Defective maturation and function of antigen-presenting cells in type 1 diabetes

Targeting macrophages with phosphatidylserine-rich liposomes as a potential antigen-specific immunotherapy for type 1 diabetes

Type 1 diabetes (T1D) results from a breakdown in immunological tolerance, with pivotal involvement of antigen-presenting cells. In this context, antigen-specific immunotherapies have been developed to arrest autoimmunity, such as phosphatidylserine (PS)-liposomes. However, the role of certain antigen-presenting cells in immunotherapy, particularly human macrophages (Mφ) in T1D remains elusive. The aim of this study was to determine the role of Mφ in antigen-specific immune tolerance and T1D. To that end, we evaluated Mφ ability to capture apoptotic-body mimicking PS-liposomes in mice and conducted a phenotypic and functional characterisation of four human monocyte-derived Mφ (MoMφ) subpopulations (M0, M1, M2a and M2c) after PS-liposomes uptake. Our findings in mice identified Mφ as the most phagocytic cell subset in the spleen and liver. In humans, while phagocytosis rates were comparable between T1D and control individuals, PS-liposome capture dynamics differed among Mφ subtypes, favouring inflammatory (M1) and deactivated (M2c) Mφ. Notably, high nanoparticle concentrations did not affect macrophage viability. PS-liposome uptake by Mφ induced alterations in membrane molecule expression related to immunoregulation, reduced secretion of IL-6 and IL-12, and diminished autologous T-cell proliferation in the context of autoantigen stimulation. These results underscore the tolerogenic effects of PS-liposomes and emphasize their potential to target human Mφ, providing valuable insights into the mechanism of action of this preclinical immunotherapy.

Candidate Biomarkers for the Prediction and Monitoring of Partial Remission in Pediatric Type 1 Diabetes

The partial remission (PR) phase, a period experienced by most patients with type 1 diabetes (T1D) soon after diagnosis, is characterized by low insulin requirements and improved glycemic control. Given the great potential of this phase as a therapeutic window for immunotherapies because of its association with immunoregulatory mechanisms and β-cell protection, our objective was to find peripheral immunological biomarkers for its better characterization, monitoring, and prediction. The longitudinal follow-up of 17 pediatric patients with new-onset T1D over one year revealed that, during the PR phase, remitter patients show increased percentages of effector memory (EM) T lymphocytes, terminally differentiated EM T lymphocytes, and neutrophils in comparison to non-remitter patients. On the contrary, remitter patients showed lower percentages of naïve T lymphocytes, regulatory T cells (TREG), and dendritic cells (DCs). After a year of follow-up, these patients also presented increased levels of regulatory B cells and transitional T1 B lymphocytes. On the other hand, although none of the analyzed cytokines (IL-2, IL-6, TGF-β1, IL-17A, and IL-10) could distinguish or predict remission, IL-17A was increased at T1D diagnosis in comparison to control subjects, and remitter patients tended to maintain lower levels of this cytokine than non-remitters. Therefore, these potential monitoring immunological biomarkers of PR support that this stage is governed by both metabolic and immunological factors and suggest immunoregulatory attempts during this phase. Furthermore, since the percentage of TREG, monocytes, and DCs, and the total daily insulin dose at diagnosis were found to be predictors of the PR phase, we next created an index-based predictive model comprising those immune cell percentages that could potentially predict remission at T1D onset. Although our preliminary study needs further validation, these candidate biomarkers could be useful for the immunological characterization of the PR phase, the stratification of patients with better disease prognosis, and a more personalized therapeutic management.

The Idd2 Locus Confers Prominent Resistance to Autoimmune Diabetes

Type 1 diabetes is an autoimmune disease characterized by pancreatic β cell destruction. It is a complex genetic trait driven by >30 genetic loci with parallels between humans and mice. The NOD mouse spontaneously develops autoimmune diabetes and is widely used to identify insulin-dependent diabetes (Idd) genetic loci linked to diabetes susceptibility. Although many Idd loci have been extensively studied, the impact of the Idd2 locus on autoimmune diabetes susceptibility remains to be defined. To address this, we generated a NOD congenic mouse bearing B10 resistance alleles on chromosome 9 in a locus coinciding with part of the Idd2 locus and found that NOD.B10-Idd2 congenic mice are highly resistant to diabetes. Bone marrow chimera and adoptive transfer experiments showed that the B10 protective alleles provide resistance in an immune cell-intrinsic manner. Although no T cell-intrinsic differences between NOD and NOD.B10-Idd2 mice were observed, we found that the Idd2 resistance alleles limit the formation of spontaneous and induced germinal centers. Comparison of B cell and dendritic cell transcriptome profiles from NOD and NOD.B10-Idd2 mice reveal that resistance alleles at the Idd2 locus affect the expression of specific MHC molecules, a result confirmed by flow cytometry. Altogether, these data demonstrate that resistance alleles at the Idd2 locus impair germinal center formation and influence MHC expression, both of which likely contribute to reduced diabetes incidence.

1,25-dihydroxyvitamin D3 induces stable and reproducible therapeutic tolerogenic dendritic cells with specific epigenetic modifications

Autologous, antigen-specific, tolerogenic dendritic cells (tolDCs) are presently assessed to reverse and possibly cure autoimmune diseases such as type 1 diabetes (T1D). Good Manufacturing Practice production and clinical implementation of such cell therapies critically depend on their stability and reproducible production from healthy donors and, more importantly, patient-derived monocytes. Here the authors demonstrate that tolDCs (modulated using 1,25-dihydroxyvitamin D3 and dexamethasone) displayed similar features, including protein, transcriptome and epigenome profiles, between two international clinical centers and between T1D and healthy donors, validating reproducible production. In addition, neither phenotype nor function of tolDCs was affected by repeated stimulation with inflammatory stimuli, underscoring their stability as semi-mature DCs. Furthermore, tolDCs exhibited differential DNA methylation profiles compared with inflammatory mature DCs (mDCs), and this was already largely established prior to maturation, indicating that tolDCs are locked into an immature state. Finally, approximately 80% of differentially expressed known T1D risk genes displayed a corresponding differential DNA methylome in tolDCs versus mDCs and metabolic and immune pathway genes were also differentially methylated and expressed. In summary, tolDCs are reproducible and stable clinical cell products unaffected by the T1D status of donors. The observed stable, semi-mature phenotype and function of tolDCs are exemplified by epigenetic modifications representative of immature-stage cells. Together, the authors’ data provide a strong basis for the production and clinical implementation of tolDCs in the treatment of autoimmune diseases such as T1D.

Islet-Resident Dendritic Cells and Macrophages in Type 1 Diabetes: In Search of Bigfoot's Print

The classical view of type 1 diabetes assumes that the autoimmune mediated targeting of insulin producing ß-cells is caused by an error of the immune system. Malfunction and stress of beta cells added the target tissue at the center of action. The innate immune system, and in particular islet-resident cells of the myeloid lineage, could function as a link between stressed ß-cells and activation and recognition by the adaptive immune system. We survey the role of islet-resident macrophages and dendritic cells in healthy islet homeostasis and pathophysiology of T1D. Knowledge of islet-resident antigen presenting cells in rodents is substantial, but quite scarce in humans, in particular regarding dendritic cells. Differences in blood between healthy and diseased individuals were reported, but it remains elusive to what extend these contribute to T1D onset. Increasing our understanding of the interaction between ß-cells and innate immune cells may provide new insights into disease initiation and development that could ultimately point to future treatment options. Here we review current knowledge of islet-resident macrophages and dendritic cells, place these in context of current clinical trials, and guide future research.

