G > A) was not mediated through autoimmunity. We have evaluated the ability of the proband’s T cells to be activated by assessing their CTLA-4 expression. A nonsignificant difference was seen in the CTLA-4 expression on CD3+ T cells compared to the healthy control at basal level and after stimulation with PMA/ionomycin. Blood transcriptomic analysis have shown a remarkable increase in abundance of transcripts related to CD71+ erythroid cells. There were no differences in the expression of modules related to autoimmunity diseases between the proband and pooled healthy controls. In addition, our novel findings show that siRNA knockdown of LRBA in mouse pancreatic β-cells leads reduced cellular proinsulin, insulin and consequently insulin secretion, without change in cell viability in cultured MIN6 cells.

IL-4 and IL-17 Are Required for House Dust Mite-Driven Airway Hyperresponsiveness in Autoimmune Diabetes-Prone Non-Obese Diabetic Mice

Allergic asthma is characterized by airway inflammation with a Th2-type cytokine profile, hyper-IgE production, mucus hypersecretion, and airway hyperreactivity (AHR). It is increasingly recognized that asthma is a heterogeneous disease implicating complex immune mechanisms resulting in distinct endotypes observed in patients. In this study, we showed that non-obese diabetic (NOD) mice, which spontaneously develop autoimmune diabetes, undergo more severe allergic asthma airway inflammation and AHR than pro-Th2 BALB/c mice upon house dust mite (HDM) sensitization and challenge. The use of IL-4-deficient NOD mice and the in vivo neutralization of IL-17 demonstrated that both IL-4 and IL-17 are responsible by the exacerbated airway inflammation and AHR observed in NOD mice. Overall, our findings indicate that autoimmune diabetes-prone NOD mice might become useful as a new HDM-induced asthma model to elucidate allergic dysimmune mechanisms involving Th2 and Th17 responses that could better mimic some asthmatic endoytpes.

Deranged regulatory T-cells and transforming growth factor-β1 levels in type 1 diabetes patients with associated autoimmune diseases

Aim:

This study was designed to enumerate regulatory T-cells (Tregs) and estimate transforming growth factor-β1 (TGF-β1) levels in type 1 diabetic (T1D) patients with respect to disease duration and associated autoimmune diseases.

Methods:

One hundred and fifty patients and twenty healthy controls were recruited in the study. The patients were subcategorized into eight categories on the basis of disease duration (new onset [NO] and long standing [LS]) and associated diseases, i.e., celiac disease (CD) and autoimmune thyroid disease (AiTD). Treg cells were assessed as CD4⁺ CD25^hi+, FOXP3⁺ cells and serum TGF-β1 levels were assessed by ELISA.

Results:

The frequency of Tregs and levels of TGF-β1 were significantly increased in the patients compared to the healthy controls. Among the different categories of the patients, no significant differences were seen for TGF- β1 levels, but for Tregs in patients with T1D and AiTD (P = 0.035). A significant correlation was also found between percentage count of Tregs and TGF-β1 levels in NO cases in all disease subcategories, but not in LS patients.

Conclusion:

Thus, there was an increased percentage of Tregs and serum levels of TGF-β1 in T1D patients, irrespective of the disease duration and associated autoimmune diseases. The significant correlation in these two parameters at the onset of the disease, but not in LS disease, indicates that the immunological milieu in LS autoimmune diseases is more complicated with disease-associated conditions such as prolonged hyperglycemia, insulin therapy, and/or continued gluten in diet. Treatment and modulation of these long-term complications for improving immunological parameters require further research.

