Apoptosis of Autoreactive CD8 Lymphocytes As a Potential Mechanism for the Abrogation of Type 1 Diabetes by Islet-specific TNF-alpha Expression at a Time when the Autoimmune Process is Already Ongoing

Annals of the New York Academy of Sciences. Apr, 2002  |  Pubmed ID: 12021099

The role of TNF-alpha in type 1 diabetes pathogenesis is controversial. Using double transgenic mice expressing (i) the glycoprotein (GP) of lymphocytic choriomeningitis virus (LCMV) as an islet self-antigen and (ii) TNF-alpha under control of a tetracycline-regulated promotor system (tTA) in the pancreatic beta cells, we could previously demonstrate a differential effect of TNF-alpha on the incidence of type 1 diabetes. Most interestingly, late expression of TNF-alpha resulted in a reversion of mice that were already diabetic to a nondiabetic state. Here we provide a model of how experienced autoaggressive CD8 lymphocytes are dying by apoptosis as a result of beta cell-specific TNF-alpha expression at a time when the autoimmune process is already ongoing.

Discrete Proteolysis of Focal Contact and Adherens Junction Components in Porphyromonas Gingivalis-infected Oral Keratinocytes: a Strategy for Cell Adhesion and Migration Disabling

Infection and Immunity. Oct, 2002  |  Pubmed ID: 12228316

Adhesive interactions of cells are critical to tissue integrity. We show that infection with Porphyromonas gingivalis, a major pathogen in the periodontal disease periodontitis, interferes with both cell-matrix and cell-cell adhesion in the oral keratinocyte cell line HOK-16. Thus, infected cells showed reduced adhesion to extracellular matrix, changes in morphology from spread to rounded, and impaired motility on purified matrices in Transwell migration assays and scratch assays. Western blot analysis of P. gingivalis-challenged HOK-16 cells revealed proteolysis of focal contact components (e.g., focal adhesion kinase), adherens junction proteins (e.g., catenins), and adhesion signaling molecules (e.g., the tyrosine kinase SRC). Proteolysis was selective, since important components of adherens junctions (E-cadherin) or signaling molecules (extracellular signal-regulated kinases ERK1/2) were not degraded. The virulence factors gingipains, cysteine proteinases expressed by P. gingivalis, are likely responsible for this proteolytic attack, since they directly digested specific proteins in pull-down experiments, and their proteolytic activity was blocked by the cysteine proteinase inhibitor N-alpha-p-tosyl-L-lysine chloromethyl ketone and also by a caspase inhibitor. Proteolysis was strain dependent, such that ATCC 33277 and 381 had high proteolytic potential, whereas W50 showed almost no proteolytic activity. These findings may help explain the formation of gingival pockets between cementum and periodontal epithelium, a hallmark of periodontitis. Furthermore, they illustrate a new pathogenetic paradigm of infection whereby bacteria may disrupt the integrity of epithelia.

Molecular Anatomy of Antigen-specific CD8(+) T Cell Engagement and Synapse Formation in Vivo

Nature Immunology. Oct, 2002  |  Pubmed ID: 12352968

Antigen-specific CD8(+) T cells are required for the clearance of most viral infections and several cancers. However, it is not clear in vivo whether CD8(+) T cells can engage multiple targets simultaneously, engagement results in the formation of an immunologic synapse or molecules involved in CD8 function are redistributed to the synapse. We used here high-resolution microscopy to visualize interactions between virus-specific effectors and target cells in vivo. Using either in situ tetramer staining or green fluorescent protein-labeled virus-specific T cells, we have shown that a single CD8(+) T cell can engage two or three targets, a synapse occurs at the site of engagement and molecules involved in attachment (lymphocyte function-associated antigen 1), signaling (Lck) and lytic activity (perforin) are differentially positioned on the T cell. In addition, we have established an in vivo approach for assessing the intricacies of antigen-specific T cell activation, migration, engagement, memory and other defining elements of adaptive immunity.

Transgenic Animal Models for Type 1 Diabetes: Linking a Tetracycline-inducible Promoter with a Virus-inducible Mouse Model

Transgenic Research. Dec, 2002  |  Pubmed ID: 12509133

Autoimmunity is thought to emerge as a consequence of genetic predispositions and environmental tiggering factors. Often the etiology and the mechanisms involved in the autoaggressive destruction of self-components are rather complex and in many cases poorly understood. Chemokines and cytokines are central mediators of inflammatory processes that are involved in initiation and progression of autoimmunity. Many animal models for human autoimmune diseases use transgenic technology to express chemokines and/or cytokines in an organ or tissue specific manner. However, most of these model systems express the transgene irreversibly without considering the time of expression as a very important parameter. Here, we review experiences that were made from using a tetracycline-inducible promotor system (tTA-system) to express TNFalpha at various times during an ongoing autoimmune process, such as the destruction of pancreatic beta-cells in a mouse model for human type 1 diabetes.

CD4+ T Cells Are Required for Secondary Expansion and Memory in CD8+ T Lymphocytes

Nature. Feb, 2003  |  Pubmed ID: 12594515

A long-standing paradox in cellular immunology concerns the conditional requirement for CD4+ T-helper (T(H)) cells in the priming of cytotoxic CD8+ T lymphocyte (CTL) responses in vivo. Whereas CTL responses against certain viruses can be primed in the absence of CD4+ T cells, others, such as those mediated through 'cross-priming' by host antigen-presenting cells, are dependent on T(H) cells. A clearer understanding of the contribution of T(H) cells to CTL development has been hampered by the fact that most T(H)-independent responses have been demonstrated ex vivo as primary cytotoxic effectors, whereas T(H)-dependent responses generally require secondary in vitro re-stimulation for their detection. Here, we have monitored the primary and secondary responses of T(H)-dependent and T(H)-independent CTLs and find in both cases that CD4+ T cells are dispensable for primary expansion of CD8+ T cells and their differentiation into cytotoxic effectors. However, secondary CTL expansion (that is, a secondary response upon re-encounter with antigen) is wholly dependent on the presence of T(H) cells during, but not after, priming. Our results demonstrate that T-cell help is 'programmed' into CD8+ T cells during priming, conferring on these cells a hallmark of immune response memory: the capacity for functional expansion on re-encounter with antigen.

