CD28 co-stimulation restores T cell responsiveness in NOD mice by overcoming deficiencies in Rac-1/p38 mitogen-activated protein kinase signaling and IL-2 and IL-4 gene transcription

Adipocytes from New Zealand obese mice exhibit aberrant proinflammatory reactivity to the stress signal heat shock protein 60

Adipocytes release immune mediators that contribute to diabetes-associated inflammatory processes. As the stress protein heat shock protein 60 (Hsp60) induces proinflammatory adipocyte activities, we hypothesized that adipocytes of diabetes-predisposed mice exhibit an increased proinflammatory reactivity to Hsp60. Preadipocytes and mature adipocytes from nonobese diabetic (NOD), New Zealand obese (NZO), and C57BL/6J mice were analyzed for Hsp60 binding, Hsp60-activated signaling pathways, and Hsp60-induced release of the chemokine CXCL-1 (KC), interleukin 6 (IL-6), and macrophage chemoattractant protein-1 (MCP-1). Hsp60 showed specific binding to (pre-)adipocytes of NOD, NZO, and C57BL/6J mice. Hsp60 binding involved conserved binding structure(s) and Hsp60 epitopes and was strongest to NZO mouse-derived mature adipocytes. Hsp60 exposure induced KC, IL-6, and MCP-1 release from (pre-)adipocytes of all mouse strains with a pronounced increase of IL-6 release from NZO mouse-derived adipocytes. Compared to NOD and C57BL/6J mouse derived cells, Hsp60-induced formation of IL-6, KC, and MCP-1 from NZO mouse-derived (pre-)adipocytes strongly depended on NF κ B-activation. Increased Hsp60 binding and Hsp60-induced IL-6 release by mature adipocytes of NZO mice suggest that enhanced adipocyte reactivity to the stress signal Hsp60 contributes to inflammatory processes underlying diabetes associated with obesity and insulin resistance.

IL-13Rα1 expression on β-cell-specific T cells in NOD mice

OBJECTIVE

Immunotherapy using peptides from the β-cell antigen GAD65 can preserve glucose homeostasis in diabetes-prone NOD mice; however, the precise mechanisms that arrest islet-reactive T cells remain unresolved. Our previous work revealed that a dominant GAD65 epitope contained two overlapping I-A(g7)-restricted determinants, 524-538 and 530-543, with the former associated with amelioration of hyperglycemia. Here, we sought to discover whether p524-538-specific T cells could directly regulate islet-reactive T cells.

RESEARCH DESIGN AND METHODS

Prediabetic NOD mice were used to determine the relationship between peptide p524-538-induced interleukin (IL)-13 and regulation of islet autoimmunity. Pancreatic lymph node (PLN) cells from mice at distinct stages of islet inflammation, peri-insulitis versus invasive insulitis, were harvested to establish the expression pattern of IL-13 receptor α1 (IL-13Rα1) on islet-associated T cells.

RESULTS

Peptide p524-538 preferentially induced IL-13-producing T cells that antagonized the release of γ-interferon by spontaneously arising GAD65 autoimmunity, and recombinant human IL-13 inhibited proliferation of islet-reactive clonotypic T cells. A subset of CD4(+) T cells in NOD and NOD.BDC2.5 T cell receptor transgenic mice expressed functional IL-13Rα1, which induced phosphorylation of signal transducer and activator of transcription 6 in the presence of cognate cytokine. Notably, the number of IL-13Rα1(+) T cells was heightened in the PLN of young NOD mice when compared with older female counterparts with advanced insulitis. Immunization with p524-538 preserved IL-13Rα1 expression on PLN T cells.

CONCLUSIONS

IL-13 may be important for regulating autoimmunity in the early stages of insulitis, and the loss of IL-13Rα1 on islet-reactive T cells may be a biomarker for fading regional immune regulation and progression to overt diabetes.

