Myeloid dendritic cells in non-obese diabetic mice have elevated costimulatory and T helper-1-inducing abilities

Genetic Restoration of Heme Oxygenase-1 Expression Protects from Type 1 Diabetes in NOD Mice

Antigen-presenting cells (APCs) including dendritic cells (DCs) play a critical role in the development of autoimmune diseases by presenting self-antigen to T-cells. Different signals modulate the ability of APCs to activate or tolerize autoreactive T-cells. Since the expression of heme oxygenase-1 (HO-1) by APCs has been associated with the tolerization of autoreactive T-cells, we hypothesized that HO-1 expression might be altered in APCs from autoimmune-prone non-obese diabetic (NOD) mice. We found that, compared to control mice, NOD mice exhibited a lower percentage of HO-1-expressing cells among the splenic DCs, suggesting an impairment of their tolerogenic functions. To investigate whether restored expression of HO-1 in APCs could alter the development of diabetes in NOD mice, we generated a transgenic mouse strain in which HO-1 expression can be specifically induced in DCs using a tetracycline-controlled transcriptional activation system. Mice in which HO-1 expression was induced in DCs exhibited a lower Type 1 Diabetes (T1D) incidence and a reduced insulitis compared to non-induced mice. Upregulation of HO-1 in DCs also prevented further increase of glycemia in recently diabetic NOD mice. Altogether, our data demonstrated the potential of induction of HO-1 expression in DCs as a preventative treatment, and potential as a curative approach for T1D.

The Role of Dendritic Cell Subsets and Innate Immunity in the Pathogenesis of Type 1 Diabetes and Other Autoimmune Diseases

Dendritic cells (DCs) are key antigen-presenting cells that have an important role in autoimmune pathogenesis. DCs control both steady-state T cell tolerance and activation of pathogenic responses. The balance between these two outcomes depends on several factors, including genetic susceptibility, environmental signals that stimulate varied innate responses, and which DC subset is presenting antigen. Although the specific DC phenotype can diverge depending on the tissue location and context, there are four main subsets identified in both mouse and human: conventional cDC1 and cDC2, plasmacytoid DCs, and monocyte-derived DCs. In this review, we will discuss the role of these subsets in autoimmune pathogenesis and regulation, as well as the genetic and environmental signals that influence their function. Specific topics to be addressed include impact of susceptibility loci on DC subsets, alterations in DC subset development, the role of infection- and host-derived innate inflammatory signals, and the role of the intestinal microbiota on DC phenotype. The effects of these various signals on disease progression and the relative effects of DC subset composition and maturation level of DCs will be examined. These areas will be explored using examples from several autoimmune diseases but will focus mainly on type 1 diabetes.

Impaired dendritic cell function in a spontaneous autoimmune polyneuropathy

Spontaneous autoimmune polyneuropathy (SAP) in B7-2 knockout NOD mice mimics the progressive form of chronic inflammatory demyelinating polyradiculoneuropathy, and is mediated by myelin protein zero (P0)-reactive Th1 cells. In this study, we focused on the effect of B7-2 deletion on the function of dendritic cells (DCs) within the context of SAP. We found that development of SAP was associated with a preponderance or increase of CD11b(+) DCs in peripheral lymph nodes and sciatic nerves. B7-2 deletion led to altered immunophenotypic properties that differ between CD11b(+) DCs and CD8α(+) DCs. Both DC subsets from B7-2 knockout NOD mice exhibited impaired capacity to capture fluorophore-labeled myelin P0, but diminished Ag-presenting function was observed only in CD11b(+) DCs. Clinical assessment, electrophysiologic studies, and splenocyte proliferation studies revealed that absence of B7-2 on DCs was sufficient to cause impaired ability to induce tolerance to P0, which could be overcome by preconditioning with IL-10. Tolerance induction by Ag-pulsed wild-type NOD DCs was dependent on IL-10 and was associated with increased CD4(+) regulatory T cells, whereas tolerance induction by IL-10-conditioned B7-2-deficient DCs was associated with increased percentages of both regulatory T cells and B10 cells in the spleen. We conclude that B7-2 deletion has an impact on the distribution of DC subsets in lymphoid organs and alters the expression of costimulatory molecules, but functional consequences are not uniform across DC subsets. Defective tolerance induction in the absence of B7-2 can be restored by preconditioning of DCs with IL-10.

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.

Curcumin ameliorates autoimmune diabetes. Evidence in accelerated murine models of type 1 diabetes

Type 1 diabetes (T1DM) is a T cell-mediated autoimmune disease that selectively destroys pancreatic β cells. The only possible cure for T1DM is to control autoimmunity against β cell-specific antigens. We explored whether the natural compound curcumin, with anti-oxidant and anti-inflammatory activities, might down-regulate the T cell response that destroys pancreatic β cells to improve disease outcome in autoimmune diabetes. We employed two accelerated autoimmune diabetes models: (i) cyclophosphamide (CYP) administration to non-obese diabetic (NOD) mice and (ii) adoptive transfer of diabetogenic splenocytes into NODscid mice. Curcumin treatment led to significant delay of disease onset, and in some instances prevented autoimmune diabetes by inhibiting pancreatic leucocyte infiltration and preserving insulin-expressing cells. To investigate the mechanisms of protection we studied the effect of curcumin on key immune cell populations involved in the pathogenesis of the disease. Curcumin modulates the T lymphocyte response impairing proliferation and interferon (IFN)-γ production through modulation of T-box expressed in T cells (T-bet), a key transcription factor for proinflammatory T helper type 1 (Th1) lymphocyte differentiation, both at the transcriptional and translational levels. Also, curcumin reduces nuclear factor (NF)-κB activation in T cell receptor (TCR)-stimulated NOD lymphocytes. In addition, curcumin impairs the T cell stimulatory function of dendritic cells with reduced secretion of proinflammatory cytokines and nitric oxide (NO) and low surface expression of co-stimulatory molecules, leading to an overall diminished antigen-presenting cell activity. These in-vitro effects correlated with ex-vivo analysis of cells obtained from curcumin-treated mice during the course of autoimmune diabetes. These findings reveal an effective therapeutic effect of curcumin in autoimmune diabetes by its actions on key immune cells responsible for β cell death.