Dual-Sized Microparticle System for Generating Suppressive Dendritic Cells Prevents and Reverses Type 1 Diabetes in the Nonobese Diabetic Mouse Model

Antigen specificity is a primary goal in developing curative therapies for autoimmune disease. Dendritic cells (DCs), as the most effective antigen presenting cells in the body, represent a key target to mediate restoration of antigen-specific immune regulation. Here, we describe an injectable, dual-sized microparticle (MP) approach that employs phagocytosable ∼1 μm and nonphagocytosable ∼30 μm MPs to deliver tolerance-promoting factors both intracellularly and extracellularly, as well as the type 1 diabetes autoantigen, insulin, to DCs for reprogramming of immune responses and remediation of autoimmunity. This poly(lactic-co-glycolic acid) (PLGA) MP system prevented diabetes onset in 60% of nonobese diabetic (NOD) mice when administered subcutaneously in 8 week old mice. Prevention of disease was dependent upon antigen inclusion and required encapsulation of factors in MPs. Moreover, administration of this “suppressive-vaccine” boosted pancreatic lymph node and splenic regulatory T cells (Tregs), upregulated PD-1 on CD4⁺ and CD8⁺ T cells, and reversed hyperglycemia for up to 100 days in recent-onset NOD mice. Our results demonstrate that a MP-based platform can reeducate the immune system in an antigen-specific manner, augment immunomodulation compared to soluble administration of drugs, and provide a promising alternative to systemic immunosuppression for autoimmunity.

LPS enhances CTB-INSULIN induction of IDO1 and IL-10 synthesis in human dendritic cells

Autoantigen-specific immunotherapy promises effective treatment for devastating tissue specific autoimmune diseases like multiple sclerosis (MS) and type 1 diabetes (T1D). Because activated dendritic cells (DCs) stimulate the differentiation of autoreactive T cells involved in the initiation of autoimmunity, blocking the activation of DCs may be an effective strategy for inhibiting tissue specific autoimmunity. Following this approach, immature DCs were shown to remain inactive after treatment with chimeric fusion proteins composed of the cholera toxin B subunit adjuvant linked to autoantigens like proinsulin (CTB-INS). Mass spectrometer analysis of human DCs treated with CTB-INS suggest that upregulation of the tryptophan catabolic enzyme indoleamine 2, 3-dioxygenase (IDO1) is responsible for inhibiting DC activation thereby resulting in a state of immunological tolerance within the DC. Here we show that the fusion protein CTB-INS inhibits human monocyte derived DC (moDC) activation through stimulation of IDO1 biosynthesis and that the resultant state of DC tolerance can be further enhanced by the presence of residual E. coli lipopolysaccharide (LPS) present in partially purified CTB-INS preparations. Additional experiments showed that LPS enhancement of DC tolerance was dependent upon stimulation of IDO1 biosynthesis. LPS stimulation of increased levels of IDO1 in the DC resulted in increased secretion of kynurenines, tryptophan degradation products known to suppress DC mediated pro-inflammatory T cell differentiation and to stimulate the proliferation of regulatory T cells (Tregs). Further, the presence of LPS in CTB-INS treated DCs stimulated the biosynthesis of costimulatory factors CD80 and CD86 but failed to upregulate maturation factor CD83, suggesting CTB-INS treated DCs may be maintained in a state of semi-activation. While treatment of moDCs with increasing amounts of LPS free CTB-INS was shown to increase DC secretion of the anti-inflammatory cytokine IL-10, the presence of residual LPS in partially purified CTB-INS preparations dramatically increased IL-10 secretion, suggesting that CTB-INS may enhance DC mediated immunological tolerance by stimulating the proliferation of anti-inflammatory T cells. While the extraction of LPS from bacterial generated CTB-INS may remove additional unknown factors that may contribute to the regulation of IDO1 levels, together, our experimental data suggest that LPS stimulates the ability of CTB-INS to induce IDO1 and IL-10 important factors required for establishment of a state of functional immunological tolerance in human DCs. Regulation of the ratio of LPS to CTB-INS may prove to be an effective method for optimization of readily available "off the shelf" CTB-INS mediated immune-therapy for tissue specific autoimmune diseases including type 1 diabetes.

Hyperglycaemia is inversely correlated with live M. bovis BCG-specific CD4+ T cell responses in Tanzanian adults with latent or active tuberculosis

Introduction

The rising prevalence of Diabetes mellitus (DM) in high TB‐endemic countries may adversely affect sustainability of TB control since DM constitutes a risk factor for development of active tuberculosis (TB). The impact of DM on TB specific adaptive immune responses remains poorly addressed, particularly in people living in Sub‐Saharan countries. We performed a functional characterization of TB specific cellular immune response in Tanzanian subjects with active or latent Mycobacterium tuberculosis (Mtb) infection stratified by their diabetic status.

Methods

HIV negative active TB patients (≥18 years) with Xpert MTB/RIF positive pulmonary TB were included before starting TB treatment in Dar es Salaam, Tanzania between April and December 2013. HIV negative healthy controls latently infected with TB but without past TB history were also included. Active and latent TB patients were stratified in two groups according to their diabetic status. Peripheral Blood Mononuclear cells were stimulated with either live M. bovis BCG or Mtb‐specific peptide pools and analyzed by intracellular cytokine staining and polychromatic flow cytometry.

Results

Our results show a lower frequency of IFN‐γ CD4⁺ T cells in patients with active TB and DM compared to patients with active TB only after live M. bovis BCG (p = 0.04) but not after Mtb peptide pools re‐stimulation. Irrespective of TB status, level of glycaemia is selectively inversely correlated with IFN‐γ and TNF‐α CD4⁺ T cell production (p = 0.02 and p = 0.03) after live M. bovis BCG stimulation.

Conclusions

These results support the hypothesis that hyperglycaemia negatively impacts antigen processing and/or presentation of whole mycobacteria delaying secretion of key cytokines involved in TB immunity.

Topical Prostaglandin E Analog Restores Defective Dendritic Cell-Mediated Th17 Host Defense Against Methicillin-Resistant Staphylococcus Aureus in the Skin of Diabetic Mice

People with diabetes are more prone to Staphylococcus aureus skin infection than healthy individuals. Control of S. aureus infection depends on dendritic cell (DC)-induced T-helper 17 (Th17)-mediated neutrophil recruitment and bacterial clearance. DC ingestion of infected apoptotic cells (IACs) drive prostaglandin E₂ (PGE₂) secretion to generate Th17 cells. We speculated that hyperglycemia inhibits skin DC migration to the lymph nodes and impairs the Th17 differentiation that accounts for poor skin host defense in diabetic mice. Diabetic mice showed increased skin lesion size and bacterial load and decreased PGE₂ secretion and Th17 cells compared with nondiabetic mice after methicillin-resistant S. aureus (MRSA) infection. Bone marrow-derived DCs (BMDCs) cultured in high glucose (25 mmol/L) exhibited decreased Ptges mRNA expression, PGE₂ production, lower CCR7-dependent DC migration, and diminished maturation after recognition of MRSA-IACs than BMDCs cultured in low glucose (5 mmol/L). Similar events were observed in DCs from diabetic mice infected with MRSA. Topical treatment of diabetic mice with the PGE analog misoprostol improved host defense against MRSA skin infection by restoring DC migration to draining lymph nodes, Th17 differentiation, and increased antimicrobial peptide expression. These findings identify a novel mechanism involved in poor skin host defense in diabetes and propose a targeted strategy to restore skin host defense in diabetes.