The induction of autoimmune hepatitis in the human leucocyte antigen-DR4 non-obese diabetic mice autoimmune hepatitis mouse model

Autoimmune hepatitis (AIH) is a chronic liver disease characterized by progressive inflammation, female preponderance and seropositivity for autoantibodies such as anti-smooth muscle actin and/or anti-nuclear, anti-liver kidney microsomal type 1 (anti-LKM1) and anti-liver cytosol type 1 (anti-LC1) in more than 80% of cases. AIH is linked strongly to several major histocompatibility complex (MHC) alleles, including human leucocyte antigen (HLA)-DR3, -DR7 and -DR13. HLA-DR4 has the second strongest association with adult AIH, after HLA-DR3. We investigated the role of HLA-DR4 in the development of AIH by immunization of HLA-DR4 (DR4) transgenic non-obese diabetic (NOD) mice with DNA coding for human CYP2D6/FTCD fusion autoantigen. Immunization of DR4 mice leads to sustained mild liver injury, as assessed biochemically by elevated alanine aminotransferase, histologically by interface hepatitis, plasma cell infiltration and mild fibrosis and immunologically by the development of anti-LKM1/anti-LC1 antibodies. In addition, livers from DR4 mice had fewer regulatory T cells (T_regs ), which had decreased programmed death (PD)-1 expression. Splenic T_regs from these mice also showed impaired inhibitory capacity. Furthermore, DR4 expression enhanced the activation status of CD8⁺ T cells, macrophages and dendritic cells in naive DR4 mice compared to naive wild-type (WT) NOD mice. Our results demonstrate that HLA-DR4 is a susceptibility factor for the development of AIH. Impaired suppressive function of T_regs and reduced PD-1 expression may result in spontaneous activation of key immune cell subsets, such as antigen-presenting cells and CD8⁺ T effectors, facilitating the induction of AIH and persistent liver damage.

A novel "humanized mouse" model for autoimmune hepatitis and the association of gut microbiota with liver inflammation

Autoimmune hepatitis (AIH) in humans is a severe inflammatory liver disease characterized by interface hepatitis, the presence of circulating autoantibodies, and hyper-gammaglobulinemia. There are two types of AIH, type 1 (AIH-1) and type 2 (AIH-2), characterized by distinct autoimmune serology. Patients with AIH-1 are positive for anti-smooth muscle and/or antinuclear autoantibodies, whereas patients with AIH-2 have anti-liver kidney microsomal type 1 and/or anti-liver cytosol type 1 autoantibodies. Cytochrome P4502D6 is the antigenic target of anti-liver kidney microsomal type 1, and formiminotransferase cyclodeaminase is the antigenic target of anti-liver cytosol type 1. It is known that AIH, both types 1 and 2, is strongly linked to the human leukocyte antigen (HLA) alleles -DR3, -DR4, and -DR7. However, direct evidence of the association of HLA with AIH is lacking. We developed a novel mouse model of AIH using the HLA-DR3 transgenic mouse on the nonobese-diabetic background by immunization of HLA-DR3- and HLA-DR3+ nonobese-diabetic mice with a DNA plasmid, coding for human cytochrome P4502D6/formiminotransferase cyclodeaminase fusion protein. Immunization with cytochrome P4502D6/formiminotransferase cyclodeaminase leads to a sustained elevation of alanine aminotransferase, development of antinuclear autoantibodies and anti-liver kidney microsomal type 1/anti-liver cytosol type 1 autoantibodies, chronic immune cell infiltration, and parenchymal fibrosis on liver histology in HLA-DR3+ mice. Immunized mice also showed an enhanced T helper 1 immune response and paucity of the frequency of regulatory T cells in the liver. Moreover, HLA-DR3+ mice with exacerbated AIH showed reduced diversity and total load of gut bacteria.

CONCLUSION

Our humanized animal model has provided a novel experimental tool to further elucidate the pathogenesis of AIH and to evaluate the efficacy and safety of immunoregulatory therapeutic interventions in vivo.

