A mouse CD8 T cell-mediated acute autoimmune diabetes independent of the perforin and Fas cytotoxic pathways: possible role of membrane TNF

The Impact of the Ca2+-Independent Phospholipase A2β (iPLA2β) on Immune Cells

The Ca²⁺-independent phospholipase A₂β (iPLA₂β) is a member of the PLA₂ family that has been proposed to have roles in multiple biological processes including membrane remodeling, cell proliferation, bone formation, male fertility, cell death, and signaling. Such involvement has led to the identification of iPLA₂β activation in several diseases such as cancer, cardiovascular abnormalities, glaucoma, periodontitis, neurological disorders, diabetes, and other metabolic disorders. More recently, there has been heightened interest in the role that iPLA₂β plays in promoting inflammation. Recognizing the potential contribution of iPLA₂β in the development of autoimmune diseases, we review this issue in the context of an iPLA₂β link with macrophages and T-cells.

Macrophage polarization is linked to Ca2+-independent phospholipase A2β-derived lipids and cross-cell signaling in mice

Phospholipases A₂ (PLA₂s) catalyze hydrolysis of the sn-2 substituent from glycerophospholipids to yield a free fatty acid (i.e., arachidonic acid), which can be metabolized to pro- or anti-inflammatory eicosanoids. Macrophages modulate inflammatory responses and are affected by Ca²⁺-independent phospholipase A₂ (PLA₂)β (iPLA₂β). Here, we assessed the link between iPLA₂β-derived lipids (iDLs) and macrophage polarization. Macrophages from WT and KO (iPLA₂β-/-) mice were classically M1 pro-inflammatory phenotype activated or alternatively M2 anti-inflammatory phenotype activated, and eicosanoid production was determined by ultra-performance LC ESI-MS/MS. As a genotypic control, we performed similar analyses on macrophages from RIP.iPLA₂β.Tg mice with selective iPLA₂β overexpression in β-cells. Compared with WT, generation of select pro-inflammatory prostaglandins (PGs) was lower in iPLA₂β^-/- , and that of a specialized pro-resolving lipid mediator (SPM), resolvin D2, was higher; both changes are consistent with the M2 phenotype. Conversely, macrophages from RIP.iPLA₂β.Tg mice exhibited an opposite landscape, one associated with the M1 phenotype: namely, increased production of pro-inflammatory eicosanoids (6-keto PGF₁α, PGE₂, leukotriene B₄) and decreased ability to generate resolvin D2. These changes were not linked with secretory PLA₂ or cytosolic PLA₂α or with leakage of the transgene. Thus, we report previously unidentified links between select iPLA₂β-derived eicosanoids, an SPM, and macrophage polarization. Importantly, our findings reveal for the first time that β-cell iPLA₂β-derived signaling can predispose macrophage responses. These findings suggest that iDLs play critical roles in macrophage polarization, and we posit that they could be targeted therapeutically to counter inflammation-based disorders.

A New Venue of TNF Targeting

The first Food and Drug Administration-(FDA)-approved drugs were small, chemically-manufactured and highly active molecules with possible off-target effects, followed by protein-based medicines such as antibodies. Conventional antibodies bind a specific protein and are becoming increasingly important in the therapeutic landscape. A very prominent class of biologicals are the anti-tumor necrosis factor (TNF) drugs that are applied in several inflammatory diseases that are characterized by dysregulated TNF levels. Marketing of TNF inhibitors revolutionized the treatment of diseases such as Crohn’s disease. However, these inhibitors also have undesired effects, some of them directly associated with the inherent nature of this drug class, whereas others are linked with their mechanism of action, being pan-TNF inhibition. The effects of TNF can diverge at the level of TNF format or receptor, and we discuss the consequences of this in sepsis, autoimmunity and neurodegeneration. Recently, researchers tried to design drugs with reduced side effects. These include molecules with more specificity targeting one specific TNF format or receptor, or that neutralize TNF in specific cells. Alternatively, TNF-directed biologicals without the typical antibody structure are manufactured. Here, we review the complications related to the use of conventional TNF inhibitors, together with the anti-TNF alternatives and the benefits of selective approaches in different diseases.

Neutralization Versus Reinforcement of Proinflammatory Cytokines to Arrest Autoimmunity in Type 1 Diabetes

As physiological pathways of intercellular communication produced by all cells, cytokines are involved in the pathogenesis of inflammatory insulitis as well as pivotal mediators of immune homeostasis. Proinflammatory cytokines including interleukins, interferons, transforming growth factor-β, tumor necrosis factor-α, and nitric oxide promote destructive insulitis in type 1 diabetes through amplification of the autoimmune reaction, direct toxicity to β-cells, and sensitization of islets to apoptosis. The concept that neutralization of cytokines may be of therapeutic benefit has been tested in few clinical studies, which fell short of inducing sustained remission or achieving disease arrest. Therapeutic failure is explained by the redundant activities of individual cytokines and their combinations, which are rather dispensable in the process of destructive insulitis because other cytolytic pathways efficiently compensate their deficiency. Proinflammatory cytokines are less redundant in regulation of the inflammatory reaction, displaying protective effects through restriction of effector cell activity, reinforcement of suppressor cell function, and participation in islet recovery from injury. Our analysis suggests that the role of cytokines in immune homeostasis overrides their contribution to β-cell death and may be used as potent immunomodulatory agents for therapeutic purposes rather than neutralized.