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.

Dendritic cell subsets in type 1 diabetes: friend or foe?

Type 1 diabetes (T1D) is a T cell mediated autoimmune disease characterized by immune mediated destruction of the insulin-producing β cells in the islets of Langerhans. Dendritic cells (DC) have been implicated in the pathogenesis of T1D and are also used as immunotherapeutic agents. Plasmacytoid (p)DC have been shown to have both protective and pathogenic effects and a newly described merocytic DC population has been shown to break tolerance in the mouse model of T1D, the non-obese diabetic (NOD) mouse. We have used DC populations to prevent the onset of T1D in NOD mice and clinical trials of DC therapy in T1D diabetes have been initiated. In this review we will critically examine the recent published literature on the role of DC subsets in the induction and regulation of the autoimmune response in T1D.

Changes in serum adhesion molecules, chemokines, cytokines, and tissue remodeling factors in euthyroid women without thyroid antibodies who are at risk for autoimmune thyroid disease: a hypothesis on the early phases of the endocrine autoimmune reaction

BACKGROUND

The target glands in spontaneous animal models of endocrine autoimmune disease show, prior to the autoimmune reaction, growth and connective tissue abnormalities, whereas the autoimmune reaction is initiated by an early accumulation of macrophages and dendritic cells in the target glands.

AIM

The aim of the study was to test the hypothesis that serum factors related to these growth and connective tissue abnormalities and the early accumulation of immune cells, ie, tissue growth/remodeling factors, adhesion molecules, chemokines, and pro- and anti-inflammatory cytokines, are related to thyroid peroxidase autoantibodies (TPO-Abs) seroconversion in subjects at risk to develop autoimmune thyroid disease (AITD).

DESIGN

A controlled study on 64 TPO-Ab-negative euthyroid female relatives with at least 1 first- or second-degree relative with documented autoimmune hyper- or hypothyroidism, 32 of whom did and 32 who did not seroconvert to TPO-Ab positivity in 5-year follow-up. The relatives were compared with 32 healthy controls. In all subjects we measured serum levels of chemokine (C-C motif) ligand (CCL)-2, CCL3, CCL4, soluble vascular cell adhesion molecule, soluble intercellular adhesion molecule-1, thrombospondin-1, vascular endothelial growth factor-A, angiopoietin 1 receptor-2, metalloproteinase-13, platelet-derived growth factor-BB, fibronectin, IL-1β, IL-6, TNF-α, IL-10, and growth differentiation factor-15 by multiplex (cytometric bead array) or a single commercial ELISA.

RESULTS

Both seroconverting and nonseroconverting family members showed an up-regulation of fibronectin and a down-regulation of platelet-derived growth factor-BB and the adhesion and migration factors CCL2, CCL4, soluble vascular cell adhesion molecule-1, angiopoietin 1 receptor-2, and metalloproteinase-13. The seroconverters differed from the nonseroconverters by an up-regulation of the proinflammatory compounds Il-1β, IL-6, and CCL3.

CONCLUSION

This study shows that euthyroid females within AITD families show a characteristic pattern of abnormalities in serum levels of tissue remodeling factors, growth factors, chemokines, (vascular) adhesion molecules, and cytokines prior to the occurrence of TPO-Abs in serum. The results provide proof of principle that preseroconversion stages and seroconversion to AITD might be predicted using serum analytes related to growth/connective tissue abnormalities and migration/accumulation abnormalities of macrophages and dendritic cells.

Reduced numbers of dendritic cells with a tolerogenic phenotype in the prediabetic pancreas of NOD mice

The NOD mouse is a widely used animal model of autoimmune diabetes. Prior to the onset of lymphocytic insulitis, DCs accumulate at the islet edges. Our recent work indicated that these DCs may derive from aberrantly proliferating local precursor cells. As CD8α(+) DCs play a role in tolerance induction in steady-state conditions, we hypothesized that the autoimmune phenotype might associate with deficiencies in CD8α(+) DCs in the prediabetic NOD mouse pancreas. We studied CD8α(+) DCs in the pancreas and pLNs of NOD and control mice, focusing on molecules associated with tolerance induction (CD103, Langerin, CLEC9A, CCR5). mRNA expression levels of tolerance-modulating cytokines were studied in pancreatic CD8α(+) DCs of NOD and control mice. In the NOD pancreas, the frequency of CD8α(+)CD103(+)Langerin(+) cells was reduced significantly compared with control mice. NOD pancreatic CD8α(+)CD103(+)Langerin(+) DCs expressed reduced levels of CCR5, CLEC9A, and IL-10 as compared with control DCs. These alterations in the CD8α(+)CD103(+)Langerin(+) DC population were not present in pLNs. We demonstrate local abnormalities in the CD8α(+) DC population in the prediabetic NOD pancreas. These data suggest that abnormal differentiation of pancreatic DCs contributes to loss of tolerance, hallmarking the development of autoimmune diabetes.