CD28 co-signaling in the adaptive immune response

T-cell proliferation and function depends on signals from the antigen-receptor complex (TCR/CD3) and by various co-receptors such as CD28 and CTLA-4. The balance of positive and negative signals determines the outcome of the T-cell response to foreign and self-antigen. CD28 is a prominent co-receptor in naïve and memory T-cell responses. Its blockade has been exploited clinically to dampen T-cell responses to self-antigen. Current evidence shows that CD28 both potentiates TCR signaling and engages a unique array of mediators (PI3K, Grb2, FLNa) in the regulation of aspects of T-cell signaling including the transcription factor NFkB. In this mini-review, we provide an up-to-date overview of our understanding of the signaling mechanisms that underlie CD28 function and its potential application to the modulation of reactivity to autoimmunity.

Variation in the Cd3 zeta (Cd247) gene correlates with altered T cell activation and is associated with autoimmune diabetes

Tuning of TCR-mediated activation was demonstrated to be critical for lineage fate in T cell development, as well as in the control of autoimmunity. In this study, we identify a novel diabetes susceptibility gene, Idd28, in the NOD mouse and provide evidence that Cd3zeta (Cd247) constitutes a prime candidate gene for this locus. Moreover, we show that the allele of the Cd3zeta gene expressed in NOD and DBA/2 mouse strains confers lower levels of T cell activation compared with the allele expressed by C57BL/6 (B6), BALB/c, and C3H/HeJ mice. These results support a model in which the development of autoimmune diabetes is dependent on a TCR signal mediated by a less-efficient NOD allele of the Cd3zeta gene.

Antibodies to CD1d enhance thymic expression of invariant NKT TCR and increase the presence of NOD thymic invariant NKT cells

Natural Killer T (NKT) cells can effect both T cell development and peripheral immune responses through T(H)1/T(H)2 cytokines. Some humans with Type 1 Diabetes Mellitus (T1DM) have numerical and functional NKT deficiencies that contribute to disease severity. Correcting these deficiencies inhibits diabetes in the non-obese diabetic (NOD) T1DM model, which shares similar deficiencies. Here we show that antibodies to CD1d, when given during early thymic development, induce specific increases in surface TCR of developing NOD and C57BL/6 CD4(+)CD8(+) (DP) invariant NKT (iNKT) cells. However, the addition of anti-CD1d causes distinct strain-specific population changes in response to treatment. These changes include: (1) a dose-dependent increase in NOD iNKT(TCR)(+) cells and, conversely, (2) an inhibition of B6 iNKT(TCR)(+) cell production. The observed NOD iNKT expansions correlated with diabetes inhibition in an in vitro T1DM system, suggesting that intrathymic anti-CD1d treatment may correct NOD numerical iNKT deficiencies through developmental TCR enhancement.

T-cell receptor-induced NF-kappaB activation is negatively regulated by E3 ubiquitin ligase Cbl-b

It has previously been shown that E3 ubiquitin ligase Casitas B-lineage lymphoma-b (Cbl-b) negatively regulates T-cell activation, but the molecular mechanism(s) underlying this inhibition is not completely defined. In this study, we report that the loss of Cbl-b selectively results in aberrant activation of NF-kappaB upon T-cell antigen receptor (TCR) ligation, which is mediated by phosphatidylinositol 3-kinase (PI3-K)/Akt and protein kinase C-theta (PKC-theta). TCR-induced hyperactivation of Akt in the absence of Cbl-b may potentiate the formation of caspase recruitment domain-containing membrane-associated guanylate kinase protein 1 (CARMA1)-B-cell lymphoma/leukemia 10 (Bcl10)-mucosa-associated lymphatic tissue 1(MALT1) (CBM) complex, which appears to be independent of PKC-theta. Cbl-b associates with PKC-theta upon TCR stimulation and regulates TCR-induced PKC-theta activation via Vav-1, which couples PKC-theta to PI3-K and allows it to be phosphorylated. PKC-theta then couples IkappaB kinases (IKKs) to the CBM complex, resulting in the activation of the IKK complex. Therefore, our data provide the first evidence to demonstrate that the down-regulation of TCR-induced NF-kappaB activation by Cbl-b is mediated coordinately by both Akt-dependent and PKC-theta-dependent signaling pathways in primary T cells.