TNF activity and T cells

TNF (tumor necrosis factor) is both a pro-inflammatory and anti-inflammatory cytokine that is central to the development of autoimmune disease, cancer, and protection against infectious pathogens. As well as a myriad other activities, TNF can be a product of T cells and can act on T cells. Here we review old and new data on the importance of TNF produced by T cells and how TNF signaling via TNFR2 may directly impact alternate aspects of T cell biology. TNF can promote the activation and proliferation of naïve and effector T cells, but also can induce apoptosis of highly activated effector T cells, further determining the size of the pathogenic or protective conventional T cell pool. Moreover, TNF can have divergent effects on regulatory T cells. It can both downregulate their suppressive capacity, but also contribute in other instances to their development or accumulation. Biologics that block TNF or stimulate TNFR2 therefore have the potential to strongly modulate the balance between effector T cells and Treg cells which could impact disease in both positive and negative manners.

Perforin and human diseases

Natural killer (NK) cells and cytotoxic T lymphocytes (CTL) use a highly toxic pore-forming protein perforin (PFN) to destroy cells infected with intracellular pathogens and cells with pre-cancerous transformations. However, mutations of PFN and defects in its expression can cause an abnormal function of the immune system and difficulties in elimination of altered cells. As discussed in this chapter, deficiency of PFN due to the mutations of its gene, PFN1, can be associated with malignancies and severe immune disorders such as familial hemophagocytic lymphohistiocytosis (FHL) and macrophage activation syndrome. On the other hand, overactivity of PFN can turn the immune system against autologous cells resulting in other diseases such as systemic lupus erythematosus, polymyositis, rheumatoid arthritis and cutaneous inflammation. PFN also has a crucial role in the cellular rejection of solid organ allografts and destruction of pancreatic β-cells resulting in type 1 diabetes. These facts highlight the importance of understanding the biochemical characteristics of PFN.

Cellular and molecular requirements for rejection of B16 melanoma in the setting of regulatory T cell depletion and homeostatic proliferation

We have recently demonstrated that adoptive transfer of regulatory T cell-depleted polyclonal T cells into lymphopenic mice leads to rejection of B16 melanoma, which generated an opportunity to study host requirements for tumor rejection when it effectively occurred. CD8(+) T cell priming and tumor rejection required tumor Ag cross-presentation, as evidenced by tumor outgrowth in Kb(-/-) bone marrow chimeric or B71/2(-/-) mice. CD4(+) T cells were additionally required for optimal tumor control, although not through classical CD4 "help," as the frequency of primed CD8(+) T cells was similar in the absence of CD4(+) T cells, and tumor rejection did not depend upon CD40-CD40L interactions or on IL-2 production by CD4(+) T cells. Rather, CD4(+) T cells appeared to act at the effector phase of tumor rejection and responded to B16-derived Ags in vitro. At the effector phase, IFN-γ production by transferred T cells, but not host cells, was necessary. IFN-γ acted either on host or tumor cells and was associated with reduced tumor vascularity. Finally, tumor rejection occurred after transfer of TNF-α, perforin, or FasL-deficient T cells. However, perforin/FasL double-knockout T cells failed to reject, arguing that the killing of B16 melanoma cells could occur either via the cytotoxic granule or Fas pathways. Collectively, these results support a model in which host tumor Ag cross-presentation primes adoptively transferred T cells, which remain functional in the setting of homeostatic proliferation and regulatory T cell depletion, and which promote tumor rejection via IFN-γ and lysis via cytotoxic granules and/or FasL.

Tumor necrosis factor-α levels correlate with postoperative pain severity in lumbar disc hernia patients: opposite clinical effects between tumor necrosis factor receptor 1 and 2

Lumbar disc hernia (LDH) is a leading cause of chronic pain in adults. The underlying pathology of chronic pain after discectomy remains unclear. Chronic local inflammation is considered to underlie painful symptomatology. In this context, we investigated tumor necrosis factor (TNF)-α, TNF receptor 1 (TNFR1), and TNF receptor 2 (TNFR2) expression at the time of surgery in LDH patients and correlated it with the severity of postoperative pain. We analyzed protein and mRNA levels from muscle, ligamentum flavum (LF), annulus fibrosus (AF), and nucleus pulposus (NP) in LDH patients and scoliosis patients (SP), who served as controls. Pain assessment with the visual analogue scale (VAS) was performed 1 day before surgery and 6 weeks and 12 months postoperatively. TNF-α protein levels were detected in AF, LF, and NP in all LDH patients, but not in SP. TNF-α mRNA was significantly greater in LDH patients than in SP; ie, 5-fold in AF, 3-fold in NP, and 2-fold in LF. For NP, TNF-α protein levels correlated with VAS scores (r=0.54 at 6-week and r=0.65 at 12-month follow-up). Also, TNFR1 protein levels in NP positively correlated with VAS scores (r=0.75 at 6-week and r=0.80 at 12-month follow-up). However, TNFR2 protein levels in AF negatively correlated with VAS scores (r=-0.60 at 6 weeks and r=-0.60 at 12 months follow-up). These data indicate that TNF-α levels could determine the clinical outcome in LDH patients after discectomy. Moreover, the opposite correlation of TNF receptors with pain sensation suggests that an unbalanced expression plays a role in the generation of pain.