Seroprotection status of hepatitis B and measles vaccines in children with type 1 diabetes mellitus

BACKGROUND

Type 1 diabetes mellitus (T1DM) is speculated to have an impaired immunological response to vaccines. This paper aimed to investigate the presence of specific antibodies against hepatitis B virus (HBV) and measles in diabetic children who had been immunized according to the standard national calendar of immunization.

METHODS

Two hundred and one diabetic children and 140 healthy controls were prospectively evaluated. Antibodies against hepatitis B (anti-HBs) and measles were detected in all individuals who completed the vaccination schedule. We noted onset of T1DM, duration of the disease, diabetes-related autoantibodies and mean HbA1c levels.

RESULTS

Some 72.6% of diabetics and 82.1% of controls had anti-HBs (+) (p=0.04). We found a reduced efficacy of measles vaccination in anti-HBs (-) diabetic children (p=0.009), even though there was no significant difference between the study and control groups. Onset of the disease was earlier in anti-HBs (-) diabetics than in controls (p=0.038). No difference with respect to other parameters was found.

CONCLUSIONS

Our data showed a reduced seroprotection rate for HBV vaccination in diabetic children and for measles with anti-HBs (-) diabetics. Larger studies should be encouraged to confirm the vaccine efficacy in diabetic children and to elucidate possible pathogenic mechanisms.

Apoptosis in pancreatic β-islet cells in Type 2 diabetes

Apoptosis plays important roles in the pathophysiology of Type 2 diabetes mellitus (T2DM). The etiology of T2DM is multifactorial, including obesity-associated insulin resistance, defective insulin secretion, and loss of β-cell mass through β-cell apoptosis. β-cell apoptosis is mediated through a milliard of caspase family cascade machinery in T2DM. The glucose-induced insulin secretion is the principle pathophysiology of diabetes and insufficient insulin secretion results in chronic hyperglycemia, diabetes. Recently, hyperglycemia-induced β-cell apoptosis has been extensively studied on the balance of pro-apoptotic Bcl-2 proteins (Bad, Bid, Bik, and Bax) and anti-apoptotic Bcl family (Bcl-2 and Bcl-xL) toward apoptosis in vitro isolated islets and insulinoma cell culture. Apoptosis can only occur when the concentration of pro-apoptotic Bcl-2 exceeds that of anti-apoptotic proteins at the mitochondrial membrane of the intrinsic pathway. A bulk of recent research on hyperglycemia-induced apoptosis on β-cells unveiled complex details on glucose toxicity on β-cells in molecular levels coupled with cell membrane potential by adenosine triphosphate generation through K+ channel closure, opening Ca2+ channel and plasma membrane depolarization. Furthermore, animal models using knockout mice will shed light on the basic understanding of the pathophysiology of diabetes as a glucose metabolic disease complex, on the balance of anti-apoptotic Bcl family and pro-apoptotic genes. The cumulative knowledge will provide a better understanding of glucose metabolism at a molecular level and will lead to eventual prevention and therapeutic application for T2DM with improving medications.

DCIR2+ cDC2 DCs and Zbtb32 Restore CD4+ T-Cell Tolerance and Inhibit Diabetes

During autoimmunity, the normal ability of dendritic cells (DCs) to induce T-cell tolerance is disrupted; therefore, autoimmune disease therapies based on cell types and molecular pathways that elicit tolerance in the steady state may not be effective. To determine which DC subsets induce tolerance in the context of chronic autoimmunity, we used chimeric antibodies specific for DC inhibitory receptor 2 (DCIR2) or DEC-205 to target self-antigen to CD11b(+) (cDC2) DCs and CD8(+) (cDC1) DCs, respectively, in autoimmune-prone nonobese diabetic (NOD) mice. Antigen presentation by DCIR2(+) DCs but not DEC-205(+) DCs elicited tolerogenic CD4(+) T-cell responses in NOD mice. β-Cell antigen delivered to DCIR2(+) DCs delayed diabetes induction and induced increased T-cell apoptosis without interferon-γ (IFN-γ) or sustained expansion of autoreactive CD4(+) T cells. These divergent responses were preceded by differential gene expression in T cells early after in vivo stimulation. Zbtb32 was higher in T cells stimulated with DCIR2(+) DCs, and overexpression of Zbtb32 in T cells inhibited diabetes development, T-cell expansion, and IFN-γ production. Therefore, we have identified DCIR2(+) DCs as capable of inducing antigen-specific tolerance in the face of ongoing autoimmunity and have also identified Zbtb32 as a suppressive transcription factor that controls T cell-mediated autoimmunity.

The gene expression profile of CD11c+ CD8α- dendritic cells in the pre-diabetic pancreas of the NOD mouse

Two major dendritic cell (DC) subsets have been described in the pancreas of mice: The CD11c+ CD8α- DCs (strong CD4+ T cell proliferation inducers) and the CD8α+ CD103+ DCs (T cell apoptosis inducers). Here we analyzed the larger subset of CD11c+ CD8α- DCs isolated from the pancreas of pre-diabetic NOD mice for genome-wide gene expression (validated by Q-PCR) to elucidate abnormalities in underlying gene expression networks. CD11c+ CD8α- DCs were isolated from 5 week old NOD and control C57BL/6 pancreas. The steady state pancreatic NOD CD11c+ CD8α- DCs showed a reduced expression of several gene networks important for the prime functions of these cells, i.e. for cell renewal, immune tolerance induction, migration and for the provision of growth factors including those for beta cell regeneration. A functional in vivo BrdU incorporation test showed the reduced proliferation of steady state pancreatic DC. The reduced expression of tolerance induction genes (CD200R, CCR5 and CD24) was supported on the protein level by flow cytometry. Also previously published functional tests on maturation, immune stimulation and migration confirm the molecular deficits of NOD steady state DC. Despite these deficiencies NOD pancreas CD11c+ CD8α- DCs showed a hyperreactivity to LPS, which resulted in an enhanced pro-inflammatory state characterized by a gene profile of an enhanced expression of a number of classical inflammatory cytokines. The enhanced up-regulation of inflammatory genes was supported by the in vitro cytokine production profile of the DCs. In conclusion, our data show that NOD pancreatic CD11c+ CD8α- DCs show various deficiencies in steady state, while hyperreactive when encountering a danger signal such as LPS.

