Defects in the differentiation and function of bone marrow-derived dendritic cells in non-obese diabetic mice

A Monocytic Barrier to the Humanization of Immunodeficient Mice

Mice with severe immunodeficiencies have become very important tools for studying foreign cells in an in vivo environment. Xenotransplants can be used to model cells from many species, although most often, mice are humanized through the transplantation of human cells or tissues to meet the needs of medical research. The development of immunodeficient mice is reviewed leading up to the current state-of-the-art strains, such as the NOD-scid-gamma (NSG) mouse. NSG mice are excellent hosts for human hematopoietic stem cell transplants or immune reconstitution through transfusion of human peripheral blood mononuclear cells. However, barriers to full hematopoietic engraftment still remain; notably, the survival of human cells in the circulation is brief, which limits overall hematological and immune reconstitution. Reports have indicated a critical role for monocytic cells - monocytes, macrophages, and dendritic cells - in the clearance of xenogeneic cells from circulation. Various aspects of the NOD genetic background that affect monocytic cell growth, maturation, and function that are favorable to human cell transplantation are discussed. Important receptors, such as SIRPα, that form a part of the innate immune system and enable the recognition and phagocytosis of foreign cells by monocytic cells are reviewed. The development of humanized mouse models has taken decades of work in creating more immunodeficient mice, genetic modification of these mice to express human genes, and refinement of transplant techniques to optimize engraftment. Future advances may focus on the monocytic cells of the host to find ways for further engraftment and survival of xenogeneic cells.

Adoptive transfer of immature dendritic cells with high HO-1 expression delays the onset of T1DM in NOD mice

AIMS

To investigate the potential of imDCs with high expression of HO-1 in preventing or delaying the onset of Type 1 diabetes mellitus (T1DM) in non-obese diabetic (NOD) mice.

MATERIALS AND METHODS

The phenotypic features of DCs in each group were assessed using flow cytometry. Western blot analysis was used to confirm the high expression of HO-1 in imDCs induced with CoPP. Additionally, flow cytometry was used to evaluate the suppressive capacity of CoPP-induced imDCs on splenic lymphocyte proliferation. Finally, the preventive effect of CoPP-induced imDCs was tested in NOD mice.

KEY FINDINGS

Compared to imDCs, CoPP-induced imDCs exhibited a reduced mean fluorescence intensity (MFI) of the co-stimulatory molecule CD80 on their surface (P < 0.05) and significantly increased HO-1 protein expression (P < 0.05). Following LPS stimulation, the MFI of co-stimulatory molecules CD80 and CD86 on the surface of CoPP-induced imDCs remained at a lower level (P < 0.05). Furthermore, there was a reduced proliferation rate of lymphocytes stimulated with anti-CD3/28 antibodies. The adoptive transfer of CoPP-imDCs significantly reduced the incidence of T1DM (16.66 % vs. control group: 66.67 %, P = 0.004). Furthermore, at 15 weeks of age, the insulitis score was also decreased in the CoPP-induced imDC treatment group (P < 0.05). There were no significant differences in serum insulin levels among all groups.

SIGNIFICANCE

ImDCs induced with CoPP and exhibiting high expression of HO-1 demonstrate a robust ability to inhibit immune responses and effectively reduce the onset of diabetes in NOD mice. This finding suggests that CoPP-induced imDCs could potentially serve as a promising treatment strategy for T1DM.