Perforin: more than just a pore-forming protein

Cellular apoptosis induced by T cells is mainly mediated by two pathways. One, granule exocytosis utilizes perforin/granzymes. The other involves signaling through death receptors of the TNF-alpha R super-family, especially FasL. Perforin plays a central role in apoptosis induced by granzymes. However, the mechanisms of perforin-mediated cytotoxicity are still not elucidated completely. Perforin is not only a pore-forming protein, but also performs multiple biological functions or perforin performs one biological function (cytolysis), but has multiple biological implications in the cellular immune responses, including regulation of proliferation of CD8+ CTLs.

Etanercept treatment in children with new-onset type 1 diabetes: pilot randomized, placebo-controlled, double-blind study

OBJECTIVE

To gather preliminary data on the feasibility and efficacy of etanercept therapy to prolong endogenous insulin production in pediatric patients with newly diagnosed type 1 diabetes.

RESEARCH DESIGN AND METHODS

This was a 24-week double-blind, randomized, placebo-controlled study conducted at the Diabetes Center, Women and Children's Hospital of Buffalo. Eighteen subjects (11 male and 7 female, aged 7.8-18.2 years) were randomly assigned to receive either placebo or etanercept. Inclusion criteria included age 3-18 years, GAD-65 and/or islet cell antibody positivity, A1C >6%, three insulin injections per day, white blood cell count 3,000-10,000, platelets >100,000, and normal liver and renal function. Intention-to-treat analysis was used.

RESULTS

A1C at week 24 was lower in the etanercept group (5.91 +/- 0.5%) compared with that in the placebo group (6.98 +/- 1.2%; P < 0.05) with a higher percent decrease from baseline than in the placebo group (etanercept 0.41 +/- 0.1 vs. placebo 0.18 +/- 0.21; P < 0.01). The percent change in C-peptide area under the curve from baseline to week 24 showed a 39% increase in the etanercept group and a 20% decrease in the placebo group (P < 0.05). From baseline to week 24 insulin dose decreased 18% in the etanercept group compared with a 23% increase in the placebo group (P < 0.05). Seventeen patients completed the study, and none withdrew because of adverse events.

CONCLUSIONS

In this small pilot study, treatment of pediatric patients newly diagnosed with type 1 diabetes with etanercept resulted in lower A1C and increased endogenous insulin production, suggesting preservation of beta-cell function. A larger study is needed to further explore safety and efficacy.

Distinct local immunogenic stimuli dictate differential requirements for CD4+ and CD8+ T cell subsets in the pathogenesis of spontaneous autoimmune diabetes

The strong MHC class II association in human as well as murine Type 1 diabetes (T1D) suggests a central role for CD4+T cells in the disease pathogenesis. Nonetheless, CD8+T cells also play a role in the pathogenic process. We describe how CD4+ or CD8+T cells can contribute differentially to the pathogenesis of T1D using the HLA-DQ8 transgenic mouse models. HLA-DQ8 transgenic mice expressing the costimulatory molecule, B7.1 (RIP.B7.1), or the proinflammatory cytokine, TNF-alpha (RIP.TNF) or both (RIP.B7.RIP.TNF) under the control of rat insulin promoter (RIP) were used. Our observations indicate that in the RIP-B7 model, CD4+T cells were absolutely required for diabetes to occur. However, when CD8+ T cells were also present, the incidence of diabetes increased. On the other hand, in the RIP-TNF model, CD8+T cells were absolutely required for diabetes to occur. Interestingly, when CD4+T cells were also present, the incidence of diabetes decreased. In the RIP-B7.RIP-TNF double transgenic mouse model, either CD4+ or CD8+T cells were sufficient to precipitate diabetes in 100% of the animals. Thus, the relative roles of CD4+ or CD8+T cells in the pathogenesis of T1D are possibly determined by the local inflammatory stimuli.

TNF-alpha is critical for antitumor but not antiviral T cell immunity in mice

TNF-alpha antagonists are widely used in the treatment of inflammatory and autoimmune diseases, but their use is associated with reactivation of latent infections. This highlights the importance of TNF-alpha in immunity to certain pathogens and raises concerns that critical aspects of immune function are impaired in its absence. Unfortunately, the role of TNF-alpha in the regulation of T cell responses is clouded by a myriad of contradictory reports. Here, we show a role for TNF-alpha and its receptors, TNFR1 and TNFR2, specifically in antitumor immunity. TNF-alpha-deficient mice exhibited normal antiviral responses associated with strong inflammation. However, TNF-alpha/TNFR1-mediated signals on APCs and TNF-alpha/TNFR2 signals on T cells were critically required for effective priming, proliferation, and recruitment of tumor-specific T cells. Furthermore, in the absence of TNF-alpha signaling, tumor immune surveillance was severely abrogated. Finally, treatment with a CD40 agonist alone or in combination with TLR2 stimuli was able to rescue proliferation of TNF-alpha-deficient T cells. Therefore, TNF-alpha signaling may be required only for immune responses in conditions of limited immunostimulatory capacity, such as tumor surveillance. Importantly, these results suggest that prolonged continuous TNF-alpha blockade in patients may have long-term complications, including potential tumor development or progression.

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.