Cytokines and Chemokines in Virus-induced Autoimmunity

Advances in Experimental Medicine and Biology. , 2003  |  Pubmed ID: 12613580

Among CXCR3 Chemokines, IFN-gamma-inducible Protein of 10 KDa (CXC Chemokine Ligand (CXCL) 10) but Not Monokine Induced by IFN-gamma (CXCL9) Imprints a Pattern for the Subsequent Development of Autoimmune Disease

Journal of Immunology (Baltimore, Md. : 1950). Dec, 2003  |  Pubmed ID: 14662890

Infection of the pancreas with lymphocytic choriomeningitis virus results in rapid and differential expression among CXCR3 chemokines. IFN-gamma-inducible protein of 10 kDa (IP-10), in contrast with monokine induced by IFN-gamma and IFN-inducible T cell-alpha chemoattractant, is strongly expressed within 24 h postinfection. Blocking of IP-10, but not monokine induced by IFN-gamma, aborts severity of Ag-specific injury of pancreatic beta cells and abrogates type 1 diabetes. Mechanistically, IP-10 blockade impedes the expansion of peripheral Ag-specific T cells and hinders their migration into the pancreas. IP-10 expression was restricted to viruses infecting the pancreas and that are capable of causing diabetes. Hence, virus-induced organ-specific autoimmune diseases may be dependent on virus tropism and its ability to alter the local milieu by selectively inducing chemokines that prepare the infected tissue for the subsequent destruction by the adaptive immune response.

Cure of Prediabetic Mice by Viral Infections Involves Lymphocyte Recruitment Along an IP-10 Gradient

The Journal of Clinical Investigation. Jan, 2004  |  Pubmed ID: 14702111

Viruses can cause but can also prevent autoimmune disease. This dualism has certainly hampered attempts to establish a causal relationship between viral infections and type 1 diabetes (T1D). To develop a better mechanistic understanding of how viruses can influence the development of autoimmune disease, we exposed prediabetic mice to various viral infections. We used the well-established NOD and transgenic RIP-LCMV models of autoimmune diabetes. In both cases, infection with the lymphocytic choriomeningitis virus (LCMV) completely abrogated the diabetic process. Interestingly, such therapeutic viral infections resulted in a rapid recruitment of T lymphocytes from the islet infiltrate to the pancreatic draining lymph node, where increased apoptosis was occurring. In both models this was associated with a selective and extensive expression of the chemokine IP-10 (CXCL10), which predominantly attracts activated T lymphocytes, in the pancreatic draining lymph node, and in RIP-LCMV mice it depended on the viral antigenic load. In RIP-LCMV mice, blockade of TNF-alpha or IFN-gamma in vivo abolished the prevention of T1D. Thus, virally induced proinflammatory cytokines and chemokines can influence the ongoing autoaggressive process beneficially at the preclinical stage, if produced at the correct location, time, and levels.

Virally Induced Inflammation Triggers Fratricide of Fas-ligand-expressing Beta-cells

Diabetes. Mar, 2004  |  Pubmed ID: 14988242

Tissue-specific expression of Fas-ligand (Fas-L) can provide immune privilege by inducing apoptosis of "invading" lymphocytes expressing Fas. However, accelerated diabetes has been reported in transgenic mice expressing Fas-L in islets (RIP-Fas-L) as a result of Fas-dependent fratricide of beta-cells after transfer of diabetogenic clones. Here we studied whether Fas-L could protect islets from autoaggressive CD8 lymphocytes in a transgenic model of virally induced diabetes (RIP-LCMV-NP transgenic mice), in which the autoaggressive response is directed to a viral nucleoprotein (NP) expressed as a transgene in beta-cells. Indeed, disease incidence after viral (lymphocytic choriomeningitis virus [LCMV]) infection was reduced by approximately 30%, which was associated with a decrease of autoaggressive CD8 NP-specific lymphocytes in islets and pancreatic draining lymph nodes. However, surprisingly, a high degree (50%) of diabetes was seen in mice that expressed only Fas-L but not the viral transgene (NP) in beta-cells after infection with LCMV. This was due to induction of Fas on beta-cells after LCMV infection of the pancreas, resulting in Fas/Fas-L-mediated fratricide. Thus, although Fas-L can lend some immune privilege to islet cells, local virus-induced inflammation will induce Fas on beta-cells, leading to their mutual destruction if Fas-L is present. Expression of Fas-L therefore might not be protective in situations in which viral inflammation can be expected, resulting in Fas induction on the targeted cell itself.

Induction, Acceleration or Prevention of Autoimmunity by Molecular Mimicry

Molecular Immunology. Feb, 2004  |  Pubmed ID: 15036917

The hypothesis that cross-reactivity between microbial and self determinants recognized by the adaptive immune system could induce autoimmune diseases is very intriguing. However, definite proof in humans is very difficult to achieve and evidence is frequently circumstantial. Therefore, animal models are instrumental for understanding, how and when mimicry could be involved in the pathogenesis of autoimmunity. In this article, we will discuss experimental scenarios, where mimicry between foreign and self determinants does not cause disease per se, but rather aggravates a pre-existing yet sub-clinical autoimmune condition. We would like to propose that molecular mimicry is more likely to impact on an already existing autoimmune process rather than precipitate novel disease by breaking of tolerance from the beginning. Already activated autoreactive cells might be easier re-activated and primed for effector functions by cross-reactive ligands than naive lymphocytes.