A Short Peptide That Mimics the Binding Domain of TGF-β1 Presents Potent Anti-Inflammatory Activity

The transforming growth factor beta 1 (TGF-β1) is a pleiotropic cytokine with multiple roles in development, wound healing, and immune regulation. TGF-β1-mediated immune dysfunction may lead to pathological conditions, such as inflammation. Chronic inflammatory process is characterized by a continuous release of pro-inflammatory cytokines, and the inhibition or the blockage of these cytokines signaling pathways are considered a target treatment. In this context, despite the high numbers of TGF-β-targeted pathways, the inducible regulatory T cells (iTreg) to control inflammation seems to be a promising approach. Our aim was to develop novel peptides through phage display (PhD) technology that could mimic TGF-β1 function with higher potency. Specific mimetic peptides were obtained through a PhD subtraction strategy from whole cell binding using TGF-β1 recombinant as a competitor during elution step. We have selected a peptide that seems to play an important role on cellular differentiation and modulation of TNF-α and IL-10 cytokines. The synthetic pm26TGF-β1 peptide tested in PBMC significantly down-modulated TNF-α and up-regulated IL-10 responses, leading to regulatory T cells (Treg) phenotype differentiation. Furthermore, the synthetic peptide was able to decrease leukocytes rolling in BALB/C mice and neutrophils migration during inflammatory process in C57BL/6 mice. These data suggest that this peptide may be useful for the treatment of inflammatory diseases, especially because it displays potent anti-inflammatory properties and do not exhibit neutrophils’ chemoattraction.

Involvement of the IL-23/IL-17 axis and the Th17/Treg balance in the pathogenesis and control of autoimmune arthritis

The T helper (Th) cell subsets are characterized by the type of cytokines produced and the master transcription factor expressed. Th1 cells participate in cell-mediated immunity, whereas Th2 cells promote humoral immunity. Furthermore, the two subsets can control each other. Thereby, Th1-Th2 balance offered a key paradigm in understanding the induction and regulation of immune pathology in autoimmune and other diseases. However, over the past decade, Th17 cells producing interleukin-17 (IL-17) have emerged as the major pathogenic T cell subset in many pathological conditions that were previously attributed to Th1 cells. In addition, the role of CD4+CD25+T regulatory cells (Treg) in controlling the activity of Th17 and other T cell subsets has increasingly been realized. Thereby, examination of the Th17/Treg balance in the course of autoimmune diseases has significantly advanced our understanding of the pathogenesis of these disorders. The differentiation of Th17 and Treg cells from naïve T cells is inter-related and controlled in part by the cytokine milieu. For example, transforming growth factor β (TGFβ) is required for Treg induction, whereas the same cytokine in the presence of IL-6 (or IL-1) promotes the differentiation of Th17. Furthermore, IL-23 plays a role in the maintenance of Th17. Accordingly, novel therapeutic approaches are being developed to target IL-23/IL-17 as well as to modulate the Th17/Treg balance in favor of immune regulation to control autoimmunity.

Role of ITGAE in the development of autoimmune diabetes in non-obese diabetic mice

There is compelling evidence that autoreactive CD8(+)T cells play a central role in precipitating the development of autoimmune diabetes in non-obese diabetic (NOD) mice, but the underlying mechanisms remain unclear. Given that ITGAE (CD103) recognizes an islet-restricted ligand (E-cadherin), we postulated that its expression is required for initiation of disease. We herein use a mouse model of autoimmune diabetes (NOD/ShiLt mice) to test this hypothesis. We demonstrate that ITGAE is expressed by a discrete subset of CD8(+)T cells that infiltrate pancreatic islets before the development of diabetes. Moreover, we demonstrate that development of diabetes in Itgae-deficient NOD mice is significantly delayed at early but not late time points, indicating that ITGAE is preferentially involved in early diabetes development. To rule out a potential contribution by closely linked loci to this delay, we treated WT NOD mice beginning at 2 weeks of age through 5 weeks of age with a depleting anti-ITGAE mAb and found a decreased incidence of diabetes following anti-ITGAE mAb treatment compared with mice that received isotype control mAbs or non-depleting mAbs to ITGAE. Moreover, a histological examination of the pancreas of treated mice revealed that NOD mice treated with a depleting mAb were resistant to immune destruction. These results indicate that ITGAE(+) cells play a key role in the development of autoimmune diabetes and are consistent with the hypothesis that ITGAE(+)CD8(+)T effectors initiate the disease process.