1,25-Dihydroxyvitamin D3 promotes tolerogenic dendritic cells with functional migratory properties in NOD mice

The biologically active form of vitamin D, 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], is able to promote the generation of tolerogenic mature dendritic cells (mDCs) with an impaired ability to activate autoreactive T cells. These cells could represent a reliable tool for the promotion or restoration of Ag-specific tolerance through vaccination strategies, for example in type 1 diabetes patients. However, successful transfer of 1,25(OH)2D3-treated mDCs (1,25D3-mDCs) depends on the capacity of 1,25(OH)2D3 to imprint a similar tolerogenic profile in cells derived from diabetes-prone donors as from diabetes-resistant donors. In this study, we examined the impact of 1,25(OH)2D3 on the function and phenotype of mDCs originating from healthy (C57BL/6) and diabetes-prone (NOD) mice. We show that 1,25(OH)2D3 is able to imprint a phenotypic tolerogenic profile on DCs derived from both mouse strains. Both NOD- and C57BL/6-derived 1,25D3-mDCs decreased the proliferation and activation of autoreactive T cells in vitro, despite strain differences in the regulation of cytokine/chemokine expression. In addition, 1,25D3-mDCs from diabetes-prone mice expanded CD25(+)Foxp3(+) regulatory T cells and induced intracellular IL-10 production by T cells in vitro. Furthermore, 1,25D3-mDCs exhibited an intact functional migratory capacity in vivo that favors homing to the liver and pancreas of adult NOD mice. More importantly, when cotransferred with activated CD4(+) T cells into NOD.SCID recipients, 1,25D3-mDCs potently dampened the proliferation of autoreactive donor T cells in the pancreatic draining lymph nodes. Altogether, these results argue for the potential of 1,25D3-mDCs to restore Ag-specific immune tolerance and arrest autoimmune disease progression in vivo.

Type 1 diabetes therapy beyond T cell targeting: monocytes, B cells, and innate lymphocytes

Recent clinical trials, investigating type 1 diabetes (T1D), have focused mainly on newly diagnosed individuals who have developed diabetes. We need to continue our efforts to understand disease processes and to rationally design interventions that will be safe and specific for disease, but at the same time not induce undesirable immunosuppression. T cells are clearly involved in the pathogenesis of T1D, and have been a major focus for both antigen-specific and non-antigen-specific therapy, but thus far no single strategy has emerged as superior. As T1D is a multifactorial disease, in which multiple cell types are involved, some of these pathogenic and regulatory cell pathways may be important to consider. In this review, we examine evidence for whether monocytes, B cells, and innate lymphocytes, including natural killer cells, may be suitable targets for intervention.

B cells as effectors and regulators of autoimmunity

A classic understanding of the interplay between B and T cell components of the immune system that drive autoimmunity, where B cells provide an effector function, is represented by systemic lupus erythematosus (SLE), an autoimmune condition characterised by the production of auto-antibodies. In SLE, CD4+T cells provide cognate help to self-reactive B cells, which in turn produce pathogenic auto-antibodies (1). Thus, B cells act as effectors by producing auto-antibody aided by T cell help such that B and T cell interactions are unidirectional. However, this paradigm of B and T cell interactions is challenged by new clinical data demonstrating that B cell depletion is effective for T cell mediated autoimmune diseases including type I diabetes mellitus (T1D) (2), rheumatoid arthritis (3), and multiple sclerosis (4). These clinical data indicate a model whereby B cells can influence the developing autoimmune T cell response, and therefore act as effectors, in ways that extend beyond the production of autoantibody (5). In this review by largely focusing on type I diabetes we will develop a hypothesis that bi-directional B and T interactions control the course of autoimmunity.

Altered phenotype of peripheral blood dendritic cells in pediatric type 1 diabetes

OBJECTIVE

Dendritic cells (DCs) are largely responsible for the activation and fine-tuning of T-cell responses. Altered numbers of blood DCs have been reported in type 1 diabetes (T1D). We aimed at characterizing the less well-known phenotypic properties of DCs in T1D.

RESEARCH DESIGN AND METHODS

In a case-control setting, samples from a total of 90 children were studied by flow cytometry or by quantitative real-time PCR (qPCR).

RESULTS

We found decreased numbers of myeloid DCs (mDCs) (8.97 vs. 13.4 cells/μL, P = 0.009, n = 31) and plasmacytoid DCs (pDCs) (9.47 vs. 14.6 cells/μL, P = 0.018, n = 30) in recent-onset T1D. Using a panel of antibodies against functionally important DC markers, we detected a decreased expression of CC chemokine receptor 2 (CCR2) on mDCs (percentage above negative control, P = 0.002, n = 29) and pDCs (median intensity, P = 0.003, n = 30) from T1D patients. In an independent series of children, the reduced expression of CCR2 was confirmed by qPCR in isolated mDCs (P = 0.043, n = 20). Serum concentrations of CCR2 ligands monocyte chemotactic protein-1 and -3 did not differ between the groups. A trend for an enhanced responsiveness of the nuclear factor-κB pathway (P = 0.063, n = 39) was seen in mDCs from children with β-cell autoantibodies, which is possibly related to the reduced CCR2 expression, since CCR2 on mDCs was downregulated by nuclear factor-κB-activating agents.

CONCLUSIONS

Given the role of CCR2 in DC chemotaxis and in DC-elicited Th1 differentiation, our results may indicate a functionally important DC abnormality in T1D affecting the initiation and quality of immune responses.

Pancreatic islet expression of chemokine CCL2 suppresses autoimmune diabetes via tolerogenic CD11c+ CD11b+ dendritic cells

Development of type 1 diabetes in the nonobese diabetic (NOD) mouse is preceded by an immune cell infiltrate in the pancreatic islets. The exact role of the attracted cells is still poorly understood. Chemokine CCL2/MCP-1 is known to attract CCR2(+) monocytes and dendritic cells (DCs). We have previously shown that transgenic expression of CCL2 in pancreatic islets via the rat insulin promoter induces nondestructive insulitis on a nonautoimmune background. We report here an unexpected reduction of diabetes development on the NOD background despite an increased islet cell infiltrate with markedly increased numbers of CD11c(+) CD11b(+) DCs. These DCs exhibited a hypoactive phenotype with low CD40, MHC II, CD80/CD86 expression, and reduced TNF-α but elevated IL-10 secretions. They failed to induce proliferation of diabetogenic CD4(+) T cells in vitro. Pancreatic lymph node CD4(+) T cells were down-regulated ex vivo and expressed the anergy marker Grail. By using an in vivo transfer system, we show that CD11c(+) CD11b(+) DCs from rat insulin promoter-CCL2 transgenic NOD mice were the most potent cells suppressing diabetes development. These findings support an unexpected beneficial role for CCL2 in type 1 diabetes with implications for current strategies interfering with the CCL2/CCR2 axis in humans, and for dendritic cell biology in autoimmunity.

Impaired inflammatory responses to multiple toll-like receptor ligands in alveolar macrophages of streptozotocin-induced diabetic mice

OBJECTIVE

To investigate the effect of hyperglycemic state on the activation of alveolar macrophages (AMs) mediated via Toll-like receptors (TLRs) typically associated with bacterial infection.