The effects of 1,25(OH)2D3 treatment on metabolic reprogramming and maturation in bone marrow-derived dendritic cells from control and diabetic mice

Activated dendritic cells (DCs) undergo significant metabolic reprogramming, which is characterized by an increase in aerobic glycolysis and a concurrent progressive loss of oxidative phosphorylation. The modulation of metabolic reprogramming is believed to be closely related to the function of DCs. Vitamin D has been reported to inhibit the maturation of DCs. DC dysfunction has been reported in diabetic patients, and hyperglycemia is associated with impaired glycolytic metabolism in immune cells. Therefore, vitamin D and diabetes may affect intracellular metabolism, thereby regulating the activity of DCs. We investigated the effect of in vitro treatment of 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) on metabolic reprogramming and maturation of bone marrow-derived dendritic cells (BMDCs) from diabetic mouse. Six-week-old male C57BLKS/J-m⁺/m⁺ mice (CON) and C57BLKS/J-db/db mice (db/db) were fed with a 10% kcal fat diet for seven weeks. BMDCs were generated by culturing bone marrow cells from the mice with rmGM-CSF (20 ng/mL) in the absence or presence of 10 nM 1,25(OH)₂D₃. The maturation of BMDCs was induced via lipopolysaccharide (LPS, 50 ng/mL) stimulation for 24 h. LPS stimulation induced iNOS protein expression and decreased the mitochondrial respiration, while increased lactate production and the expression of glycolytic pathway-related genes (Glut1 and Pfkfb3) in BMDCs from both CON and db/db groups. In LPS-stimulated mature BMDCs, 1,25(OH)₂D₃ treatment decreased the expression of surface markers related to immunostimulatory functions (MHC class II, CD80, CD86, and CD40) and production of IL-12p70 in both CON and db/db groups. While the mRNA level of the gene related to glucose uptake (Glut1) was increased in both groups, lactate production was decreased by 1,25(OH)₂D₃ treatment. mTORC1 activity was suppressed following 1,25(OH)₂D₃ treatment. Collectively, our findings confirmed that metabolic reprogramming occurred in BMDCs following LPS stimulation. In vitro 1,25(OH)₂D₃ treatment induced tolerogenic phenotypes by reducing the expression of surface markers, as well as cytokine production. However, no significant difference was observed regarding the effects of 1,25(OH)₂D₃ treatment on metabolic conversion and maturation of BMDCs between the control and diabetic mice. Additionally, the decreased aerobic glycolysis induced by the 1,25(OH)₂D₃ treatment appeared to be associated with the diminished maturation of BMDCs, and mTORC1 appears to play a key role in the 1,25(OH)₂D₃-mediated regulation of glycolysis.

Syngeneic bone marrow transplantation in combination with PI3K inhibitor reversed hyperglycemia in later-stage streptozotocin-induced diabetes

Background

Type 1 diabetes (T1D) is a multiple factor autoimmune disease characterized by T cell-mediated immune destruction of islet β cells. Autologous hematopoietic stem cell transplantation (AHSCT) has been a novel strategy for patients with new-onset T1D, but not for those with a later diagnosis. Disturbance of regulatory T cells (Tregs) likely contributes to poor response after transplantation in later-stage T1D. Inhibition of phosphoinositide 3-kinases (PI3K)/Akt signaling maintains Tregs’ homeostasis.

Methods

We built a later-stage streptozotocin (STZ)-induced T1D mouse model. Syngeneic bone marrow transplantation (syn-BMT) was performed 20 days after the onset of diabetes in combination with BKM120 (a PI3K inhibitor). Meanwhile, another group of STZ-diabetic mice were transplanted with bone marrow cells cocultured with BKM120 in vitro for 24 h. Fasting glucose and glucose tolerance were recorded during the entire experimental observation after syn-BMT. Samples were collected 126 days after syn-BMT. Hematoxylin and eosin (H&E) staining was used to detect the effect of PI3K inhibitor combined with syn-BMT on morphology of the T1D pancreas. CD4⁺CD25⁻ T cells and CD4⁺CD25⁺ T cells were sorted by magnetic cell sorting (MACS), then fluorescence activated cell sorting (FACS) and quantitative real-time PCR (qPCR) were used to detect the effect of PI3K inhibitor on modulating immune disorder and restoring the function of Treg cells.

