Using transgenic mouse models to dissect the pathogenesis of virus-induced autoimmune disorders of the islets of Langerhans and the central nervous system

A Humanized Mouse Strain That Develops Spontaneously Immune-Mediated Diabetes

To circumvent the limitations of available preclinical models for the study of type 1 diabetes (T1D), we developed a new humanized model, the YES-RIP-hB7.1 mouse. This mouse is deficient of murine major histocompatibility complex class I and class II, the murine insulin genes, and expresses as transgenes the HLA-A*02:01 allele, the diabetes high-susceptibility HLA-DQ8A and B alleles, the human insulin gene, and the human co-stimulatory molecule B7.1 in insulin-secreting cells. It develops spontaneous T1D along with CD4⁺ and CD8⁺ T-cell responses to human preproinsulin epitopes. Most of the responses identified in these mice were validated in T1D patients. This model is amenable to characterization of hPPI-specific epitopes involved in T1D and to the identification of factors that may trigger autoimmune response to insulin-secreting cells in human T1D. It will allow evaluating peptide-based immunotherapy that may directly apply to T1D in human and complete preclinical model availability to address the issue of clinical heterogeneity of human disease.

Viral Infections and Autoimmune Disease: Roles of LCMV in Delineating Mechanisms of Immune Tolerance

Viral infections are a natural part of our existence. They can affect us in many ways that are the result of the interaction between the viral pathogen and our immune system. Most times, the resulting immune response is beneficial for the host. The pathogen is cleared, thus protecting our vital organs with no other consequences. Conversely, the reaction of our immune system against the pathogen can cause organ damage (immunopathology) or lead to autoimmune disease. To date, there are several mechanisms for virus-induced autoimmune disease, including molecular mimicry and bystander activation, in support of the “fertile field” hypothesis (terms defined in our review). In contrast, viral infections have been associated with protection from autoimmunity through mechanisms that include Treg invigoration and immune deviation, in support of the “hygiene hypothesis”, also defined here. Infection with lymphocytic choriomeningitis virus (LCMV) is one of the prototypes showing that the interaction of our immune system with viruses can either accelerate or prevent autoimmunity. Studies using mouse models of LCMV have helped conceive and establish several concepts that we now know and use to explain how viruses can lead to autoimmune activation or induce tolerance. Some of the most important mechanisms established during the course of LCMV infection are described in this short review.

Proteomic Analysis of Antiprotease Immunoglobulin-E Anti-Sperm Autoantibodies in Chronic Urticaria After Vasectomy

Some types of chronic urticaria (CU) are associated with autoreactive immunoglobulin (Ig)E, as well as IgG. In the syndrome of autoimmune thyroid disease and CU, autoreactive IgE, as well as IgG against host thyroid tissue, is present. The author describes a patient with new onset of CU after vasectomy with evidence of both autoreactive IgE and IgG anti-sperm antibodies (ASA). Autoreactive sperm proteins are enzymes opposed to structural sperm antigens producing ASA in infertility and after anti-spermatocyte vaccines. The author suggests that autoreactive proteins with enzymatic activity either in host proteins, aeroallergens, or viral proteins may have increased propensity to generate autoreactive IgE. This model of autoimmune IgE ASA generation by sperm and other host enzymatic proteins in CU can be tested using proteomic technology. INTRODUCTION

Molecular mimicry: its evolution from concept to mechanism as a cause of autoimmune diseases

On a clonal level, certain antibodies and T cells can interact with dissimilar antigens found in microbes and in host cells. More than 5% of over 800 monoclonal antibodies derived from multiple RNA and DNA viruses, as well as from a large number of T cell clones, engage in such interactions. Several of these cross-reactions, which we termed molecular mimicry, are against unique host proteins involved in autoimmune responses and diseases. Thus, molecular mimicry initiated as a host response to a virus or a microbial infection, but alternatively cross-reacting with an appropriate host-antigen, can be a mechanism for instigating an autoimmune disease. Molecular mimicry provides an explanation for the genetic observation that identical twins rarely manifest the same autoimmune disease and the documented epidemiologic evidence that microbial and/or viral infections often precede autoimmune disorders.