Moderate Intensity Training Impact on the Inflammatory Status and Glycemic Profiles in NOD Mice

The nonobese diabetic (NOD) mouse represents a well-established experimental model analogous to human type 1 diabetes mellitus (T1D) as it is characterized by progressive autoimmune destruction of pancreatic β-cells. Experiments were designed to investigate the impact of moderate-intensity training on T1D immunomodulation and inflammation. Under a chronic exercise regime, NOD mice were trained on a treadmill for 12 weeks (12 m/min for 30 min, 5 d/wk) while age-matched, control animals were left untrained. Prior to and upon completion of the training period, fed plasma glucose and immunological soluble factors were monitored. Both groups showed deteriorated glycemic profiles throughout the study although trained mice tended to be more compensated than controls after 10 weeks of training. An exercise-induced weight loss was detected in the trained mice with respect to the controls from week 6. After 12 weeks, IL-6 and MIP-1β were decreased in the trained animals compared to their baseline values and versus controls, although not significantly. Morphometric analysis of pancreata revealed the presence of larger infiltrates along with decreased α-cells areas in the control mice compared to trained mice. Exercise may exert positive immunomodulation of systemic functions with respect to both T1D and inflammation, but only in a stringent therapeutic window.

Regulatory T cells with CD62L or TNFR2 expression in young type 1 diabetic patients: relation to inflammation, glycemic control and micro-vascular complications

BACKGROUND

Alteration of regulatory T cells (Tregs) may contribute to ineffective suppression of proinflammatory cytokines in type 1 diabetes.

AIM

We determined the percentage of Tregs expressing CD62L or tumor necrosis factor receptor type 2 (TNFR2) in 70 young type 1 diabetic patients compared with 30 controls and assessed their relation to inflammation, glycemic control and micro-vascular complications.

METHODS

High-sensitivity C-reactive protein (hs-CRP), hemoglobin A1c (HbA1c), tumor necrosis factor alpha (TNF-α) and interleukin-10 (IL-10) were assessed with flow cytometric analysis of Tregs, Tregs expressing CD62L or TNFR2.

RESULTS

The percentage of CD4(+)CD25(high) T cells and CD4(+)CD25(high)CD62L(high) cells were significantly decreased while CD4(+)CD25(high)TNFR2(+) T cells were elevated in patients with micro-vascular complications than those without and controls (p<0.001). ROC curve revealed that the cutoff values of Tregs, Tregs expressing CD62L and Tregs expressing TNFR2 (7.46%, 24.2% and 91.9%, respectively) could detect micro-vascular complications. Significant negative correlations were observed between Tregs expressing CD62L and disease duration, FBG, HbA1c, urinary albumin excretion and hs-CRP, whereas, positive correlations were found between Tregs expressing TNFR2 and these variables (p<0.05). TNF-α was significantly increased while IL-10 was decreased among patients with micro-vascular complications than those without (p<0.05).

CONCLUSIONS

Alteration in the frequency of Tregs and Tregs expressing CD62L or TNFR2 in type 1 diabetes is associated with increased inflammation, poor glycemic control and risk of micro-vascular complications.