Results

Our investigation showed syn-BMT in combination with BKM120 effectively maintained normoglycemia in later-stage T1D. The disease remission effects may be induced by the rebalance of Th17/Tregs dysregulation and restoration of Tregs’ immunosuppressive function by BKM120 after syn-BMT.

Conclusions

These results may reveal important connections for PI3K/Akt inhibition and Tregs’ homeostasis in T1D after transplantation. AHSCT combining immunoregulatory strategies such as PI3K inhibition may be a promising therapeutic approach in later-stage T1D.

Exopolysaccharide Produced by Lactobacillus Plantarum Induces Maturation of Dendritic Cells in BALB/c Mice

Lactobacillus plantarum (L. plantarum) exopolysaccharide (EPS) is an important bioactive component in fermented functional foods. However, there is a lack of data concerning the effects of L. plantarum EPS on maturation of mouse dendritic cells (DCs). In this study, we purified L. plantarum EPS and examined its effects on cytokines production by dendritic cells in serum and intestinal fluid of BALB/c mice, then investigated its effects on phenotypic and functional maturation of mouse bone marrow-derived dendritic cells (BMDCs). Cytokines (nitric oxide, IL-12p70, IL-10 and RANTES) in serum and intestinal fluid were analyzed by enzyme linked immunosorbent assay (ELISA) after the mice received EPS for 2, 5 and 7 days, respectively. DCs derived from bone marrow of BALB/c mouse were treated with EPS, then the phenotypic maturation of BMDCs was analyzed using flow cytometer and the functional maturation of BMDCs was analyzed by ELISA, and, lastly, mixed lymphocyte proliferation was performed. We found the molecular weight of purified EPS was approximately 2.4×106 Da and it was composed of ribose, rhamnose, arabinose, xylose, mannose, glucose and galactose in a molar ratio of 2:1:1:10:4:205:215. We observed that L. plantarum EPS enriched production of nitric oxide, IL-12p70 and RANTES, and decreased the secretion of IL-10 in the serum or intestinal fluid as well as in the supernatant of DCs treated with the EPS. The EPS also up-regulated the expression of MHC II and CD86 on DCs surface and promoted T cells to proliferate in vitro. Our data provide direct evidence to suggest that L. plantarum EPS can effectively induce maturation of DCs in mice.

Reduced interferon-α production by dendritic cells in type 1 diabetes does not impair immunity to influenza virus

The increased risk and persistence of infections in diabetic condition is probably associated with defects in the cellular immune responses. We have previously shown a decrease in the production of interferon (IFN)-α by dendritic cells (DCs) in diabetic subjects. The basal level of IFN-α in splenic plasmacytoid DCs (pDCs) is also lower in non-obese diabetic (NOD) mice compared to prediabetic mice. The objective of this study was to analyse the ability of diabetic mice to mobilize innate and CD8(+) T cell-mediated immune response to influenza A virus (IAV) with the live influenza A/Puerto Rico/8/1934 H1N1 (PR8) strain or with its immunodominant CD8(+) T cell epitopes. We found that following immunization with IAV, the level of IFN-α in diabetic mice was increased to the level in prediabetic mice. Immunization of NOD mice with the immunodominant IAV PR8 peptide induced clonal expansion of IFN-γ-producing CD8(+) T cells similar to the response observed in prediabetic mice. Thus, diabetic and prediabetic NOD mice have a similar capacity for IFN-α and IFN-γ production by pDCs and CD8(+) T cells, respectively. Therefore, the DC-related immune defect in diabetic NOD mice does not impair their capacity to develop an effective immune response to IAV. Our results suggest that reduced IFN-α production by diabetic human and mouse DCs is not an impediment to an effective immunity to IAV in type 1 diabetic subjects vaccinated with live attenuated influenza vaccine.

