Virus persists in beta cells of islets of Langerhans and is associated with chemical manifestations of diabetes

No measurable adverse effects of Lassa, Morogoro and Gairo arenaviruses on their rodent reservoir host in natural conditions

BACKGROUND

In order to optimize net transmission success, parasites are hypothesized to evolve towards causing minimal damage to their reservoir host while obtaining high shedding rates. For many parasite species however this paradigm has not been tested, and conflicting results have been found regarding the effect of arenaviruses on their rodent host species. The rodent Mastomys natalensis is the natural reservoir host of several arenaviruses, including Lassa virus that is known to cause Lassa haemorrhagic fever in humans. Here, we examined the effect of three arenaviruses (Gairo, Morogoro and Lassa virus) on four parameters of wild-caught Mastomys natalensis: body mass, head-body length, sexual maturity and fertility. After correcting for the effect of age, we compared these parameters between arenavirus-positive (arenavirus RNA or antibody) and negative animals using data from different field studies in Guinea (Lassa virus) and Tanzania (Morogoro and Gairo viruses).

RESULTS

Although the sample sizes of our studies (1297, 749 and 259 animals respectively) were large enough to statistically detect small differences in body conditions, we did not observe any adverse effects of these viruses on Mastomys natalensis. We did find that sexual maturity was significantly positively related with Lassa virus antibody presence until a certain age, and with Gairo virus antibody presence in general. Gairo virus antibody-positive animals were also significantly heavier and larger than antibody-free animals.

CONCLUSION

Together, these results suggest that the pathogenicity of arenaviruses is not severe in M. natalensis, which is likely to be an adaptation of these viruses to optimize transmission success. They also suggest that sexual behaviour might increase the probability of M. natalensis to become infected with arenaviruses.

Progress and challenges for treating Type 1 diabetes

It has been more than 30 years since the initial trials of Cyclosporin A to treat patients with new onset Type 1 diabetes (T1D). Since that time, there have been insights into genetic predisposition to the disease, the failures of immune tolerance, and mechanisms that cause the immune mediated β cell destruction. The genetic loci associated affect lymphocyte development and tolerance mechanisms. Discoveries related to the roles of specific immune responses gene such as the major histocompatibility complex, PTPN22, CTLA-4, IL-2RA, as well as the mechanisms of antigen presentation in the thymus have suggested ways in which autoreactivity may follow changes in the functions of these genes that are associated with risk. Antigens that are recognized by the immune system in patients with T1D have been identified. With this information, insights into the novel cellular mechanisms leading to the initiation and orchestration of β cell killing have been developed such as the presentation of unique antigens within the islets. Clinical trials have been performed, some of which have shown efficacy in improving β cell function but none have been able to permanently prevent loss of insulin secretion. The reasons for the lack of long term success are not clear but may include the heterogeneity of the immune response and in individual responses to immune therapies, recurrence of autoimmunity after the initial effects of the therapies, or even intrinsic mechanisms of β cell death that proceeds independently of immune attack after initiation of the disease. In this review, we cover developments that have led to new therapeutics and characteristics of patients who may show the most benefits from therapies. We also identify areas of incomplete understanding that might be addressed to develop more effective therapeutic strategies.

Proinsulin misfolding and endoplasmic reticulum stress during the development and progression of diabetes

To maintain copious insulin granule stores in the face of ongoing metabolic demand, pancreatic beta cells must produce large quantities of proinsulin, the insulin precursor. Proinsulin biosynthesis can account for up to 30-50% of total cellular protein synthesis of beta cells. This puts pressure on the beta cell secretory pathway, especially the endoplasmic reticulum (ER), where proinsulin undergoes its initial folding, including the formation of three evolutionarily conserved disulfide bonds. In normal beta cells, up to 20% of newly synthesized proinsulin may fail to reach its native conformation, suggesting that proinsulin is a misfolding-prone protein. Misfolded proinsulin molecules can either be refolded to their native structure or degraded through ER associated degradation (ERAD) and autophagy. These degraded molecules decrease proinsulin yield but do not otherwise compromise beta cell function. However, under certain pathological conditions, proinsulin misfolding increases, exceeding the genetically determined threshold of beta cells to handle the misfolded protein load. This results in accumulation of misfolded proinsulin in the ER - a causal factor leading to beta cell failure and diabetes. In patients with Mutant INS-gene induced diabetes of Youth (MIDY), increased proinsulin misfolding due to insulin gene mutations is the primary defect operating as a "first hit" to beta cells. Additionally, increased proinsulin misfolding can be secondary to an unfavorable ER folding environment due to genetic and/or environmental factors. Under these conditions, increased wild-type proinsulin misfolding becomes a "second hit" to the ER and beta cells, aggravating beta cell failure and diabetes. In this article, we describe our current understanding of the normal proinsulin folding pathway in the ER, and then review existing links between proinsulin misfolding, ER dysfunction, and beta cell failure in the development and progression of type 2, type 1, and some monogenic forms of diabetes.