Virally Induced Inflammation and Therapeutic Avenues in Type 1 Diabetes

Endocrinology and Metabolism Clinics of North America. Mar, 2004  |  Pubmed ID: 15053894

CD8alphaalpha-mediated Survival and Differentiation of CD8 Memory T Cell Precursors

Science (New York, N.Y.). Apr, 2004  |  Pubmed ID: 15105501

Memory T cells are long-lived antigen-experienced T cells that are generally accepted to be direct descendants of proliferating primary effector cells. However, the factors that permit selective survival of these T cells are not well established. We show that homodimeric alpha chains of the CD8 molecule (CD8alphaalpha) are transiently induced on a selected subset of CD8alphabeta+ T cells upon antigenic stimulation. These CD8alphaalpha molecules promote the survival and differentiation of activated lymphocytes into memory CD8 T cells. Thus, memory precursors can be identified among primary effector cells and are selected for survival and differentiation by CD8alphaalpha.

Initiation of Autoimmunity

Current Opinion in Immunology. Dec, 2004  |  Pubmed ID: 15511670

It has recently become clear that several factors must coincide for the initiation of autoimmunity. At minimum, these involve a genetic predisposition, naive lymphocytes that can react with autoantigens and a precipitating event that leads to T and/or B cell activation. Inter-individual variations in these factors probably explain the significant complexity associated with autoimmune diseases; however, quantitative issues are also important because clinical disease will manifest only if a sufficient amount of cellular material has been destroyed. Therefore, the presence of autoreactive lymphocytes does not always signify disease; rather, the kinetics of their generation, their resulting numbers and the regulation of their activation and effector functions (destructive versus regulatory) will determine the ultimate outcome and make the difference between subclinical autoimmunity and disease.

IP-10 and Type 1 Diabetes: a Question of Time and Location

Autoimmunity. Jun, 2004  |  Pubmed ID: 15518041

Chemokines are key signal molecules that attract cells of the host immune system to the site of a potential threat. Virus infections usually induce a massive chemokine and cytokine burst and therefore recruit a large plethora of leukocytes to the site of infection with the goal to restrict and abrogate viral spread. The down side of this massive excitation of the human defense system is non-specific activation of potentially self-reactive lymphocytes. Coupled with an antigen-specific event, for example molecular mimicry between host components and viral proteins, autoimmunity might be the consequence in susceptible individuals. However, activated immune components with autoaggressive potential must find their target and must remain in one site sufficiently long in order to cause chronic tissue damage. In this review we will focus on the influence of the chemokine IP-10 (CXCL10) on the trafficking of autoaggressive cells during the immunopathogenesis of type 1 diabetes (T1D) and explain why IP-10 can have a dual effect on T1D depending on time and location of expression.

A Viral Epitope That Mimics a Self Antigen Can Accelerate but Not Initiate Autoimmune Diabetes

The Journal of Clinical Investigation. Nov, 2004  |  Pubmed ID: 15520861

We document here that infection of prediabetic mice with a virus expressing an H-2Kb-restricted mimic ligand to a self epitope present on beta cells accelerates the development of autoimmune diabetes. Immunization with the mimic ligand expanded autoreactive T cell populations, which was followed by their trafficking to the islets, as visualized in situ by tetramer staining. In contrast, the mimic ligand did not generate sufficient autoreactive T cells in naive mice to initiate disease. Diabetes acceleration did not occur in H-2Kb-deficient mice or in mice tolerized to the mimic ligand. Thus, arenavirus-expressed mimics of self antigens accelerate a previously established autoimmune process. Sequential heterologous viral infections might therefore act in concert to precipitate clinical autoimmune disease, even if single exposure to a viral mimic does not always cause sufficient tissue destruction.

Manipulating the Type 1 Vs Type 2 Balance in Type 1 Diabetes

Immunologic Research. , 2004  |  Pubmed ID: 15531772

Virus infections cause a strong inflammatory reaction that is dominated by the expression of type 1 cytokines and chemokines. Such an aggressive immune response by the host is necessary to eliminate intracellular pathogens. However, because of this shift in the type 1 vs type 2 balance of the immune response, virus infections are potential candidates for triggering autoimmune diseases, such as type 1 diabetes (T1D), herpes stromal keratitis, or multiple sclerosis (MS). In this review we will focus on the pathogenesis of T1D in a virus-induced transgenic mouse model and discuss possibilities of how an aggressive type 1-dominated immune response can be restrained and autoimmunity be abrogated.

IP-10 and Type 1 Diabetes: a Question of Time and Location

Autoimmunity. Aug, 2004  |  Pubmed ID: 15672495

Chemokines are key signal molecules that attract cells of the host immune system to the site of a potential threat. Virus infections usually induce a massive chemokine and cytokine burst and therefore recruit a large plethora of leukocytes to the site of infection with the goal to restrict and abrogate viral spread. The down side of this massive excitation of the human defense system is non-specific activation of potentially self-reactive lymphocytes. Coupled with an antigen-specific event, for example molecular mimicry between host commponents and viral proteins, autoimmunity might be the consequence in susceptible individuals. However, activated immune components with autoaggressive potential must find their target and must remain in one site sufficiently long in order to cause chronic tissue damage. In this review we will focus on the influence of the chemokine IP-10 (CXCL10) on the trafficking of autoaggressive cells during the immunopathogenesis of type 1 diabetes (T1D) and explain why IP-10 can have a dual effect on T1D depending on time and location of expression.