METHODS

AMs obtained from normoglycemic control mice and streptozotocin-induced diabetic mice were stimulated ex vivo with the following: a TLR2 ligand, peptidoglycan (PGN); a TLR4 ligand, lipopolysaccharide (LPS); or a TLR5 ligand, flagellin (FLG). Cytokine production and mRNA expression were measured by ELISA and real-time PCR, respectively. TLR expression was assessed by real-time PCR and flow cytometry.

RESULTS

AMs from diabetic mice produced significantly less TNF-α after PGN or FLG stimulation, and less IL-6 after FLG stimulation, compared with AMs from control mice. The decrease in the production of these cytokines was associated with reduced mRNA expression of the corresponding cytokines. In contrast, production of TNF-α and IL-6 after LPS stimulation did not differ between groups. Furthermore, there was no substantial difference in the expression of TLR2, TLR4, and TLR5 in AMs between the groups. The increased JNK phosphorylation induced by PGN or FLG stimulation was downregulated in AMs from diabetic mice.

CONCLUSIONS

Hyperglycemic state impairs the reactivity of AMs to multiple TLR ligands. This effect might result from hyperglycemia-induced alteration of intracellular signaling and is unlikely due to the modulation of TLR expression.

Differential role of NF-κB, ERK1/2 and AP-1 in modulating the immunoregulatory functions of bone marrow-derived dendritic cells from NOD mice

Tolerogenic dendritic cells represent a promising immunotherapy in autoimmunity. However, the molecular mechanisms that drive tolerogenic DCs functions are not well understood. We used GM-CSF or GM-CSF+IL-4 to generate tolerogenic (GM/DCs) and immunogenic (IL-4/DCs) BMDCs from NOD mice, respectively. GM/DCs were resistant to maturation, produced large amounts of IL-10 but not IL-12p70. GM/DCs displayed a reduced capacity to activate diabetogenic CD8(+) T-cells and were efficient to induce Tregs expansion and conversion. LPS stimulation triggered ERK1/2 activation that was sustained in GM/DCs but not in IL-4/DCs. ERK1/2 and AP-1 were involved in IL-10 production in GM/DCs but not in their resistance to maturation. Supershift analysis showed that NF-κB DNA binding complex contains p52 and p65 in GM/DCs, whereas it contains p52, p65 and RelB in IL-4/DCs. ChIP experiments revealed that p65 was recruited to IL-10 promoter following LPS stimulation of GM/DCs whereas its binding to IL-12p35 promoter was abolished. Our results suggest that immunoregulatory functions of GM/DCs are differentially regulated by ERK1/2, AP-1 and NF-κB pathways.

IL-2 production by dendritic cells promotes Foxp3(+) regulatory T-cell expansion in autoimmune-resistant NOD congenic mice

Il2 allelic variation in non-obese diabetic mice imparts marked resistance to type 1 diabetes. IL-2 is pivotal for the fitness and homeostasis of Foxp3(+) regulatory T (T(reg)) cells, and the Idd3(B6) locus augments IL-2 production by effector T cells, which in turn enhances the potency of T(reg) cell functions. Given the important role dendritic cells (DCs) play in T(reg) cell-mediated tolerance induction, we hypothesized that DCs from Idd3(B6) congenic mice contribute to increased T(reg) cell activity. Here, we observed that CD11c(+) DCs, harboring protective Idd3(B6) genes, are endowed with the capacity to secrete IL-2, enabling them to preferentially promote T(reg) cell functions in vitro and in vivo. Our results show that Il2 gene variation may imprint DCs to favor T-cell regulation of autoimmunity.

The regulatory role of dendritic cells in the induction and maintenance of T-cell tolerance

The induction and maintenance of T-cell tolerance to tissue antigens is essential to prevent autoimmunity. Combinations of central and peripheral mechanisms act in parallel to inactivated, eliminated or control autoreactive T cells. Both centrally and peripherally, a key requirement for self-tolerance is the presentation of self-antigens in a correct context. There is now evidence to suggest that dendritic cells (DCs) play a fundamental role in the development of central and peripheral tolerance. In this review, we summarize recent progress toward the definition of the multiple roles of DCs in these processes. We will also discuss the association between defects in the DC compartment and the development of autoimmune responses, with particular reference to DC deregulation in the context of type I diabetes.

CD4+ CD25+ regulatory T cells prevent type 1 diabetes preceded by dendritic cell-dominant invasive insulitis by affecting chemotaxis and local invasiveness of dendritic cells

Development of type 1 diabetes (T1D) is preceded by invasive insulitis. Although CD4(+)CD25(+) regulatory T cells (nTregs) induce tolerance that inhibits insulitis and T1D, the in vivo cellular mechanisms underlying this process remain largely unclear. Using an adoptive transfer model and noninvasive imaging-guided longitudinal analyses, we found nTreg depletion did not affect systemic trafficking and tissue localization of diabetogenic CD4(+) BDC2.5 T (BDC) cells in recipient mice prior to development of T1D. In addition, neither the initial expansion/activation of BDC cells nor the number of CD11c(+) or NK cells in islets and pancreatic lymph nodes were altered. Unexpectedly, our results showed nTreg depletion led to accelerated invasive insulitis dominated by CD11c(+) dendritic cells (ISL-DCs), not BDC cells, which stayed in the islet periphery. Compared with control mice, the phenotype of ISL-DCs and their ability to stimulate BDC cells did not change during invasive insulitis development. However, ISL-DCs from nTreg-deficient recipient mice showed increased in vitro migration toward CCL19 and CCL21. These results demonstrated invasive insulitis dominated by DCs, not CD4(+) T cells, preceded T1D onset in the absence of nTregs, and suggested a novel in vivo function of nTregs in T1D prevention by regulating local invasiveness of DCs into islets, at least partly, through regulation of DC chemotaxis toward CCL19/CCL21 produced by the islets.

Emerging roles for B lymphocytes in Type 1 diabetes

Self-reactive B lymphocytes play two main pathological roles in autoimmune diseases: as secretors of autoantibodies and as specialized antigen-presenting cells that present self-components to autoreactive T lymphocytes. In recognition of these roles, recent clinical trials have utilized B-lymphocyte-depleting monoclonal antibodies to treat various autoimmune diseases, with encouraging results in those where humoral autoimmunity is clearly important. Surprisingly, recent results in animal models suggest that B-lymphocyte depletion may also be effective in the treatment of T-lymphocyte-mediated autoimmune diseases, such as Type 1 diabetes (T1D). This article reviews the experimental evidence that has uncovered pathogenic as well as regulatory roles for B lymphocytes in the prodrome of T1D and how this information is being used to develop novel therapeutic strategies to treat the disease.