Abnormalities of dendritic cell precursors in the pancreas of the NOD mouse model of diabetes

The non-obese diabetic (NOD) mouse is a widely used animal model for the study of human diabetes. Before the start of lymphocytic insulitis, DC accumulation around islets of Langerhans is a hallmark for autoimmune diabetes development in this model. Previous experiments indicated that an inflammatory influx of these DCs in the pancreas is less plausible. Here, we investigated whether the pancreas contains DC precursors and whether these precursors contribute to DC accumulation in the NOD pancreas. Fetal pancreases of NOD and control mice were isolated followed by FACS using ER-MP58, Ly6G, CD11b and Ly6C. Sorted fetal pancreatic ER-MP58(+) cells were cultured with GM-CSF and tested for DC markers and antigen processing. CFSE labeling and Ki-67 staining were used to determine cell proliferation in cultures and tissues. Ly6C(hi) and Ly6C(low) precursors were present in fetal pancreases of NOD and control mice. These precursors developed into CD11c(+) MHCII(+) CD86(+) DCs capable of processing DQ-OVA. ER-MP58(+) cells in the embryonic and pre-diabetic NOD pancreas had a higher proliferation capacity. Our observations support a novel concept that pre-diabetic DC accumulation in the NOD pancreas is due to aberrant enhanced proliferation of local precursors, rather than to aberrant "inflammatory infiltration" from the circulation.

IFN regulatory factors 4 and 8 expression in the NOD mouse

Dendritic cells (DCs) contribute to islet inflammation and its progression to diabetes in NOD mouse model and human. DCs play a crucial role in the presentation of autoantigen and activation of diabetogenic T cells, and IRF4 and IRF8 are crucial genes involved in the development of DCs. We have therefore investigated the expression of these genes in splenic DCs during diabetes progression in NOD mice. We found that IRF4 expression was upregulated in splenocytes and in splenic CD11c⁺ DCs of NOD mice as compared to BALB/c mice. In contrast, IRF8 gene expression was higher in splenocytes of NOD mice whereas its expression was similar in splenic CD11c⁺ DCs of NOD and BALB/c mice. Importantly, levels of IRF4 and IRF8 expression were lower in tolerogenic bone marrow derived DCs (BMDCs) generated with GM-CSF as compared to immunogenic BMDCs generated with GM-CSF and IL-4. Analysis of splenic DCs subsets indicated that high expression of IRF4 was associated with increased levels of CD4⁺CD8α⁻IRF4⁺CD11c⁺ DCs but not CD4⁻CD8α⁺IRF8⁺CD11c⁺ DCs in NOD mice. Our results showed that IRF4 expression was up-regulated in NOD mice and correlated with the increased levels of CD4⁺CD8α⁻ DCs, suggesting that IRF4 may be involved in abnormal DC functions in type 1 diabetes in NOD mice.

Tolerogenic dendritic cells in autoimmune diseases: crucial players in induction and prevention of autoimmunity

The immune system has evolved to coordinate responses against numerous invading pathogens and simultaneously remain silent facing self-antigens and those derived from commensal organisms. But, if both processes are not maintained in strict balance, a potential threat can emerge due to the risk of chronic inflammation and/or autoimmunity development. Therefore, there is a negative immune regulation where tolerogenic dendritic cells (tDCs) participate actively. Under steady-state conditions, tDC are notably involved in the elimination of autoreactive T cells at the thymus, and in the control of T cells specific to self and harmless antigens in the periphery. But in the presence of foreign antigens in an inflammatory milieu, dendritic cells (DCs) mature and induce T cells activation and their migration to B cell areas to assist in antibody production. Additionally, there are other factors such as infections, anti tumoral immune responses, trauma-mediated disruption, etc. that may induce alterations in the balance between tolerogenic and immunogenic functions of DCs and instigate the development of autoimmune diseases (ADs). Therefore, in recent years, DCs have emerged as therapeutic targets to control of ADs. Diverse strategies in vitro and/or in animal models of ADs have explored the tolerogenic functions of DCs and demonstrated their feasibility to prevent or control an autoimmune process, but still leaving a void in their application in clinical assays. The purpose of this paper is to give a general overview of the current literature on the significance of tDCs in tolerance maintenance to self and innocuous antigens, the most relevant alterations involved in the pathophysiology of ADs, the cellular and molecular mechanisms involved in their tolerogenic function and the current strategies used to exploit their tolerogenic potential.

GM-CSF induces bone marrow precursors of NOD mice to skew into tolerogenic dendritic cells that protect against diabetes

We have reported that GM-CSF treatment of NOD mice suppressed diabetes by increasing the number of tolerogenic dendritic cells (tDCs) and Tregs in the periphery. Here, we have investigated whether GM-CSF acted on NOD bone marrow DCs precursors to skew their differentiation to tDCs. DCs were generated from the bone marrow of GM-CSF-treated (GM.BMDCs) and PBS-treated (PBS.BMDCs) NOD mice and were assessed for their ability to acquire tolerogenic properties. Upon LPS stimulation, GM.BMDCs became fully mature, expressed high levels of PD-L1 and produced more IL-10 and less IL-12p70 and IFN-gamma than PBS.BMDCs. In addition, LPS-stimulated GM.BMDCs possessed a reduced capacity to activate diabetogenic CD8(+) T cells in a PD-1/PD-L1-dependent manner. A single injection of LPS-stimulated GM.BMDCs in NOD mice resulted in long-term protection from diabetes, in contrast to LPS-stimulated PBS.BMDCs. Our results showed that GM-CSF-treatment acted on bone marrow precursors to skew their differentiation into tDCs that protected NOD mice against diabetes.

Dendritic cell-based therapy in Type 1 diabetes mellitus

Dendritic cell (DC) immunotherapy is a clinical reality. Despite two decades of considerable data demonstrating the feasibility of using DCs to prolong transplant allograft survival and to prevent autoimmunity, only now are these cells entering clinical trials in humans. Type 1 diabetes is the first autoimmune disorder to be targeted for treatment in humans using autologous-engineered DCs. This review will highlight the role of DCs in autoimmunity and the manner in which they have been engineered to treat these disorders in rodent models, either via the induction of immune hyporesponsiveness, which may be cell- and/or antigen-specific, or indirectly by upregulation of other immune cell networks.