Dominant-negative effects of a novel mutated Ins2 allele causes early-onset diabetes and severe beta-cell loss in Munich Ins2C95S mutant mice

The novel diabetic mouse model Munich Ins2(C95S) was discovered within the Munich N-ethyl-N-nitrosourea mouse mutagenesis screen. These mice exhibit a T-->A transversion in the insulin 2 (Ins2) gene at nucleotide position 1903 in exon 3, which leads to the amino acid exchange C95S and loss of the A6-A11 intrachain disulfide bond. From 1 month of age onwards, blood glucose levels of heterozygous Munich Ins2(C95S) mutant mice were significantly increased compared with controls. The fasted and postprandial serum insulin levels of the heterozygous mutants were indistinguishable from those of wild-type littermates. However, serum insulin levels after glucose challenge, pancreatic insulin content, and homeostasis model assessment (HOMA) beta-cell indices of heterozygous mutants were significantly lower than those of wild-type littermates. The initial blood glucose decrease during an insulin tolerance test was lower and HOMA insulin resistance indices were significantly higher in mutant mice, indicating the development of insulin resistance in mutant mice. The total islet volume, the volume density of beta-cells in the islets, and the total beta-cell volume of heterozygous male mutants was significantly reduced compared with wild-type mice. Electron microscopy of the beta-cells of male mutants showed virtually no secretory insulin granules, the endoplasmic reticulum was severely enlarged, and mitochondria appeared swollen. Thus, Munich Ins2(C95S) mutant mice are considered a valuable model to study the mechanisms of beta-cell dysfunction and death during the development of diabetes.

The dual role of Fas-ligand as an injury effector and defense strategy in diabetes and islet transplantation

The exact process that leads to the eruption of autoimmune reactions against beta cells and the evolution of diabetes is not fully understood. Macrophages and T cells may launch an initial immune reaction against the pancreatic islets of Langerhans, provoking inflammation and destructive insulitis. The information on the molecular mechanisms of the emergence of beta cell injury is controversial and points to possibly important roles for the perforin-granzyme, Fas-Fas-ligand (FasL) and tumor-necrosis-factor-mediated apoptotic pathways. FasL has several unique features that make it a potentially ideal immunomodulatory tool. Most important, FasL is selectively toxic to cytotoxic T cells and less harmful to regulatory T cells. This review discusses the intrinsic sensitivity of beta cells to FasL-mediated apoptosis, the conditions that underlie this beta cell sensitivity, and the feasibility of using FasL to arrest autoimmunity and prevent islet allograft rejection. In both the autoimmune and transplant settings, it is imperative to progress from the administration of nonspecific immunosuppressive therapy to the concept of beta-cell-specific immunomodulation. FasL evolves as a prime candidate for antigen-specific immunomodulation.

A critical role for granzyme B, in addition to perforin and TNFalpha, in alloreactive CTL-induced mouse pancreatic beta cell death

BACKGROUND

The precise effector mechanisms and molecular mediators used by alloreactive cytotoxic T lymphocytes to kill transplanted pancreatic beta cells are poorly defined. We have used mouse (H2b-anti-d) CTLs raised in strains deficient in various key cytotoxic effector molecules to assess the importance of the various signaling pathways mobilized to kill primary mouse pancreatic islet cells, the beta cell line NIT-1, and NIT-1 cells overexpressing dominant-negative FADD and Bcl-2.

METHODS

Death of target cells was assessed using 51Cr release assays.

RESULTS

In short-term assays (<5 hours) beta cell death did not require a functional FasL/Fas pathway, and was not inhibited by Bcl-2. However, the absence of either perforin or granzyme B resulted in cell survival. By contrast, a crucial role for granzyme B was not seen when hematopoietic P815 cells were used as targets, indicating differential regulation of apoptosis. Interestingly, coincubation with CTL for 24 hours revealed an additional but less potent "late phase" of beta cell death that did not require perforin. This delayed death was blocked by dominant-negative FADD, but not by Bcl-2, and was likely to be due to TNFalpha secretion.

CONCLUSIONS

This study suggests that strategies to protect beta cells from allogeneic CTL attack will need to inhibit the perforin/granzyme and probably also the TNFalpha pathway. As there are no known pharmacological approaches to blocking perforin, therapeutic approaches based on overexpressing both dominant negative FADD and an inhibitor of granzyme B may hold promise in prolonging beta cell survival in the allogeneic setting.

Efficient gene delivery to human and rodent islets with double-stranded (ds) AAV-based vectors

Transplantation of allogeneic pancreatic islets is an effective approach to treat type 1 diabetes. To bypass the need for systemic administration of immunosuppression drugs following transplantation, approaches to genetically modify allogeneic islets to express anti-inflammatory, immunosuppressive, or antiapoptotic proteins prior to transplantation are being developed. Adeno-associated viral (AAV) based vectors have been used for gene transfer to islets, but the efficiency of functional transduction is low. Recently, double-stranded (ds) or double-copy (dc) based AAV vectors have been developed that allow for more rapid and efficient AAV-mediated transgene expression following transduction. Here we demonstrate that intact human and murine islets can be transduced with dsAAV2-eGFP efficiently compared to single-stranded AAV2-eGFP. Furthermore, our results demonstrate that murine islets transduced with dsAAV2-eGFP have normal islet glucose responsiveness, viability, and islet insulin content. Transplantation of the dsAAV2-eGFP transduced islet restored normal glycemia in diabetic mice without eliciting an immune response. Significant dsAAV2-mediated eGFP expression was observed in the islet grafts for at least 6 months post-transplant. Finally, we demonstrated that dsAAV serotypes 2, 6, and 8 infect human islets efficiently. Taken together, these results suggest that dsAAV based vectors are highly appropriate for gene transfer to islets to facilitate transplantation.