Functional alterations of proinflammatory monocytes by T regulatory cells: implications for the prevention and reversal of type 1 diabetes

The onset and development of type 1 diabetes (T1D) occurs in genetically predisposed individuals, and is attributed to autoimmune destruction of pancreatic beta-cells involving a multitude of immune mechanisms. Defects in immune regulation may play a central role in T1D, involving impaired function and communication of both myeloid and lymphoid cells of the innate and adaptive immune compartments. Dendritic cells and regulatory T (Treg) cells are part of this network, which seem to be hampered in their quest to control and regulate tissue-destructive autoimmunity. Recent studies have shown that in vivo activated CD16- blood monocytes exhibiting proinflammatory features are present in diabetic subjects. These monocytes may govern T cell-mediated immune responses towards the development of tissue-destructive Th1 and Th17 subtypes, and give rise to inflammatory macrophages in tissues. Differential effects of cytokines IFN-gamma and IL-4 in the development of inflammatory macrophages, and the distinct developmental pathways of proinflammatory or tissue-repair-associated monocytes suggest that controlling the activity of these monocytes could be part of an immune intervention strategy to prevent T1D. Similarly, strategies to target autoantigens to immature, steady-state dendritic cells could guide the immune response away from Th1 and Th17 immune effectors. This review examines potential approaches to this goal by manipulation of myeloid and lymphoid cell regulatory networks in T1D.

Invariant natural killer T-cell control of type 1 diabetes: a dendritic cell genetic decision of a silver bullet or Russian roulette

OBJECTIVE

In part, activation of invariant natural killer T (iNKT)-cells with the superagonist alpha-galactosylceramide (alpha-GalCer) inhibits the development of T-cell-mediated autoimmune type 1 diabetes in NOD mice by inducing the downstream differentiation of antigen-presenting dendritic cells (DCs) to an immunotolerogenic state. However, in other systems iNKT-cell activation has an adjuvant-like effect that enhances rather than suppresses various immunological responses. Thus, we tested whether in some circumstances genetic variation would enable activated iNKT-cells to support rather than inhibit type 1 diabetes development.

RESEARCH DESIGN AND METHODS

We tested whether iNKT-conditioned DCs in NOD mice and a major histocompatibility complex-matched C57BL/6 (B6) background congenic stock differed in capacity to inhibit type 1 diabetes induced by the adoptive transfer of pathogenic AI4 CD8 T-cells.

RESULTS

Unlike those of NOD origin, iNKT-conditioned DCs in the B6 background stock matured to a state that actually supported rather than inhibited AI4 T-cell-induced type 1 diabetes. The induction of a differing activity pattern of T-cell costimulatory molecules varying in capacity to override programmed death-ligand-1 inhibitory effects contributes to the respective ability of iNKT-conditioned DCs in NOD and B6 background mice to inhibit or support type 1 diabetes development. Genetic differences inherent to both iNKT-cells and DCs contribute to their varying interactions in NOD and B6.H2(g7) mice.

CONCLUSIONS

This great variability in the interactions between iNKT-cells and DCs in two inbred mouse strains should raise a cautionary note about considering manipulation of this axis as a potential type 1 diabetes prevention therapy in genetically heterogeneous humans.

Pre-existing autoimmunity determines type 1 diabetes outcome after Flt3-ligand treatment

Redirection of immune responses by manipulation of antigen-presenting cells is an emerging strategy for immunosuppressive treatment of autoimmune diseases. In vivo expansion of dendritic cells (DC) by Fms-like tyrosine kinase-3 (Flt3)-Ligand (FL) treatment was shown to delay diabetes onset in the NOD model of autoimmune diabetes. However, we show here that Flt3 stimulation actually accelerates autoimmunity when autoreactive CD8 T cells are detectable in blood prior to treatment. With autoreactive CD8 cells present, the capacity of FL to expand DCs and induce Treg remained intact, but both numbers and the functional response of islet-specific CD8s were boosted. Also, the inhibitory receptor PD-1 on (autoreactive) CD8 T cells and its ligand PD-L1 on Treg were no longer upregulated. These data highlight the need to pre-screen for T cell autoreactivity prior to generalized DC expansion and illustrate how accelerated disease can occur when the intended initiation of regulatory mechanisms is impaired later in diabetogenesis.

Innovative Immune-Based Therapeutic Approaches for the Treatment of Type 1 Diabetes Mellitus

Type 1 diabetes mellitus is an autoimmune disease caused by a culmination of noxious processes of autoimmunity composed of various components of the innate and adaptive immune systems. Current treatment of type 1 diabetes focuses on restraining the endocrine disease without affecting the autoimmune process that underlies it. Prevention of this disease requires immune modulation and early intervention. New therapeutic approaches can be classified on the basis of the immunological arm targeted, that is, T-cell immune modulation (using cytokines, anti-CD3 monoclonal antibodies, and peptide MHC class II dimers), innate immune system modulation (using alpha-galactosylceramide or peptide 277), or specific antigen vaccination (glutamic acid decarboxylase and insulin). Here we review the most promising therapies developed based on these targets and emphasize those that have reached human phase clinical investigation.

Tuberculosis in poorly controlled type 2 diabetes: altered cytokine expression in peripheral white blood cells

BACKGROUND

Although the biological basis for the increased susceptibility of diabetic patients to tuberculosis remains unclear, the world is undergoing a type 2 diabetes pandemic. We hypothesize that chronic hyperglycemia leads to immunocompromise that facilitates progression to active tuberculosis. To assess this possibility, we determined whether patients with tuberculosis and diabetes (particularly those with chronic hyperglycemia), compared with patients with tuberculosis who did not have diabetes, presented altered cytokine responses to a mycobacterial antigen.

METHODS

Samples of whole blood from patients with tuberculosis and diabetes and from patients with tuberculosis who did not have diabetes was stimulated in vitro with purified protein derivative from Mycobacterium tuberculosis. We then determined whether there was an association between the levels of innate and adaptive cytokines secreted in response to the antigen and diabetes status, or diabetes with chronic hyperglycemia (measured by glycosylated hemoglobin level), after controlling for possible confounders.

RESULTS

Innate and type 1 cytokine responses were significantly higher in patients with tuberculosis who had diabetes than in nondiabetic control subjects. The effect was consistently and significantly more marked in diabetic patients with chronic hyperglycemia.

CONCLUSIONS

These data provide preliminary evidence that type 2 diabetes, especially type 2 diabetes involving chronic hyperglycemia, is associated with an altered immune response to M. tuberculosis. More-detailed knowledge of the underlying mechanisms should focus on the effect of chronic hyperglycemia on the immune response to help in understanding the enhanced susceptibility of diabetic patients to tuberculosis.

Control of type 1 diabetes by CD4+Foxp3+ regulatory T cells: lessons from mouse models and implications for human disease

In recent years, there has been a revival of the concept of CD4(+) regulatory T (T(reg)) cells as being a central control point in various immune responses, including autoimmune responses and immunity to transplants, allergens, tumours and infectious microbes. The current literature suggests that T(reg) cells are diverse in their phenotype and mechanism(s) of action, and as such, may constitute a myriad of naturally occurring and induced T cell precursors with variable degrees of regulatory potential. In this review, we summarize research from various laboratories, including our own, showing that CD4(+)Foxp3(+) T(reg) cells are critical in the control of type 1 diabetes (T1D) in mouse models and humans. In this review, we also discuss cellular and molecular determinants that impact CD4(+)Foxp3(+) T(reg) cell development and function and consequential resistance to organ-specific autoimmune disease. Recent advances in the use of CD4(+)Foxp3(+) T(reg) cellular therapy to promote immunological tolerance in the absence of long-term generalized immunosuppression are also presented.