Genetic and Pharmacologic Models for Type 1 Diabetes

Type 1 diabetes (T1D) is characterized by a partial or total insufficiency of insulin. The premiere animal model of autoimmune T cell-mediated T1D is the NOD mouse. A dominant negative mutation in the mouse insulin 2 gene (Ins2Akita ) produces a severe insulin deficiency syndrome without autoimmune involvement, as do a variety of transgenes overexpressed in beta cells. Pharmacologically-induced T1D (without autoimmunity) elicted by alloxan or streptozotocin at high doses can generate hyperglycemia in almost any strain of mouse by direct toxicity. Multiple low doses of streptozotocin combine direct beta cell toxicity with local inflammation to elicit T1D in a male sex-specific fashion. A summary of protocols relevant to the management of these different mouse models will be covered in this overview.

Molecular anatomy and number of antigen specific CD8 T cells required to cause type 1 diabetes

We quantified CD8 T cells needed to cause type 1 diabetes and studied the anatomy of the CD8 T cell/beta (β) cell interaction at the immunologic synapse. We used a transgenic model, in situ tetramer staining to distinguish antigen specific CD8 T cells from total T cells infiltrating islets and a variety of viral mutants selected for functional deletion(s) of various CD8 T cell epitopes. Twenty percent of CD8 T cells in the spleen were specific for all immunodominant and subdominant viral glycoprotein (GP) epitopes. CTLs to the immunodominant LCMV GP33-41 epitope accounted for 63% of the total (12.5% of tetramers). In situ hybridization analysis demonstrated only 1 to 2% of total infiltrating CD8 T cells were specific for GP33 CD8 T cell epitope, yet diabetes occurred in 94% of mice. The immunologic synapse between GP33 CD8 CTL and β cell contained LFA-1 and perforin. Silencing both immunodominant epitopes (GP33, GP276–286) in the infecting virus led to a four-fold reduction in viral specific CD8 CTL responses, negligible lymphocyte infiltration into islets and absence of diabetes.

Insulin-dependent type 1 diabetes (T1D) is characterized by elevated blood sugar, lymphocytic infiltration into the islets of Langerhans and T cell destruction of beta (β) cells. β cells produce insulin whose function is to maintain and regulate glucose hemostasis. However, in vivo, the numbers of antigen specific T cells that migrate to the islets to cause T1D, the engagement of such T cells with β cells at the immunologic synapse and the molecules expressed at the synapse are not clear. Using a transgenic model of virus induced T1D, a panel of viruses with CD8 T cell epitope mutations and in situ tetramer hybridization, we note of the total CD8 T cells infiltrating the islets, only 1–2% are antigen specific recognizing the immunodominant virus CD8 T cell epitope expressed on β cells. Immunohistochemical analysis of the synapse found between antigen specific CD8 T cells and β cells displays attachment by LFA-1 and presence of perforin, the molecule indicative of lytic activity.

Extraneural manifestations of prion infection in GPI-anchorless transgenic mice

Earlier studies indicated that transgenic (tg) mice engineered to express prion protein (PrP) lacking the glycophosphatidylinositol (GPI⁻/⁻) membrane anchor formed abnormal proteinase-resistant prion (PrPsc) amyloid deposits in their brains and hearts when infected with the RML strain of murine scrapie. In contrast, RML scrapie infection of normal mice with a GPI-anchored PrP did not deposit amyloid with PrPsc in the brain or the heart. Here we report that scrapie-infected GPI⁻/⁻ PrP tg mice also deposit PrP and transmissible infectious material in the gut, kidneys, and islets of Langerhans. Similar to previously reported amyloid deposits in the brain and heart, amyloid deposits were found in the gut; however, no amyloid deposited in the islets. By high-resolution electron microscopy, we show PrP is located primarily in α cells and also β cells. Islets contain abundant insulin and there is no abnormality in glucose metabolism in infected GPI⁻/⁻ PrP tg mice.