Dendritic cell-directed CTLA-4 engagement during pancreatic beta cell antigen presentation delays type 1 diabetes

The levels of expression of alternatively spliced variants of CTLA-4 and insufficient CTLA-4 signaling have been implicated in type 1 diabetes. Hence, we hypothesized that increasing CTLA-4-specific ligand strength on autoantigen-presenting dendritic cells (DCs) can enhance ligation of CTLA-4 on T cells and lead to modulation of autoreactive T cell response. In this study, we show that DC-directed enhanced CTLA-4 engagement upon pancreatic beta cell Ag presentation results in the suppression of autoreactive T cell response in NOD mice. The T cells from prediabetic NOD mice treated with an agonistic anti-CTLA-4 Ab-coated DC (anti-CTLA-4-Ab DC) showed significantly less proliferative response and enhanced IL-10 and TGF-beta1 production upon exposure to beta cell Ags. Furthermore, these mice showed increased frequency of Foxp3+ and IL-10+ T cells, less severe insulitis, and a significant delay in the onset of hyperglycemia compared with mice treated with control Ab-coated DCs. Further analyses showed that diabetogenic T cell function was modulated primarily through the induction of Foxp3 and IL-10 expression upon Ag presentation by anti-CTLA-4-Ab DCs. The induction of Foxp3 and IL-10 expression appeared to be a consequence of increased TGF-beta1 production by T cells activated using anti-CTLA-4-Ab DCs, and this effect could be enhanced by the addition of exogenous IL-2 or TGF-beta1. Collectively, this study demonstrates the potential of a DC-directed CTLA-4 engagement approach not only in treating autoimmunity in type 1 diabetes, but also in altering diabetogenic T cell function ex vivo for therapy.

Aberrancies in Antigen-presenting Cells and T Cells in Autoimmune Thyroid Disease. A Role in Faulty Tolerance Induction

Various thyrocyte, monocyte, macrophage, DC and T cell abnormalities exist in the animal models of spontaneously developing autoimmune thyroiditis and in patients with autoimmune thyroid disease. An aberrant interaction between such abnormal thyrocytes, abnormal professional antigen-presenting cells (APC) and abnormal T cells forms the basis for the atypical autoimmune reaction targeting thyroid antigens. In the atypical interaction more than one gene and various environmental factors are involved. The genetic and environmental factors must act together to induce full-blown disease. Although there is a general blueprint for the development of destructive autoimmune thyroiditis, thyrocyte and immune cell abnormalities differ between the various animal models and the various forms of autoimmune thyroid disease (either associated with type 1 diabetes, associated with bipolar disorder or not associated). This tells us that there are different etio-pathogenic forms of destructive autoimmune thyroiditis. Whether such heterogeneity is also the case for the etio-pathogenesis of Graves' disease remains unknown. Animal models of spontaneously developing Graves' disease would be helpful in unraveling this question. If indeed there are various etio-pathogenic routes in different patients that lead to destructive autoimmune thyroiditis, then tailor-made therapeutic approaches need to be carried out in attempts to correct the underlying immune abnormalities in individual patients or to prevent the development of destructive autoimmune thyroiditis in individuals at risk. While in some forms of destructive autoimmune thyroiditis (f.i. those associated with bipolar disorder) immune suppression should be the first choice of intervention, other forms (f.i. those associated with type 1 diabetes) may benefit from immune stimulation in certain pre-stages of the disease (to restore f.i. the faulty APC function characteristic of this condition). Obviously a more precise determination of the spectrum of cell-mediated immune abnormalities is required in individual cases of destructive autoimmune thyroiditis, before therapies that aim at correcting the immune abnormalities can be tested successfully.

Involvement of SOCS3 in regulation of CD11c+ dendritic cell-derived osteoclastogenesis and severe alveolar bone loss

To investigate the role of suppressor of cytokine signaling (SOCS) molecules in periodontal immunity and RANKL-mediated dendritic cell (DC)-associated osteoclastogenesis, we analyzed SOCS expression profiles in CD4(+) T cells and the effect of SOCS3 expression in CD11c(+) DCs during periodontal inflammation-induced osteoclastogenesis and bone loss in nonobese diabetic (NOD) versus humanized NOD/SCID mice. Our results of ex vivo and in vitro analyses showed that (i) there is significantly higher SOCS3 expression associated with RANKL(+) T-cell-mediated bone loss in correlation with increased CD11c(+) DC-mediated osteoclastogenesis; (ii) the transfection of CD11c(+) DC using an adenoviral vector carrying a dominant negative SOCS3 gene significantly abrogates TRAP and bone-resorptive activity; and (iii) inflammation-induced TRAP expression, bone resorption, and SOCS3 activity are not associated with any detectable change in the expression levels of TRAF6 and mitogen-activated protein kinase signaling adaptors (i.e., Erk, Jnk, p38, and Akt) in RANKL(+) T cells. We conclude that SOCS3 plays a critical role in modulating cytokine signaling involved in RANKL-mediated DC-derived osteoclastogenesis during immune interactions with T cells and diabetes-associated severe inflammation-induced alveolar bone loss. Therefore, the development of SOCS3 inhibitors may have therapeutic potential as the target to halt inflammation-induced bone loss under pathological conditions in vivo.