Pancreatic islet autoimmunity

Type 1 diabetes (T1D) represents 10 to 15% of all forms of diabetes. Its incidence shows a consistent rise in all countries under survey. Evidence for autoimmunity in human T1D relies on the detection of insulitis, of islet cell antibodies, of activated β-cell-specific T lymphocytes and on the association of T1D with a restricted set of class II major histocompatibility complex (MHC) alleles. However, mechanisms that initiate the failure of immune tolerance to β-cell autoantigens remain elusive in common forms of T1D. T1D commonly develop as a multifactorial disease in which environmental factors concur with a highly multigenic background. The disease is driven by the activation of T-lymphocytes against pancreatic β-cells. Several years elapse between initial triggering of the autoimmune response to β cells, as evidenced by the appearance or islet cell autoantibodies, and the onset of clinical diabetes, defining a prediabetes stage. Active mechanisms hold back autoreactive effector T-cells in prediabetes, in particular a subset of CD4+ T-cells (T(reg)) and other regulatory T-cells, such as invariant NKT cells. There is evidence in experimental models that systemic or local infections can trigger autoimmune reactions to β-cells. However, epidemiological observations that have accumulated over years have failed to identify undisputable environmental factors that trigger T1D. Moreover, multiple environmental factors may intervene in the disease evolution and protective as weel as triggering environmental factors may be involved. Available models also indicate that local signals within the islets are required for full-blown diabetes to develop. Many autoantigens that are expressed by β-cells but also by the other endocrine islet cells and by neurons are recognized by lymphocytes along the development of T1D. The immune image of β-cells is that of native components of the β-cell membrane, as seen by B-lymphocytes, and of fragments of intracellular β-cell proteins in the form of peptides loaded onto class I MHC molecules on the β-cell surface and class I and class II molecules onto professional antigen presenting cells. Given the key role of T lymphocytes in T1D, the cartography of autoantigen-derived peptides that are presented to class I-restricted CD8(+) T-cells and class II-restricted CD4(+) T-cells is of outmost importance and is a necessary step in the development of diagnostic T-cell assays and of immunotherapy of T1D.

Coxsackievirus B4 and type 1 diabetes pathogenesis: contribution of animal models

The role of enteroviruses, in particular type B coxsackieviruses (CV-B), in type 1 diabetes (T1D) pathogenesis is supported by epidemiological, clinical and experimental observations.The investigation of T1D pathogenesis benefits from the contribution of animal models called spontaneously diabetic. Among these animals the non-obese diabetic (NOD) mouse and the bio-breeding diabetes-prone (BBDP) rat present a genetic susceptibility manifested by the expression of an autoimmune diabetes similar to the pathology observed in human beings. Other models whose genetic predisposition is less known are of considerable contribution as well. Numerous major observations relative to several aspects of T1D pathogenesis in the context of CV-B infections, such as susceptibility, diabetogenicity, pancreatotropism, mechanisms of beta cells destruction and others, have been deduced thanks to investigations with animal models. Despite their limits, these models are necessary in improving our knowledge of the role of enteroviruses, like CV-B4, in the pathogenesis of T1D, and the recent advances ensuing from their contribution may have important therapeutic and preventive spin-offs.

Viral infections as potential triggers of type 1 diabetes

During the last decades, the incidence of type 1 diabetes (T1D) has increased significantly, reaching percentages of 3% annually worldwide. This increase suggests that besides genetical factors environmental perturbations (including viral infections) are also involved in the pathogenesis of T1D. T1D has been associated with viral infections including enteroviruses, rubella, mumps, rotavirus, parvovirus and cytomegalovirus (CMV). Although correlations between clinical presentation with T1D and the occurrence of a viral infection that precedes the development of overt disease have been recognized, causalities between viruses and the diabetogenic process are still elusive and difficult to prove in humans. The use of experimental animal models is therefore indispensable, and indeed more insight in the mechanism by which viruses can modulate diabetogenesis has been provided by studies in rodent models for T1D such as the biobreeding (BB) rat, nonobese diabetic (NOD) mouse or specific transgenic mouse strains. Data from experimental animals as well as in vitro studies indicate that various viruses are clearly able to modulate the development of T1D via different mechanisms, including direct beta-cell lysis, bystander activation of autoreactive T cells, loss of regulatory T cells and molecular mimicry. Data obtained in rodents and in vitro systems have improved our insight in the possible role of viral infections in the pathogenesis of human T1D. Future studies will hopefully reveal which human viruses are causally involved in the induction of T1D and this knowledge may provide directions on how to deal with viral infections in diabetes-susceptible individuals in order to delay or even prevent the diabetogenic process.