Preservation of β-cell function during immune-mediated, B7-1-dependent α-cell destruction

Type 1 diabetes (T1D) is an autoimmune disease in which the pancreatic beta-cells are destroyed in an immune-mediated process. In one mouse model of T1D, the co-expression of the costimulatory molecule, B7-1, and the pro-inflammatory cytokine, tumor necrosis factor (TNF)-alpha, on the beta-cells leads to massive insulitis and loss of beta-cells, resulting in T1D. Here, we have investigated whether the specific loss of beta-cells is due to an intrinsic defect in the beta-cells or is a direct consequence of B7-1 expression. We show that transgenic mice expressing TNF-alpha on the beta-cells and B7-1 on the alpha-cells are resistant to the development of diabetes despite B7-1-dependent loss of alpha-cells and a massive islet inflammation consisting of T cells, B cells, macrophages and dendritic cells. Furthermore, islets with alpha-cell expression of B7-1 develop alpha-cell destruction and heavy infiltration, but maintain functional beta-cells when they are engrafted into diabetic mice that co-express TNF-alpha and B7-1 on the beta-cells. Thus, our results show that the beta-cells are able to survive in a severely inflamed organ where the neighboring alpha-cells are destroyed, suggesting that in this model B7-1 expression on the target cells is the primary determinant for the loss of islet cells.

Regulation of apoptosis by endoplasmic reticulum pathways

Apoptotic programmed cell death pathways are activated by a diverse array of cell extrinsic and intrinsic signals, most of which are ultimately coupled to the activation of effector caspases. In many instances, this involves an obligate propagation through mitochondria, causing egress of critical proapoptotic regulators to the cytosol. Central to the regulation of the mitochondrial checkpoint is a complex three-way interplay between members of the BCL-2 family, which are comprised of an antiapoptotic subgroup including BCL-2 itself, and the proapoptotic BAX,BAK and BH3-domain-only subgroups. Constituents of all three of these BCL-2 classes, however, also converge on the endoplasmic reticulum (ER), an organelle whose critical contributions to apoptosis is only now becoming apparent. In addition to propagating death-inducing stress signals itself, the ER also contributes in a fundamental way to Fas-mediated apoptosis and to p53-dependent pathways resulting from DNA damage and oncogene expression. Mobilization of ER calcium stores can initiate the activation of cytoplasmic death pathways as well as sensitize mitochondria to direct proapoptotic stimuli. Additionally, the existence of BCL-2-regulated initiator procaspase activation complexes at the ER membrane has also been described. Here, we review the potential underlying mechanisms involved in these events and discuss pathways for ER-mitochondrial crosstalk pertinent to a number of cell death stimuli.

Activation and functional significance of the renin-angiotensin system in mice with cardiac restricted overexpression of tumor necrosis factor

BACKGROUND

The functional significance of cross-regulation between the renin-angiotensin system (RAS) and tumor necrosis factor (TNF) has been established in nonmyocyte cell types; however, the degree and functional significance of the interaction between RAS and TNF has not been characterized in the heart.

METHODS AND RESULTS

We examined the expression of components of the RAS in a line of transgenic mice (MHCsTNF) with cardiac restricted overexpression of TNF. When examined at 4, 8, and 12 weeks of age, the MHCsTNF mice had increased activation of myocardial RAS, as shown by an increase in ACE mRNA level and ACE activity and increased angiotensin II peptide levels. Furthermore, myocardial angiotensin receptor mRNA and protein levels were reduced in the MHCsTNF mice, consistent with homologous desensitization of the receptors. However, expression of renin and angiotensinogen was not increased in MHCsTNF mice compared with littermate controls. To determine the functional significance of RAS activation in the MHCsTNF mice, we treated the mice with an angiotensin type I receptor antagonist, losartan (30 mg/kg), or diluent from 4 to 8 weeks of age. Analysis of cardiac structure with MRI showed that treatment with losartan normalized left ventricular mass and wall thickness. Furthermore, treatment with losartan reduced myocardial collagen content and reduced the incidence of myocyte apoptosis.

CONCLUSIONS

Taken together, these results show that there are functionally significant interactions between RAS and TNF in the heart and that these interactions play an important role in the development and progression of left ventricular remodeling.

Defective cytotoxic granule-mediated cell death pathway impairs T lymphocyte homeostasis

Hemophagocytic syndrome is a severe and often fatal syndrome resulting from excessive activation and proliferation of T lymphocytes and macrophages. Onset of a hemophagocytic syndrome characterized the course of several human inherited immune disorders, all of them resulting from molecular defects of the perforin-dependent cytotoxic process exerted by both T and Natural Killer (NK) lymphocytes. These disorders highlight the determinant role of this lytic pathway in the control of lymphocyte expansion and homeostasis. New effectors of this secretory pathway have been thus identified.

