Effect of tumor necrosis factor alpha on insulin-dependent diabetes mellitus in NOD mice. I. The early development of autoimmunity and the diabetogenic process

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.

Tolerogenic strategies to halt or prevent type 1 diabetes

A variety of therapeutic strategies have been developed to tolerize autoreactive T cells and prevent autoimmune pathology. In terms of type 1 diabetes, prevention strategies can inhibit the priming and expansion of autoreactive T cells; however, a cure for diabetes would require tolerance to be established in the presence of primed effector cells together with replacement of the destroyed beta cell mass. Replacement of beta cells could be accomplished by transplantation of islets or stem cells or through islet regeneration. We will focus here on tolerogenic strategies that have been used to prevent onset of type 1 diabetes and discuss the potential for a cure.

TNF-alpha receptor 1 (p55) on islets is necessary for the expression of LIGHT on diabetogenic T cells

Insulin-dependent diabetes mellitus results from T-cell-mediated destruction of pancreatic islet beta cells. Both CD4 and CD8 T cells have been shown to be independently capable of beta cell destruction. However, the mechanism of beta cell destruction has remained elusive. It has previously been shown that the absence of TNF-alpha receptor 1 (p55) on the islets protected islets from CD4 T-cell-mediated destruction as long as the T cells did not have access to wild-type islets in vivo. Wild-type and TNF-alpha receptor 1 (p55) deficient islets induce similar levels of proliferation of BDC2.5 T cells. In this study, we demonstrate that islet TNF-alpha receptor 1 (p55) influences the expression of LIGHT (TNFSF-14), a TNF family member with both cytolytic and costimulatory properties, on BDC2.5 T cells and the expression of its receptor HVEM (TNFRSF-14) by islets, indicating a role for LIGHT-HVEM interactions in autoimmune diabetes.

A dual role for TNF-alpha in type 1 diabetes: islet-specific expression abrogates the ongoing autoimmune process when induced late but not early during pathogenesis

We report here that islet-specific expression of TNF-alpha can play a dual role in autoimmune diabetes, depending on its precise timing in relation to the ongoing autoimmune process. In a transgenic model (rat insulin promoter-lymphocytic choriomeningitis virus) of virally induced diabetes, TNF-alpha enhanced disease incidence when induced through an islet-specific tetracycline-dependent promoter system early during pathogenesis. Blockade of TNF-alpha during this phase prevented diabetes completely, suggesting its pathogenetic importance early in disease development. In contrast, TNF-alpha expression abrogated the autoimmune process when induced late, which was associated with a reduction of autoreactive CD8 lymphocytes in islets and their lytic activities. Thus, the fine-tuned kinetics of an autoreactive process undergo distinct stages that respond in a differential way to the presence of TNF-alpha. This observation has importance for understanding the complex role of inflammatory cytokines in autoimmunity.

Resident and infiltrating central nervous system APCs regulate the emergence and resolution of experimental autoimmune encephalomyelitis

During experimental autoimmune encephalomyelitis (EAE), autoreactive Th1 T cells invade the CNS. Before performing their effector functions in the target organ, T cells must recognize Ag presented by CNS APCs. Here, we investigate the nature and activity of the cells that present Ag within the CNS during myelin oligodendrocyte glycoprotein-induced EAE, with the goal of understanding their role in regulating inflammation. Both infiltrating macrophages (Mac-1(+)CD45(high)) and resident microglia (Mac-1(+)CD45(int)) expressed MHC-II, B7-1, and B7-2. Macrophages and microglia presented exogenous and endogenous CNS Ags to T cell lines and CNS T cells, resulting in IFN-gamma production. In contrast, Mac-1(-) cells were inefficient APCs during EAE. Late in disease, after mice had partially recovered from clinical signs of disease, there was a reduction in Ag-presenting capability that correlated with decreased MHC-II and B7-1 expression. Interestingly, although CNS APCs induced T cell cytokine production, they did not induce proliferation of either T cell lines or CNS T cells. This was attributable to production by CNS cells (mainly by macrophages) of NO. T cell proliferation was restored with an NO inhibitor, or if the APCs were obtained from inducible NO synthase-deficient mice. Thus, CNS APCs, though essential for the initiation of disease, also play a down-regulatory role. The mechanisms by which CNS APCs limit the expansion of autoreactive T cells in the target organ include their production of NO, which inhibits T cell proliferation, and their decline in Ag presentation late in disease.

IFN-gamma/TNF-alpha synergism as the final effector in autoimmune diabetes: a key role for STAT1/IFN regulatory factor-1 pathway in pancreatic beta cell death

Fas ligand (FasL), perforin, TNF-alpha, IL-1, and NO have been considered as effector molecule(s) leading to beta cell death in autoimmune diabetes. However, the real culprit(s) in beta cell destruction have long been elusive, despite intense investigation. We and others have demonstrated that FasL is not a major effector molecule in autoimmune diabetes, and previous inability to transfer diabetes to Fas-deficient nonobese diabetic (NOD)-lpr mice was due to constitutive FasL expression on lymphocytes from these mice. Here, we identified IFN-gamma/TNF-alpha synergism as the final effector molecules in autoimmune diabetes of NOD mice. A combination of IFN-gamma and TNF-alpha, but neither cytokine alone, induced classical caspase-dependent apoptosis in insulinoma and pancreatic islet cells. IFN-gamma treatment conferred susceptibility to TNF-alpha-induced apoptosis on otherwise resistant insulinoma cells by STAT1 activation followed by IFN regulatory factor (IRF)-1 induction. IRF-1 played a central role in IFN-gamma/TNF-alpha-induced cytotoxicity because inhibition of IRF-1 induction by antisense oligonucleotides blocked IFN-gamma/TNF-alpha-induced cytotoxicity, and transfection of IRF-1 rendered insulinoma cells susceptible to TNF-alpha-induced cytotoxicity. STAT1 and IRF-1 were expressed in pancreatic islets of diabetic NOD mice and colocalized with apoptotic cells. Moreover, anti-TNF-alpha Ab inhibited the development of diabetes after adoptive transfer. Taken together, our results indicate that IFN-gamma/TNF-alpha synergism is responsible for autoimmune diabetes in vivo as well as beta cell apoptosis in vitro and suggest a novel signal transduction in IFN-gamma/TNF-alpha synergism that may have relevance in other autoimmune diseases and synergistic anti-tumor effects of the two cytokines.

Protection against diabetes and improved NK/NKT cell performance in NOD.NK1.1 mice congenic at the NK complex

The NK1.1 cell surface receptor, which belongs to the NKR-P1 gene cluster, has been bred onto nonobese diabetic (NOD) mice for two purposes. The first was to tag NK and NKT cells for easier experimental identification of those subsets and better analysis of their implication in type 1 diabetes. The second was to produce a congenic strain carrying Idd6, a susceptibility locus that has been repeatedly mapped in the vicinity of the NKR-P1 gene cluster and the NK complex, to explore the impact of this locus upon autoimmune diabetes. NOD.NK1.1 mice express the NK1.1 marker selectively on the surface of their NK and NKT cell subsets. In addition, the mice manifest reduced disease incidence and improved NK and NKT cell performance, as compared with wild-type NOD mice. The association of those two features in the same congenic strain constitutes a strong argument in favor of Idd6 being associated to the NK complex. This could explain at the same time the multiple alterations of innate immunity reported in NOD mice and the fact that disease onset can be readily modified by boosting the innate immune system of the mouse.