Molecular and cellular mechanisms, pathogenesis, and treatment of insulin-dependent diabetes obtained through study of a transgenic model of molecular mimicry

The portrait of autoimmune diabetes mellitus or type I diabetes can be copied by a transgenic model in which either the nucleoprotein (NP) or glycoprotein (GP) of lymphocytic choriomeningitis virus (LCMV) is expressed in beta cells of the islets of Langerhans. In the absence of further environmental insult, diabetes does not occur. However, when LCMV or a dissimilar virus that shares cross-reactive T cell epitopes with LCMV initiates infection, diabetes ensues. If the self "viral" transgene is expressed only in the beta cells, then diabetes occurs acutely within 8 to 12 days. Specific antiviral (self) CD8 T cells are mandatory for disease, but CD4 T cells are not. In this instance, diabetes can occur in the absence of infection if interferon gamma or B7.1 molecules are also expressed in the islets but not when IL-2, IL-4, IL-10, or IL-12 is similarly expressed. In contrast, both CD8 and CD4 antiviral (self) specific T cells are required when the self "viral" transgene is expressed concomitantly in beta cells and in the thymus. In this instance, infection by LCMV or cross-reacting virus is essential to cause diabetes. Further, the time from onset of infection until disease depends, in part, on the host's MHC background and its quantitative influence on negative selection of high-avidity antiviral (self) T cells. Knowledge of the cells, their numbers, and the molecules required to cause diabetes allows the design of successful strategies to treat and prevent the autoimmune disease.

How viral infections affect the autoimmune process leading to type 1 diabetes

Despite a large body of evidence describing associations between viruses and the development of type 1 diabetes (T1D) in genetically prone individuals, clearly defining causative infectious agents has not been successful. A likely explanation is that the link between infections and autoimmunity is more multifaceted than we initially assumed. Viral footprints might be hard to detect systemically or in the target organ once autoimmunity has been initiated, and several infections might have to act in concert to precipitate clinical autoimmunity. Furthermore, cells cross-reactive between viral and self-antigens might express low avidity T cell receptors and only be present transiently in the blood of affected individuals. In addition, there are two new observations from animal models that we should take into account at this point: first, viral infections alone might not be able to induce disease in the absence of other inflammatory factors (supporting the "fertile field hypothesis" [M.G. von Herrath et al., Microorganisms and autoimmunity: making the barren field fertile? Nat. Rev. Microbiol. 1 (2003) 151-157, ]). Second, increasing evidence indicates that viruses can play a role in preventing rather than enhancing T1D development (supporting the "hygiene hypothesis" [J.F. Bach, Protective role of infections and vaccinations on autoimmune diseases. J. Autoimmun. 16 (2001) 347-353]). In this article we will present an overview of the early events and requirements that could account for T1D predisposition and development, and explain how these can be modulated by viral infections. Focusing on coxsackie B and lymphocytic choriomeningitis virus infections, we will discuss new data that can hopefully help us understand how virus-induced inflammation can positively or negatively affect the clinical outcome of islet-autoimmunity and T1D.

Peptides from common viral and bacterial pathogens can efficiently activate diabetogenic T-cells

Cross-reactivity between an autoantigen and unknown microbial epitopes has been proposed as a molecular mechanism involved in the development of insulin-dependent diabetes (type 1 diabetes). Type 1 diabetes is an autoimmune disease that occurs in humans and the nonobese diabetic (NOD) mouse. BDC2.5 is an islet-specific CD4+ T-cell clone derived from the NOD mouse whose natural target antigen is unknown. A biometrical analysis of screening data from BDC2.5 T-cells and a positional scanning synthetic combinatorial library (PS-SCL) was used to analyze and rank all peptides in public viral and bacterial protein databases and identify potential molecular mimic sequences with predicted reactivity. Selected sequences were synthesized and tested for stimulatory activity with BDC2.5 T-cells. Active peptides were identified, and some of them were also able to stimulate spontaneously activated T-cells derived from young, pre-diabetic NOD mice, indicating that the reactivity of the BDC2.5 T-cell is directed at numerous mouse peptides. Our results provide evidence for their possible role as T-cell ligands involved in the activation of diabetogenic T-cells.

Cure of prediabetic mice by viral infections involves lymphocyte recruitment along an IP-10 gradient

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.

Cure of prediabetic mice by viral infections involves lymphocyte recruitment along an IP-10 gradient

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.