Pathogenesis of autoimmune hepatitis: from break of tolerance to immune-mediated hepatocyte apoptosis

Understanding the pathogenesis and progression of autoimmune hepatitis (AIH) at the molecular level could prove essential in developing new preventive and therapeutic strategies. Recently developed murine models have enabled the identification of various mechanisms involved in the development and perpetuation of this autoimmune disorder. Studies on these models have shown that a peripheral break of tolerance against liver-expressed antigens is sufficient to induce an autoimmune liver disease, which can occur without prior liver damage. Recent data have also shown that the liver selectively recruits and induces the apoptosis of activated CD8+ T cells after an immune response. This process of T-cell trapping involves the expression of specific chemokines and adhesion molecules, and these molecules are believed to play an important role in the initiation and perpetuation of autoimmune hepatitis. Hepatocyte apoptosis, induced by autoreactive T cells, follows specific pathways that could be targeted by new therapeutic agents. Basic research on the break of immune tolerance against liver antigens would be beneficial for patients with autoimmune hepatitis, as well as those suffering from other chronic inflammatory liver diseases, such as primary biliary cirrhosis and graft-versus-host diseases.

Natural regulatory T cells in infectious disease

This review discusses the control exerted by natural CD4(+) CD25(+) regulatory T cells (natural T(reg) cells) during infectious processes. Natural T(reg) cells may limit the magnitude of effector responses, which may result in failure to adequately control infection. However, natural T(reg) cells also help limit collateral tissue damage caused by vigorous antimicrobial immune responses. We describe here various situations in which the balance between natural T(reg) cells and effector immune functions influences the outcome of infection and discuss how manipulating this equilibrium might be exploited therapeutically.

Disease mimicry--a pathogenetic concept for T cell-mediated autoimmune disorders triggered by molecular mimicry?

Molecular mimicry is considered as a mechanism by which infectious pathogens may break immunological tolerance and cause autoimmune disease. It implicates that peptides shared between pathogen and host may induce cross-reactive immune reactions. According to this hypothesis, the resulting autoimmune response actually represents a secondary immune response. It is mediated by cross-reactive T cells that have been educated in a primary immune response against a particular pathogen. Using psoriasis vulgaris as a model, this article discusses the potential functional consequences molecular mimicry should have for the resulting autoimmune disease. It proposes that due to the functional memory of T cells, which is an integral feature of adaptive immunity, the phenotype of an autoimmune disease induced by molecular mimicry should reflect the immune mechanisms raised in the primary immune response. This process might be called 'disease mimicry'.

Expression of preproinsulin-2 gene shapes the immune response to preproinsulin in normal mice

Deciphering mechanisms involved in failure of self tolerance to preproinsulin-2 is a key issue in type 1 diabetes. We used nonautoimmune 129SV/Pas mice lacking preproinsulin-2 to study the immune response to preproinsulin-2. In these mice, a T cell response was detected after immunization with several preproinsulin-2 peptides and confirmed by generating hybridomas. Activation of some of these hybridomas by wild-type (wt) islet cells or recombinant murine proinsulin-2 demonstrated that two epitopes can be generated from the naturally expressed protein. Although T cells from wt mice responded to preproinsulin-2 peptides, we could not detect a response to the naturally processed epitopes in these mice. Moreover, after immunization with recombinant whole proinsulin-2, a T cell response was detected in preproinsulin-2-deficient but not in wt mice. This suggests that islet preproinsulin-2-autoreactive T cells are functionally eliminated in wt mice. We used a transplantation model to evaluate the relevance of reactivity to preproinsulin-2 in vivo. Wild-type preproinsulin-2-expressing islets transplanted in preproinsulin-2-deficient mice elicited a mononuclear cell infiltration and insulin Abs. Graft infiltration was further increased by immunization with preproinsulin-2 peptides. Preproinsulin-2 expression thus shapes the immune response and prevents self reactivity to the islet. Moreover, islet preproinsulin-2 primes an immune response to preproinsulin-2 in deficient mice.