Soluble adhesion molecules in preclinical type 1 diabetes. The Childhood Diabetes in Finland Study Group

We measured the concentrations of the soluble forms of the intercellular adhesion molecule-1 (sICAM-1) and L-selectin in 95 autoantibody-positive siblings of children with type 1 diabetes and 95 sex- and age-matched siblings testing negative for diabetes-associated autoantibodies to assess the possible role of soluble adhesion molecules as markers of progressive ss-cell destruction in preclinical diabetes and their ability to discriminate between those siblings who progress to clinical disease and those who remain nondiabetic. We observed an inverse correlation between age and the levels of both sICAM-1 (r = -0.31, p < 0.001) and sL-selectin (r = -0.27, p < 0.001) in the control siblings but no association with HLA-DR phenotypes. There was no difference in the circulating levels of soluble adhesion molecules between the antibody-positive and negative siblings. Among the antibody-positive siblings, those with at least three autoantibodies had higher sICAM-1 levels (p < 0.01) than those testing positive for only one, and siblings with three autoantibodies or more had higher concentrations of sL-selectin (p < 0.01) than those with two autoantibodies. Siblings with an islet cell antibody level of 20 Juvenile Diabetes Foundation units or more had higher sICAM-1 concentrations than those with a level below 20 (p < 0.001), and those testing positive for antibodies to the protein tyrosine phosphatase-related IA-2 antigen had increased levels of both sICAM-1 (p = 0.03) and sL-selectin (p = 0.02) compared with siblings who tested negative. The antibody-positive siblings who progressed to clinical type 1 diabetes were significantly younger than the nonprogressors (p < 0.001) and had higher levels of sICAM-1 initially (p < 0.001). The difference in sICAM-1 concentrations remained significant (p = 0.03) after age adjustment. Our results indicate that concentrations of soluble adhesion molecules are increased in the autoantibody-positive siblings who have the highest risk of developing clinical diabetes, suggesting that ss-cell destruction is reflected in increased circulating levels of these molecules. This is supported by the observation of elevated sICAM-1 concentrations in the 29 siblings who actually progressed to clinical type 1 diabetes. Peripheral levels of soluble adhesion molecules are not able to discriminate between progressors and nonprogressors, however, due to substantial overlapping between these two groups.

Staphylococcal enterotoxin-B-induced lethal shock in mice is T-cell-dependent, but disease susceptibility is defined by the non-T-cell compartment

Here we introduce a murine model for SEB-induced lethal shock that relies on the administration of SEB alone and does not involve hepatotoxicity by avoiding pretreatment with the hepatotoxin D-galactosamine. In the absence of D-gal, we first identified SEB-susceptible and -resistant H-2(k)-congenic mouse strains. In contrast with what is well established for the classic D-gal-dependent model and what therefore is anticipated for the human disease, the levels of TNF produced did not define susceptibility in our model. The SEB-induced TNF response in vitro and in vivo was stronger in resistant B10.BR mice than in susceptible C3H/HeJ mice. Neither the magnitude nor the quality of the T cell response induced by SEB defined susceptibility. Adoptive transfer experiments in C3H-SCID recipient mice demonstrated that induction of the disease is T-cell-dependent. T cells from resistant and susceptible mice both transferred disease susceptibility to H-2(k)-congenic C3H-SCID mice, indicating that disease susceptibility is downstream from T cell activation, at the level of the target organ itself, which responds differently to T-cell-induced inflammation.

Vaccination with empty plasmid DNA or CpG oligonucleotide inhibits diabetes in nonobese diabetic mice: modulation of spontaneous 60-kDa heat shock protein autoimmunity

Nonobese diabetic (NOD) mice develop insulitis and diabetes through a process involving autoimmunity to the 60-kDa heat shock protein (HSP60). Treatment of NOD mice with HSP60 or with peptides derived from HSP60 inhibits this diabetogenic process. We now report that NOD diabetes can be inhibited by vaccination with a DNA construct encoding human HSP60, with the pcDNA3 empty vector, or with an oligonucleotide containing the CpG motif. Prevention of diabetes was associated with a decrease in the degree of insulitis and with down-regulation of spontaneous proliferative T cell responses to HSP60 and its peptide p277. Moreover, both the pcDNA3 vector and the CpG oligonucleotide induced specific Abs, primarily of the IgG2b isotype, to HSP60 and p277, and not to other islet Ags (glutamic acid decarboxylase or insulin) or to an unrelated recombinant Ag expressed in bacteria (GST). The IgG2b isotype of the specific Abs together with the decrease in T cell proliferative responses indicate a shift of the autoimmune process to a Th2 type in treated mice. These results suggest that immunostimulation by bacterial DNA motifs can modulate spontaneous HSP60 autoimmunity and inhibit NOD diabetes.

Adjuvant-induced improvement of glucose intolerance in type 2 diabetic KK-Ay mice through interleukin-1 and tumor necrosis factor-alpha

We reported that administration of complete Freund's adjuvant (CFA) improved glucose tolerance test (GTT) results in obese diabetic KK-Ay mice. In this study, we investigated its mechanism. An injection with CFA remarkably improved GTT for more than a week in KK-Ay mice, although insulin response was not changed compared with saline controls. The hypoglycemic effect of insulin was significantly, but partially, potentiated in the CFA-treated mice compared with the controls, suggesting that CFA stimulated insulin-mediated and non-insulin-mediated glucose disposal. Improvement in the GTT with CFA was partially transferable to nontreated mice by peritoneal exudative cells, but not spleen or lymph node cells. Pretreatment with anti-interleukin (IL)-1 alpha and -1 beta antibodies or anti-tumor necrosis factor (TNF)-alpha antibody significantly abrogated the improvement in the GTT with CFA. The results indicate that CFA-induced improvement in glucose intolerance in KK-Ay mice was mediated at least by IL-1 and TNF-alpha.

Divergent roles for p55 and p75 tumor necrosis factor receptors in the pathogenesis of MOG(35-55)-induced experimental autoimmune encephalomyelitis

To clarify the role of tumor necrosis factor (TNF) in the inflammatory aspects of autoimmunity vs its potential role in the apoptotic elimination of autoreactive effector cells, we assessed the roles of the p55 (TNFR1/Tnfrsf1a/CD120a) and p75 (TNFR2/Tnfrsf1b/CD120b) TNF receptors in the pathogenesis of MOG(35-55)-induced experimental autoimmune encephalomyelitis (EAE). TNFR p55/p75(-/-) double knockout mice were completely resistant to clinical disease. TNFR p55(-/-) single knockout mice were also totally resistant to EAE, exhibiting reduced MOG(35-55)- specific proliferative responses and Th1 cytokine production, despite displaying equivalent DTH responses. Importantly, IL-5 was significantly increased in p55(-/-) mice. In contrast, p75(-/-) knockout mice exhibited exacerbated EAE, enhanced Th1 cytokine production, and enhanced CD4(+) and F4/80(+) CNS infiltration. Thus, p55/TNFR1 is required for the initiation of pathologic disease, whereas p75/TNFR2 may be important in regulating the immune response. These results have important implications for therapies targeting p55 and p75 receptors for treating autoimmune diseases.