Innate immunity and its role in type 1 diabetes

PURPOSE OF REVIEW

Over the last 2 decades, studies addressing mechanisms of type 1 diabetes have focused primarily on the role of T lymphocytes in disease mechanisms. Recent investigations, however, suggest that the innate immune system plays a key role in promoting the response of autoreactive T cells triggering type 1 diabetes. The discovery of toll-like receptors in the 1990s has led to a better understanding of signaling pathways involved in initiating innate immune pathways and how these pathways may be associated with mechanisms leading to autoimmune disease. This review focuses on recent studies on the role of Toll-like receptors and innate pathways in triggering type 1 diabetes.

RECENT FINDINGS

Data from animal models of type 1 diabetes provide strong support to the hypothesis that Toll-like receptor-induced innate signaling pathways are involved in the proinflammatory process leading to autoimmune diabetes. Studies performed in peripheral blood cells and sera from patients with type 1 diabetes indicate that aberrant innate functions might exist in such patients, but the relevance of these alterations to the mechanism leading to type 1 diabetes is currently unclear.

SUMMARY

The discovery that innate signaling pathways are involved in the mechanism that may trigger islet inflammation and destruction holds great promise for the identification of new innate signaling molecules that could be targeted to specifically inhibit the autoimmune process to prevent autoimmune diabetes.

Differential contributions of APC subsets to T cell activation in nonobese diabetic mice

Despite the pivotal role of dendritic cells (DC) in shaping immunity, little is known about their functionality in type 1 diabetes. Moreover, due to the paucity of DC in vivo, functional studies have relied largely upon in vitro-expanded cells to elucidate type 1 diabetes-associated functional abnormalities. In this study, we provide a comprehensive analysis of the functional capabilities of in vivo-derived DC subsets from NOD mice by comparing DC to other NOD APC types and to DC from autoimmune-resistant strains. NOD DC closely resemble those from nonautoimmune strains with respect to costimulation and cytokine production. The exception is the CD8alpha(+)CD11b(-)DC subset which is numerically reduced in NOD spleens, but not in the pancreatic lymph nodes, while DC from both tissues produce little IL-12 in this strain. This defect results in unusual deferral toward macrophage-derived IL-12 in NOD mice; NOD macrophages produce aberrantly high IL-12 levels that can overcompensate for the DC defect in Th1 polarization. APC subset use for autoantigen presentation also differs in NOD mice. NOD B cells overshadow DC at activating islet-reactive T cells, whereas DC and B cells in NOD-resistant mice are functionally comparable. Differential involvement of APC subsets in T cell activation and tolerance induction may prove to be a crucial factor in the selection and expansion of autoreactive T cells.

Immunomodulation of autoimmune diabetes by dendritic cells

The biology and properties of dendritic cells (DCs) have been intensely studied in the research areas of infectious diseases, tumor immunology, and vaccine development. This unique subset of immune cells has recently also moved to the center of interest for basic and clinical research in autoimmunity, owing not only to the extraordinary importance of DCs in the initiation and sustenance of adaptive immune responses, but also to more recent discoveries about their profound ability to control and downregulate ongoing T-cell responses. We review current progress of using DCs in mice for induction and propagation of autoimmune T-cell responses and their therapeutic potential to dampen or even stop beta-cell-specific autoimmunity. Finally, we offer our perspective on how basic research progress in DC technology, mostly from mouse models, may translate into emerging diagnostic and therapeutic applications for human type 1 diabetes.

Granulocyte-macrophage colony-stimulating factor prevents diabetes development in NOD mice by inducing tolerogenic dendritic cells that sustain the suppressive function of CD4+CD25+ regulatory T cells

Autoimmune diabetes results from a breakdown of self-tolerance that leads to T cell-mediated beta-cell destruction. Abnormal maturation and other defects of dendritic cells (DCs) have been associated with the development of diabetes. Evidence is accumulating that self-tolerance can be restored and maintained by semimature DCs induced by GM-CSF. We have investigated whether GM-CSF is a valuable strategy to induce semimature DCs, thereby restoring and sustaining tolerance in NOD mice. We found that treatment of prediabetic NOD mice with GM-CSF provided protection against diabetes. The protection was associated with a marked increase in the number of tolerogenic immature splenic DCs and in the number of Foxp3+CD4+CD25+ regulatory T cells (Tregs). Activated DCs from GM-CSF-protected mice expressed lower levels of MHC class II and CD80/CD86 molecules, produced more IL-10 and were less effective in stimulating diabetogenic CD8+ T cells than DCs of PBS-treated NOD mice. Adoptive transfer experiments showed that splenocytes of GM-CSF-protected mice did not transfer diabetes into NOD.SCID recipients. Depletion of CD11c+ DCs before transfer released diabetogenic T cells from the suppressive effect of CD4+CD25+ Tregs, thereby promoting the development of diabetes. These results indicated that semimature DCs were required for the sustained suppressive function of CD4+CD25+ Tregs that were responsible for maintaining tolerance of diabetogenic T cells in NOD mice.

Immunoregulatory dendritic cells to prevent and reverse new-onset Type 1 diabetes mellitus

Herein, the authors provide an overview of where dendritic cells lie in the immunopathology of autoimmune Type 1 diabetes mellitus and how dendritic cell-based therapy may be usefully translated to treat and reverse the disease. The immunopathology of Type 1 diabetes mellitus offers a number of windows at which immunotherapy can be applied to delay, stop and even reverse the autoimmune processes, especially in light of the recent antibody-based accomplishment of improvement in residual beta-cell mass function. As in almost all cell-specific inflammatory processes, dendritic cells are central regulators of diabetes onset and progression. This realisation, along with accumulating data confirming a role for dendritic cells in maintaining and inducing tolerance in multiple therapeutic settings, has prompted a line of investigation to identify the most effective embodiments of dendritic cells for diabetes immunotherapy.