Preferential escape of subdominant CD8+ T cells during negative selection results in an altered antiviral T cell hierarchy

Negative selection is designed to purge the immune system of high-avidity, self-reactive T cells and thereby protect the host from overt autoimmunity. In this in vivo viral infection model, we show that there is a previously unappreciated dichotomy involved in negative selection in which high-avidity CD8(+) T cells specific for a dominant epitope are eliminated, whereas T cells specific for a subdominant epitope on the same protein preferentially escape deletion. Although this resulted in significant skewing of immunodominance and a substantial depletion of the most promiscuous T cells, thymic and/or peripheral deletion of high-avidity CD8(+) T cells was not accompanied by any major change in the TCR V beta gene family usage or an absolute deletion of a single preferred complementarity-determining region 3 length polymorphism. This suggests that negative selection allows high-avidity CD8(+) T cells specific for subdominant or cryptic epitopes to persist while effectively deleting high-avidity T cells specific for dominant epitopes. By allowing the escape of subdominant T cells, this process still preserves a relatively broad peripheral TCR repertoire that can actively participate in antiviral and/or autoreactive immune responses.

Virus-induced autoimmunity: potential role of viruses in initiation, perpetuation, and progression of T-cell-mediated autoimmune disease

Virus infections have been implicated in the initiation of multiple human autoimmune diseases. This article focuses on reviewing the role of viruses in initiation, progression, and perpetuation of autoimmune diseases. Various mechanisms by which virus infections can induce autoimmune responses including molecular mimicry, epitope spreading, direct bystander activation, and release of cryptic epitopes are discussed. Evidence implicating virus infections in the pathogenesis of various human autoimmune diseases is reviewed. Last, the characteristics of animal models that have been developed for the study of the potential role of viruses in the initiation and progression of autoimmune disease are reviewed.

Role of interferon regulatory factor-1 in double-stranded RNA-induced iNOS expression by mouse islets

Environmental factors, such as viral infection, have been implicated as potential triggering events leading to the initial destruction of pancreatic beta cells during the development of autoimmune diabetes. Double-stranded RNA (dsRNA), the active component of a viral infection that stimulates antiviral responses in infected cells, has been shown in combination with interferon-gamma (IFN-gamma) to stimulate inducible nitric oxide synthase (iNOS) expression and nitric oxide production and to inhibit beta cell function. Interferon regulatory factor-1 (IRF-1), the activation of which is induced by dsRNA, viral infection, and IFN-gamma, regulates the expression of many antiviral proteins, including PKR, type I IFN, and iNOS. In this study, we show that IRF-1 is not required for dsRNA + IFN-gamma-stimulated iNOS expression and nitric oxide production by mouse islets. In contrast to islets, dsRNA + IFN-gamma fails to induce iNOS expression or nitric oxide production by macrophages isolated from IRF-1(-/-) mice; however, dsRNA + IFN-gamma induces similar levels of IL-1 release by macrophages isolated from both IRF-1(-/-) and IRF-1(+/+) mice. Importantly, we show that dsRNA- or dsRNA + IFN-gamma-stimulated IRF-1 expression by mouse islets and peritoneal macrophages is independent of PKR. These results indicate that IRF-1 is required for dsRNA + IFN-gamma-induced iNOS expression and nitric oxide production by mouse peritoneal macrophages but not by mouse islets. These findings suggest that dsRNA + IFN-gamma stimulates iNOS expression by two distinct PKR-independent mechanisms; one that is IRF-1-dependent in macrophages and another that is IRF-1-independent in islets.