The role of the proteasome in autoimmunity

Type 1 diabetes is believed to be caused by T cell-mediated autoimmunity, with a prediabetic state characterized by the production of autoantibodies specific for proteins expressed by pancreatic beta cells. The non-obese diabetic (NOD) mouse is a spontaneous model of Type 1 diabetes with a strong genetic component that maps to the major histocompatibility complex (MHC) region of the genome. A specific proteasome defect has now been identified in NOD mouse lymphocytes that results from down-regulation of expression of the proteasome subunit LMP2, which is encoded by a gene in the MHC genomic region. This defect both prevents the proteolytic processing required for the production and activation of the transcription factor nuclear factor-kappaB (NF-kappaB), which plays an important role in immune and inflammatory responses, in addition to increasing the susceptibility of the affected cells to apoptosis induced by tumor necrosis factor-alpha (TNF-alpha). The proteasome dysfunction is both tissue- and developmental stage-specific and likely contributes to disease pathogenesis and tissue targeting.

Age-related alterations in IL-1beta, TNF-alpha, and IL-6 concentrations in parotid acinar cells from BALB/c and non-obese diabetic mice

IL-1beta, TNF-alpha, and IL-6 have been implicated in the destruction of parotid gland acinar cells (but not duct cells) in autoimmune sialoadenitis. Here we report the temporal alterations of these cytokines in parotid acinar cells that may lead to this specificity in cell death in the non-obese diabetic (NOD) mouse model for Sjögren's syndrome. Immunohistochemistry on paraffin sections of parotid gland from 5- and 10-week-old BALB/c and NOD mice confirmed the presence of many peri-acinar lymphoid nodules but few T-cells and macrophages between acinar cells. RT-PCR on enzymatically dispersed mouse parotid acinar cells (MPACs) showed no bands for CD3varepsilon, CD20, or F4/80 regardless of mouse strain or age. By ELISA, MPACs from 10-week-old NODs showed a small but highly significant (p<0.003) increase in IL-1beta and a large significant decrease (p<0.008) in IL-6 compared to 5-week-old NODs. Norepinephrine-stimulated amylase release from MPACs was not different regardless of mouse strain or age. These data show that alterations in acinar cell production of IL-1beta and IL-6 in aging NODs precede periductal lymphoid aggregates and acinar cell secretory dysfunction. (J Histochem Cytochem 48:1033-1041,2000)

Beta cell destruction in the development of autoimmune diabetes in the non-obese diabetic (NOD) mouse

In the non-obese diabetic (NOD) mouse model of Type 1 (insulin-dependent) diabetes, evidence suggests that pancreatic beta cells are destroyed in part by apoptotic mechanisms. The precise mechanisms of beta cell destruction leading to diabetes remain unclear. The NOD mouse has been studied to gain insight into the cellular and molecular mediators of beta cell death, which are discussed in this review. Perforin, secreted by CD8(+) T cells, remains one of the only molecules confirmed to be implicated in beta cell death in the NOD mouse. There are many other molecules, including Fas ligand and cytokines such as interferon-gamma, interleukin-1 and tumor necrosis factor-alpha, which may lead to beta cell destruction either directly or indirectly via regulation of toxic molecules such as nitric oxide. As beta cell death can occur in the absence of perforin, these other factors, in addition to other as yet unidentified factors, may be important in the development of diabetes. Effective protection of NOD mice from beta cell destruction may therefore require inhibition of multiple effector mechanisms.

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.

Significant role for Fas in the pathogenesis of autoimmune diabetes

Programmed cell death represents an important pathogenic mechanism in various autoimmune diseases. Type I diabetes mellitus (IDDM) is a T cell-dependent autoimmune disease resulting in selective destruction of the beta cells of the islets of Langerhans. beta cell apoptosis has been associated with IDDM onset in both animal models and newly diagnosed diabetic patients. Several apoptotic pathways have been implicated in beta cell destruction, including Fas, perforin, and TNF-alpha. Evidence for Fas-mediated lysis of beta cells in the pathogenesis of IDDM in nonobese diabetic (NOD) mice includes: 1) Fas-deficient NOD mice bearing the lpr mutation (NOD-lpr/lpr) fail to develop IDDM; 2) transgenic expression of Fas ligand (FasL) on beta cells in NOD mice may result in accelerated IDDM; and 3) irradiated NOD-lpr/lpr mice are resistant to adoptive transfer of diabetes by cells from NOD mice. However, the interpretation of these results is complicated by the abnormal immune phenotype of NOD-lpr/lpr mice. Here we present novel evidence for the role of Fas/FasL interactions in the progression of NOD diabetes using two newly derived mouse strains. We show that NOD mice heterozygous for the FasL mutation gld, which have reduced functional FasL expression on T cells but no lymphadenopathy, fail to develop IDDM. Further, we show that NOD-lpr/lpr mice bearing the scid mutation (NOD-lpr/lpr-scid/scid), which eliminates the enhanced FasL-mediated lytic activity induced by Fas deficiency, still have delayed onset and reduced incidence of IDDM after adoptive transfer of diabetogenic NOD spleen cells. These results provide evidence that Fas/FasL-mediated programmed cell death plays a significant role in the pathogenesis of autoimmune diabetes.

Low CD86 expression in the nonobese diabetic mouse results in the impairment of both T cell activation and CTLA-4 up-regulation

The nonobese diabetic (NOD) mouse spontaneously develops autoimmune insulin-dependent diabetes mellitus and serves as a model for human type I diabetes. NOD spleen cells proliferate to a lesser extent than those from C57BL/6 and BALB/c mice in response to anti-CD3. To investigate the cause of this reduced T cell proliferation, costimulatory molecule expression was investigated. It was found that NOD macrophages, dendritic cells, and T cells, but not B cells, expressed lower basal levels of CD86, but not CD80, CD28, or CD40, compared with C57BL/6 and BALB/c. This low CD86 expression was not dependent on the MHC haplotype or on diabetes development since the NOD-related, diabetes-free mouse strains NON (H-2nb1) and NOR (H-2g7) exhibited similar low levels of CD86 expression and proliferation. Furthermore, following activation, the relative up-regulation of CTLA-4, as compared with CD28, was more pronounced on C57BL/6 and BALB/c T cells as shown by an increased CTLA-4/CD28 ratio. This activation-induced increase in the CTLA-4/CD28 ratio was markedly reduced on NOD T cells compared with the other two strains. The low CD86 expression in NOD mice may account for the reduced increase in both proliferation and the CTLA-4/CD28 ratio, since reducing CD86 expression in C57BL/6 and BALB/c cultures to NOD levels significantly reduces the proliferation and the CTLA-4/CD28 ratio. Therefore, we propose that a low level of CD86 expression in the NOD mouse contributes to a defective regulation of autoreactive T cells by preventing the full activation of T cells and therefore the up-regulation of CTLA-4.