Fas is detectable on beta cells in accelerated, but not spontaneous, diabetes in nonobese diabetic mice

Fas (CD95) is a potential mechanism of pancreatic beta cell death in type 1 diabetes. beta cells do not constitutively express Fas but it is induced by cytokines. The hypothesis of this study is that Fas expression should be measurable on beta cells for them to be killed by this mechanism. We have previously reported that up to 5% of beta cells isolated from nonobese diabetic (NOD) mice are positive for Fas expression by flow cytometry using autofluorescence to identify beta cells. We have now found that these are not beta cells but contaminating dendritic cells, macrophages, and B lymphocytes. In contrast beta cells isolated from NODscid mice that are recipients of T lymphocytes from diabetic NOD mice express Fas 18-25 days after adoptive transfer but before development of diabetes. Fas expression on beta cells was also observed in BDC2.5, 8.3, and 4.1 TCR-transgenic models of diabetes in which diabetes occurs more rapidly than in unmodified NOD mice. In conclusion, Fas is observed on beta cells in models of diabetes in which rapid beta cell destruction occurs. Its expression is likely to reflect differences in the intraislet cytokine environment compared with the spontaneous model and may indicate a role for this pathway in beta cell destruction in rapidly progressive models.

TNF plays an essential role in tumor regression after adoptive transfer of perforin/IFN-gamma double knockout effector T cells

We have recently shown that effector T cells (T(E)) lacking either perforin or IFN-gamma are highly effective mediators of tumor regression. To rule out compensation by either mechanism, T(E) deficient in both perforin and IFN-gamma (perforin knockout (PKO)/IFN-gamma knockout (GKO)) were generated. The adoptive transfer of PKO/GKO T(E) mediated complete tumor regression and cured wild-type animals with established pulmonary metastases of the B16BL6-D5 (D5) melanoma cell line. PKO/GKO T(E) also mediated tumor regression in D5 tumor-bearing PKO, GKO, or PKO/GKO recipients, although in PKO/GKO recipients efficacy was reduced. PKO/GKO T(E) exhibited tumor-specific TNF-alpha production and cytotoxicity in a 24-h assay, which was blocked by the soluble TNFRII-human IgG fusion protein (TNFRII:Fc). Blocking TNF in vivo by administering soluble TNFR II fusion protein (TNFRII:Fc) significantly reduced the therapeutic efficacy of PKO/GKO, but not wild-type T(E). This study identifies perforin, IFN-gamma, and TNF as a critical triad of effector molecules that characterize therapeutic antitumor T cells. These insights could be used to monitor and potentially tune the immune response to cancer vaccines.

Functional significance of the perforin/granzyme cell death pathway

Perforin/granzyme-induced apoptosis is the main pathway used by cytotoxic lymphocytes to eliminate virus-infected or transformed cells. Studies in gene-disrupted mice indicate that perforin is vital for cytotoxic effector function; it has an indispensable, but undefined, role in granzyme-mediated apoptosis. Despite its vital importance, the molecular and cellular functions of perforin and the basis of perforin and granzyme synergy remain poorly understood. The purpose of this review is to evaluate critically recent findings on cytotoxic granule-mediated cell death and to assess the functional significance of postulated cell-death pathways in appropriate pathophysiological contexts, including virus infection and susceptibility to experimental or spontaneous tumorigenesis.

Mechanism of T cell-mediated endothelial apoptosis

BACKGROUND

Cytotoxic T lymphocyte (CTL)-mediated destruction of allogeneic vascular endothelium is important in the pathogenesis of both acute and chronic allograft rejection. Despite the importance of this phenomenon, the effector mechanisms responsible for endothelial cell killing are not well defined, and conflicting conclusions have been reached based on variation in experimental methodology.

METHODS

We used a recently described method for isolating mouse vascular endothelium to evaluate endothelial cell lysis by CTLs. Endothelial cell destruction was assessed in vitro both by 51Cr release and DNA fragmentation using wild-type and lpr (Fas deficient) endothelium of C3H/HeJ (H2(k)) mice by MHC alloantigen-specific T cells of wild-type, gld (Fas ligand deficient), and perforin-deficient mice on a C57BL/6 (H2(b)) background.

RESULTS

Although maximal lysis of 56.6+/-0.8% was seen when using wild-type targets and effectors, only a moderate decrease in apoptosis to 37.6+/-4.0% was detected when the Fas/Fas ligand death receptor pathway was eliminated. This decrease in cytotoxicity occurred despite the preserved functional capacity of this pathway. Alternatively, a significant decrease in cytotoxicity to 17.4+/-4.7% was seen when the perforin/granzyme exocytosis pathway was eliminated.

CONCLUSIONS

These data indicate that CTLs destroy vascular endothelium primarily by the perforin/granzyme exocytosis pathway with only a minor contribution to apoptosis by the Fas/Fas ligand death receptor pathway. These data are critical for the proper interpretation of studies evaluating acute and chronic allograft rejection and for the design of rational strategies to ameliorate vascular injury concomitant to the rejection process.

Efficient transduction of pancreatic islets by feline immunodeficiency virus vectors1

BACKGROUND

Pancreatic islets transplanted into immunocompetent diabetic subjects are rapidly lost to apoptotic or lytic death or both. Genetic engineering of islets before transplantation with protective genes may enhance their posttransplantation survival. Accomplishing this goal requires the development of a safe, efficient vector for islet gene delivery.

METHODS

The ability of feline immunodeficiency virus (FIV) vectors to transfer a green fluorescent protein (GFP) gene to NIT-1 cells and primary islets was measured and compared with murine leukemia virus (MLV) and human immunodeficiency virus (HIV) vectors. Islets were examined using confocal microscopy to determine the extent and pattern of infection. Toxicity of the procedure was assessed via measurement of glucose stimulation indices and by reversion of diabetic mice using either FIV-infected or control islet transplants.