Different Diabetogenic Potential of Autoaggressive CD8+ Clones Associated with IFN-gamma-inducible Protein 10 (CXC Chemokine Ligand 10) Production but Not Cytokine Expression, Cytolytic Activity, or Homing Characteristics

Journal of Immunology (Baltimore, Md. : 1950). Mar, 2005  |  Pubmed ID: 15728483

Type 1 diabetes mellitus is an autoimmune disease characterized by T cell-mediated destruction of the insulin-producing beta cells in the islets of Langerhans. From studies in animal models, CD8(+) T cells recognizing autoantigens such as islet-specific glucose-6-phosphatase catalytic subunit-related protein, insulin, or glutamic acid decarboxylase (GAD) are believed to play important roles in both the early and late phases of beta cell destruction. In this study, we investigated the factors governing the diabetogenic potential of autoreactive CD8(+) clones isolated from spleens of NOD mice that had been immunized with GAD65(515-524) or insulin B-chain(15-23) peptides. Although these two clones were identical in most phenotypic and functional aspects, for example cytokine production and killing of autologous beta cells, they differed in the expression of IFN-gamma-inducible protein-10, which was only produced at high levels by the insulin-specific clone, but not by the GAD65-specific clone, and other autoantigen-specific nonpathogenic CD8 T cell clones. Interestingly, upon i.p. injection into neonatal mice, only the insulin B-chain(15-23)-reactive CD8(+) T clone accelerated diabetes in all recipients after 4 wk, although both insulin- and GAD-reactive clones homed to pancreas and pancreatic lymph nodes with similar kinetics. Diabetes was associated with increased pancreatic T cell infiltration and, in particular, recruitment of macrophages. Thus, secretion of IFN-gamma-inducible protein-10 by autoaggressive CD8(+) lymphocytes might determine their diabetogenic capacity by affecting recruitment of cells to the insulitic lesion.

Infections and Autoimmunity--good or Bad?

Journal of Immunology (Baltimore, Md. : 1950). Jun, 2005  |  Pubmed ID: 15944245

The relationship between infections and autoimmunity is complex. Current evidence indicates that microbes can initiate, enhance, or, conversely, abrogate autoimmunity. In this paper, we will review experimental examples illustrating mechanisms involved in these three scenarios. Microbial infections can act as environmental triggers inducing or promoting autoimmunity resulting in clinical manifestations of autoimmune disease in genetically predisposed individuals. However, increasing evidence suggests the opposite outcome, which is the prevention or amelioration of autoimmune processes following microbial encounters. These latter observations support conceptually the "hygiene hypothesis," suggesting that cleaner living conditions will lead to enhanced incidence of autoimmune disorders, asthma, and allergies. Because proof of concept in humans is difficult to obtain, we will discuss relevant animal model data in context with likely or proven human associations. Knowledge of mechanisms that underlie either positive or negative effects of infections on autoimmunity will facilitate exploration of molecular details for prospective clinical studies in the future.

Islet-specific Expression of CXCL10 Causes Spontaneous Islet Infiltration and Accelerates Diabetes Development

Journal of Immunology (Baltimore, Md. : 1950). Sep, 2005  |  Pubmed ID: 16148094

During inflammation, chemokines are conductors of lymphocyte trafficking. The chemokine CXCL10 is expressed early after virus infection. In a virus-induced mouse model for type 1 diabetes, CXCL10 blockade abrogated disease by interfering with trafficking of autoaggressive lymphocytes to the pancreas. We have generated transgenic rat insulin promotor (RIP)-CXCL10 mice expressing CXCL10 in the beta cells of the islets of Langerhans to evaluate how bystander inflammation influences autoimmunity. RIP-CXCL10 mice have islet infiltrations by mononuclear cells and limited impairment of beta cell function, but not spontaneous diabetes. RIP-CXCL10 mice crossed to RIP-nucleoprotein (NP) mice expressing the NP of the lymphocytic choriomeningitis virus in the beta cells had massively accelerated type 1 diabetes after lymphocytic choriomeningitis virus infection. Mechanistically, we found a drastic increase in NP-specific, autoaggressive CD8 T cells in the pancreas after infection. In situ staining with H-2D(b)(NP(396)) tetramers revealed islet infiltration by NP-specific CD8 T cells in RIP-NP-CXCL10 mice early after infection. Our results indicate that CXCL10 expression accelerates the autoimmune process by enhancing the migration of Ag-specific lymphocytes to their target site.

Molecular Mimicry, Bystander Activation, or Viral Persistence: Infections and Autoimmune Disease

Clinical Microbiology Reviews. Jan, 2006  |  Pubmed ID: 16418524

Virus infections and autoimmune disease have long been linked. These infections often precede the occurrence of inflammation in the target organ. Several mechanisms often used to explain the association of autoimmunity and virus infection are molecular mimicry, bystander activation (with or without epitope spreading), and viral persistence. These mechanisms have been used separately or in various combinations to account for the immunopathology observed at the site of infection and/or sites of autoimmune disease, such as the brain, heart, and pancreas. These mechanisms are discussed in the context of multiple sclerosis, myocarditis, and diabetes, three immune-medicated diseases often linked with virus infections.

Cure of Chronic Viral Infection and Virus-induced Type 1 Diabetes by Neutralizing Antibodies

Clinical & Developmental Immunology. Mar, 2006  |  Pubmed ID: 16603445

The use of neutralizing antibodies is one of the most successful methods to interfere with receptor-ligand interactions in vivo. In particular blockade of soluble inflammatory mediators or their corresponding cellular receptors was proven an effective way to regulate inflammation and/or prevent its negative consequences. However, one problem that comes along with an effective neutralization of inflammatory mediators is the general systemic immunomodulatory effect. It is, therefore, important to design a treatment regimen in a way to strike at the right place and at the right time in order to achieve maximal effects with minimal duration of immunosuppression or hyperactivation. In this review, we reflect on two examples of how short time administration of such neutralizing antibodies can block two distinct inflammatory consequences of viral infection. First, we review recent findings that blockade of IL-10/IL-10R interaction can resolve chronic viral infection and second, we reflect on how neutralization of the chemokine CXCL10 can abrogate virus-induced type 1 diabetes.