Neonatal tumor necrosis factor alpha promotes diabetes in nonobese diabetic mice by CD154-independent antigen presentation to CD8(+) T cells

Neonatal islet-specific expression of tumor necrosis factor (TNF)-alpha in nonobese diabetic mice promotes diabetes by provoking islet-infiltrating antigen-presenting cells to present islet peptides to autoreactive T cells. Here we show that TNF-alpha promotes autoaggression of both effector CD4(+) and CD8(+) T cells. Whereas CD8(+) T cells are critical for diabetes progression, CD4(+) T cells play a lesser role. TNF-alpha-mediated diabetes development was not dependent on CD154-CD40 signals or activated CD4(+) T cells. Instead, it appears that TNF-alpha can promote cross-presentation of islet antigen to CD8(+) T cells using a unique CD40-CD154-independent pathway. These data provide new insights into the mechanisms by which inflammatory stimuli can bypass CD154-CD40 immune regulatory signals and cause activation of autoreactive T cells.

Rheumatoid arthritis and its animal models: the role of TNF-alpha and the possible absence of specific immune reactions

Rheumatoid arthritis is an organ-specific inflammatory disease of humans. Recent studies have focused on associations with non-MHC genes, new autoantigens and the role of innate immune responses. The success of anti-TNF-alpha in the majority (but, interestingly, not all) of patients has implications for disease mechanisms but the dangers of long-term therapy are becoming clearer. A number of new models of arthritis have been defined and emphasize the importance of the genetic make-up of the host. Attention has also focused on why the joint is a particularly vulnerable site for inflammatory responses.

NOD mice are defective in proteasome production and activation of NF-kappaB

The nonobese diabetic (NOD) mouse is an animal model of human type I diabetes with a strong genetic component that maps to the major histocompatibility complex (MHC) of the genome. We have identified in NOD lymphocytes a specific proteasome defect that results from the lack of the LMP2 subunit. The pronounced proteasome defect results in defective production and activation of the transcription factor NF-kappaB, which plays an important role in immune and inflammatory responses as well as in preventing apoptosis induced by tumor necrosis factor alpha. The defect in proteasome function in NOD mouse splenocytes was evident from impaired NF-kappaB subunit p50 and p52 generation by proteolytic processing and impaired degradation of the NF-kappaB-inhibitory protein IkappaBalpha. An obligatory role of MHC-linked proteasome subunits in transcription factor processing and activation has been established in a spontaneous-disease model and mutant cells similarly lacking the MHC-encoded subunit. These data suggest that NOD proteasome dysfunction is due to a tissue- and developmental-stage-specific defect in expression of the MHC-linked Lmp2 gene, resulting in altered transcription factor NF-kappaB activity, and that this defect contributes to pathogenesis in NOD mice. These observations are consistent with the diverse symptomatology of type I diabetes and demonstrate clear sex-, tissue-, and age-specific differences in the expression of this error which parallel the initiation and disease course of insulin-dependent (type I) diabetes mellitus.

Cytokines that regulate autoimmune responses

Autoimmune responses are controlled by complex regulatory circuits. Previous work has revealed that factors controlling autoimmunity can act both as potentiating and inhibitory agents, depending upon the site and timing of exposure. Recent advances in this complex field have at least partially uncovered the mechanism whereby these regulatory molecules participate in autoimmune processes. IL-12 production in the absence of infection may predispose to autoimmunity. IL-4 and transforming growth factor beta may suppress autoreactive T cells. Proinflammatory cytokines may ameliorate autoimmunity, dependent on the timing and level of production. In many cases, cytokines may act via antigen-presenting cells.

Platelet expression of tumour necrosis factor-alpha (TNF-alpha), TNF receptors and intercellular adhesion molecule-1 (ICAM-1) in patients with proliferative diabetic retinopathy

Microvascular complications of insulin-dependent diabetes mellitus (IDDM) have been strongly associated with platelet abnormalities, whilst TNF-alpha has been implicated in the pathogenesis of this condition. However, at present it is not clear whether human circulating platelets express TNF-alpha or TNF receptors (TNF-R) or whether impaired expression of these molecules and of the TNF-reactive adhesion molecule ICAM-1 may be associated with platelet abnormalities in patients with IDDM. On this basis we investigated the platelet expression of these molecules in patients with IDDM complicated or uncomplicated by proliferative diabetic retinopathy (PDR) and in healthy subjects. We observed that the proportion of platelets staining for TNF-alpha was significantly higher in IDDM patients with active PDR than in patients without microvascular complications (P = 0.0078), quiescent PDR (P = 0.003) or healthy subjects (P = 0.0013). Patients with active PDR also showed a higher proportion of platelets expressing TNF-RI (P = 0. 0052) and TNF-RII (P = 0.015) than healthy controls or patients with quiescent PDR (P = 0.009 and 0.0006, respectively). In addition, the percentage of ICAM-1+ platelets was significantly higher in patients with active PDR than in patients with quiescent PDR (P = 0.0065) or normal subjects (P = 0.013). There was a direct correlation between platelet expression of TNF-alpha and that of TNF-R in PDR patients, indicating that platelet staining for TNF-alpha may be due to binding of this cytokine to its receptors. The results suggest that increased platelet expression of TNF-alpha, TNF-R and ICAM-1 in IDDM patients may constitute important markers of thrombocyte abnormalities during the development of microvascular complications of diabetes mellitus.

Presence of CpG DNA and the Local Cytokine Milieu Determine the Efficacy of Suppressive DNA Vaccination in Experimental Autoimmune Encephalomyelitis

We here study the adjuvant properties of immunostimulatory DNA sequences (ISS) and coinjected cytokine-coding cDNA in suppressive vaccination with DNA encoding an autoantigenic peptide, myelin basic protein peptide 68–85, against Lewis rat experimental autoimmune encephalomyelitis (EAE). EAE is an autoaggressive, T1-mediated disease of the CNS. ISS are unmethylated CpG motifs found in bacterial DNA, which can induce production of type 1 cytokines in vertebrates through the innate immune system. Because ISS in the plasmid backbone are necessary for efficient DNA vaccination, we studied the effect of one such ISS, the 5′-AACGTT-3′ motif, in our system. Treatment with a DNA vaccine encoding myelin basic protein peptide 68–85 and containing three ISS of 5′-AACGTT-3′ sequence suppressed clinical signs of EAE, while a corresponding DNA vaccine without such ISS had no effect. We further observed reduced proliferative T cell responses in rats treated with the ISS-containing DNA vaccine, compared with controls. We also studied the possible impact of coinjection of plasmid DNA encoding rat cytokines IL-4, IL-10, GM-CSF, and TNF-α with the ISS-containing DNA vaccine. Coinjection of IL-4-, IL-10-, or TNF-α-coding cDNA inhibited the suppressive effect of the DNA vaccine on EAE, whereas GM-CSF-coding cDNA had no effect. Coinjection of cytokine-coding cDNA with the ISS-deficient DNA vaccine failed to alter clinical signs of EAE. We conclude that the presence of ISS and induction of a local T1 cytokine milieu is decisive for specific protective DNA vaccination in EAE.