T cell subsets and their signature cytokines in autoimmune and inflammatory diseases

CD4(+) T helper (Th) cells are critical for proper immune cell homeostasis and host defense, but are also major contributors to pathology of autoimmune and inflammatory diseases. Since the discovery of the Th1/Th2 dichotomy, many additional Th subsets were discovered, each with a unique cytokine profile, functional properties, and presumed role in autoimmune tissue pathology. This includes Th1, Th2, Th17, Th22, Th9, and Treg cells which are characterized by specific cytokine profiles. Cytokines produced by these Th subsets play a critical role in immune cell differentiation, effector subset commitment, and in directing the effector response. Cytokines are often categorized into proinflammatory and anti-inflammatory cytokines and linked to Th subsets expressing them. This article reviews the different Th subsets in terms of cytokine profiles, how these cytokines influence and shape the immune response, and their relative roles in promoting pathology in autoimmune and inflammatory diseases. Furthermore, we will discuss whether Th cell pathogenicity can be defined solely based on their cytokine profiles and whether rigid definition of a Th cell subset by its cytokine profile is helpful.

CP-690550 Treatment Ameliorates Established Disease and Provides Long-Term Therapeutic Effects in an SKG Arthritis Model

Although pathogenesis of human rheumatoid arthritis (RA) remains unclear, arthritogenic T cells and downstream signaling mediators have been shown to play critical roles. An increasing numbers of therapeutic options have been added for the effective control of RA. Nevertheless, there is still a category of patients that fails treatment and suffers from progressive disease. The recently developed immunosuppressant CP-690550, a small molecule JAK kinase inhibitor, has been implicated as an important candidate treatment modality for autoimmune arthritis. In this study, we evaluated the therapeutic effect of CP-690550 on established arthritis using an SKG arthritis model, a pathophysiologically relevant animal model for human RA. CP-690550 treatment revealed remarkable long-term suppressive effects on SKG arthritis when administered to the well-advanced disease (clinical score 3.5~4.0). The treatment effect lasted at least 3 more weeks after cessation of drug infusion, and suppression of disease was correlated with the reduced pro-inflammatory cytokines, including IL-17, IFN-γ, and IL-6 and increased level of immunoregulatory IL-10.

Growth hormone prevents the development of autoimmune diabetes

Evidence supports a relationship between the neuroendocrine and the immune systems. Data from mice that overexpress or are deficient in growth hormone (GH) indicate that GH stimulates T and B-cell proliferation and Ig synthesis, and enhances maturation of myeloid progenitor cells. The effect of GH on autoimmune pathologies has nonetheless been little studied. Using a murine model of type 1 diabetes, a T-cell-mediated autoimmune disease characterized by immune cell infiltration of pancreatic islets and destruction of insulin-producing β-cells, we observed that sustained GH expression reduced prodromal disease symptoms and eliminated progression to overt diabetes. The effect involves several GH-mediated mechanisms; GH altered the cytokine environment, triggered anti-inflammatory macrophage (M2) polarization, maintained activity of the suppressor T-cell population, and limited Th17 cell plasticity. In addition, GH reduced apoptosis and/or increased the proliferative rate of β-cells. These results support a role for GH in immune response regulation and identify a unique target for therapeutic intervention in type 1 diabetes.

Regulatory T cells exhibit decreased proliferation but enhanced suppression after pulsing with sirolimus

Although regulatory T cells (Tregs) suppress allo-immunity, difficulties in their large-scale production and in maintaining their suppressive function after expansion have thus far limited their clinical applicability. Here we have used our nonhuman primate model to demonstrate that significant ex vivo Treg expansion with potent suppressive capacity can be achieved and that Treg suppressive capacity can be further enhanced by their exposure to a short pulse of sirolimus. Both unpulsed and sirolimus-pulsed Tregs (SPTs) are capable of inhibiting proliferation of multiple T cell subpopulations, including CD4(+) and CD8(+) T cells, as well as antigen-experienced CD28(+) CD95(+) memory and CD28(-) CD95(+) effector subpopulations. We further show that Tregs can be combined in vitro with CTLA4-Ig (belatacept) to lead to enhanced inhibition of allo-proliferation. SPTs undergo less proliferation in a mixed lymphocyte reaction (MLR) when compared with unpulsed Tregs, suggesting that Treg-mediated suppression may be inversely related to their proliferative capacity. SPTs also display increased expression of CD25 and CTLA4, implicating signaling through these molecules in their enhanced function. Our results suggest that the creation of SPTs may provide a novel avenue to enhance Treg-based suppression of allo-immunity, in a manner amenable to large-scale ex vivo expansion and combinatorial therapy with novel, costimulation blockade-based immunosuppression strategies.