FoxP3 maintains Treg unresponsiveness by selectively inhibiting the promoter DNA-binding activity of AP-1

Regulatory T cells (Tregs) have been shown to play a crucial role in maintaining self-tolerance and suppressing autoimmunity. The forkhead transcription factor, FoxP3, is a key molecule necessary and sufficient for Tregs development and function. However, the molecular mechanisms by which FoxP3 regulates the phenotypic (anergic) and the functional (suppressive) characteristics of Tregs are not well defined. Here we found that the promoter DNA-binding activity of AP-1 transcription factors is selectively inhibited in the naturally occurring CD4+ CD25+ Tregs from mice. The impaired AP-1 DNA binding is not the result of the decreased nuclear translocation of AP-1 family transcription factors, including c-Jun, JunB, and c-Fos. FoxP3 significantly suppresses both the transcriptional activity and promoter DNA-binding of AP-1 by interacting with c-Jun. The N-terminus of FoxP3, but not its C-terminus forkhead domain, specifically interacts with phosphorylated c-Jun and alters c-Jun subnuclear distribution. This N-terminus of FoxP3 with nuclear localization signals (FoxP3N/NLS) is able to suppress AP-1 transcriptional activity. Ectopic expression of FoxP3N/NLS sufficiently induces the unresponsiveness of mouse primary CD4+ CD25- T cells, whereas the full-length FoxP3 is required for the suppressive functions of Tregs. These findings uncover one of the mechanisms underlying how FoxP3 maintains the unresponsiveness of Tregs.

Negative regulation of CD40-mediated B cell responses by E3 ubiquitin ligase Casitas-B-lineage lymphoma protein-B

It has been documented that CD40 is essential for B cell function. Casitas-B-lineage lymphoma protein-b (Cbl-b), an adapter protein and ubiquitin ligase, has been shown to regulate the activation of T and B cells through their Ag receptors. In this study, we report that CD40-induced B cell proliferation is significantly augmented in mice lacking Cbl-b. Furthermore, Cbl-b(-/-) mice display enhanced thymus-dependent Ab responses and germinal center formation, whereas introduction of CD40 deficiency abolishes these effects. Hyper thymus-dependent humoral response in Cbl-b(-/-) mice is in part due to an intrinsic defect in B cells. Mechanistically, Cbl-b selectively down-modulates CD40-induced activation of NF-kappaB and JNK. Cbl-b associates with TNF receptor-associated factor 2 upon CD40 ligation, and inhibits the recruitment of TNF receptor-associated factor 2 to the CD40. Together, our data suggest that Cbl-b attenuates CD40-mediated NF-kappaB and JNK activation, thereby suppressing B cell responses.

Enhanced cardiac allograft survival by Vav1-Rac signaling blockade in a mouse model

BACKGROUND

Vav1-Rac signaling plays a pivotal role in TCR/antigen and CD28 signals for T cell activation. However, pharmacological interference of this signaling has not been tested in the prevention of alloimmune-mediated allograft rejection. It has been demonstrated that 6-thio-GTP, a metabolite of azathioprine, specifically inhibits Vav1-Rac activity in T lymphocytes. Here we show the immunosuppressive efficacy of 6-thio-GTP in the prevention of cardiac allograft rejection.

METHODS

T cell proliferations were measured by (3)H-thymidine uptake. The immunosuppressive activities of 6-thio-GTP were tested in the cardiac allograft model of C57BL/6 (H-2(b)) to Balb/c (H-2(d)) mice.

RESULTS

6-Thio-GTP inhibited TCR/alloantigen stimulated T cell proliferation and CD28-dependent T cell survival. Administration of 6-thio-GTP (0.5 mg/kg) prolonged graft survival to 13.8+/-2.39 days compared to 8.3+/-0.48 days in PBS controls (p<0.0001). Combination of 6-thio-GTP (0.5 mg/kg) with CsA (15 mg/kg) enhanced graft survival from 15.0+/-1.61 days in CsA treated recipients to 36.8+/-2.17 days in those received 20 days of combination therapy of CsA and 6-thio-GTP (p<0.0001), or to 42.7+/-16.63 days in the group treated with 20 days of CsA and 60 days of 6-thio-GTP (p<0.0001). Lymphocytes from 6-thio-GTP treated recipients with long-term surviving grafts (>60 days) displayed reduced proliferative response to alloantigen and higher frequencies of regulatory T cells (Treg).