SOCS-1 Protects from Virally-induced CD8 T Cell Mediated Type 1 Diabetes

Journal of Autoimmunity. Nov, 2006  |  Pubmed ID: 17045460

CD8(+) cytotoxic T lymphocytes (CTL) can rapidly kill beta-cells and therefore contribute to the development of type 1 diabetes (T1D). CTL-mediated beta-cell killing can occur via perforin-mediated lysis, Fas-Fas-L interaction, and the secretion of TNF-alpha or IFN-gamma. The secretion of IFN-gamma can contribute to beta-cell death directly by eliciting nitric oxide production, and indirectly by upregulating MHC class I and 'unmasking' beta-cells for recognition by CTL. Earlier studies in the RIP-LCMV mouse model of diabetes showed that disruption of beta-cell IFN-gamma signaling alone abolished the direct detrimental effects of IFN-gamma, but not MHC class I upregulation. Suppressor of cytokine signaling-1 (SOCS-1) represses several crucial cytokine signaling pathways simultaneously, among them IFN-gamma and IL-1-beta. We therefore evaluated the protective capacity of islet cell SOCS-1 expression in the CD8(+) mediated RIP-LCMV diabetes model. Clinical disease was prevented in over 90% of the mice. Not only absence of MHC-I and Fas upregulation, but also resistance to cytokine-induced killing of beta-cells and a complete lack of CXCL-10 (IP10) production in islets led to a lack of islet infiltration and impaired activation of autoaggressive CD4(+) and CD8(+) T-cells in these mice. Thus, SOCS expression renders beta-cells resistant to CTL attack in a mouse model of T1D.

Cure of Chronic Viral Infection and Virus-induced Type 1 Diabetes by Neutralizing Antibodies

Clinical & Developmental Immunology. Jun-Dec, 2006  |  Pubmed ID: 17162375

The use of neutralizing antibodies is one of the most successful methods to interfere with receptor-ligand interactions in vivo. In particular blockade of soluble inflammatory mediators or their corresponding cellular receptors was proven an effective way to regulate inflammation and/or prevent its negative consequences. However, one problem that comes along with an effective neutralization of inflammatory mediators is the general systemic immunomodulatory effect. It is therefore important to design a treatment regimen in a way to strike at the right place and at the right time in order to achieve maximal effects with minimal duration of immunosuppression or hyperactivation. In this review we reflect on two examples of how short time administration of such neutralizing antibodies can block two distinct inflammatory consequences of viral infection. First, we review recent findings that blockade of IL-10/IL-10R interaction can resolve chronic viral infection and second, we reflect on how neutralization of the chemokine CXCL10 can abrogate virus-induced type 1 diabetes.

Chemokines As Drug Targets in Type 1 Diabetes

Endocrine, Metabolic & Immune Disorders Drug Targets. Mar, 2007  |  Pubmed ID: 17346199

Acute or chronic inflammation is thought to play a major role in the etiology and/or pathogenesis of autoimmune disease. Often viral infections are the initial cause for a local inflammatory reaction resulting in tissue infiltration by activated leukocytes. The activation and trafficking of these leukocytes to the site of inflammation is conducted by chemoattractant cytokines, termed chemokines. Depending on the genetic background and the history of previous infections, such infiltrating leukocytes can potentially include autoaggressive lymphocytes with specificity to tissue antigens. The number of specific precursor lymphocytes, strength of activation and degree of counteracting immunoregulatory measures determine whether such an autoimmune incident ultimately results in autoimmune disease. Thus, by blocking the initial inflammatory insult one could in theory prevent the excessive attraction of autoaggressive lymphocytes to the inflammation site and the subsequent formation of a pattern that leads to autoimmune disease. This review focuses on blocking of chemokines in animal models of type 1 diabetes and discusses the possible applications of such treatments in human autoimmune disease.

Minimal Impact of a De Novo-expressed Beta-cell Autoantigen on Spontaneous Diabetes Development in NOD Mice

Diabetes. Apr, 2007  |  Pubmed ID: 17395746

During an autoimmune process, the autoaggressive response spreads from the initiating autoantigen to other antigens expressed in the target organ. Based on evidence from experimental models for multiple sclerosis, such "antigenic spreading" can play an important role in the exacerbation of clinical disease. We evaluated whether pathogenesis of spontaneous diabetes in NOD mice could be accelerated in a similar way when a novel autoantigen was expressed in pancreatic beta-cells. Unexpectedly, we found that the expression of the lymphocytic choriomeningitis virus nucleoprotein only led to marginal enhancement of diabetes, although such NOD-nucleoprotein mice were not tolerant to nucleoprotein. Although the frequency of nucleoprotein-specific CD8 T-cells in the pancreatic draining lymph node was comparable with the frequency of islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP)-specific T-cells, more IGRP-specific CD8 T-cells were found both systemically and in the islets where there was a fourfold increase. Interestingly, and in contrast to nucleoprotein-specific CD8 T-cells, IGRP-specific T-cells showed increased CXCR3 expression. Thus, autoreactivity toward de novo-expressed beta-cell autoantigens will not accelerate autoimmunity unless large numbers of antigen-experienced autoreactive T-cells expressing the appropriate chemokine receptors are present.