Comparing the Relative Role of Perforin/Granzyme Versus Fas/Fas Ligand Cytotoxic Pathways in CD8+ T Cell-Mediated Insulin-Dependent Diabetes Mellitus

CD8+ cytotoxic T cells play a critical role in initiating insulin-dependent diabetes mellitus. The relative contribution of each of the major cytotoxic pathways, perforin/granzyme and Fas/Fas ligand (FasL), in the induction of autoimmune diabetes remains controversial. To evaluate the role of each lytic pathway in β cell lysis and induction of diabetes, we have used a transgenic mouse model in which β cells expressing the influenza virus hemagglutinin (HA) are destroyed by HA-specific CD8+ T cells from clone-4 TCR-transgenic mice. Upon adoptive transfer of CD8+ T cells from perforin-deficient clone-4 TCR mice, there was a 30-fold increase in the number of T cells required to induce diabetes. In contrast, elimination of the Fas/FasL pathway of cytotoxicity had little consequence. When both pathways of cytolysis were eliminated, mice did not become diabetic. Using a model of spontaneous diabetes, which occurs in double transgenic neonates that express both clone-4 TCR and Ins-HA transgenes, mice deficient in either the perforin or FasL/Fas lytic pathway become diabetic soon after birth. This indicates that, in the neonate, large numbers of autoreactive CD8+ T cells can lead to destruction of islet β cells by either pathway.

Failure of exogenously administered interferon-gamma or blockage of endogenous interleukin-4 with specific inhibitors to augment the incidence of autoimmune diabetes in male NOD mice

Interferon (IFN)-gamma and interleukin (IL)-4 are prototypic type 1 and type 2 cytokines which are known to play pathogenetic and protective roles, respectively, in NOD mouse IDDM. The capacity of male NOD mice to produce more IL-4 and less IFN-gamma within the insulitic lesions than females has been suggested to contribute to their lower incidence of diabetes. In this study we have tested the effects of prolonged prophylactic treatment of male NOD mice with rat IFN-gamma, mouse IFN-gamma, anti-IL-4 monoclonal antibody (mAb) and recombinant murine soluble IL-4 receptor (smIL-4R) on the diabetogenic events leading to insulitis and diabetes. None of these treatments influenced spontaneous and/or cyclophosphamide-induced autoimmune diabetogenesis in male NOD mice. Control mice exhibited comparable histological signs of insulitis and incidence of diabetes to those treated with either mouse/rat IFN-gamma or specific IL-4 inhibitors. On the contrary, both clinical and histological signs of diabetes were suppressed by prophylactic treatment with anti-IFN-gamma mAb. These findings indicate that the autoimmune diathesis of male NOD mice towards IDDM cannot be augmented by manipulation of endogenous IFN-gamma or IL-4.

Tumor necrosis factor-alpha and the progression of diabetes in non-obese diabetic mice

In the past decade, a wealth of information has accumulated through studies in non-obese diabetic (NOD) mice regarding the molecular and cellular events that participate in the progression to diabetes in insulin-dependent diabetes mellitus (IDDM). One molecule that has received considerable attention is the inflammatory cytokine tumor necrosis factor-alpha (TNF-alpha). TNF-alpha has been demonstrated to have a positive or negative effect on the progression to diabetes in NOD mice, although the mechanism by which TNF-alpha exerts these differential outcomes is unknown. Here we describe a new NOD model for analyzing the role of TNF-alpha in IDDM, TNF-alpha-NOD mice. TNF-alpha-NOD mice express TNF-alpha solely in their islets from neonatal life onwards, and develop accelerated progression to diabetes. This rapid progression to diabetes is related to earlier and more aggressive infiltration of the islets with immune cells and an enhancement in the presentation of islet antigen in situ in the islets by islet-infiltrating antigen-presenting cells to T cells. Although adoptive transfer studies demonstrated that TNF-alpha can enhance presentation of islet antigen to both effector CD4+ and CD8+ T cells, further investigations in TNF-alpha-NOD mice deficient in either CD4+ or CD8+ T cells demonstrated that diabetes progression is dependent on CD8+ T cells, with CD4+ T cells playing a lesser role. The data accumulating from TNF-alpha-NOD mice, described in this review, indicates novel pathways by which inflammatory stimuli can precipitate autoimmunity, and suggests newer approaches in the design of therapeutic treatments that prevent beta-cell destruction in IDDM.

TNF Receptor 1-Dependent β Cell Toxicity as an Effector Pathway in Autoimmune Diabetes

Autoimmune diabetes is characterized by a chronic progressive inflammatory autoimmune reaction that ultimately causes the selective elimination of pancreatic β cells. To address the question of whether the cell death-inducing cytokines TNF and lymphotoxin α are involved in this process, we generated nonobese diabetic (NOD) mice that are deficient for TNF receptor 1 (TNFR1 or TNFRp55). Insulitis developed in these mice similarly to that in normal control NOD mice, but progression to diabetes was completely abrogated. Since this was probably due to the complex immunomodulatory effects of TNF and lymphotoxin α signaled via TNFR1 on lymphohemopoietic cells, adoptive transfer experiments with spleen cells from diabetic NOD mice were conducted. It was found that the absence of TNFR1 in recipients delayed diabetes induced by normal control and precluded diabetes induced by perforin-deficient spleen cells. In a CD8+ T cell-mediated model of diabetes, however, diabetes induced by adoptive transfer of TCR transgenic lymphocytic choriomeningitis virus glycoprotein-specific CD8+ T cells was not delayed by the absence of TNFR1 in recipient mice. Together with the described expression patterns of perforin and TNF in the mononuclear islet infiltrates of NOD mice, these results indicate that two diabetogenic effector mechanisms are delivered by distinct cell populations: CD8+ T cells lyse β cells via perforin-dependent cytotoxicity, whereas CD4+ T cells, macrophages, and dendritic cells contribute to diabetes development via TNFR1-dependent β cell toxicity.

In autoimmune diabetes the transition from benign to pernicious insulitis requires an islet cell response to tumor necrosis factor alpha

The islet-infiltrating and disease-causing leukocytes that are a hallmark of insulin-dependent diabetes mellitus produce and respond to a set of cytokine molecules. Of these, interleukin 1beta, tumor necrosis factor (TNF)-alpha, and interferon (IFN)-gamma are perhaps the most important. However, as pleiotropic molecules, they can impact the path leading to beta cell apoptosis and diabetes at multiple points. To understand how these cytokines influence both the formative and effector phases of insulitis, it is critical to determine their effects on the assorted cell types comprising the lesion: the effector T cells, antigen-presenting cells, vascular endothelium, and target islet tissue. Here, we report using nonobese diabetic chimeric mice harboring islets deficient in specific cytokine receptors or cytokine-induced effector molecules to assess how these compartmentalized loss-of-function mutations alter the events leading to diabetes. We found that islets deficient in Fas, IFN-gamma receptor, or inducible nitric oxide synthase had normal diabetes development; however, the specific lack of TNF- alpha receptor 1 (p55) afforded islets a profound protection from disease by altering the ability of islet-reactive, CD4(+) T cells to establish insulitis and subsequently destroy islet beta cells. These results argue that islet cells play a TNF-alpha-dependent role in their own demise.