RESULTS

FIV effectively transduces islets with no untoward effect on the insulin secretion capacity of the beta cells. When FIV, HIV, and MLV GFP vectors were standardized to the same 293 cell titer and used to infect NIT-1 cells or whole islets, the FIV transduced equal or greater numbers of cells relative to the HIV vector and significantly more than the MLV vector. Islets transduced with FIV GFP were transplanted in a murine model for diabetes and were shown to revert diabetes and express GFP 4 weeks after transduction and 3 weeks after transplantation.

CONCLUSIONS

FIV transduction is a nontoxic and efficient method to genetically modify pancreatic islets and may prove promising for delivering genes to augment islet survival after transplantation.

Lymphocyte-mediated cytotoxicity

Virtually all of the measurable cell-mediated cytotoxicity delivered by cytotoxic T lymphocytes and natural killer cells comes from either the granule exocytosis pathway or the Fas pathway. The granule exocytosis pathway utilizes perforin to traffic the granzymes to appropriate locations in target cells, where they cleave critical substrates that initiate DNA fragmentation and apoptosis; granzymes A and B induce death via alternate, nonoverlapping pathways. The Fas/FasL system is responsible for activation-induced cell death but also plays an important role in lymphocyte-mediated killing under certain circumstances. The interplay between these two cytotoxic systems provides opportunities for therapeutic interventions to control autoimmune diseases and graft vs. host disease, but oversuppression of these pathways may also lead to increased viral susceptibility and/or decreased tumor cell killing.

Downregulation of apoptosis in the target tissue prevents low-dose streptozotocin-induced autoimmune diabetes

3,7-dimethyl-1-(5-oxohexyl) xanthine, pentoxifylline (PTX) is shown to affect cytokine-induced apoptosis in several experimental models and clinical conditions. It had been also shown to prevent insulitis and hyperglycemia in non-obese diabetic (NOD) mice, and mice and rats susceptible to diabetes induction with multiple low-doses of streptozotocin (MLD-STZ). We therefore analysed the development of diabetes and apoptosis of pancreatic beta islet cells in CBA/mice after diabetes induction with MLD-STZ. We have evaluated the effect of PTX on the level of apoptosis in the islet at different time intervals after diabetes induction. Complementary histological and immunohistochemical studies and analyses of the expression of cytokines and nitric oxide have also been done. It was concluded that PTX significantly attenuated apoptosis of the beta-cells in the islet and suppressed the induction of diabetes. Our data are compatible with the notion that interferon-gamma (IFN-gamma)/tumor necrosis factor (TNF)/nitric oxide (NO)-induced apoptosis of beta-cells in experimental diabetes is attenuated by PTX.

Insulin expression levels in the thymus modulate insulin-specific autoreactive T-cell tolerance: the mechanism by which the IDDM2 locus may predispose to diabetes

Type 1 diabetes results from autoimmune destruction of the insulin-producing pancreatic beta-cells. Evidence from our laboratory and others has suggested that the IDDM2 locus determines diabetes susceptibility by modulating levels of insulin expression in the thymus: the diabetes-protective class III alleles at a repeat polymorphism upstream of the insulin gene are associated with higher levels than the predisposing class I. To directly demonstrate the effect of thymic insulin expression levels on insulin-specific autoreactive T-cell selection, we have established a mouse model in which there is graded thymic insulin deficiency in linear correlation with insulin gene copy numbers, while pancreatic insulin remains unaltered. We showed that mice expressing low thymic insulin levels present detectable peripheral reactivity to insulin, whereas mice with normal levels show no significant response. We conclude that thymic insulin levels play a pivotal role in insulin-specific T-cell self-tolerance, a relation that provides an explanation for the mechanism by which the IDDM2 locus predisposes to or protects from diabetes.

beta-Cell death during progression to diabetes

The hallmark of type 1 diabetes is specific destruction of pancreatic islet beta-cells. Apoptosis of beta-cells may be crucial at several points during disease progression, initiating leukocyte invasion of the islets and terminating the production of insulin in islet cells. beta-Cell apoptosis may also be involved in the occasional evolution of type 2 into type 1 diabetes.

Beta-cell-targeted expression of a dominant-negative hepatocyte nuclear factor-1 alpha induces a maturity-onset diabetes of the young (MODY)3-like phenotype in transgenic mice

Mutations in the transcription factor hepatocyte nuclear factor-1 alpha (HNF-1 alpha) cause maturity-onset diabetes of the young 3, a severe form of diabetes characterized by pancreatic beta-cell dysfunction. We have used targeted expression of a dominant-negative mutant of HNF-1 alpha to specifically suppress HNF-1 alpha function in beta-cells of transgenic mice. We show that males expressing the mutant protein became overtly diabetic within 6 wk of age, whereas females displayed glucose intolerance. Transgenic males exhibited impaired glucose-stimulated insulin secretion, detected both in vivo and in the perfused pancreas. Pancreatic insulin content was markedly decreased in diabetic animals, whereas the glucagon content was increased. Postnatal islet development was altered, with an increased alpha-cell to beta-cell ratio. beta-Cell ultrastructure showed signs of severe beta-cell damage, including mitochondrial swelling. This animal model of maturity-onset diabetes of the young 3 should be useful for the further elucidation of the mechanism by which HNF-1 alpha deficiency causes beta-cell dysfunction in this disease.