Animal Models for Autoimmune Hepatitis

Autoimmunity Reviews. Apr, 2007  |  Pubmed ID: 17412303

The liver is the target of adverse immune reactions in three putative autoimmune diseases: autoimmune hepatitis (AIH), primary biliary cirrhosis (PBC) and primary sclerosing cholangitis (PSC). These three diseases can be distinguished by clinical, histological, and immunological features. However, especially on the level of specific antibody formation an overlap can occur, which sometimes complicates diagnosis. In this review, we will concentrate on autoimmune hepatitis and the current state of animal models for this severe disease. AIH is characterized by the presence of interface hepatitis and portal plasma cell infiltration, hypergammaglobulinemia, and autoantibodies. The hallmark of type 2 AIH is the generation of autoantibodies of the LKM-1 type. The major target of these antibodies is the cytochrome P450 isoform 2D6 (CYP2D6). In the past several attempts have been made to develop a reliable animal model that reflects the persistent hepatic destruction that occurs in human AIH. However, most models were only successful in causing a transient form of hepatic damage and often used rather complex ways of disease induction.

Systemic Anti-TNFalpha Treatment Restores Diabetes-impaired Skin Repair in Ob/ob Mice by Inactivation of Macrophages

The Journal of Investigative Dermatology. Sep, 2007  |  Pubmed ID: 17460730

To date, diabetes-associated skin ulcerations represent a therapeutic problem of clinical importance. The insulin-resistant type II diabetic phenotype is functionally connected to obesity in rodent models of metabolic syndrome through the release of inflammatory mediators from adipose tissue. Here, we used the impaired wound-healing process in obese/obese (ob/ob) mice to investigate the impact of obesity-mediated systemic inflammation on cutaneous wound-healing processes. Systemic administration of neutralizing monoclonal antibodies against tumor necrosis factor (TNF)alpha (V1q) or monocyte/macrophage-expressed EGF-like module-containing mucin-like hormone receptor-like (Emr)-1 (F4/80) into wounded ob/ob mice at the end of acute wound inflammation initiated a rapid and complete neo-epidermal coverage of impaired wound tissue in the presence of a persisting diabetic phenotype. Wound closure in antibody-treated mice was paralleled by a marked attenuation of wound inflammation. Remarkably, anti-TNFalpha- and anti-F4/80-treated mice exhibited a strong reduction in circulating monocytic cells and reduced numbers of viable macrophages at the wound site. Our data provide strong evidence that anti-TNFalpha therapy, widely used in chronic inflammatory diseases in humans, might also exert effects by targeting "activated" TNFalpha-expressing macrophage subsets, and that inactivation or depletion of misbehaving macrophages from impaired wounds might be a novel therapeutic clue to improve healing of skin ulcers.

Viral Infection--a Cure for Type 1 Diabetes?

Current Medicinal Chemistry. , 2007  |  Pubmed ID: 17691946

Autoimmune diseases are thought to arise as a detrimental combination of genetic predisposition and environmental factors. Because of their potential for direct cellular damage and causing extensive inflammation, viruses are one of the major candidates for triggering autoimmunity. Although there is epidemiological evidence, direct proof for viruses as causative agents for autoimmune disease is hard to get since most viruses have been eliminated from the system by the time of diagnosis. However, evidence from various animal models suggests that viruses can indeed initiate or accelerate autoimmune diseases, such as type 1 diabetes or experimental allergic encephalomyelitis. In contrast, viruses have been also demonstrated to abrogate autoimmune disease in animal models. These observations might offer one explanation why increased frequencies of allergies and autoimmune diseases parallel with higher hygienic standards. This review reflects on the epidemiological evidence for the association of viruses with autoimmune diseases, the experimental evidence for viruses to abrogate an ongoing autoimmune destruction and evaluates the possibility for a therapeutic application.

Breaking Tolerance to the Natural Human Liver Autoantigen Cytochrome P450 2D6 by Virus Infection

The Journal of Experimental Medicine. Jun, 2008  |  Pubmed ID: 18474629

Autoimmune liver diseases, such as autoimmune hepatitis (AIH) and primary biliary cirrhosis, often have severe consequences for the patient. Because of a lack of appropriate animal models, not much is known about their potential viral etiology. Infection by liver-tropic viruses is one possibility for the breakdown of self-tolerance. Therefore, we infected mice with adenovirus Ad5 expressing human cytochrome P450 2D6 (Ad-2D6). Ad-2D6-infected mice developed persistent autoimmune liver disease, apparent by cellular infiltration, hepatic fibrosis, "fused" liver lobules, and necrosis. Similar to type 2 AIH patients, Ad-2D6-infected mice generated type 1 liver kidney microsomal-like antibodies recognizing the immunodominant epitope WDPAQPPRD of cytochrome P450 2D6 (CYP2D6). Interestingly, Ad-2D6-infected wild-type FVB/N mice displayed exacerbated liver damage when compared with transgenic mice expressing the identical human CYP2D6 protein in the liver, indicating the presence of a stronger immunological tolerance in CYP2D6 mice. We demonstrate for the first time that infection with a virus expressing a natural human autoantigen breaks tolerance, resulting in a chronic form of severe, autoimmune liver damage. Our novel model system should be instrumental for studying mechanisms involved in the initiation, propagation, and precipitation of virus-induced autoimmune liver diseases.

New Animal Models for Autoimmune Hepatitis

Seminars in Liver Disease. Aug, 2009  |  Pubmed ID: 19675999

Autoimmune hepatitis (AIH) is often diagnosed late in the disease course and usually requires lifelong immunosuppressive therapy. Unfortunately, the etiology of the disease and the mechanisms leading to the autoimmune destruction of the liver parenchyma are only poorly understood. For a long time, one reason for this lack of apprehension was the absence of reliable animal models with a chronic immune response against liver tissues. Initial attempts to break tolerance against hepatocytes usually just resulted in mild, transient hepatitis flares. Recently, however, some approaches have been made to establish models of chronic AIH that reflect the immunopathogenic mechanisms seen in humans. In this article, we reflect on recent models, focusing on their feasibility and chances for success in providing a platform for studying the mechanisms of autoimmune liver destruction and the development of possible therapeutic interventions.