Viral infections: their elusive role in regulating susceptibility to autoimmune disease

Viral infections may trigger autoimmune disease. Complicating our understanding of how viral infections promote disease is the realization that viral infections can sometimes prevent auto-aggressive reactions. Here, we will discuss recent findings that provide insights into how viral infections may alter susceptibility to autoimmunity.

Diabetogenic potential of human pathogens uncovered in experimentally permissive beta-cells

Pancreatic beta-cell antiviral defense plays a critical role in protection from coxsackievirus B4 (CVB4)-induced diabetes. In the present study, we tested the hypothesis that interferon (IFN)-induced antiviral defense determines beta-cell survival after infection by the human pathogen CVB3, cytomegalovirus (CMV), and lymphocytic choriomeningitis virus (LCMV). We demonstrated that mice harboring beta-cells that do not respond to IFN because of the expression of the suppressor of cytokine signaling-1 (SOCS-1) succumb to an acute form of type 1 diabetes after infection with CVB3. Interestingly, the tropism of the virus was altered in SOCS-1 transgenic (Tg) mice, and CVB3 was detected in islet cells of SOCS-1-Tg mice before beta-cell loss and the onset of diabetes. Furthermore, insulitis was increased in SOCS-1-Tg mice after infection with murine CMV, and a minority of the mice developed overt diabetes. However, infection with LCMV failed to cause beta-cell destruction in SOCS-1 Tg mice. These findings suggest that CVB3 can cause diabetes in a host lacking adequate beta-cell antiviral defense, and that incomplete target cell antiviral defense may enhance susceptibility to diabetes triggered by CMV. In conclusion, suppressed beta-cell antiviral defense reveals the diabetogenic potential of two pathogens previously linked to the onset of type 1 diabetes in humans.

Disruption of differentiated functions during viral infection in vivo. V. Mapping of a locus involved in susceptibility of mice to growth hormone deficiency due to persistent lymphocytic choriomeningitis virus infection

Lymphocytic choriomeningitis virus (LCMV) Armstrong strain selectively and persistently infects the majority of growth hormone (GH) producing cells in the anterior lobe of pituitary glands of C3H/St mice but negligibly infects GH producing cells of BALB/WEHI mice (Oldstone et al., Virology 142, 175--182, 1985; Oldstone et al., Science 218, 1125--1127, 1982). Although infected GH cells remain free of structural damage, disrupted initiation of GH transcription (Klavinskis and Oldstone, J. Gen. Virol. 68, 1867--1873, 1989; Valsamakis et al., Virology 156, 214--220, 1987) occurs with a resultant decrease in the synthesis of GH, leading to a failure of growth and development (Oldstone et al., Science 218, 1125--1127, 1982). Microsatellite mapping of DNA obtained from 101 individual C3H/St x BALB/WEHI F1 x F1 mice shows that the growth failure correlates with host genes linked (P value 0.0008) on chromosome 17 just outside of the H-2D MHC site between D17 Mit24 and D17 Mit51, a distance of 2.5 cM. The genetic mapping done here excludes alpha-dystroglycan (alpha-DG), a known receptor for LCMV (Cao et al., Science 282, 2079--2081, 1998) in pathogenesis of GH disease, as alpha-DG is encoded in the mouse by a gene residing on chromosome 9 (Yotsumoto et al., Hum. Mol. Genet. 5, 1259--1267, 1996).

Obstacles to identifying viruses that cause autoimmune disease

In addition to a clear genetic disposition, environmental factors and viral infections are thought to play a role in the pathogenesis of autoimmune diseases such as type I diabetes or multiple sclerosis (MS). This article will explore, by use of paradigms developed in a transgenic mouse model, why it has been so difficult to prove a causative association between viral infections and autoimmunity. Potential pathogenetic mechanisms and their impact on devising the best strategy to prove such an association will be discussed. These thoughts might also be important for applying new immune interventions in type I diabetes or MS.

Virus-induced diabetes in a transgenic model: role of cross-reacting viruses and quantitation of effector T cells needed to cause disease

Virus-specific cytotoxic T lymphocytes (CTL) at frequencies of >1/1, 000 are sufficient to cause insulin-dependent diabetes mellitus (IDDM) in transgenic mice whose pancreatic beta cells express as "self" antigen a protein from a virus later used to initiate infection. The inability to generate sufficient effector CTL for other cross-reacting viruses that fail to cause IDDM could be mapped to point mutations in the CTL epitope or its COO(-) flanking region. These data indicate that IDDM and likely other autoimmune diseases are caused by a quantifiable number of T cells, that neither standard epidemiologic markers nor molecular analysis with nucleic acid probes reliably distinguishes between viruses that do or do not cause diabetes, and that a single-amino-acid change flanking a CTL epitope can interfere with antigen presentation and development of autoimmune disease in vivo.