Cutting edge: control of CD8+ T cell activation by CD4+CD25+ immunoregulatory cells

CD4(+)CD25(+) regulatory T cells inhibit organ-specific autoimmune diseases induced by CD4(+)CD25(-) T cells and are potent suppressors of CD4(+)CD25(-) T cell activation in vitro. We demonstrate that CD4(+)CD25(+) T cells also suppress both proliferation and IFN-gamma production by CD8(+) T cells induced either by polyclonal or Ag-specific stimuli. CD4(+)CD25(+) T cells inhibit the activation of CD8(+) responders by inhibiting both IL-2 production and up-regulation of IL-2Ralpha-chain (CD25) expression. Suppression is mediated via a T-T interaction as activated CD4(+)CD25(+) T cells suppress the responses of TCR-transgenic CD8(+) T cells stimulated with soluble peptide-MHC class I tetramers in the complete absence of APC. These results broaden the immunoregulatory role played by CD4(+)CD25(+) T cells in the prevention of autoimmune diseases, but also raise the possibility that they may hinder the induction of effector CD8(+) T cells to tumor or foreign Ags.

Defective function of Fas in patients with type 1 diabetes associated with other autoimmune diseases

Fas (CD95) triggers programmed cell death and is involved in cell-mediated cytotoxicity and in shutting off the immune response. Inherited loss-of-function mutations hitting the Fas system cause the autoimmune/lymphoproliferative syndrome (ALPS). We have recently shown that ALPS patients' families display increased frequency of common autoimmune diseases, including type 1 diabetes. This work evaluates Fas function in type 1 diabetic patients without typical ALPS. Cell death induced by anti-Fas monoclonal antibody was investigated in T-cells from 13 patients with type 1 diabetes alone and 19 patients with type 1 diabetes plus other autoimmune diseases (IDDM-P). Moreover, we analyzed 19 patients with thyroiditis alone (TYR), because most IDDM-P patients displayed thyroiditis. Frequency of resistance to Fas-induced cell death was significantly higher in patients with IDDM-P (73%) than in type 1 diabetic (23%) or TYR (16%) patients or in normal control subjects (3%). The defect was specific because resistance to methyl-prednisolone-induced cell death was not significantly increased in any group. Fas was always expressed at normal levels, and no Fas mutations were detected in four Fas-resistant IDDM-P patients. Analysis of the families of two Fas-resistant patients showing that several members were Fas-resistant suggests that the defect has a genetic component. Moreover, somatic fusion of T-cells from Fas-resistant subjects and the Fas-sensitive HUT78 cell line generates Fas-resistant hybrid cells, which suggests that the Fas resistance is due to molecules exerting a dominant-negative effect on a normal Fas system. These data suggest that Fas defects may be a genetic factor involved in the development of polyreactive type 1 diabetes.

Endothelial-derived nitric oxide and angiotensinogen: blood pressure and metabolism during mouse pregnancy

The regulation of blood pressure during pregnancy involves several biological pathways. Candidate genes implicated in hypertensive diseases during pregnancy include those of the renin-angiotensin system and nitric oxide synthase (NOS). We evaluated blood pressure and metabolic characteristics during pregnancy in mutant mice. These included mice with a null mutation in the endothelial NOS (eNOS) gene (Nos3(-/-)), four copies of the angiotensinogen gene (Agt(2/2)), and mutations in both genes [four copies of Agt and heterozygous deficient for eNOS (Agt(2/2)Nos3(+/-)), four copies of Agt and homozygous deficient for eNOS (Agt(2/2)Nos3(-/-))]. Blood pressure measurements of nulliparous females from mutant strains were compared with two common laboratory strains C57Bl6/J and SV129 throughout their first pregnancy. Serum and urine analysis for the evaluation of renal and liver physiology were measured in the prepregnant state and during the third trimester of pregnancy. Throughout pregnancy blood pressures in all mutant strains were higher compared with controls. Agt(2/2)Nos3(-/-) showed the highest blood pressures and C57Bl6/J the lowest. Control mice, but not mutant mice, showed a second trimester decline in blood pressure. No immediate differences were noted regarding behavioral characteristics, renal or liver function parameters. Mice deficient for eNOS, mice with overexpression of Agt, and mice with mutations in both genes demonstrated higher blood pressure throughout pregnancy. There was no evidence of renal dysfunction, liver dysfunction, or hemolysis among any of the strains studied. We conclude that Nos3 and Agt are important genes in the regulation of blood pressure during pregnancy.

The temporal importance of TNFalpha expression in the development of diabetes

The inflammatory cytokine tumor necrosis factor alpha (TNFalpha) has been linked to the development of several autoimmune diseases. By adapting the tetracycline-regulated gene transcription system, we generated a murine model where islet-specific expression of TNFalpha could be repressed/derepressed within 48 hr following introduction/removal of tetracycline in the drinking water. Here we describe the temporal importance of TNFalpha in diabetes development in mice expressing islet-specific B7-1 and TNFalpha. We show that the duration of TNFalpha-mediated inflammation, not the putative maturity of the immune system at the time of TNFalpha expression, determines diabetes progression. Further, we have described an interval between 21 and 25 days following initiation of TNFalpha expression where the fate of islet-reactive T cells is decided.