Adenovirus E3 MHC Inhibitory Genes but Not TNF/Fas Apoptotic Inhibitory Genes Expressed in Beta Cells Prevent Autoimmune Diabetes

Proceedings of the National Academy of Sciences of the United States of America. Nov, 2009  |  Pubmed ID: 19887639

To mimic events and molecules involved in type 1 insulin-dependent diabetes mellitus (T1D), we previously designed a transgenic (tg) mouse model where the viral nucleoprotein (NP) gene of lymphocytic choriomeningitis virus (LCMV) was expressed in the thymus to delete high affinity antiself (virus) T cells and in insulin-producing beta cells of the islets of Langerhans. Such tg mice, termed RIP-LCMV, fail to spontaneously develop diabetes. In contrast, when these mice are challenged with LCMV, they develop diabetes as they display hyperglycemia, low to absent levels of pancreatic insulin, and abundant mononuclear cell infiltrates in the islets. However, expressing the adenovirus early region (E3) gene in beta cells along with the LCMV transgene aborted the T1D. The present study utilizes this combined tg model (RIP LCMV x RIP E3) to define the requirement(s) of either pro-apoptotic TNF and Fas pathways or MHC class I up-regulation on beta cells for virus-induced T1D. Inhibitors to either pathway (TNF/Fas or MHC class I) are encoded in the E3 gene complex. To accomplish this task either the E3 region encoding the inhibitors of TNF and Fas pathways or the region encoding gp-19, a protein that inhibits transport of MHC class I molecules out of the endoplasmic reticulum were deleted in the RIP LCMV x RIP E3 model. Thus only the gp-19 is required to abort the virus-induced T1D. In contrast, removal of TNF- and Fas-pathway inhibitory genes had no effect on E3-mediated prevention of T1D.

Enterovirus Infection of Human Beta-cells Activates Dendritic Cells and Triggers Innate Antiviral Responses: Are Enteroviruses Convicted Now?

Diabetes. May, 2010  |  Pubmed ID: 20427698

Cytochrome P450 2D6 As a Model Antigen

Digestive Diseases (Basel, Switzerland). , 2010  |  Pubmed ID: 20460894

Cytochrome P450 2D6 (CYP2D6) has been identified as the major autoantigen in type 2 autoimmune hepatitis (AIH). However, because of a lack of appropriate animal models, the etiology of AIH is still poorly understood. We generated a mouse model for AIH using the human CYP2D6 as a triggering molecule for autoimmunity. We infected wild-type FVB mice with an adenovirus expressing human CYP2D6 (Ad-2D6) to break self-tolerance to the mouse CYP2D6 homologues. Ad-2D6-infected mice showed persistent features of liver damage including hepatic fibrosis, cellular infiltrations, focal-to-confluent necrosis and generation of anti-CYP2D6 antibodies, which predominantly recognized the identical immunodominant epitope recognized by LKM-1 antibodies from AIH patients. Interestingly, Ad-2D6 infection of transgenic mice expressing the human CYP2D6 (CYP2D6 mice) resulted in delayed kinetics and reduced severity of liver damage. However, the quantity and quality of anti-CYP2D6 antibodies was only moderately reduced in CYP2D6 mice. In contrast, the frequency of CYP2D6-specific CD4 and CD8 T cells was dramatically decreased in CYP2D6 mice, indicating the presence of a strong T cell tolerance to human CYP2D6 established in CYP2D6 mice, but not in wild-type mice. CYP2D6-specific T cells reacted to human CYP2D6 peptides with intermediate homology to the mouse homologues, but not to those with high homology, indicating that molecular mimicry rather than molecular identity breaks tolerance and subsequently causes severe persistent autoimmune liver damage. The CYP2D6 model provides a platform to investigate mechanisms involved in the immunopathogenesis of autoimmune-mediated chronic hepatic injury and evaluate possible ways of therapeutic interference.

CXCL10 Promotes Liver Fibrosis by Prevention of NK Cell Mediated Hepatic Stellate Cell Inactivation

Journal of Autoimmunity. Dec, 2010  |  Pubmed ID: 20932719

Chemokines, such as CXCL10, promote hepatic inflammation in chronic or acute liver injury through recruitment of leukocytes to the liver parenchyma. The CXCL10 receptor CXCR3, which is expressed on a subset of leukocytes, plays an important part in Th1-dependent inflammatory responses. Here, we investigated the role of CXCL10 in chemically induced liver fibrosis. We used carbon tetrachloride (CCl(4)) to trigger chronic liver damage in wildtype C57BL/6 and CXCL10-deficient mice. Fibrosis severity was assessed by Sirius Red staining and intrahepatic leukocyte subsets were investigated by immunohistochemistry. We have further analyzed hepatic stellate cell (HSC) distribution and activation and investigated the effect of CXCL10 on HSC motility and proliferation. In order to demonstrate a possible therapeutic intervention strategy, we have examined the anti-fibrotic potential of a neutralizing anti-CXCL10 antibody. Upon CCl(4) administration, CXCL10-deficient mice showed massively reduced liver fibrosis, when compared to wildtype mice. CXCL10-deficient mice had less B- and T lymphocyte and dendritic cell infiltrations within the liver and the number and activity of HSCs was reduced. In contrast, natural killer (NK) cells were more abundant in CXCL10-deficient mice and granzyme B expression was increased in areas with high numbers of NK cells. Further detailed analysis revealed that HSCs express CXCR3, respond to CXCL10 and secrete CXCL10 when stimulated with IFNγ. Blockade of CXCL10 with a neutralizing antibody exhibited a significant anti-fibrotic effect. Our data suggest that CXCL10 is a pro-fibrotic factor, which participates in a crosstalk between hepatocytes, HSCs and immune cells. NK cells seem to play an important role in controlling HSC activity and fibrosis. CXCL10 blockade may constitute a possible therapeutic intervention for hepatic fibrosis.