The vicious cycle of apoptotic beta-cell death in type 1 diabetes

Autoimmune insulitis, the cause of type 1 diabetes, evolves through several discrete stages that culminate in beta-cell death. In the first stage, antigenic epitopes of B-cell-specific peptides are processed by antigen presenting cells in local lymph nodes, and auto-reactive lymphocyte clones are propagated. Subsequently, cell-mediated and direct cytokine-mediated reactions are generated against the beta-cells, and the beta-cells are sensitized to apoptosis. Ironically, the beta-cells themselves contribute some of the cytokines and chemokines that provoke the immune reaction within the islets. Once this vicious cycle of autoimmunity is fully developed, the fate of the beta-cells in the islets is sealed, and clinical diabetes inevitably ensues. Differences in various aspects of these concurrent events appear to underlie the significant discrepancies in experimental data observed in experimental models that simulate autoimmune insulitis.

Systemic expression of heme oxygenase-1 ameliorates type 1 diabetes in NOD mice

Heme oxygenase-1 (HO-1) is an enzyme with potent immunoregulatory capacity. To evaluate the effect of HO-1 on autoimmune diabetes, female NOD mice at 9 weeks of age received a single intravenous injection of a recombinant adeno-associated virus bearing HO-1 gene (AAV-HO-1; 0.5 x 10(10)-2.5 x 10(10) viruses/mouse). In a dose-dependent manner, HO-1 transduction reduced destructive insulitis and the incidence of overt diabetes examined over a 15-week period. HO-1-mediated protection was associated with a lower type 1 T-helper cell (Th1)-mediated response. Adaptive transfer experiments in NOD.scid mice demonstrated that splenocytes isolated from AAV-HO-1-treated mice were less diabetogenic. Flow cytometry analysis revealed no significant difference in the percentages of CD4(+)CD25(+) regulatory T-cells between saline-treated and AAV-HO-1-treated groups. However, the CD11c(+) major histocompatibility complex II(+) dendritic cell population was much lower in the AAV-HO-1-treated group. A similar protective effect against diabetes was observed in NOD mice subjected to carbon monoxide (CO) gas (250 ppm CO for 2 h, twice per week). These data suggest that HO-1 slows the progression to overt diabetes in pre-diabetic NOD mice by downregulating the phenotypic maturity of dendritic cells and Th1 effector function. CO appears to mediate at least partly the beneficial effect of HO-1 in this disease setting.

Dendritic cell immunotherapy for autoimmune diabetes

Dendritic cells (DC) play important roles in the initiation of immune responses and maintenance of self-tolerance. We have been studying the role of DC in the pathogenesis of type 1 diabetes and exploring the ability of specific DC subsets to prevent diabetes in non-obese diabetic (NOD) mice. DC subsets that prevent diabetes in this model have a mature phenotype and induce the production of regulatory Th2 cells. We review here recent advances in this area and highlight the importance of optimizing culture conditions and purification methods in the isolation of therapeutic DC.

Defects in differentiation of bone-marrow derived dendritic cells of the BB rat are partly associated with IDDM2 (the lyp gene) and partly associated with other genes in the BB rat background

BB rats develop various organ-specific autoimmune diseases, e.g. autoimmune diabetes and thyroiditis and have proven important to dissect genetic factors that govern autoimmune disease development. The lymphopenia (lyp) gene (iddm2) is linked to autoimmune disease development and is a major genetic difference between diabetes-resistant (DR) and diabetes-prone (DP) BB rats. To study the effects of the lyp gene and other genes on dendritic cell (DC) differentiation from bone-marrow precursors, such differentiation was studied in BB-DP, BB-DR, Wistar and F344 control rats. DC of BB-DP rats showed a lower MHC class II expression as compared to BB-DR, Wistar and F344 rats. LPS-maturation did not restore this low MHC class II expression. DC of BB-DP rats also showed a poor capability to terminally differentiate into mature T cell stimulatory DC under the influence of LPS and produced significantly lower quantities of IL-10, yet these aberrancies were also found in BB-DR rats but did not occur in control rats. This study thus shows that various aberrancies exist in the differentiation of myeloid DC from bone-marrow precursors in the BB rat model of organ-specific autoimmunity. These aberrancies are multigenically determined and partly associated with iddm2 (lyp gene) and partly associated with other genes in the BB rat.

The NOD mouse: a model of immune dysregulation

Autoimmunity is a complex process that likely results from the summation of multiple defective tolerance mechanisms. The NOD mouse strain is an excellent model of autoimmune disease and an important tool for dissecting tolerance mechanisms. The strength of this mouse strain is that it develops spontaneous autoimmune diabetes, which shares many similarities to autoimmune or type 1a diabetes (T1D) in human subjects, including the presence of pancreas-specific autoantibodies, autoreactive CD4+ and CD8+ T cells, and genetic linkage to disease syntenic to that found in humans. During the past ten years, investigators have used a wide variety of tools to study these mice, including immunological reagents and transgenic and knockout strains; these tools have tremendously enhanced the study of the fundamental disease mechanisms. In addition, investigators have recently developed a number of therapeutic interventions in this animal model that have now been translated into human therapies. In this review, we summarize many of the important features of disease development and progression in the NOD strain, emphasizing the role of central and peripheral tolerance mechanisms that affect diabetes in these mice. The information gained from this highly relevant model of human disease will lead to potential therapies that may alter the development of the disease and its progression in patients with T1D.