The potential role of dendritic cells in the therapy of Type 1 diabetes

Type 1 diabetes (T1D) is the result of T-cell mediated autoimmune destruction of pancreatic islet β-cells. The two current treatments for T1D are based on insulin or islet-cell replacement rather than the pathogenesis of T1D and remain problematic. Islet/pancreas transplantation does not cater for the majority of sufferers due to the lack of supply of organs and the need for continuous immunosuppression regimens. The mainstay treatment is insulin replacement, but this is disruptive to lifestyle and does not protect against severe long-term complications. An early vaccination and long-term restoration of immune tolerance to self-antigens in T1D patients (reversing the immunopathogenesis of the disease) would be preferable. Dendritic cells (DCs) are potent APCs and play an important role in inducing and maintaining immune tolerance. Targeting DCs through different DC surface molecules shows effective modulation of immune responses. Their feasibility for immunotherapy to prolong transplant survival and cancer immunotherapy has been demonstrated. Therefore, DCs could potentially be used in the treatment of autoimmune diseases. This review summarizes new insights into DCs as a potential therapeutic target for the treatment of T1D.

Efferocytosis promotes suppressive effects on dendritic cells through prostaglandin E2 production in the context of autoimmunity

Introduction

Efferocytosis is a crucial process by which apoptotic cells are cleared by phagocytes, maintaining immune tolerance to self in the absence of inflammation. Peripheral tolerance, lost in autoimmune processes, may be restored by the administration of autologous dendritic cells loaded with islet apoptotic cells in experimental type 1 diabetes.

Objective

To evaluate tolerogenic properties in dendritic cells induced by the clearance of apoptotic islet cells, thus explaining the re-establishment of tolerance in a context of autoimmunity.

Methods

Bone marrow derived dendritic cells from non-obese diabetic mice, a model of autoimmune diabetes, were generated and pulsed with islet apoptotic cells. The ability of these cells to induce autologous T cell proliferation and to suppress mature dendritic cell function was assessed, together with cytokine production. Microarray experiments were performed using dendritic cells to identify differentially expressed genes after efferocytosis.

Results

Molecular and functional changes in dendritic cells after the capture of apoptotic cells were observed. 1) Impaired ability of dendritic cells to stimulate autologous T cell proliferation after the capture of apoptotic cells even after proinflammatory stimuli, with a cytokine profile typical for immature dendritic cells. 2) Suppressive ability of mature dendritic cell function. 3) Microarray-based gene expression profiling of dendritic cells showed differential expression of genes involved in antigen processing and presentation after efferocytosis. 4) Prostaglandin E2 increased production was responsible for immunosuppressive mechanism of dendritic cells after the capture of apoptotic cells.

Conclusions

The tolerogenic behaviour of dendritic cells after islet cells efferocytosis points to a mechanism of silencing potential autoreactive T cells in the microenvironment of autoimmunity. Our results suggest that dendritic cells may be programmed to induce specific immune tolerance using apoptotic cells; this is a viable strategy for a variety of autoimmune diseases.

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.

APC activation restores functional CD4(+)CD25(+) regulatory T cells in NOD mice that can prevent diabetes development

Background

Defects in APC and regulatory cells are associated with diabetes development in NOD mice. We have shown previously that NOD APC are not effective at stimulating CD4⁺CD25⁺ regulatory cell function in vitro. We hypothesize that failure of NOD APC to properly activate CD4⁺CD25⁺ regulatory cells in vivo could compromise their ability to control pathogenic cells, and activation of NOD APC could restore this defect, thereby preventing disease.