Early Production of IL-22 but Not IL-17 by Peripheral Blood Mononuclear Cells Exposed to Live Borrelia Burgdorferi: the Role of Monocytes and Interleukin-1

PLoS Pathogens. , 2010  |  Pubmed ID: 20976193

If insufficiently treated, Lyme borreliosis can evolve into an inflammatory disorder affecting skin, joints, and the CNS. Early innate immunity may determine host responses targeting infection. Thus, we sought to characterize the immediate cytokine storm associated with exposure of PBMC to moderate levels of live Borrelia burgdorferi. Since Th17 cytokines are connected to host defense against extracellular bacteria, we focused on interleukin (IL)-17 and IL-22. Here, we report that, despite induction of inflammatory cytokines including IL-23, IL-17 remained barely detectable in response to B. burgdorferi. In contrast, T cell-dependent expression of IL-22 became evident within 10 h of exposure to the spirochetes. This dichotomy was unrelated to interferon-γ but to a large part dependent on caspase-1 and IL-1 bioactivity derived from monocytes. In fact, IL-1β as a single stimulus induced IL-22 but not IL-17. Neutrophils display antibacterial activity against B. burgdorferi, particularly when opsonized by antibodies. Since neutrophilic inflammation, indicative of IL-17 bioactivity, is scarcely observed in Erythema migrans, a manifestation of skin inflammation after infection, protective and antibacterial properties of IL-22 may close this gap and serve essential functions in the initial phase of spirochete infection.

Viral Triggers for Autoimmunity: is the 'glass of Molecular Mimicry' Half Full or Half Empty?

Journal of Autoimmunity. Feb, 2010  |  Pubmed ID: 19716269

In this review we want to consider some of the requirements for autoimmune disease to develop and how this may be reproduced in animal models. Besides a genetic predisposition, environmental triggering factors seem to play a central role in the etiology of many autoimmune diseases. In theory, a structural similarity or identity between the host and an invading pathogen might cause the immune system of the host to react not only to the pathogen but also to self-components. However, in order for such a process of molecular mimicry to induce autoimmunity the mechanisms of maintaining tolerance or ignorance to the self-components need to be circumvented. Subsequently, in order to advance autoimmunity to overt autoimmune disease the frequency and avidity of autoaggressive lymphocytes has to be of sufficient magnitude. Intuitively, one would assume that tolerance might be stronger to identical structures than to structures that just share a certain degree of similarity. Self-reactive lymphocytes with high-avidity are more likely to be deleted or functionally silenced by central and/or peripheral tolerance mechanisms. Thus, perfect mimicry between identical structures might fail in inducing autoimmunity because of efficient tolerance mechanisms. In contrast, imperfect mimicry between similar but not identical structures might on one hand circumvent tolerance but on the other hand result in the generation of lymphocytes with only low- to intermediate avidity. Here we examine animal models that use the concept of molecular mimicry as a potential mechanism for inducing or accelerating autoimmunity. We focus on the RIP-LCMV model for type 1 diabetes and the novel cytochrome P450 2D6 (CYP2D6) model for autoimmune hepatitis, which use either identical or similar triggering and target antigens.

Do Viral Infections Protect from or Enhance Type 1 Diabetes and How Can We Tell the Difference?

Cellular & Molecular Immunology. May, 2011  |  Pubmed ID: 21258361

Virus infections have been implicated in both initiation of and protection from autoimmune diseases, such as type 1 diabetes (T1D). In this review we intend to reflect on recent evidence how viruses might on the one hand be involved in the pathogenesis of T1D and on the other hand induce a state of protection from autoimmune-mediated damage. It is important to acknowledge that human individuals encounter more than just one virus infection in their lifetime. Therefore, it is important to integrate more than just one possible environmental triggering factor for autoimmune diseases to occur.

Epitope Spreading of the Anti-CYP2D6 Antibody Response in Patients with Autoimmune Hepatitis and in the CYP2D6 Mouse Model

Journal of Autoimmunity. Nov, 2011  |  Pubmed ID: 21795021

Autoimmune hepatitis (AIH) is a serious chronic inflammatory disease of the liver with yet unknown etiology and largely uncertain immunopathology. The hallmark of type 2 AIH is the generation of liver kidney microsomal-1 (LKM-1) autoantibodies, which predominantly react to cytochrome P450 2D6 (CYP2D6). The identification of disease initiating factors has been hampered in the past, since antibody epitope mapping was mostly performed using serum samples collected late during disease resulting in the identification of immunodominant epitopes not necessarily representing those involved in disease initiation. In order to identify possible environmental triggers for AIH, we analyzed for the first time the spreading of the anti-CYP2D6 antibody response over a prolonged period of time in AIH patients and in the CYP2D6 mouse model, in which mice infected with Adenovirus-human CYP2D6 (Ad-h2D6) develop antibodies with a similar specificity than AIH patients. Epitope spreading was analyzed in six AIH-2-patients and in the CYP2D6 mouse model using SPOTs membranes containing peptides covering the entire CYP2D6 protein. Despite of a considerable variation, both mice and AIH patients largely focus their humoral immune response on an immunodominant epitope early after infection (mice) or diagnosis (patients). The CYP2D6 mouse model revealed that epitope spreading is initiated at the immunodominant epitope and later expands to neighboring and remote regions. Sequence homologies to human pathogens have been detected for all identified epitopes. Our study demonstrates that epitope spreading does indeed occur during the pathogenesis of AIH and supports the concept of molecular mimicry as a possible initiating mechanism for AIH.