Modulation of dendritic cells using granulocyte-macrophage colony-stimulating factor (GM-CSF) delays type 1 diabetes by enhancing CD4+CD25+ regulatory T cell function

Abnormalities in DC function are implicated in defective immune regulation that leads to type-1 diabetes (T1D) in NOD mice and humans. In this study, we used GM-CSF and Flt3-L to modulate DC function in NOD mice and observed the effects on T1D development. Treatment with either ligand at earlier stages of insulitis suppressed the development of T1D. Unlike Flt3-L, GM-CSF was more effective in suppressing T1D, even when administered at later stages of insulitis. In vitro studies and in vivo adoptive transfer experiments revealed that CD4+CD25+ T cells from GM-CSF-treated mice could suppress effector T cell response and T1D. This suppression is likely mediated through enhanced IL-10 and TGF-beta1 production. Adoptive transfer of GM-CSF exposed DCs to naive mice resulted in an expansion of Foxp3+ T cells and a significant delay in T1D onset. Our results indicate that GM-CSF acted primarily on DCs and caused an expansion of Foxp3+ Tregs which delayed the onset of T1D in NOD mice.

Type 1 diabetes patients have significantly lower frequency of plasmacytoid dendritic cells in the peripheral blood

Dendritic cells uniquely orchestrate the delicate balance between T cell immunity and regulation and an imbalance favoring immunogenic rather than tolerogenic DC is believed to contribute to the development of autoimmune diseases such as type 1 diabetes (T1D). In this study, we determined the frequencies of three blood DC subsets (pDC, mDC1 and mDC2) in 72 T1D patients and 75 normal controls using the Miltenyi blood DC enumeration kit. The frequency of blood pDC was found to be negatively correlated with subject age in both normal controls and T1D patients (p=0.0007), while the frequency of mDC1 and mDC2 do not change significantly with subject age. More importantly, the mean frequency of pDC in blood was, after adjusting for age, significantly lower in T1D (mean=0.127%) than controls (mean=0.188%) (p<6.0 x 10(-5)), whereas no difference was observed for mDC1 and mDC2 between T1D and controls. Furthermore, T1D patients have a lower proportion of pDC and higher proportion of mDC1 among the total blood DC population than normal controls. These results indicate that the frequency of blood pDC and the pDC/mDC1 ratio are negatively associated with T1D.

Comparative therapeutic effects of orally administered 1,25-dihydroxyvitamin D(3) and 1alpha-hydroxyvitamin D(3) on type-1 diabetes in non-obese diabetic mice fed a normal-calcaemic diet

Frequent injections of the hormonal form of vitamin D(3), 1,25 dihydroxyvitamin D(3) (1,25D3) reportedly inhibits autoimmune type 1 diabetes (T1D) in non-obese diabetic (NOD) mice by correcting some of the abnormalities in antigen-presenting cells which contribute the development of pathogenic T cell responses. This route of administration greatly elevates the levels of these compounds in the bloodstream for hours after treatment, which requires mice to be fed diets formulated to contain much reduced levels of Ca to avoid the toxic effects of hypercalcaemia. In the current work, we demonstrate that feeding 1,25D3 or its synthetic precursor, 1alpha(OH) vitamin D(3) (1alphaD3), as part of a T1D supportive chow diet containing normal levels of Ca, is an effective means of reducing the incidence of disease in NOD mice, but the doses required for protection elicited hypercalcaemia. However, T1D protection elicited by D3 analogue feeding appears, at least partially, to have an immunological basis, as splenic T cells from treated mice had a decreased capacity to adoptively transfer disease. Protection is associated with an increased proportion of T cells with CD4+ forkhead box P3+ regulatory phenotype within the islet infiltrate of treated animals. The 1alphaD3 precursor is converted rapidly to the active 1,25D3 isoform in vivo. However, feeding the 1alphaD3 analogue elicited stronger T1D protection than the 1,25D3 compound, but also induced more severe hypercalcaemia. In future, the dietary supplementation of novel low-calcaemic D3 analogues may enable their continuous delivery at levels that inhibit T1D development in susceptible humans consuming normal levels of Ca.

Protein transduction: identification, characterization and optimization

Protein transduction domains (PTDs), both naturally occurring and synthetic, have been increasingly employed to deliver biologically active agents to a variety of cell types in vitro and in vivo. In addition to the previously characterized arginine-rich PTDs, including Tat (transactivator of transcription), Antp (Antennapedia) and PTD-5, we have demonstrated that lysine and ornithine, as well as arginine, homopolymers are able to mediate transduction of a wide variety of agents. To screen for optimal PTDs, we have used as a therapeutic cargo a peptide derived from IKK {IkappaB [inhibitor of NF-kappaB (nuclear factor kappaB)] kinase} beta, able to bind to the IKK regulatory subunit [NEMO (NF-kappaB essential modulator)], preventing formation of an active kinase complex. This peptide, termed NBD, is able to block activation of NF-kappaB, but not basal activity. We demonstrate that PTD-mediated delivery of NBD using certain PTDs, in particular 8K (octalysine), is therapeutic following systemic delivery in murine models of inflammatory bowel disease, diabetes and muscular dystrophy. In addition, we have developed a peptide phage display library screening method for novel transduction peptides able to facilitate tissue-specific internalization of marker protein complexes. Using this approach, we have identified transduction peptides that are able to facilitate internalization of large protein complexes into tumours, airway epithelia, synovial fibroblasts, cardiac tissue and HEK-293 (human embryonic kidney) cells in culture and/or in vivo.

The cross-regulatory relationship between human dendritic and regulatory T cells and its role in type 1 diabetes mellitus

Dendritic cells (DCs) and T regulatory (Treg) cells play a crucial role in maintaining the tolerance needed to prevent the onset of autoimmunity that leads to the development of type 1 diabetes mellitus (T1DM). Various experimental studies have shown that human DC subsets are involved in the induction of anergy in T cells and in the differentiation of conventional CD4(+) and CD8(+) lymphocytes into the respective subtypes of Treg cells. Treg cells, in turn, have been shown to modulate the function of DCs to exhibit tolerogenic properties. To evaluate whether T1DM development is related to abnormalities in DCs and Treg cells, many attempts have been made to characterize these cell types in diabetic individuals and in subjects at risk of developing the disease. This review aims to supply an update on the progress made in these aspects of T1DM research.

Interaction between antigen presenting cells and autoreactive T cells derived from BXSB mice with murine lupus

Systemic lupus erythematosus (SLE) is a typical autoimmune disease involving multiple systems and organs. Ample evidence suggests that autoreactive T cells play a pivotal role in the development of this autoimmune disorder. This study was undertaken to investigate the mechanisms of interaction between antigen presenting cells (APCs) and an autoreactive T cell (ATL1) clone obtained from lupus-prone BXSB mice. ATL1 cells, either before or after gamma-ray irradiation, were able to activate naive B cells, as determined by B cell proliferation assays. Macrophages from BXSB mice were able to stimulate the proliferation of resting ATL1 cells at a responder/stimulator (R/S) ratio of 1/2.5. Dendritic cells (DCs) were much more powerful stimulators for ATL1 cells on a per cell basis. The T cell stimulating ability of macrophages and B cells, but not DCs, was sensitive to gamma-ray irradiation. Monoclonal antibodies against mouse MHC-II and CD4 were able to block DC-mediated stimulation of ATL1 proliferation, indicating cognate recognition between ATL1 and APCs. Our data suggest that positive feedback loops involving macrophages, B cells and autoreactive T cells may play a pivotal role in keeping the momentum of autoimmune responses leading to autoimmune diseases.