CONCLUSION

Vav1-Rac inhibitor 6-thio-GTP prolongs allograft survival alone or in combination with CsA by suppression of alloreactive T cell activation. Our findings suggest the therapeutic potential of pharmacological interference of Vav1-Rac signaling for transplantation.

Induction of T-cell activation or anergy determined by the combination of intensity and duration of T-cell receptor stimulation, and sequential induction in an individual cell

It has been shown that anergic T cells have important roles in peripheral tolerance, although the precise mechanism for inducing anergy is still unclear. We analysed the kinetics of anergy induction at an individual cell level by flow cytometry. We first successfully obtained T helper type 1 (Th1) cells that had been made uniform with the level of interferon-gamma (IFN-gamma) production induced by antigen stimulation. We then used these Th1 cells to evaluate the degree of anergy for each Th1 cell treated with an anti-CD3 monoclonal antibody according to the level of IFN-gamma secretion. Our results demonstrate that anergic stimulation could induce both activation and anergy, depending on the duration and intensity of stimulation at the level of an individual cell. Each Th1 cell was first activated and then gradually became anergic depending on the duration of stimulation. The duration of the stimulus required for inducing anergy became shorter as the intensity of stimulation became stronger. We also show that the calcineurin signal controlled the induction of activation or anergy depending on the activity. This study contributes to better understanding of the precise mechanism for inducing T-cell anergy.

Strategies for targeting T-cells in allergic diseases and asthma

T helper (Th) 2 lymphocytes play a crucial role in the initiation, progression and persistence of allergic diseases, including asthma. Drugs that interfere with the activation of T-cells or more selectively Th2-specific signaling molecules and drugs that prevent the selective migration into lung tissue are promising novel strategies for the treatment of allergic asthma. Although the mainstay asthma therapy of inhaled glucocorticoids is rather effective, targeting Th2 cells may be an important alternative in childhood. Regulatory T-cells (Treg cells) have a physiological role in protection of unwanted immune responses to auto-antigens and allergens. Literature data indicate that an imbalance between Th2 and Treg cells may underlie development and disease expression of allergic asthma. Drugs or immunotherapies that stimulate these counter-Treg cells may limit aberrant Th2 responses leading to suppression of symptoms. Furthermore, these types of treatments may offer the perspective of disease modification and long-term relief of symptoms.

Insulin-dependent diabetes loci Idd5 and Idd9 increase sensitivity to experimental autoimmune encephalomyelitis

The spontaneous development of autoimmune diabetes in NOD mice suggests that they are unable to establish and maintain immunologic self-tolerance. Congenic NOD mice expressing B10-derived alleles are protected from pancreatic beta cell destruction and autoimmune diabetes. To determine if the B10 alleles in loci Idd5 and Idd9 could influence susceptibility to autoimmunity in other organs, we compared MOG35-55-induced EAE in NOD mice to that of diabetes-resistant NOD.B10.Idd5 and NOD.B10.Idd9 mice. Surprisingly, the severity and chronicity of EAE were enhanced in the diabetes-resistant congenic mice. Our findings indicate that some alleles may influence susceptibility to immune-mediated damage in an organ or tissue-specific fashion, and highlight the necessity of disease-specific investigations.

Quantitative proteomic and transcriptional analysis of the response to the p38 mitogen-activated protein kinase inhibitor SB203580 in transformed follicular lymphoma cells