Methodology/Principal Findings

To test these hypotheses, we used the well-documented ability of complete Freund's adjuvant (CFA), an APC activator, to prevent disease in NOD mice. Phenotype and function of CD4⁺CD25⁺ regulatory cells from untreated and CFA-treated NOD mice were determined by FACS, and in vitro and in vivo assays. APC from these mice were also evaluated for their ability to activate regulatory cells in vitro. We have found that sick NOD CD4⁺CD25⁺ cells expressed Foxp3 at the same percentages, but decreased levels per cell, compared to young NOD or non-NOD controls. Treatment with CFA increased Foxp3 expression in NOD cells, and also increased the percentages of CD4⁺CD25⁺Foxp3⁺ cells infiltrating the pancreas compared to untreated NOD mice. Moreover, CD4⁺CD25⁺ cells from pancreatic LN of CFA-treated, but not untreated, NOD mice transferred protection from diabetes. Finally, APC isolated from CFA-treated mice increased Foxp3 and granzyme B expression as well as regulatory function by NOD CD4⁺CD25⁺ cells in vitro compared to APC from untreated NOD mice.

Conclusions/Significance

These data suggest that regulatory T cell function and ability to control pathogenic cells can be enhanced in NOD mice by activating NOD APC.

Resolving the conundrum of islet transplantation by linking metabolic dysregulation, inflammation, and immune regulation

Although type 1 diabetes cannot be prevented or reversed, replacement of insulin production by transplantation of the pancreas or pancreatic islets represents a definitive solution. At present, transplantation can restore euglycemia, but this restoration is short-lived, requires islets from multiple donors, and necessitates lifelong immunosuppression. An emerging paradigm in transplantation and autoimmunity indicates that systemic inflammation contributes to tissue injury while disrupting immune tolerance. We identify multiple barriers to successful islet transplantation, each of which either contributes to the inflammatory state or is augmented by it. To optimize islet transplantation for diabetes reversal, we suggest that targeting these interacting barriers and the accompanying inflammation may represent an improved approach to achieve successful clinical islet transplantation by enhancing islet survival, regeneration or neogenesis potential, and tolerance induction. Overall, we consider the proinflammatory effects of important technical, immunological, and metabolic barriers including: 1) islet isolation and transplantation, including selection of implantation site; 2) recurrent autoimmunity, alloimmune rejection, and unique features of the autoimmune-prone immune system; and 3) the deranged metabolism of the islet transplant recipient. Consideration of these themes reveals that each is interrelated to and exacerbated by the other and that this connection is mediated by a systemic inflammatory state. This inflammatory state may form the central barrier to successful islet transplantation. Overall, there remains substantial promise in islet transplantation with several avenues of ongoing promising research. This review focuses on interactions between the technical, immunological, and metabolic barriers that must be overcome to optimize the success of this important therapeutic approach.

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.

Functional deficiencies of granulocyte-macrophage colony stimulating factor and interleukin-3 contribute to insulitis and destruction of beta cells

The pathogenesis of type 1 diabetes (T1D) involves the immune-mediated destruction of insulin-producing beta cells in the pancreatic islets of Langerhans. Genetic analysis of families with a high incidence of T1D and nonobese diabetic (NOD) mice, a prototypical model of the disorder, uncovered multiple susceptibility loci, although most of the underlying immune defects remain to be delineated. Here we report that aged mice doubly deficient in granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-3 (IL-3) manifest insulitis, destruction of insulin-producing beta cells, and compromised glucose homeostasis. Macrophages from mutant mice produce increased levels of p40 after LPS stimulation, whereas concurrent ablation of interferon-gamma (IFN-gamma) ameliorates the disease. The administration of antibodies that block cytotoxic T lymphocyte associated antigen-4 (CTLA-4) to young mutant mice precipitates the onset of insulitis and hyperglycemia. These results, together with previous reports of impaired hematopoietic responses to GM-CSF and IL-3 in patients with T1D and in NOD mice, indicate that functional deficiencies of these cytokines contribute to 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.

Roles of dendritic cells and regulatory T cells in autoantigen-induced murine immune tolerance model

AIM: To investigate the important roles of dendritic cells (DC) and CD4⁺CD25⁺ regulatory T cells in immune prevention against insulin dependent diabetes (IDDM) by autoantigen insulin administration.