Impaired IL-4 production by CD8+ T cells in NOD mice is related to a defect of c-Maf binding to the IL-4 promoter

CD8(+) T cells play an important role in the induction of the autoimmune response in non-obese diabetic (NOD) mice. Here we describe abnormalities in the control of cytokine production by NOD CD8(+) T cells. NOD CD8(+) T cells had an increased propensity to produce IFN-gamma upon TCR activation, in both adult and 2-week-old mice. NOD CD8(+) T cells had a reduced capacity to produce IL-4 in type 2 conditions compared to CD8(+) T cells from the diabetes-resistant strains BALB/c and C57BL/6. Both GATA-3 and c-Maf, two positive transactivators for IL-4 gene expression, were expressed in type 2 conditions at comparable levels in NOD CD8(+) T cells. The GATA-3 was functional since normal levels of IL-5 were produced and the IL-4 promoter was hyperacetylated in NOD CD8(+) T cells. In contrast, c-Maf failed to bind to its responsive element as determined by chromatin immunoprecipitation (ChIP) assay. These results suggest that NOD CD8(+) T cells possess an increased propensity to produce IFN-gamma and impaired c-Maf-dependent DNA binding activities in vivo that lead to reduced IL-4 production following TCR activation. These defects may facilitate the development of the autoimmune response by inducing an overall type 1-biased immune response in NOD mice.

T cell hyperactivity in lupus as a consequence of hyperstimulatory antigen-presenting cells

Sle3 is an NZM2410-derived lupus susceptibility locus on murine chromosome 7. Congenic recombination has resulted in a novel mouse strain, B6.Sle3, associated with serum antinuclear autoantibodies (ANAs), T cell hyperactivity, and elevated CD4/CD8 ratios. An OVA-specific TCR transgene was used as a tool to demonstrate that Sle3 facilitated heightened T cell expansion in vitro, and in vivo, following antigen challenge. Indeed, continued T cell expansion was noted even in response to a tolerogenic signal. However, these phenotypes did not appear to be T cell intrinsic but were dictated by hyperstimulatory B6.Sle3 APCs. Importantly, B6.Sle3-derived DCs and macrophages appeared to be significantly more mature/activated, less apoptotic, and more proinflammatory and were better at costimulating T cells in vitro, compared with the B6 counterparts. Finally, the adoptive transfer of B6.Sle3-derived DCs into healthy B6 recipients elicited increased CD4/CD8 ratios and serum ANAs, 2 cardinal Sle3-associated phenotypes. We posit that their heightened expression of various costimulatory molecules, including CD80, CD106, I-A, and CD40, and their elevated production of various cytokines, including IL-12 and IL-1beta, may explain why Sle3-bearing DCs may be superior at breaching self tolerance. These studies provide mechanistic evidence indicating that intrinsic abnormalities in DCs and possibly other myeloid cells may dictate several of the phenotypes associated with systemic lupus, including ANA formation and T cell hyperactivity.

1,25-Dihydroxyvitamin D3 alters the profile of bone marrow-derived dendritic cells of NOD mice

1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] prevents autoimmune diabetes in nonobese diabetic (NOD) mice. A major target for 1,25(OH)(2)D(3) in the immune system is the dendritic cell (DC). Since important DC abnormalities have been described in NOD mice, we investigated the effects of 1,25(OH)(2)D(3) on the yield and phenotype of DCs generated from bone marrow of NOD mice compared to control congenic nonobese diabetes-resistant (NOR) mice. In both mouse strains, exposure of the bone marrow-derived cells to 1,25(OH)(2)D(3) increased the proportion of CD11c(+) DCs after culture. Surface expression of MHC II, CD86, and CD54 on NOR-derived DCs was decreased after 1,25(OH)(2)D(3) treatment, while CD40 remained unchanged. On NOD-derived DCs, 1,25(OH)(2)D(3) only inhibited the expression of MHC II and CD86. 1,25(OH)(2)D(3) inhibited IL-12 and IL-10 secretion after IFNgamma and LPS stimulation. In vitro treatment with 1,25(OH)(2)D(3) alters DC yield from bone marrow cultures and alters the phenotype of the cells in NOD as well as in NOR mice. NOD-derived DCs were more resistant to the 1,25(OH)(2)D(3) effects than were NOR-derived DCs.

Treatment with granulocyte colony-stimulating factor prevents diabetes in NOD mice by recruiting plasmacytoid dendritic cells and functional CD4(+)CD25(+) regulatory T-cells

Accumulating evidence that granulocyte colony-stimulating factor (G-CSF), the key hematopoietic growth factor of the myeloid lineage, not only represents a major component of the endogenous response to infections, but also affects adaptive immune responses, prompted us to investigate the therapeutic potential of G-CSF in autoimmune type 1 diabetes. Treatment with G-CSF protected NOD mice from developing spontaneous diabetes. G-CSF triggered marked recruitment of dendritic cells (DCs), particularly immature CD11c(lo)B220(+) plasmacytoid DCs, with reduced costimulatory signal expression and higher interferon-alpha but lower interleukin-12p70 release capacity than DCs in excipient-treated mice. G-CSF recipients further displayed accumulation of functional CD4(+)CD25(+) regulatory T-cells that produce transforming growth factor-beta1 (TGF-beta1) and actively suppressed diabetes transfer by diabetogenic effector cells in secondary NOD-SCID recipients. G-CSF's ability to promote key tolerogenic interactions between DCs and regulatory T-cells was demonstrated by enhanced recruitment of TGF-beta1-expressing CD4(+)CD25(+) cells after adoptive transfer of DCs isolated from G-CSF- relative to vehicle-treated mice into naive NOD recipients. The present results suggest that G-CSF, a promoter of tolerogenic DCs, may be evaluated for the treatment of human type 1 diabetes, possibly in association with direct inhibitors of T-cell activation. They also provide a rationale for a protective role of the endogenous G-CSF produced during infections in early diabetes.