Peripheral T-cell tolerance defined through transgenic mouse studies

Selection in the thymus restricted by MHC and self-peptide shapes the diverse reactivities of the T-cell population which subsequently seeds into the peripheral tissues, in anticipation of the universe of pathogen antigens to which the organism may be exposed. A necessary corollary is the potential for T-cell self-reactivity (autoimmunity) in the periphery. Transgenic mouse models in which transgene expression in the thymus is prevented or excluded, have been particularly useful for determining the immunological outcome when T-cells encounter transgene-encoded 'self' antigen in peripheral tissues. Data suggest that non-mutually exclusive mechanisms of T-cells 'ignoring' self-antigen, T-cell deletion, T-cell anergy and T-cell immunoregulation have evolved to prevent self-reactivity while maintaining T-cell diversity. The peripheral T-cell repertoire, far from being static following maturation through the thymus, is in a dynamic stated determined by these peripheral selective and immunoregulatory influences. This article reviews the evidence with particular reference to CD8+ive T-cells.

Pancreatic beta-cell damage mediated by beta-cell production of interleukin-1. A novel mechanism for virus-induced diabetes

Viral infection is one environmental factor that may initiate beta-cell damage during the development of autoimmune diabetes. Formed during viral replication, double-stranded RNA (dsRNA) activates the antiviral response in infected cells. In combination, synthetic dsRNA (polyinosinic-polycytidylic acid, poly(I-C)) and interferon (IFN)-gamma stimulate inducible nitric-oxide synthase (iNOS) expression, inhibit insulin secretion, and induce islet degeneration. Interleukin-1 (IL-1) appears to mediate dsRNA + IFN-gamma-induced islet damage in a nitric oxide-dependent manner, as the interleukin-1 receptor antagonist protein prevents dsRNA + IFN-gamma-induced iNOS expression, inhibition of insulin secretion, and islet degeneration. IL-1beta is synthesized as an inactive precursor protein that requires cleavage by the IL-1beta-converting enzyme (ICE) for activation. dsRNA and IFN-gamma stimulate IL-1beta expression and ICE activation in primary beta-cells, respectively. Selective ICE inhibition attenuates dsRNA + IFN-gamma-induced iNOS expression by primary beta-cells. In addition, poly(I-C) + IFN-gamma-induced iNOS expression and nitric oxide production by human islets are prevented by interleukin-1 receptor antagonist protein, indicating that human islets respond to dsRNA and IFN-gamma in a manner similar to rat islets. These studies provide biochemical evidence for a novel mechanism by which viral infection may initiate beta-cell damage during the development of autoimmune diabetes. The viral replicative intermediate dsRNA stimulates beta-cell production of pro-IL-1beta, and following cleavage to its mature form by IFN-gamma-activated ICE, IL-1 then initiates beta-cell damage in a nitric oxide-dependent fashion.

Chondrocyte antigen expression, immune response and susceptibility to arthritis

The association of HLA-B27 with certain forms of arthritis implies a role for MHC class I-restricted T cells in the arthritic process. Our aim was to study CD8(+) T cell responses towards specific antigens localized in joint tissue. Known determinants were introduced into chondrocytes of transgenic (TG) mice, under the control of the cis-regulatory sequences of the human type II collagen gene (COL2A1). Two Escherichia coli beta-galactosidase (beta-gal)-expressing lines were derived (CIIL73 and CIIL64) as well as two lines (CIINP) expressing influenza A virus nucleoprotein (NP). Expression of the antigens could be demonstrated in cartilaginous tissues. The TG lines showed variable degrees of responsiveness towards the transgene-introduced antigens; whilst 75% of CIIL73 mice had an impaired cytotoxic T lymphocyte (CTL) response towards beta-gal, the response in CIIL64 mice was essentially normal. However, both lines displayed normal proliferative and antibody responses to beta-gal. A reduced CTL response was seen to NP in the CIINP lines in approximately 65% of the animals. In spite of the persistence of T cell responses to the transgene antigens in these lines, induction of CTL responses alone has so far failed to induce clinical signs of arthritis. Interestingly, some animals expressing beta-gal were susceptible to arthritis following challenge with type II collagen alone, whilst their non-TG littermates and TG mice from other lines remained unaffected. As beta-gal is expressed by E. coli, a component of the normal gut flora, this suggests a possible role for gut-derived immune responses. We believe these lines could form the basis of a model for studying links between intestinal inflammation and arthritis.