METHODS: The model of IDDM was established by intraperitoneal injection of low-dose streptozotocin (STZ) 40 mg/kg per day for 5 consecutive days in Balb/c mice. The bovine insulin (100 μg) in incomplete Freund's adjuvant (IFA, emulsified 1∶1) was given subcutaneously to the mice weekly for 4 wk. The blood glucose was examined once a week and all the mice were killed after 5 wk. Pancreas tissues were collected for histopathological examination. DC precursor cells from bone marrow and lymphocytes from spleen were isolated. The phenotype of DC and CD4⁺ CD25⁺ regulatory T cells were analyzed by fluorescence activated cell sorter (FACS). DC-stimulated proliferation of lymphacytes was determined by allo-mixed lymphocyte reaction (aMLR).

RESULTS: The level of blood glucose was decreased significantly after insulin injection in comparison with that in the model control group (13.79 ± 2.71 mmol/L vs 20.98 ± 1.43 mmol/L, P < 0.05). Fewer lymphocytes infiltration was observed and pancreatic histological structure was intact. The surface marker CD11c on DC from bone marrow was decreased markedly in IDDM mice (26.4%) than that in normal mice (47.5%). DC differentiated abnormally, and the capacity of stimulating proliferation of allogeneic T cell was weakened as compared with that of normal mice (1.47 ± 0.01 vs 2.93 ± 0.01, P < 0.01, and 1.32 ± 0.01 vs 2.94 ± 0.02, P < 0.01, at DC/T ratios of 1∶10 and 1∶20, respectively). The percentage of CD4⁺CD25⁺ T cells were decreased to 1.43%, while it was 5.09% in normal mice. In contrast, blood glucose in mice given insulin subcutaneously was well controlled, and the amount of DC with CD11c was increased (50% approximately); the expression of CD86 and MHC-Ⅱ was low (26.6% and 28.8%, respectively) and MLR showed that DC capacity in stimulating T cell proliferation was lower than those from the normal mice, but higher than those from IDDM model mice (2.30 ± 0.06 and 2.17 ± 0.02, at DC/T ratios of 1∶10 and 1∶20, respectively); the percentage of CD4⁺CD25⁺ T cells from spleen was enhanced to 7.15%.

CONCLUSION: Subcutaneous administration of insulin can confer protection to mice against IDDM induced by STZ. The immune protection of autoantigen may be associated with the establishment of immune tolerance by improving the function of abnormal DC and promoting the production of CD4⁺CD25⁺ T cells in vivo.

Evidence for an enhanced adhesion of DC to fibronectin and a role of CCL19 and CCL21 in the accumulation of DC around the pre-diabetic islets in NOD mice

The non-obese diabetic (NOD) mouse is a widely used animal model for the study of human diabetes. The lymphocytic (peri-)insulitis is preceded by an early accumulation of dendritic cells (DC) around the islets of Langerhans. This DC accumulation is thought to derive from an influx of monocytes attracted by pro-inflammatory chemokines. Besides chemokines, extracellular matrix (ECM) proteins play an important role in the accumulation of leukocytes in tissues. We studied the expression of the chemokines CCL2, CCL5, CXCL10, CCL19 and CCL21 over time in pancreases of NOD and control mice by ELISA on pancreas lysates as well as by immunohistochemistry. In addition, we studied the adhesive capacity of bone marrow-derived DC (BMDC) to ECM components. DC in the NOD pancreas accumulated at sites with an intense expression of fibronectin. In vitro, NOD BMDC showed increased fibronectin adhesion and increased VLA-5 expression. At the time of early DC accumulation (<10 wk), the lymphoid tissue-related chemokines CCL19 and CCL21 were increased. Our findings support the view that the early accumulation of DC around the NOD islets is not the consequence of an enhanced attraction of precursors and immature DC by pro-inflammatory chemokines. It rather might be the consequence of an aberrantly enhanced adhesion and retention of NOD DC.