Cytokine production in NOD mice on prophylactic insulin therapy

We investigated whether cytokines produced primarily by monocytes/macrophages (IL-1alpha), Th1-lymphocytes (IFNgamma), or Th2-lymphocytes (IL-4) are modulated in diabetes-prone NOD mice by insulin treatment as used in prophylaxis studies. The cytokines were measured by ELISA in plasma and in supernatants of spleen cells activated ex vivo by lipopolysaccharide plus phytohemagglutinin. Insulin, 0.25-0.50 IU/day, was given subcutaneously for 8 weeks starting in 4-week-old female mice. The insulin-treated and control NOD mice showed similar weight gains and, by the end of the study, both groups exhibited cell infiltration in about 25% of their islets. IL-1alpha, IFNgamma and IL-4 were generally below detection in plasma of prediabetic animals and controls. Diabetic NOD mice, aged 28-45 weeks, had significantly elevated plasma IL-1alpha: 154+/-39 pg/ml (mean+/-SEM, p<0.0001). While ex vivo activated NOD splenocytes released similar amounts of IL-1alpha, insulin therapy increased the levels from 99+/-17 to 155+/-19 pg/10(6) cells (p<0.05). Supernatants of activated splenocytes from prediabetic NOD mice had lower levels of IL-4 (<15 pg/10(6) cells) compared with those from BALB/c mice (88+/-22 pg/10(6) cells; p<0.01), and this deficiency was partially compensated for when the NOD mice were given insulin (27+/-8; p<0.01). The levels of IFNgamma were comparable and largely unaffected by insulin treatment. Hence, insulin therapy appears to partially normalize an otherwise deficient Th2 response in NOD mice.

Evidence for control of tumour necrosis factor-alpha (TNF-alpha) activity by TNF receptors in patients with proliferative diabetic retinopathy

TNF-alpha has been implicated in the pathogenesis of insulin- dependent diabetes mellitus (IDDM). At present there are no studies linking serum levels of soluble TNF receptors (sTNF-R) to the development of diabetic microvascular complications such as proliferative diabetic retinopathy (PDR), or to the production of TNF-alpha in these patients. We investigated serum levels of sTNF receptors (sTNF-RI and sTNF-RII) in IDDM patients with or without PDR, and related these to the in vitro production of TNF-alpha upon activation of whole blood and isolated mononuclear cells (MNC). We observed higher serum levels of sTNF-RI in IDDM patients with active (range 945-6630 pg/ml; P = 0.029) or quiescent PDR (range 1675-4970 pg/ml; P = 0.00092) than in individuals with IDDM without retinopathy (range 657-2617 pg/ml) or healthy controls (range 710-1819 pg/ml; P = 0.0092 and 0.0023, respectively). Increased serum levels of sTNF-RII were also seen in IDDM patients with active PDR (range 1749-5218 pg/ml; P = 0.034) or quiescent PDR (range 1494-5249 pg/ml; P = 0.0084) when compared with disease controls (range 1259-4210 pg/ml) or healthy subjects (range 1237-4283 pg/ml). Whole blood production of biologically active TNF-alpha was lower in PDR patients than in disease (P = 0.04) and healthy controls (P < 0.005), contrasting with a higher production of TNF-alpha by lipopolysaccharide (LPS)-activated MNC from PDR patients (P = 0.013). Inhibition of TNF-alpha by TNF-R in plasma supernatants of activated blood from PDR patients was demonstrated by increase of TNF-alpha activity in the presence of anti-TNF-RI and anti-TNF-RII antibodies. These observations suggest that abnormalities in TNF-alpha production and control may operate during the development of microvascular complications of diabetes mellitus.

TNF accelerates the onset but does not alter the incidence and severity of myelin basic protein-induced experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) induction in TNF gene-targeted mice has resulted in conflicting reports in part due to the strong association of TNF with the MHC locus. To define the participation of TNF in EAE development, we back-crossed TNF-deficient mice (H-2b) into the SJL/J strain and directly compared them to H-2b congenic SJL or inbred SJL/J mice. Induction of EAE with myelin basic protein (MBP) revealed that H-2b congenic SJL mice are fully susceptible, indicating that the H-2b haplotype does not affect disease susceptibility. Using H-2b congenic SJL mice we show here that TNF deficiency modifies the normal course of EAE by considerably delaying the onset for approximately 5 days, suggesting that TNF is required for the normal initiation of MBP-induced EAE. However, TNF-deficient mice eventually developed severe EAE with perivascular inflammation and primary demyelination similar to wild-type controls, indicating that TNF is not essential during these processes. Taken together, these results indicate that although TNF is not required for the progression of MBP-induced EAE, it contributes positively by advancing the onset of disease.

Initiation of autoimmune diabetes by developmentally regulated presentation of islet cell antigens in the pancreatic lymph nodes

Little is known about the events triggering lymphocyte invasion of the pancreatic islets in prelude to autoimmune diabetes. For example, where islet-reactive T cells first encounter antigen has not been identified. We addressed this issue using BDC2.5 T cell receptor transgenic mice, which express a receptor recognizing a natural islet beta cell antigen. In BDC2.5 animals, activated T cells were found only in the islets and the lymph nodes draining them, and there was a close temporal correlation between lymph node T cell activation and islet infiltration. When naive BDC2.5 T cells were transferred into nontransgenic recipients, proliferating cells were observed only in pancreatic lymph nodes, and this occurred significantly before insulitis was detectable. Surprisingly, proliferation was not seen in 10-day-old recipients. This age-dependent dichotomy was reproduced in a second transfer system based on an unrelated antigen artificially expressed on beta cells. We conclude that beta cell antigens are transported specifically to pancreatic lymph nodes, where they trigger reactive T cells to invade the islets. Systemic or extrapancreatic T cell priming, indicative of activation via molecular mimicry or superantigens, was not seen. Compromised presentation of beta cell antigens in the pancreatic lymph nodes of juvenile animals may be the root of a first "checkpoint" in diabetes progression.

The effect of local production of cytokines in the pathogenesis of insulin-dependent diabetes mellitus

Insulin-dependent diabetes mellitus (IDDM) is an autoimmune disease mediated by self-reactive T cells that induce inflammation and destruction of pancreatic islet beta cells. A widely held belief is that T helper lymphocytes carrying a type 1 inflammatory phenotype are the major players in generating IDDM. However, recent evidence shows that cytokines belonging to the Th2 pathway can also induce autoimmune diabetes. The expression of cytokines directly within the pancreatic islets of transgenic mice helped to characterize the modulatory effects that Th1 or Th2 cytokines play on T cell-mediated autoimmune responses and diabetogenesis. This review describes the new information that these transgenic models have provided in understanding the exceedingly complex cytokine network and its role in the pathogenesis of IDDM.

Lymphotoxin α3 Induces Chemokines and Adhesion Molecules: Insight into the Role of LTα in Inflammation and Lymphoid Organ Development

Lymphotoxin (LT) plays an important role in inflammation and lymphoid organ development, though the mechanisms by which it promotes these processes are poorly understood. Toward this end, the biologic activities of a recently generated recombinant murine (m) LTα preparation were evaluated. This cytokine preparation was effective at inducing cytotoxicity of WEHI target cells with 50% maximal killing observed with 1.2 ng/ml. mLTα also induced the expression of inflammatory mediators in the murine endothelial cell line bEnd.3. rmLTα induced expression of the adhesion molecules VCAM, ICAM, E-selectin, and the mucosal addressin cellular adhesion molecule, MAdCAM-1. When mLTα, human (h) LTα, and mTNF-α were compared, mLTα was the most potent inducer of MAdCAM-1. None of these cytokines induced the peripheral node addressin, PNAd. mLTα also induced expression of the chemokines RANTES, IFN-inducible protein 10 (IP-10), and monocyte chemotactic protein 1 (MCP-1). mRNA levels peaked 4 h following treatment with mLTα and declined through the 24-h treatment period. LTα also induced chemokine protein within 8 h of treatment, which increased through the 24-h treatment period. These data demonstrate that the proinflammatory effects of LTα3 may be mediated in part through the induction of adhesion molecule and chemokine expression. Further, LTα3 may promote development of lymphoid tissue through induction of chemokines and the mucosal addressin MAdCAM-1. These data confirm previous observations in transgenic and knockout mice that LTα3 in the absence of LTβ carries out unique biologic activities.