Improved Outcomes in NOD Mice Treated with a Novel Th2 Cytokine-Biasing NKT Cell Activator

Activation of CD1d-restricted invariant NKT (iNKT) cells by alpha-galactosylceramide (alphaGalCer) significantly suppresses development of diabetes in NOD mice. The mechanisms of this protective effect are complex, involving both Th1 and Th2 cytokines and a network of regulatory cells including tolerogenic dendritic cells. In the current study, we evaluated a newly described synthetic alphaGalCer analog (C20:2) that elicits a Th2-biased cytokine response for its impact on disease progression and immunopathology in NOD mice. Treatment of NOD mice with alphaGalCer C20:2 significantly delayed and reduced the incidence of diabetes. This was associated with significant suppression of the late progression of insulitis, reduced infiltration of islets by autoreactive CD8(+) T cells, and prevention of progressive disease-related changes in relative proportions of different subsets of dendritic cells in the draining pancreatic lymph nodes. Multiple favorable effects observed with alphaGalCer C20:2 were significantly more pronounced than those seen in direct comparisons with a closely related analog of alphaGalCer that stimulated a more mixed pattern of Th1 and Th2 cytokine secretion. Unlike a previously reported Th2-skewing murine iNKT cell agonist, the alphaGalCer C20:2 analog was strongly stimulatory for human iNKT cells and thus warrants further examination as a potential immunomodulatory agent for human disease.

New aspects on inflammation in allergic diseases

BACKGROUND

Allergic disease has currently reached epidemic proportions, with a high percentage of individuals in the developed world exhibiting an allergic response after exposure to some common environmental factors. Although new strategies for the treatment and management of allergic diseases have decreased the mortality rate, a high percentage of affected persons still require frequent hospitalization and experience decreased quality of life.

METHODS

An internet-based literature search was performed for recent contributions on the underlying mechanisms provoking an allergic response and their potential for therapeutic approaches.

RESULTS

Novel concepts on allergic responses have emerged: allergic disease may result from an imbalance between allergen activation of regulatory T cells and effector T helper 2 cells (Th2), a process in which dendritic cells are key players. Cytokines such as interleukin (IL)-6, IL-21, IL-25, and human thymic stromal lymphopoietin (TSLP) seem to be important contributors in allergic processes. New data on IgE effector responses and on the IgE-independent mechanisms involved in allergic reactions have resolved some unanswered questions about these reactions.

CONCLUSIONS

These new findings on allergic diseases have important implications for diagnosis and management, with potential improvements in prevention and treatment, which could provide a cure in the future.

Reduced IFN-alpha secretion by blood dendritic cells in human diabetes

Characterization of dendritic cells (DC) in human diabetes has been restricted to monocyte-derived DC in type 1 diabetes, whose physiological relevance to endogenous DC is uncertain. Here, we provide the first report characterizing the phenotype and function of endogenous DC subsets in type 1 and type 2 diabetes. We show that DC subsets in each diabetic group exhibit normal properties concerning frequency and activation state, as determined using 4-color flow cytometry of whole blood cells. DC maturation is also intact as confirmed by their efficacious ability to stimulate T cell proliferation in an allogeneic MLR assay. Yet we found that DC are poor producers of IFN-alpha (P < 0.05) in human diabetes. IFN-alpha is a potent antiviral agent and therefore its reduced levels may interfere with T cell-mediated immune responses leading to increased susceptibility and persistence of infections in persons with diabetes.

Deficiency in NOD antigen-presenting cell function may be responsible for suboptimal CD4+CD25+ T-cell-mediated regulation and type 1 diabetes development in NOD mice

Various defects in antigen-presenting cells (APCs) and T-cells, including regulatory cells, have been associated with type 1 diabetes development in NOD mice. CD4(+)CD25(+) regulatory cells play a crucial role in controlling various autoimmune diseases, and a deficiency in their number or function could be involved in disease development. The current study shows that NOD mice had fewer CD4(+)CD25(+) regulatory cells, which expressed normal levels of glucocorticoid-induced tumor necrosis factor receptor and cytotoxic T-lymphocyte-associated antigen-4. We have also found that NOD CD4(+)CD25(+) cells regulate poorly in vitro after stimulation with anti-CD3 and NOD APCs in comparison with B6 CD4(+)CD25(+) cells stimulated with B6 APCs. Surprisingly, stimulation of NOD CD4(+)CD25(+) cells with B6 APCs restored regulation, whereas with the reciprocal combination, NOD APCs failed to activate B6 CD4(+)CD25(+) cells properly. Interestingly, APCs from disease-free (>30 weeks of age), but not diabetic, NOD mice were able to activate CD4(+)CD25(+) regulatory function in vitro and apparently in vivo because only spleens of disease-free NOD mice contained potent CD4(+)CD25(+) regulatory cells that prevented disease development when transferred into young NOD recipients. These data suggest that the failure of NOD APCs to activate CD4(+)CD25(+) regulatory cells may play an important role in controlling type 1 diabetes development in NOD mice.

B cells in the spotlight: innocent bystanders or major players in the pathogenesis of type 1 diabetes

It has long been established that type 1 diabetes (T1D) is a T cell-mediated autoimmune disease, with CD4+ and CD8+ T cells being largely responsible for the destruction of beta cells within the pancreatic islets of Langerhans. Although autoantibodies specific for islet cell proteins are regularly detected in individuals with T1D and can be utilized as effective markers for predicting the onset of disease, they are not believed to be directly pathogenic to beta cells. Thus, activation of autoantibody-secreting B cells has long been regarded as a secondary consequence of the ongoing self-reactive T cell response. However, recently, studies in the nonobese diabetic mouse model of disease have demonstrated that B cells are an important component in the development of T1D by virtue of their ability to act as the preferential antigen presenting cell population required for efficient expansion of diabetogenic CD4+ T cells. Furthermore, autoantibodies might also be responsible for mediating early beta cell pathogenesis in this model.

The interactions of dendritic cells with antigen-specific, regulatory T cells that suppress autoimmunity

Dendritic cells (DCs) are important for several aspects of the development and function of CD4(+) CD25(+) regulatory T cells (Tregs), which are critical for maintaining peripheral tolerance and preventing autoimmunity. In cultures from human thymus, dendritic cells (DCs) conditioned with thymic stromal lymphopoietin (TSLP) mediate the production of Tregs from CD4(+) CD25(-) thymocytes. In cultures from mouse lymphoid organs, CD86-rich DCs induce the proliferation and improved suppressive function of antigen-specific Tregs. DC-expanded, antigen-specific Tregs show greatly enhanced efficacy relative to polyclonal populations in blocking experimental autoimmunity. In several animal models including NOD diabetes, Tregs directed to one autoantigen are able to block autoimmunity induced by multiple antigens from the target organ. Distinct states of DC differentiation or maturation are likely to be important for the emerging roles of DCs in the biology of Tregs, particularly the control of autoimmunity in an antigen-dependent manner.