Hematopoietic stem cells from NOD mice exhibit autonomous behavior and a competitive advantage in allogeneic recipients

Type 1 diabetes is a systemic autoimmune disease that can be cured by transplantation of hematopoietic stem cells (HSCs) from disease-resistant donors. Nonobese diabetic (NOD) mice have a number of features that distinguish them as bone marrow transplant recipients that must be understood prior to the clinical application of chimerism to induce tolerance. In the present studies, we characterized NOD HSCs, comparing their engraftment characteristics to HSCs from disease-resistant strains. Strikingly, NOD HSCs are significantly enhanced in engraftment potential compared with HSCs from disease-resistant donors. Unlike HSCs from disease-resistant strains, they do not require graft-facilitating cells to engraft in allogeneic recipients. Additionally, they exhibit a competitive advantage when coadministered with increasing numbers of syngeneic HSCs, produce significantly more spleen colony-forming units (CFU-Ss) in vivo in allogeneic recipients, and more granulocyte macrophage–colony-forming units (CFU-GMs) in vitro compared with HSCs from disease-resistant controls. NOD HSCs also exhibit significantly enhanced chemotaxis to a stromal cell–derived factor 1 (SDF-1) gradient and adhere significantly better on primary stroma. This enhanced engraftment potential maps to the insulin-dependent diabetes locus 9 (Idd9) locus, and as such the tumor necrosis factor (TNF) receptor family as well as ski/sno genes may be involved in the mechanism underlying the autonomy of NOD HSCs. These findings may have important implications to understand the evolution of autoimmune disease and impact on potential strategies for cure.

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.

Flt3-ligand treatment prevents diabetes in NOD mice

The mechanism by which mixed chimerism reverses autoimmunity in type 1 diabetes has not been defined. NOD mice have a well-characterized defect in the production of myeloid progenitors that is believed to contribute significantly to the autoimmune process. We therefore investigated whether chimerism induces a correction of this defect. Mixed chimerism restored production of myeloid progenitors in NOD mice to normal levels. Notably, NOD bone marrow cells as well as donor bone marrow cells produced the mature myeloid progeny, and the level of donor chimerism was not correlated with the degree of restoration of the defect. Moreover, NOD bone marrow cells cultured with Flt3-ligand developed a heat-stable antigen-positive/Ly6C+ population comprised primarily of mature myeloid dendritic cells, suggesting that the underlying abnormality is not cell intrinsic but rather due to a block in development of mature myeloid progeny, including myeloid dendritic cells. Strikingly, treatment of NOD mice with Flt3-ligand significantly decreased insulitis and progression to diabetes and was associated with a significant increase in myeloid dendritic cells and in vivo induction of CD4+/CD25+ cells in the pancreatic lymph node. Therefore, Flt3-ligand treatment and/or the establishment of mixed chimerism in prediabetic candidates may provide a benign and novel approach to treat diabetes.

Increased serum levels of MRP-8/14 in type 1 diabetes induce an increased expression of CD11b and an enhanced adhesion of circulating monocytes to fibronectin

The recruitment of monocytes from the bloodstream is crucial in the accumulation of macrophages and dendritic cells in type 1 diabetic pancreases. Adhesion via integrins to endothelium and extracellular matrix proteins, such as fibronectin (FN), and the production of myeloid-related protein (MRP)-8, -14, and -8/14 by recently transmigrated monocytes are thought to be instrumental in such recruitment. We determined the FN-adhesive capacity and integrin expression of monocytes of type 1 and type 2 diabetic patients and related them to the subjects' serum levels of MRP-8, -14 and -8/14. Monocytes of type 1 diabetic patients displayed an increased adhesion to fibronectin in comparison with type 2 patients and healthy control subjects but had a normal expression of the FN binding integrins CD29, CD49a, CD49d, and CD49e (although CD11b and CD18 expression was increased). MRP-8/14, which was increased in the sera of type 1 diabetic patients, induced healthy donor monocytes to adhere to FN and upregulate CD11b expression in a dosage-dependent manner. The observed MRP-induced increased adhesion of monocytes to FN and upregulation of CD11b most likely contributed to a facilitated accumulation of monocytes and monocyte-derived cells at the site of inflammation, in this case the pancreatic islets.