Local expression of TNFalpha in neonatal NOD mice promotes diabetes by enhancing presentation of islet antigens

The relationship of inflammation to autoimmunity has been long observed, but the underlying mechanisms are unclear. Here, we demonstrate that islet-specific expression of TNFalpha in neonatal nonobese diabetic mice accelerated diabetes. In neonatal transgenic mice, disease was preceded by apoptosis of some beta cells, upregulation of MHC class I molecules on residual islet cells, and influx and activation of both antigen-presenting cells bearing MHC-islet peptide complexes and T cells. Infiltrating dendritic cells/macrophages, but not B cells, from neonatal islets activated islet-specific T cells in vitro. Thus, inflammation can trigger autoimmunity by recruiting and activating dendritic cells/macrophages to present self-antigens to autoreactive T cells.

Contribution of T cells to the development of autoimmune diabetes in the NOD mouse model

The nonobese diabetic (NOD) mouse spontaneously develops an autoimmune diabetes that shares many immunogenetic features with human insulin-dependent diabetes mellitus (IDDM), type 1 diabetes. The mononuclear cell infiltrates in the islet, which results in the development of insulitis (a prerequisite step for the development of diabetes) are primarily composed of T cells. It is now well accepted that these T cells play important roles in initiating and propagating an autoimmune process, which in turn destroys insulin-producing islet beta cells in the pancreas. T cells are subdivided into CD4+ helper T cells and CD8+ cytotoxic T cells. CD4+ T cells are further subdivided into Th1 and Th2 cells based on profiles of cytokine production, and these two T-cell populations counterregulate each other. Because many autoimmune diseases are Th1 T-cell mediated, current studies have focused on manipulating the Th1/Th2 imbalance to suppress the autoimmune process in the NOD model. Furthermore, the incidence of disease is much higher in females than that in males, suggesting an involvement of sex-steroid hormones in the development of diabetes. Understanding insights of the mechanism of immune-mediated islet cell destruction and the interaction between the immune and the neuroendocrine system may, therefore, provide new therapeutic means of preventing this chronic debilitating disease.

Systemic delivery of interleukin 10 by intramuscular injection of expression plasmid DNA prevents autoimmune diabetes in nonobese diabetic mice

We previously demonstrated that intramuscular plasmid injection serves as a useful method of long-term systemic delivery of cytokines. In the present study, we assess intramuscular DNA injection as a means of systemically delivering interleukin 10 (IL-10), a cytokine with immunosuppressive properties, and preventing the progression of autoimmune diabetes in the nonobese diabetic (NOD) mouse, an excellent model for human insulin-dependent diabetes mellitus (IDDM). We injected IL-10 expression plasmid (pCAGGS-IL10) or a control pCAGGS plasmid into the muscles of NOD mice twice at 3 and 5 weeks of age. IL-10 was detectable by ELISA in the sera of mice injected with pCAGGS-IL10 for more than 2 weeks after the injection. Although the severity of insulitis at 13 weeks of age was not improved by the intramuscular injection of pCAGGS-IL10, the incidence of diabetes was markedly reduced in NOD mice injected with pCAGGS-IL10 as compared with those injected with pCAGGS or as compared with nontreated NOD mice. These results show that the progression of autoimmune diseases in mice can effectively be suppressed by intramuscular DNA injection, and suggest that this method is potentially applicable to the treatment of human autoimmune diseases.

Low dose poly I:C prevents diabetes in the diabetes prone BB rat

Poly I:C, an inducer of IFN-alpha and other cytokines, has been used to study the development of diabetes in both the BioBreeding (BB) diabetes prone rat and non-obese diabetic (NOD) mouse animal models of insulin-dependent diabetes mellitus (IDDM). Surprisingly, poly I:C accelerates the disease in the BB rat while inhibiting it in the NOD mouse. Since cytokines can have dose related opposing effects on immune responses, we hypothesized that the paradoxical effect of polyinosinic polycytidylic acid (poly I:C) on diabetes in the two animal models is dose related. Accordingly, we compared the incidence of diabetes and degree of insulitis in diabetes prone BB rats administered saline and poly I:C at doses (0.05 microg/g body weight and 0.1 microg/g body weight) up to 100-fold lower than doses (poly-5 microg/g) previously found to accelerate diabetes. In addition, the non-specific suppressor activity of mononuclear splenocytes from BB rats administered low dose (poly-0.05 microg/g body weight), high dose (poly-5 microg/g body weight), and saline were compared. The development of diabetes was inhibited in rats treated with each dose of poly I:C. The degree of insulitis in poly-I:C treated animals was also less severe. The total white blood cell count and proportion of RT6+ T-cells and each T-cell subset were unaltered by poly I:C. When compared to splenocytes of control animals, splenocytes from poly I:C (0.05 microg/g body weight) treated rats suppressed responder cell proliferation to concanavalin A and alloantigen. However, spleen cells from high dose poly-I:C did not suppress responder cell proliferation to alloantigen. In adoptive transfer studies, the administration of spleen cells from poly-0.05 treated rats decreased the development of diabetes in recipient BB rats. In vitro studies also demonstrated that poly-I:C inhibits the proliferative response of BB rat spleen cells to concanavalin A. The administration of poly-0.05, but not poly-5.0, decreased TNF-alpha mRNA and IL-10 mRNA content in spleen cells. We conclude that poly I:C, at a dose 100 times lower than that required to accelerate diabetes prevents the development of diabetes in BB rates by interfering with the development of insulitis. The induction of suppressor cell activity induced by low dose poly-I:C in vivo and the inhibition of T-cell responses by poly-I:C in vitro suggests that the diabetes sparing activity of poly I:C is mediated by augmented immunoregulatory cell activity. Further studies with poly I:C may be important in increasing our understanding of the pathogenesis of IDDM and provide a means to prevent it.

T cell receptor (TCR) engagement leads to activation-induced splicing of tumor necrosis factor (TNF) nuclear pre-mRNA

Inducible gene expression is primarily regulated at the level of transcription. Additional steps of "processing" pre-mRNA, involved in the regulation of induced gene expression, have not been previously reported. Here we report a novel mechanism of "activation-induced splicing" of preexisting tumor necrosis factor (TNF) message (pre-mRNA) in naive T lymphocytes after engagement of the T cell receptor (TCR), which still occurs after inhibition of transcription. Expression of TNF has been previously demonstrated to be regulated at both the transcriptional and translational levels. However, neither the large pool of TNF mRNA observed in activated T cells nor TNF protein production, which peaks very shortly after activation, can be solely attributed to increased transcription. Evidence is presented that activation-induced splicing of TNF pre-mRNA plays a significant role in the rapid production of TNF seen in activated T cells. Activation triggers processing of TNF pre-mRNA that has accumulated in naive T cells (before activation-induced transcription), and the mature TNF mRNA is translocated to the cytoplasm for rapid translation and protein production. This novel form of activation-induced splicing of TNF may allow T cells to mount an immediate response to activation stimuli under physiological conditions.