Virus and Autoimmunity: Induction of Autoimmune Disease in Mice by Mouse T Lymphotropic Virus (MTLV) Destroying CD4+ T Cells

Neonatal infection of the mouse T lymphotropic virus (MTLV), a member of herpes viridae, causes various organ-specific autoimmune diseases, such as autoimmune gastritis, in selected strains of normal mice. The infection selectively depletes CD4+ T cells in the thymus and periphery for 2–3 wk from 1 wk after infection. Thymectomy 3 wk after neonatal MTLV infection enhances the autoimmune responses and produces autoimmune diseases at higher incidences and in a wider spectrum of organs than MTLV infection alone. On the other hand, inoculation of peripheral CD4+ cells from syngeneic noninfected adult mice prevents the autoimmune development. These autoimmune diseases can be adoptively transferred to syngeneic athymic nude mice by CD4+ T cells. The virus is not detected by bioassay in the organs/tissues damaged by the autoimmune responses. Furthermore, similar autoimmune diseases can be induced in normal mice by manipulating the neonatal thymus/T cells (e.g., by neonatal thymectomy) without virus infection. These results taken together indicate that neonatal MTLV infection elicits autoimmune disease by primarily affecting thymocytes/T cells, not self Ags. It may provoke or enhance thymic production of CD4+ pathogenic self-reactive T cells by altering the thymic clonal deletion mechanism, or reduce the production of CD4+ regulatory T cells controlling self-reactive T cells, or both. The possibility is discussed that other T cell-tropic viruses may cause autoimmunity in humans and animals by affecting the T cell immune system, not the self Ags to be targeted by the autoimmunity.

Pathological changes in the islet milieu precede infiltration of islets and destruction of beta-cells by autoreactive lymphocytes in a transgenic model of virus-induced IDDM

RIP-LCMV transgenic mice that express the viral glycoprotein (GP) or nucleoprotein (NP) from lymphocytic choriomeningitis virus (LCMV) under control of the rat insulin promoter (RIP) in pancreatic beta-cells develop autoimmune diabetes (IDDM) after infection with LCMV. Previous reports have described that the viral infection activates naive, potentially autoreactive CD8+ cytotoxic T-lymphocytes (CTL) that are present in the periphery of these mice, thus leading to the breaking of immunological unresponsiveness to the viral self-antigen expressed on beta-cells. However, we find that adoptive transfer of such CTL that were active in vitro and in vivo into uninfected RIP-LCMV recipients rarely resulted in hyperglycemia nor in insulitis, despite their ability to home to the islets and induce peri-insulitis. These observations indicated that, in addition to activated autoreactive lymphocytes, other factor(s) were required for beta-cell destruction. The present study shows that upregulation of MHC class II molecules associated with the attraction/activation of antigen presenting cells (APCs) to the islets occurs as soon as 2 days after LCMV inoculation of transgenic mice, clearly before CD4+ and CD8+ lymphocytes are found entering the islets (days 6 and 7 after LCMV inoculation). In contrast, although some MHC class II upregulation is also found in islets of non-transgenic mice 2-4 days after LCMV infection, no insulitis or IDDM develops and MHC is downregulated to normal (pre-infection) levels by day 7-10 in these mice. Associated with the activation of APCs and MHC upregulation observed in transgenic mice, viral (LCMV) infection of islets was detectable 2 days post-viral inoculation in some mice. Thus, beta-cell destruction by activated autoreactive lymphocytes is a multifactorial process that is likely to require changes within the islet milieu or dysfunction of islets.

Interferon-gamma is essential for destruction of beta cells and development of insulin-dependent diabetes mellitus