Double-stranded RNA-dependent protein kinase is not required for double-stranded RNA-induced nitric oxide synthase expression or nuclear factor-kappaB activation by islets

Environmental factors, such as viral infection, have been implicated in the destruction of beta-cells during the development of autoimmune diabetes. Double-stranded RNA (dsRNA), produced during viral replication, is an active component of a viral infection that stimulates antiviral responses in infected cells. Previous studies have shown that treatment of rat islets with dsRNA in combination with gamma-interferon (IFN-gamma) results in a nitric oxide-dependent inhibition of glucose-stimulated insulin secretion. This study examines the role of nuclear factor-kappaB (NF-kappaB) and the dsRNA-dependent protein kinase (PKR) in dsRNA + IFN-gamma-induced nitric oxide synthase (iNOS) expression and nitric oxide production by rat, mouse, and human islets. Treatment of rat and human islets with dsRNA in the form of polyinosinic-polycytidylic acid (poly IC) and IFN-gamma resulted in iNOS expression and nitric oxide production. Inhibitors of NF-kappaB activation-the proteasome inhibitor MG-132 and the antioxidant pyrrolidine-dithiocarbamate (PDTC)-prevented poly IC + IFN-gamma-induced iNOS expression and nitric oxide production. Incubation of rat islets for 3 h or human islets for 2 h with poly IC alone or poly IC + IFN-gamma resulted in NF-kappaB nuclear translocation and degradation of the NF-kappaB inhibitor protein, IkappaB, events that are prevented by MG-132. PKR has been shown to participate in dsRNA-induced NF-kappaB activation in a number of cell types, including mouse embryonic fibroblasts. However, poly IC stimulated NF-kappaB nuclear translocation and IkappaB degradation to similar levels in islets isolated from mice devoid of PKR (PKR-/-) and wild-type mice (PKR+/+). Furthermore, the genetic absence of PKR did not affect dsRNA + IFN-gamma-induced iNOS expression, nitric oxide production, or the inhibitory actions of these agents on glucose-stimulated insulin secretion. These results suggest that 1) NF-KB activation is required for dsRNA + IFN-gamma-induced iNOS expression, 2) PKR is not required for either dsRNA-induced NF-kappaB activation or dsRNA + IFN-y-induced iNOS expression by islets, and 3) PKR is not required for dsRNA + IFN-gamma-induced inhibition of glucose-stimulated insulin secretion by islets.

Pathogenetic role of autoantibodies in neurological diseases

Autoreactive B cells and antibodies can be detected in a variety of neurological diseases. Their causative role has been established in some disorders and they are obviously involved in the pathogenesis of others. Some mechanisms engendering B-cell autoimmunity in animal models have been shown to operate in humans. Factors that determine B-cell immune-response patterns and the effector pathways have been identified. B-cell responses to CNS-restricted autoantigens are governed by distinctive immune reactions. Evidence has accumulated that the CNS is a permissive and, under inflammatory conditions, even a B-cell-supporting micro-environment. Data from human and animal experiments have enhanced our understanding of B-cell physiology in health and neurological disease, which has relevant diagnostic and therapeutic implications.

Organ-specific immune responses associated with infectious disease

The immune response to infection can vary markedly in different organs of the same animal. In some organs, the infection can resolve with subsequent immunity to re-infection, whereas in other organs, pathogens can persist. Here, Christian Engwerda and Paul Kaye highlight the importance of defining organ-specific immune mechanisms for developing strategies that deal effectively with infectious diseases and their associated pathologies.