Factors influencing the effects of murine cytomegalovirus on the pancreas

BACKGROUND

As human cytomegalovirus (HCMV) infections are implicated in insulin-dependent diabetes mellitus (IDDM), the effects of murine (M)CMV infection of inbred mice on the pancreas are of interest.

RESULTS

Inflammation and periacinar oedema peaked on day 3 and were replaced by a focal inflammation, but infected cells were rare. The islets were spared in C57BL mice. Insulitis normally seen in non-obese diabetic (NOD) mice was accelerated, but infected NOD mice did not become glycosuric. Isotypes of total and autoreactive antibodies suggested a shift to a Th 1 response (IgG2a) in all MCMV-infected mice. MCMV-induced pancreatitis was not affected by MHC genes but was similar or less severe in BALB/c mice. As these lack the Cmv1 gene, which provides a protective natural killer (NK) cell response in C57BL congenic mice, the C57BL background may carry a pancreatitis susceptibility gene able to counter NK-mediated restriction of viral replication. Consistently, congenic mice expressing Cmvl on a BALB/c background did not display pancreatitis, unless depleted of NK cells. In vivo treatment with soluble cytokine receptors suggested that interleukin 1 (IL-1) and/or tumour necrosis factor alpha contribute to acinar necrosis in C57BL mice.

TNF, apoptosis and autoimmunity: a common thread?

A subset of cytokine mediators belonging to the tumor necrosis factor (TNF) family cause apoptosis, acting through receptors and signaling pathways that have recently come to light. Further, at least one autoimmune disease results from a defined defect of apoptosis (mutations of the Fas ligand or its receptor). It is offered that many, and perhaps most autoimmune diseases may result from primary defects of apoptosis. Such defects may cause reflexive overproduction of TNF and other pro-apoptotic cytokines. The collateral damage produced by these mediators may be of pathogenetic importance in complex autoimmune disorders such as rheumatoid arthritis and Crohn disease, wherein TNF blockade is known to have ameliorative effects.

Neutralizing TNF-alpha activity modulates T-cell phenotype and function in experimental autoimmune uveoretinitis

Inhibiting TNF-alpha activity prevents tissue destruction without inhibiting retinal T cell infiltration in experimental autoimmune uveoretinitis (EAU) in Lewis rats. To further determine the role of TNF-alpha in autoimmune uveitis we characterized T cells isolated from retinae after treatment with a TNF-alpha antagonist. TNF-alpha activity was neutralized in vivo with a p55 TNF-alpha receptor-Ig fusion protein (sTNFr-Ig), administered 8 and 10 days after induction of EAU with heterologous retinal antigens. Retinal T-cell phenotype expression was examined by flow cytometry with respect to OX22 status (CD45RBlow or CD45RBhigh), activation (OX40 and CD25 expression) and rate of T-cell apoptosis (Annexin V+PI- expression). Lymphocyte reactivity was assessed by proliferation responses and cytokine production to retinal antigens. Despite greater than 40% of CD4+ T cells being activated at the height of disease, the proportion of OX22low expression was reduced and T cells exhibited reduced IFN-gamma and elevated IL-4 production. Retinal T cells maintained antigen-specific proliferation and demonstrated a low apoptotic rate. Although in both animal groups, comparable numbers of T cells were isolated, neutralizing TNF activity suppressed Th1 effector mechanisms protecting against target organ damage.

Tumor necrosis factor alpha gene regulation: enhancement of C/EBPbeta-induced activation by c-Jun

Tumor necrosis factor alpha (TNF alpha) is a key regulatory cytokine whose expression is controlled by a complex set of stimuli in a variety of cell types. Previously, we found that the monocyte/macrophage-enriched nuclear transcription factor C/EBPbeta played an important role in the regulation of the TNF alpha gene in myelomonocytic cells. Abundant evidence suggests that other transcription factors participate as well. Here we have analyzed interactions between C/EBPbeta and c-Jun, a component of the ubiquitously expressed AP-1 complex. In phorbol myristate acetate (PMA)-treated Jurkat T cells, which did not possess endogenous C/EBPbeta, expression of c-Jun by itself had relatively little effect on TNF alpha promoter activity. However, the combination of C/EBPbeta and c-Jun was synergistic, resulting in greater than 130-fold activation. This effect required both the leucine zipper and DNA binding domains, but not the transactivation domain, of c-Jun, plus the AP-1 binding site centered 102/103 bp upstream of the transcription start site in the TNF alpha promoter. To determine if C/EBPbeta and c-Jun might cooperate to regulate the cellular TNF alpha gene in myelomonocytic cells, U937 cells that possess endogenous C/EBPbeta and were stably transfected with either wild-type c-Jun or the transactivation domain deletion mutant (TAM-67) were examined. U937 cells expressing ectopic wild-type c-Jun or TAM-67 secreted over threefold more TNF alpha than the control line in response to PMA plus lipopolysaccharide. Transient transfection of the U937 cells expressing TAM-67 suggested that TAM-67 binding to the -106/-99-bp AP-1 binding site cooperated with endogenous C/EBPbeta in the activation of the -120 TNF alpha promoter-reporter. DNA binding assays using oligonucleotides derived from the TNF alpha promoter suggested that C/EBPbeta and c-Jun interact in vitro and that the interaction may be DNA dependent. Our data demonstrate that the TNF alpha gene is regulated by the interaction of the ubiquitous AP-1 complex protein c-Jun and the monocyte/macrophage-enriched transcription factor C/EBPbeta and that this interaction contributes to the expression of the cellular TNF alpha gene in myelomonocytic cells. This interaction was unique in that it did not require the c-Jun transactivation domain, providing new insight into the cell-type-specific regulation of the TNF alpha gene.

Dendritic Cells and Macrophages Are the First and Major Producers of TNF-α in Pancreatic Islets in the Nonobese Diabetic Mouse

The nonobese diabetic (NOD) mouse spontaneously develops autoimmune insulin-dependent diabetes mellitus (IDDM) and serves as an animal model for human type I diabetes. TNF-α is known to be produced by islet-infiltrating mononuclear cells during insulitis and subsequent β cell destruction and has been implicated in the pathogenesis of IDDM. Previously, T cells have been suggested as the main source of TNF-α in the islet infiltrate. However, on immunohistochemical analysis of TNF-α expression in islets, we are able to show that the staining pattern of TNF-α resembles that of dendritic cells (DC) and macrophages (Mφ) rather than T cells and that TNF-α is expressed in islets at the very early stages of insulitis when no T cells are detected. On double staining for TNF-α and cell surface markers, we can demonstrate that TNF-α staining clearly correlates with DC and Mφ, whereas there is a poor correlation with T cells. This feature was observed at both early and late stages of insulitis. TNF-α expression was also seen in NOD-SCID islets, in addition to a peri-islet infiltration consisting of DC and Mφ, indicating that T cells are not required for the early DC and Mφ infiltration and TNF-α expression in islets. In conclusion, our results show that DC and Mφ are the major, early source of TNF-α in the NOD islet infiltrate and that TNF-α can be expressed independently of T cells, indicating that the early DC and Mφ infiltration and expression of TNF-α are crucial in initiation of diabetes.