TGF-β and IL-23 gene expression in unstimulated PBMCs of patients with diabetes

The protective effects of TGF-β have been documented in various autoimmune diseases, mostly in organ-specific autoimmunity including type 1 diabetes mellitus (T1DM). However, TGF-β also plays a role as a pro-inflammatory mediator by induction of Th17 cytokine production. IL-23 also plays a key role in differentiation of Th17 cells, which are implicated in pathogenesis of autoimmune conditions including T1DM. The aim of this study was to investigate and compare the difference in the level of TGF-β1 and IL-23 gene expression in unstimulated peripheral blood mononuclear cells (PBMCs) of patients with different forms of diabetes compared with normal healthy controls subjects. Patients with T1DM were grouped as early-onset T1DM (N = 20) with age at diagnosis <18 years and late-onset T1DM (N = 20) with the age at onset >18 years. Patients with T2DM (N = 20) and normal healthy controls (N = 20) were recruited from the same area. TGF-β1 and IL-23 gene expression in fresh unstimulated PBMCs was determined in each group using quantitative real-time PCR. The results confirmed that a significant difference in TGF-β1 and IL-23 gene expression was observed in both forms of juvenile-onset T1DM and adult-onset T1DM compared to the controls and T2DM patients. There was no significant difference for TGF-β gene expression in patients with T2DM and controls. We therefore conclude that our results support the previous data on TGF-β gene down-regulation in T1DM. Also up-regulation of IL-23 has been observed in T1DM whilst it was down-regulated in T2DM. We also found no significant difference between juvenile-onset and adult-onset T1DM indicating same mechanism might be involved in the pathogenesis of both types. More studies on different cytokines in Th17 pathways are required to further confirm our finding.

The soluble CTLA-4 splice variant protects from type 1 diabetes and potentiates regulatory T-cell function

OBJECTIVE

CTLA4 gene variation associates with multiple autoimmune disorders, including type 1 diabetes. The CTLA4 susceptibility allele was found to generate decreased levels of mRNA encoding soluble CTLA-4 (sCTLA-4) relative to the full-length isoform, the functional consequence of which is as yet unknown. In this study, we investigated the contribution of sCTLA-4 to immune regulation with the aim to elucidate the functional basis of the disease association of CTLA4.

RESEARCH DESIGN AND METHODS

To model the disease-associated splicing variation of CTLA4, we generated NOD mice in which sCTLA-4 mRNA is silenced by RNA interference.

RESULTS

We found that loss of sCTLA-4 impairs the function of regulatory T (Treg) cells. This functional defect could be attributed, at least in part, to the failure of sCTLA-4 knockdown (KD) Treg cells to downregulate dendritic cell costimulation. sCTLA-4 KD Treg cells, in contrast with wild-type Treg cells, failed to inhibit colitis induced by transfer of CD4(+)CD45RB(hi) cells into NOD.SCID animals. Furthermore, diminished sCTLA-4 expression accelerated the onset of autoimmune diabetes in transgenic mice.

CONCLUSIONS

Our results demonstrate that sCTLA-4 participates in immune regulation by potentiating the function of Treg cells. The functional outcome of silencing this splice variant in the NOD model provides an explanation for the association of CTLA4 variation with autoimmunity. Lower sCTLA-4 expression from the susceptibility allele may directly affect the suppressive capacity of Treg cells and thereby modulate disease risk. Our unprecedented approach establishes the feasibility of modeling splicing variations relevant to autoimmunity.