The p38 mitogen-activated protein kinase (MAPK) is a key mediator of stress, extracellular-, growth factor-, and cytokine-induced signaling, and has been implicated in the development of cancer. Our previous work showed evidence for p38 MAPK activation in a subset of transformed follicular lymphomas (Elenitoba-Johnson et al. (2003) Proc. Natl. Acad. Sci. U.S.A. 100, 7259). We demonstrated that inhibition of p38 MAPK by SB203580 resulted in dose- and time-dependent caspase-3-mediated apoptosis. In order to further elucidate the basis of the cellular effects of SB203580, we have employed a systems biologic approach involving cDNA microarray and quantitative proteomic analysis of transformed follicular lymphoma derived-cells (OCI Ly-1) treated with SB203580. Gene expression profiling revealed differential expression (>/=1.5-fold) of 374 genes/ESTs in cells treated for 3 h and 515 genes/ESTs in cells treated for 21 h. The majority (52% at 3 h and 91% at 21 h) were down-regulated, including genes encoding growth cytokines, transcriptional regulators and cytoskeletal proteins. Quantitative proteomic analysis using ICAT-LC-MS/MS identified 277 differentially expressed proteins at 3 h and 350 proteins at 21 h of treatment with SB203580, the majority of which were also down-regulated. Analysis of functional groups of the differentially expressed proteins implicated components of diverse overlapping pathways including the IL-6/phosphatidylinositol 3-kinase, insulin-like growth factor 2/Ras/Raf, WNT8d/Frizzled, MAPK-activated protein kinase 2, and nuclear factor kappaB. The differential phosphorylation status of selected kinase-active proteins was validated by Western blotting analysis. Our complementary genomic and proteomic approach reveal the global cellular consequences of SB203580 treatment and provide insights into its growth inhibitory effect on transformed follicular lymphoma cells.

Donor-specific antigen transfusion-mediated skin-graft tolerance results from the peripheral deletion of donor-reactive CD8+ T cells

BACKGROUND

The mechanism of donor-specific transfusion (DST)-induced long-term skin-graft survival is examined in 2CF1 (2C x dm2) transgenic and B6F1 (C57BL/6 x dm2) nontransgenic mice in which CB6F1 (Balb/c x B6) DST and donor skin grafts differ from 2CF1 or B6F1 recipients only at major histocompatibility complex class I Ld.

METHODS

Saline (control) or allogeneic CB6F1 spleen cells were injected intravenously into 2CF1 and B6F1 mice. One week later, CB6F1 tail skin was transplanted onto the dorsum of these mice. Fluorescence-activated cell sorter analysis (flow cytometric analysis) of peripheral blood was performed 2 days before DST, 5 days after DST, and 7, 14, 21, 28, and 75 days after skin grafting. Splenocyte responsiveness was measured by in vitro mixed lymphocyte culture and cytotoxic T lymphocyte. Cytokine protein production (interleukin [IL]-2 and interferon-gamma) was measured by enzyme-linked immunosorbent assay.

RESULTS

Whereas all CB6F1 skin grafts in control saline-treated 2CF1 and B6F1 mice were rejected, 100% of 2CF1 and B6F1 pretreated with CB6F1 DST accepted the class I Ld disparate donor skin indefinitely. DST followed by a CB6F1 skin graft led to a significant deletion of donor-reactive CD8+ T cells by fluorescence-activated cell sorter analysis and decreased production of the inflammatory cytokines IL-2 and interferon-gamma. The hyporesponsiveness of residual CD8+ T cells in mixed lymphocyte culture and cytotoxic T lymphocyte to Ld after DST was restored to normal by IL-2.

CONCLUSION

These findings demonstrate that administration of DST uniformly results in long-term Ld+ skin-allograft acceptance. This tolerance induction is related to both a significant decrease in donor-reactive CD8+ transgenic T cells and anergy of the residual CD8+ T cells.

Defect in activation-induced cell death in non-obese diabetic (NOD) T lymphocytes

Activation-induced cell death (AICD) represents a major means of peripheral tolerance induction, eliminating effector cells. NOD mice, a widely used model for autoimmune diabetes, are characterized by high levels of circulating T lymphocytes and by resistance to several apoptosis-inducing signals. The aim of this study was to analyse AICD in peripheral NOD T lymphocytes. First, we demonstrated in an in vitro AICD model that NOD T lymphocytes are more resistant to AICD (64+/-2%) compared to non-autoimmune C57BL/6 T lymphocytes (73+/-2%), but also diabetes-resistant NOR T lymphocytes (76+/-3%, P<0.05). Moreover, both CD4(+)and CD8(+)subsets were affected. Analysis of the cellular and molecular pathways revealed lower caspase 8 levels, a central caspase proximally involved in the AICD-pathway (fluorescence of 258+/-47 in NOD vs. 441+/-16 in NOR and 414+/-61 in C57BL/6 T lymphocytes, P<0.05). Gene expression analysis using real-time RT-PCR additionally revealed low expression of Fas and FasL, the death receptor system activating caspase 8 and contributing to AICD. Additionally, low IL-2 levels, together with high TGFbeta and Bclx-L levels, confirm the presence of a NOD-specific AICD-resistance profile. In conclusion, we present cellular and molecular evidence for disturbed AICD mechanisms in NOD T lymphocytes. This resistance in AICD may contribute to defective tolerance induction to autoantigens in NOD mice.