Bone Marrow Precursors of Nonobese Diabetic Mice Develop into Defective Macrophage-Like Dendritic Cells In Vitro

The NOD mouse spontaneously develops autoimmune diabetes. Dendritic cells (DC) play a crucial role in the autoimmune response. Previous studies have reported a defective DC generation in vitro from the NOD mouse bone marrow (BM), but a deviated development of myeloid precursors into non-DC in response to GM-CSF was not considered. In this study, we demonstrate several abnormalities during myeloid differentiation of NOD BM precursors using GM-CSF in vitro. 1) We found reduced proliferation and increased cell death in NOD cultures, which explain the previously reported low yield of DC progeny in NOD. Cell yield in NOR cultures was normal. 2) In a detailed analysis GM-CSF-stimulated cultures, we observed in both NOD and NOR mice an increased frequency of macrophages, identified as CD11c(+)/MHCII(-) cells with typical macrophage morphology, phenotype, and acid phosphatase activity. This points to a preferential maturation of BM precursors into macrophages in mice with the NOD background. 3) The few CD11c(+)/MHCII(high) cells that we obtained from NOD and NOR cultures, which resembled prototypic mature DC, appeared to be defective in stimulating allogeneic T cells. These DC had also strong acid phosphatase activity and elevated expression of monocyte/macrophage markers. In conclusion, in this study we describe a deviated development of myeloid BM precursors of NOD and NOR mice into macrophages and macrophage-like DC in vitro. Potentially, these anomalies contribute to the dysfunctional regulation of tolerance in NOD mice yet are insufficient to induce autoimmune diabetes because they occurred partly in NOR mice.

Passive transfer of flt-3L-derived dendritic cells delays diabetes development in NOD mice and associates with early production of interleukin (IL)-4 and IL-10 in the spleen of recipient mice

CD11c+/CD11b+dendritic cells (DC) with high levels of major histocompatibility complex (MHC) class II and co-stimulatory molecules have been derived from spleen cells cultured with granulocyte-macrophage colony stimulating factor (GM-CSF) + flt-3L + interleukin (IL)-6 (flt-3L-DC). Investigating in vivo the function of DC in non-obese diabetic mice (NOD), we showed that a single injection of this in vitro-derived subset of DC prevents the development of diabetes into prediabetic female mice. In contrast, DC derived from bone marrow cells cultured with GM-CSF + IL-4 [bone marrow (BM)-DC] induced no protection. Moreover, protection against diabetes following injection of flt-3L-DC was associated with IL-4 and IL-10 production in the spleen and the pancreatic lymph nodes of recipient mice, indicating that this DC population is able to polarize the immune response towards a Th2 pathway. As we shown previously, NOD BM-DC exhibit an enhanced capacity to produce IL-12p70 in response to lipopolysaccharide (LPS) and anti-CD40 stimulation compared to BM-DC from control mice. In contrast, NOD flt-3L-DC, as their control mouse counterpart, produced no IL-12p70 to these stimuli. Our findings show that a subset of DC, characterized by a mature phenotype and the absence of IL-12p70 production can be derived from NOD mouse spleen favouring IL-4 and IL-10 regulatory responses and protection from diabetes development.

Characterization of dendritic cells in humans with type 1 diabetes

The characterization of dendritic cells (DCs) in diabetes has primarily examined in vitro-generated DCs. In this study, we have compared the composition and phenotype of naturally occurring DCs within the peripheral blood of subjects with type 1 diabetes, latent-onset autoimmune diabetes in adults, and nondiabetic controls. We find that circulatory DC subsets exist in normal frequencies and phenotypic states in diabetic patients. In vivo, DCs were located around the pancreatic islets in type 1 diabetic patients, but were absent in pancreatic tissue of normal controls. These findings provide new insight toward understanding the pathological role of DCs in type 1 diabetes.

Dendritic cells, T cell tolerance and therapy of adverse immune reactions

Dendritic cells (DC) are uniquely able to either induce immune responses or to maintain the state of self tolerance. Recent evidence has shown that the ability of DC to induce tolerance in the steady state is critical to the prevention of the autoimmune response. Likewise, DC have been shown to induce several type of regulatory T cells including Th2, Tr1, Ts and NKT cells, depending on the maturation state of the DC and the local microenvironment. DC have been shown to have therapeutic value in models of allograft rejection and autoimmunity, although no success has been reported in allergy. Several strategies, including the use of specific DC subsets, genetic modification of DC and the use of DC at various maturation stages for the treatment of allograft rejection and autoimmune disease are discussed. The challenge for the future use of DC therapy in human disease is to identify the appropriate DC for the proposed therapy; a task made more daunting by the extreme plasticity of DC that has recently been demonstrated. However, the progress achieved to date suggests that these are not insurmountable obstacles and that DC may become a useful therapeutic tool in transplantation and autoimmune disease.

Granulocyte-dendritic cell unbalance in the non-obese diabetic mice

Several investigators, including ourselves, have reported lower yield of GM-CSF bone marrow-derived dendritic cells (DC) with altered MHC class II and co-stimulatory molecules expression in the non-obese diabetic (NOD) mice. However, whether this defect was intrinsic to the DC lineage and/or related to abnormal expansion of other cell types responding to GM-CSF remained an opened issue. We performed phenotypical and morphological analysis of cells from GM-CSF-supplemented-bone marrow-cultures and of freshly isolated bone marrow and blood cells from unmanipulated prediabetic NOD mice. The results show a heretofore undescribed bias towards generation of granulocytes in NOD mice, concomitant with quantitative and qualitative alterations of the DC lineage in both the bone marrow and the blood of this mouse strain. We propose that increased generation of granulocytes in NOD mice might contribute to autoimmunity. First, high numbers of granulocytes per se might favor inflammatory environment. Second, granulocytes, by interfering with DC development, might favor unbalanced antigen presenting cell function leading to T cell autoimmunity.