Superantigens: mechanisms by which they may induce, exacerbate and control autoimmune diseases

Superantigens are polypeptide molecules produced by a broad range of infectious microorganisms which elicit excessive and toxic T-cell responses in mammalian hosts. In light of this property and the fact that autoimmune diseases are frequently the sequelae of microbial infections, it has been suggested that superantigens may be etiologic agents of autoreactive immunological responses resulting in initiation, exacerbation or relapse of autoimmune diseases. This article relates the biology of superantigens to possible mechanisms by which they may exert these activities and reviews the evidence for their roles in various human and animal models of autoimmune disease. Finally, a mechanism of active suppression by superantigen-activated CD4+ T-cells that could be exploited for therapy as well as prophylaxis of human autoimmune diseases is proposed.

Viruses, host responses, and autoimmunity

Conceptually, the initiation of autoimmune disease can be described as a three-stage process involving both genetic and environmental influences. This process begins with the development of an autoimmune cellular repertoire, followed by activation of these autoreactive cells in response to a localized target and, finally, the immune system's failure to regulate these self-reactive constituents. Viruses have long been associated with inciting autoimmune disorders. Two mechanisms have been proposed to explain how a viral infection can overcome immunological tolerance to self-components and initiate an organ-specific autoreactive process; these mechanisms are molecular mimicry and bystander activation. Both pathways, as discussed here, could play pivotal roles in the development of autoimmunity without necessarily excluding each other. Transgene technology has allowed us and others to examine more closely the roles of these mechanisms in mice and to dissect the requirements for initiating disease. These results demonstrate that bystander activation is the most likely explanation for disease development. Additional evidence suggests a further role for viruses in the reactivation and chronicity of autoimmune diseases. In this scenario, a second invasion by a previously infecting virus may restimulate already existing autoreactive lymphocytes, and thereby contribute to the diversity of the immune response.

Double-stranded RNA inhibits beta-cell function and induces islet damage by stimulating beta-cell production of nitric oxide

Viral infection has been implicated as a triggering event that may initiate beta-cell damage during the development of autoimmune diabetes. In this study, the effects of the viral replicative intermediate, double-stranded RNA (dsRNA) (in the form of synthetic polyinosinic-polycytidylic acid (poly IC)) on islet expression of inducible nitric oxide synthase (iNOS), production of nitric oxide, and islet function and viability were investigated. Treatment of rat islets with poly(IC) + interferon-gamma (IFN-gamma) stimulates the time- and concentration-dependent expression of iNOS and production of nitrite by rat islets. iNOS expression and nitrite production by rat islets in response to poly(IC) + IFN-gamma correlate with an inhibition of insulin secretion and islet degeneration, effects that are prevented by the iNOS inhibitor aminoguanidine (AG). We have previously shown that poly(IC) + IFN-gamma activates resident macrophages, stimulating iNOS expression, nitric oxide production and interleukin-1 (IL-1) release. In addition, in response to tumor necrosis factor-alpha (TNF-alpha) + lipopolysaccharide, activated resident macrophages mediate beta-cell damage via intraislet IL-1 release followed by IL-1-induced iNOS expression by beta-cells. The inhibitory and destructive effects of poly(IC) + IFN-gamma, however, do not appear to require resident macrophages. Treatment of macrophage-depleted rat islets for 40 h with poly(IC) + IFN-gamma results in the expression of iNOS, production of nitrite, and inhibition of insulin secretion. The destructive effects of dsRNA + IFN-gamma on islets appear to be mediated by a direct interaction with beta-cells. Poly IC + IFN-gamma stimulates iNOS expression and inhibits insulin secretion by primary beta-cells purified by fluorescence-activated cell sorting. In addition, AG prevents the inhibitory effects of poly(IC) + IFN-gamma on glucose-stimulated insulin secretion by beta-cells. These results indicate that dsRNA + IFN-gamma interacts directly with beta-cells stimulating iNOS expression and inhibiting insulin secretion in a nitric oxide-dependent manner. These findings provide biochemical evidence for a novel mechanism by which viral infection may directly mediate the initial destruction of beta-cells during the development of autoimmune diabetes.