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.

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.

Increased generation of dendritic cells from myeloid progenitors in autoimmune-prone nonobese diabetic mice

Aberrant dendritic cell (DC) development and function may contribute to autoimmune disease susceptibility. To address this hypothesis at the level of myeloid lineage-derived DC we compared the development of DC from bone marrow progenitors in vitro and DC populations in vivo in autoimmune diabetes-prone nonobese diabetic (NOD) mice, recombinant congenic nonobese diabetes-resistant (NOR) mice, and unrelated BALB/c and C57BL/6 (BL/6) mice. In GM-CSF/IL-4-supplemented bone marrow cultures, DC developed in significantly greater numbers from NOD than from NOR, BALB/c, and BL/6 mice. Likewise, DC developed in greater numbers from sorted (lineage(-)IL-7Ralpha(-)SCA-1(-)c-kit(+)) NOD myeloid progenitors in either GM-CSF/IL-4 or GM-CSF/stem cell factor (SCF)/TNF-alpha. [(3)H]TdR incorporation indicated that the increased generation of NOD DC was due to higher levels of myeloid progenitor proliferation. Generation of DC with the early-acting hematopoietic growth factor, flt3 ligand, revealed that while the increased DC-generative capacity of myeloid-committed progenitors was restricted to NOD cells, early lineage-uncommitted progenitors from both NOD and NOR had increased DC-generative capacity relative to BALB/c and BL/6. Consistent with these findings, NOD and NOR mice had increased numbers of DC in blood and thymus and NOD had an increased proportion of the putative myeloid DC (CD11c(+)CD11b(+)) subset within spleen. These findings demonstrate that diabetes-prone NOD mice exhibit a myeloid lineage-specific increase in DC generative capacity relative to diabetes-resistant recombinant congenic NOR mice. We propose that an imbalance favoring development of DC from myeloid-committed progenitors predisposes to autoimmune disease in NOD mice.

A defect in bone marrow derived dendritic cell maturation in the nonobesediabetic mouse

The pathogenesis of diabetes in the nonobese diabetic (NOD) mouse is characterized by a selective destruction of the insulin-producing beta-cells in the islets of Langerhans mediated by autoreactive T cells. The function of T cells is controlled by dendritic cells (DC), which are not only the most potent activators of naïve T cells, but also contribute significantly to the establishment of central and peripheral tolerance. In this study, we demonstrate that the NOD mouse (H2: K(d), Ag(7), E*, D(b)) shows selective phenotypic and functional abnormalities in DC derived from bone marrow progeny cells in response to GM-CSF (DC(NOD)). NOD DC, in contrast to CBA DC, have very low levels of intracellular I-A molecules and cell surface expression of MHC class II, CD80, CD86 and CD40 but normal beta 2-microglobulin expression. Incubation with the strong inflammatory stimulus of LPS and IFN-gamma does not increase class II MHC, CD80 or CD86, but upregulates the level of CD40. The genetic defect observed in the DC(NOD) does not map to the MHC, because the DC from the MHC congenic NOD.H2(h4) mouse (H2: K(k), A(k), E(k), D(k)) shares the cell surface phenotype of the DC(NOD). DC from these NOD.H2(h4) also fail to present HEL or the appropriate HEL-peptide to an antigen-specific T cell hybridoma. However all the DC irrespective of origin were able to produce TNF-alpha, IL-6, low levels of IL-12(p70) and NO in response to LPS plus IFN-gamma. A gene or genes specific to the NOD strain, but outside the MHC region, therefore must regulate the differentiation of DC in response to GM-CSF. This defect may contribute to the complex genetic aetiology of the multifactorial autoimmune phenotype of the NOD strain.