Transforming growth factor-beta: recent advances on its role in immune tolerance

Transforming growth factor (TGF-β1) is a pleiotropic cytokine, secreted by immune and nonhematopoietic cells. TGF-β is involved in many different critical processes, such as embryonal development, cellular maturation and differentiation, wound healing, and immune regulation. It maintains immune homeostasis by acting as a potent immune suppressor through inhibition of proliferation, differentiation, activation, and effector function of immune cells. Paradoxically, depending on the context, it displays proinflammatory properties by being a potent chemoattractant for neutrophils and promoting inflammation. In addition, it does not only induce differentiation into the anti-inflammatory Treg cells, but also into the proinflammatory Th17 and Th9 cells and inhibits Th22 differentiation. TGF-β has been demonstrated to be involved in multiple pathologies. In infections, it protects against collateral damages caused by the immune system, but it also promotes immune evasion and chronic infections. In autoimmune diseases, a TGF-β dysfunction leads to the loss of tolerance to self-antigens. In cancer, TGF-β is a potent inhibitor of cell proliferation and acts as a tumor suppressor at the beginning of tumorogenesis. However, once the cells become resistant to TGF-β, it mainly supports tumor growth and metastasis by promoting immune evasion and angiogenesis. In asthma, it is assumed to promote allergen tolerance, but plays a detrimental role in irreversible remodeling of the airways. Despite the high numbers of TGF-β-targeted pathways, it is a promising drug target for treatment of autoimmunity, cancer, fibrosis, if cell specificity can be achieved.This review summarizes the progresses that have been accomplished on the understanding of TGF-β's signaling in the immune homeostasis and its role in pathogenesis.

Dysregulation of thymic clonal deletion and the escape of autoreactive T cells

Events ongoing in the thymus are critical for deleting developing thymocytes specific for tissue antigens, and establishing self-tolerance within the T cell compartment. Aberrant thymic negative selection, however, is believed to generate a repertoire with increased self-reactivity, which in turn can contribute to the development of T cell-mediated autoimmunity. In this review, mechanisms that regulate the efficacy of negative selection and influence the deletion of autoreactive thymocytes will be discussed.

Suppressive and pro-inflammatory roles for IL-4 in the pathogenesis of experimental drug-induced liver injury: a review

IMPORTANCE OF THE FIELD

Idiosyncratic drug reactions resulting in drug-induced liver injury (DILI) account for approximately 13% of acute liver failure cases in the US. Idiosyncratic drug reactions are the third most common cause of liver transplantation, exceeded only by acetaminophen and indeterminate causes. Clinical evidence suggests that idiosyncratic DILI is triggered by drug hapten-altered self proteins resulting in hepatocellular injury. An example of this type of DILI is hepatitis that develops in susceptible individuals following administration of halogenated volatile anesthetics, dihydralazine, carbamazepine or diclofenac.

AREAS COVERED IN THIS REVIEW

In this review, we describe research in animal models that supports a critical role for suppressive and pro-inflammatory roles for IL-4 in the pathogenesis of immune-mediated DILI.

WHAT THE READER WILL GAIN

The reader will gain insights into the roles of IL-4 in the development of experimental DILI. The reader will gain tools to assist in the translation of these findings to those in patients with immune-mediated DILI, as well as other inflammatory diseases of the liver. The reader will then be made aware of gaps in knowledge in the pathogenesis of DILI where research could result in significant advances in the care of these complicated patients.

TAKE HOME MESSAGE

In experimental immune-mediated DILI, IL-4 suppresses regulatory responses to CYP2E1 autoantigens but induces pro-inflammatory responses to drug haptens.