Deficient activation and resistance to activation-induced apoptosis of CD8+ T cells is associated with defective peripheral tolerance in nonobese diabetic mice

Activation-induced cell death (AICD) is a mechanism of homeostasis that limits the clonal expansion of autoreactive T cells and regulates central and peripheral tolerance. In nonobese diabetic (NOD) mice, defects in central and peripheral tolerance are associated with a proliferative hyporesponsiveness of thymocytes and peripheral T cells elicited upon TCR activation. We investigated whether these defects in tolerance induction and hyporesponsiveness of NOD T cells manifest in an altered susceptibility to TCR-induced AICD. TCR-activated NOD splenic CD4+ and CD8+ T cells are more resistant to AICD than control strain C57BL/6, BALB/c, and NOR T cells. NOR CD4+ but not CD8+ T cells are resistant to TCR-induced AICD. Whereas c-FLIP expression is reduced in activated T cells from control strains, it persists in activated NOD CD8+ T cells and is accompanied by diminished activity of caspase-3 and -8. IL-4 reduces this c-FLIP expression and increases caspase-3 and -8 activity in activated NOD CD8+ T cells. Moreover, IL-4 and CD28 costimulation restores the susceptibility of NOD CD8+ T cells to AICD, and this is associated with increased expression of CD25, CD95, CD95L, and TNFR2. Thus, deficient activation of CD8+ T cells and their greater resistance to TCR-induced AICD may mediate defective peripheral tolerance and the development of T1D in NOD mice.

Interleukin-6 promotes the production of interleukin-4 and interleukin-5 by interleukin-2-dependent and -independent mechanisms in freshly isolated human T cells

T helper 2 (Th2) cytokines [interleukin (IL)-4 and IL-5] play a central role in the development of allergic immune responses. After allergen provocation, the expression of Th2 cytokines is rapidly up-regulated in atopy and asthma. IL-6 is a multifunctional cytokine that is able to direct Th2 immune responses and is secreted by multiple tissue cell types. This study shows that IL-6 induces up-regulation of IL-4 and IL-5 after short (5 min) preincubation periods in freshly isolated, alpha-CD3/alpha-CD28-stimulated T cells. After longer preincubation periods with IL-6 (12 and 24 hr), the priming effect on IL-4 production gradually disappears, whereas the effect on IL-5 becomes more pronounced. In contrast, a small but significant inhibitory effect is found on the production of the Th1 cytokine interferon-gamma. Additional experiments indicate that the long-term priming effect of IL-6 on IL-5 production is dependent on IL-2 signalling. This is not the case for the short-term IL-6 effect on IL-5 secretion, where the p38 mitogen-activated protein kinase-dependent induction of activator protein-1 DNA-binding activity is involved, independent of signal transducer and activator of transcription 3 phosphorylation. In summary, these data demonstrate that the short-term and long-term priming effects of IL-6 on Th2 cytokine production are regulated by different mechanisms.

T-cell education in autoimmune diabetes: teachers and students

Type 1 diabetes mellitus is a classical example of a T-cell-mediated autoimmune disease. Several aberrations in immune regulation have been described in both human diabetes patients and animal models of type 1 diabetes. In this review, we summarize how proposed immune defects might be implicated in the loss of T-cell tolerance towards self in autoimmune diabetes in humans, nonobese diabetic (NOD) mice and Biobreeding (BB) rats. For this purpose, we will discuss the tolerance-inducing mechanisms that an autoreactive T cell should encounter from its genesis to its pathogenic role in the pancreas, in order of appearance. These comprise central tolerance mechanisms (i.e. positive and negative selection in the thymus) and those mechanisms operative in the periphery (i.e. activation-induced cell death and regulatory T cells).