Type 1 diabetes: the facts fit a deficient inhibitory signal given by MHC class II

This paper presents a hypothesis regarding the aetiology of Type 1 (autoimmune) diabetes, which suggests that autoimmunity is normally prevented by an inhibitory or negative signal delivered by MHC molecules, and that in Type 1 diabetes it is the inability of beta cells to deliver sufficient negative signal from MHC Class II that drives the underlying autoimmune process. Based on a broad survey of the diabetes literature, a list of clinical, pathological, experimental and epidemiological 'facts' about Type 1 diabetes is presented which are considered to be widely accepted as proven. The new theory is then compared to other recent theories on the aetiology of diabetes with regard to its ability to explain these accepted 'facts'.

Expression of a Schistosoma mansoni 28-kilodalton glutathione S-transferase in the livers of transgenic mice and its effect on parasite infection

Schistosomiasis is a debilitating tropical disease for which an effective vaccine is needed. A 28-kDa glutathione S-transferase from Schistosoma mansoni (Sm28GST) has been shown to induce protective immunity. Sm28GST possesses significant sequence identity to mammalian GST isoforms. In order to study self-reactivity in mice immunized with Sm28GST and the concomitant phenomena of immune tolerance and epitope suppression, as well as their consequences for the protective immunity induced by this vaccination, we developed transgenic (Tg) mice that express Sm28GST under the control of a part of the mouse transferrin gene promoter. A study of (P28)Tg mice showed that the expression of Sm28GST was strictly localized in pericentrolobular hepatocytes. No histological change, inflammatory infiltrates, or modification of seric L-aspartate: 2-oxoglutarate aminotransferase concentration was observed over an 18-month period, despite a cross-reactivity between Sm28GST and a mouse molecule of 30 kDa. The immunoglobulin G anti-Sm28GST response of (P28)Tg mice immunized with recombinant Sm28GST was lower (P < 0.001) than that observed in non-(P28)Tg littermates and inversely proportional of Sm28GST liver expression. The response of non-(P28)Tg mouse spleen cells to Sm28GST stimulation was greater (P < 0.01) than that observed with (P28)Tg mouse spleen cells. (P28)Tg mice infected with 40 S. mansoni furcocercariae harbored more worms (P < 0.05) than did non-(P28)Tg control mice. The increase in the level of infection in (P28)Tg mice was reflected in concomitant increases in the numbers of adult worms and schistosome eggs found in livers and intestines after whole-body perfusion at 56 days postinfection, but no relative increase in the fertility of individual female worms was observed. The results obtained argue for the involvement of Sm28GST in reducing levels of infection and support the view that this enzyme has a central role in the maintenance of parasite viability, at least during its migration through host tissues.

Virus-induced autoimmune disease: transgenic approach to mimic insulin-dependent diabetes mellitus and other autoimmune diseases

The technology of cloning viral genes and expressing them in vivo under cell-specific promoters allows to dissect the role of viruses, host self proteins, host genetics and immune responses in the complex etiology of autoimmune disease. Expression of a viral transgene, that is really a marker for a host "self" protein per se in beta cells of the islets of Langerhans, need not cause disease. In our model, expression of a viral gene was not associated with disease over the lifetime of the animal. However, when the host becomes infected with a virus encoding the same gene as the transgene or one closely related to it, a resultant immune response directed against the virus also recognizes the transgene leading to progressive T-cell-mediated response and destruction of the tissue expressing the viral ("self") gene, leading to autoimmune disease. This multifactorial process is influenced by whether the viral transgene is expressed in the thymus as well as in the disease-related cell or target tissue. Thymic expression influences negative selection of responder lymphocytes and thus delays the onset of the autoimmune disorder. Further, the MHC haplotype or other background genes of an individual undergoing autoimmune dysfunction play a role in the affinity of binding of the transgene products to the MHC molecule and influence the degree of negative selection that occurs, thereby influencing the vigor of the resulting immune response. The current ability to express host or viral genes in unique cell populations, and to make double- or triple-tg mice in which various cytokine genes or lymphocyte activation genes can be expressed along with the viral gene, offers a unique possibility for molecular dissection of autoimmunity. With the information on hand, approaches to the prevention and treatment of human autoimmune disease are likely to be uncovered. Finally, animal models are available in which the onset, progression and control of molecular mimicry can be evaluated. Future studies should define roles played by cytokines, bystander and immune-specific cross-reactivity to viruses and other microbes in several autoimmune diseases.