Regulatory T cells and immune tolerance to tumors

Immune cells infiltrate tumors and make up a significant component of the multicellular cancer micro-environment, yet the immune system often fails to prevent tumor formation and progression. One explanation for this paradox is the presence of tolerance-promoting regulatory T cells (Tregs) that counteract antitumor immune cells. Tregs were known to be essential for maintaining self-tolerance. Recently, Tregs have been found to promote tolerance to tumors in mouse models. Moreover, Treg infiltration in human tumors and malignant ascites is associated with worse clinical outcomes for various types of cancers. As many reviews have discussed the development and function of Tregs, this review focuses on the cellular and molecular mechanisms by which Tregs influence antitumor immune responses, and also discusses how these mechanisms might be exploited to develop innovative immune-based approaches that can improve cancer therapy.

The role of the physician-scientist in bridging basic and clinical research in type 1 diabetes

PURPOSE OF REVIEW

In a relatively short time, advances in both basic science and clinical medicine have revolutionized the way we understand disease processes and suggested novel approaches that may be able to be used to treat or cure some of the most relevant human afflictions. In type 1 diabetes, one unintended consequence of this has been the polarization of the investigational groups (i.e., immunologists and endocrinologists) interested in developing novel therapies for this condition. This review will examine how and why such polarization exists, and why past and current approaches to develop critically needed translational investigators may be falling short.

RECENT FINDINGS

Despite significant efforts to increase the number of individuals trained in both basic science and clinical medicine, the number of academic physician-scientists is on the decline. Increased demands from academic institutions coupled with severe difficulty in securing extramural funding are probably playing important roles in this concerning trend.

SUMMARY

Type 1 diabetes will continue to be a significant strain on individuals, their families and society until a cure is found. More than ever, there is a critical need to support appropriately trained translational investigators who can best facilitate bringing the promise of basic research to clinical reality.

Animal models of immune thrombocytopenia (ITP)

With regards to research animal models related to immune thrombocytopenia (ITP), there is an extensive literature of over 300 publications published since 1959. It appears that many of these models either confirm what has been found in human ITP or, in some instances, are the first to describe a phenomenon related to ITP that is still of relevance today in human medicine. These models will undoubtedly play a significant role in the future research of human ITP particularly related to understanding of the pathogenesis of the disorder and the development of novel therapeutics. This review will highlight some of the major animal models utilized for ITP research and will present a somewhat historical aspect of the subject.

Feedback control of regulatory T cell homeostasis by dendritic cells in vivo

CD4⁺CD25⁺Foxp3⁺ natural regulatory T cells (T reg cells) maintain self-tolerance and suppress autoimmune diseases such as type 1 diabetes and inflammatory bowel disease (IBD). In addition to their effects on T cells, T reg cells are essential for maintaining normal numbers of dendritic cells (DCs): when T reg cells are depleted, there is a compensatory Flt3-dependent increase in DCs. However, little is known about how T reg cell homeostasis is maintained in vivo. We demonstrate the existence of a feedback regulatory loop between DCs and T reg cells. We find that loss of DCs leads to a loss of T reg cells, and that the remaining T reg cells exhibit decreased Foxp3 expression. The DC-dependent loss in T reg cells leads to an increase in the number of T cells producing inflammatory cytokines, such as interferon γ and interleukin 17. Conversely, increasing the number of DCs leads to increased T reg cell division and accumulation by a mechanism that requires major histocompatibility complex II expression on DCs. The increase in T reg cells induced by DC expansion is sufficient to prevent type 1 autoimmune diabetes and IBD, which suggests that interference with this feedback loop will create new opportunities for immune-based therapies.

The development and function of regulatory T cells

Regulatory T cells (Tregs) are a critical subset of T cells that mediate peripheral tolerance. There are two types of Tregs: natural Tregs, which develop in the thymus, and induced Tregs, which are derived from naive CD4(+) T cells in the periphery. Tregs utilize a variety of mechanisms to suppress the immune response. While Tregs are critical for the peripheral maintenance of potential autoreactive T cells, they can also be detrimental by preventing effective anti-tumor responses and sterilizing immunity against pathogens. In this review, we will discuss the development of natural and induced Tregs as well as the role of Tregs in a variety of disease settings and the mechanisms they utilize for suppression.

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.