Autoimmune mediated destruction of beta cells of the islets of Langerhans leads to insulin-dependent diabetes mellitus (IDDM). Rat insulin promoter (RIP) lymphocytic choriomeningitis virus (LCMV) transgenic mice that express the nucleoprotein (NP) or glycoprotein (GP) of LCMV under control of the RIP in their beta cells develop IDDM after infection with LCMV and serve as a model for virus-induced IDDM. Recently, Kagi et al. (Kagi, D., B. Odermatt, P. Ohashi, R.M. Zinkernagel, and H. Hengartner, 1996, J. Exp. Med. 183:2143-2149) showed, using RIP LCMV perforin-deficient mice, that IDDM does not occur in the absence of perforin. They concluded that perforin-mediated killing by cytotoxic T lymphocytes (CTLs) is the main factor needed for beta cell injury and destruction. Here we provide evidence that killing of beta cells is more complex and multifactorial. By the use of our RIP LCMV model, we show that in perforin competent but interferon-gamma (IFN-gamma)-deficient mice, beta cell injury is limited and IDDM does not occur. For these studies, double transgenic mice were generated that were genetically deficient in the production of IFN-gamma and express LCMV NP or GP in their beta cells. In such mice, IDDM was aborted despite the generation of LCMV-specific antiself CTLs that displayed normal cytolytic activity in vitro and in vivo and entered the pancreas. However, mononuclear infiltration into the islets did not occur, and upregulation of class I and II molecules usually found in islets of RIP LCMV single transgenic mice after LCMV infection preceding the onset of clinical IDDM was not present in these bigenic mice. Our findings indicate that in addition to perforin, beta cell destruction, development of insulitis, and IDDM also depend on the cytokine INF-gamma, presumably through enhancement of major histocompatibility complex expression and antigen presentation.

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

Viruses have often been associated with autoimmune diseases. One mechanism by which self-destruction can be triggered is molecular mimicry. Many examples of cross-reactive immune responses between pathogens and self-antigens have been described. This review presents two transgenic models of autoimmune disease induced by a virus through activation of anti-self lymphocytes. Viral antigens are expressed as transgenes either in beta-cells of the pancreas or in the oligodendrocytes of the CNS. Infection by a virus encoding the same gene activated autoreactive T cells that cleared the viral infection, and as a consequence of transgene expression resulted in organ-specific autoimmune disease. In both transgenic mouse models, autoreactive lymphocytes that escaped thymic negative selection were present in the periphery. Several factors are described that play a role in the regulation of the self-reactive process precipitated by a viral infection. These include the quantity of activated autoreactive T cells, the affinity of these T cells, the number of memory T cells generated following primary infection, costimulation by accessory molecules, and the types and locations of cytokines produced. In addition, unique barriers exist in target tissues that prevent or suppress autoreactive responses and define to a large extent the outcome of disease. Restimulation of autoreactive memory lymphocytes may be required to bypass these barriers and enhance autoimmune disease. Therapy directed at modifying these factors can reduce and even prevent autoimmune disease after it has been initiated.

Infections and autoimmune endocrine disease

The literature examined in this review points to the possible involvement of infectious agents in the pathogenesis of autoimmune endocrine diseases, primarily autoimmune thyroid disease and diabetes mellitus. Various mechanisms have been proposed to explain induction of autoimmunity by infection but it seems that three possibilities may be important in individuals susceptible to developing autoimmune disease: molecular mimicry (perhaps to retroviruses); polyclonal T cell activation (by an endogenous superantigen or an infecting organism); and MHC class II antigen induction. It seems reasonable that all three mechanisms operate together or separately in different individuals. Data continue to accumulate in favour of infectious agents being important initiators of autoimmune disease.

Replication and persistence of coxsackieviruses B3 in human fibroblasts

Although in some cases a carrier state of Coxsackieviruses in human fibroblasts was described, the persistence mechanism has remained unknown. Our results demonstrate a replication of Coxsackievirus B3 (CVB3) in diploid human fibroblasts that is dependent on the virus strain as well as on the cell line involved. Two CVB3 Nancy strains could be multiplied over more than 10 passages in cell line H, whereas CVB3 strains SH"C" and SH"W" did not longer form infectious virus following several passages in these fibroblasts. None of the CVB3 strains replicated in cell lines J and K after a few passages. These results were not influenced by variations of culture conditions such as duration of incubation (3 or 7 days), temperature (33 or 37 degrees C) or application of trypsin. In line H, only 3-5 per cent of human fibroblasts were virus-infected. This was demonstrated by 1. antigen evidence by immunofluorescence, 2. determination of infectious centres, and 3. virus reproduction in dependence on MOI of the virus. We observed a carrier state of CVB3 Nancy strains over 16 cell passages in line H fibroblasts infected once. As shown in virus passage experiments, only few cells were productively infected. An addition of specific anti-CVB3 antiserum terminated this persistent infection. Generally, no cytopathic effect was observed. However, in one case a cell destruction by CVB3 Nancy "P" at the end of the life-time of the carrier cells could be found. This virus caused a complete cytopathic effect during more than 10 passages in line H and could still be neutralized by CVB3-specific antiserum.

Self and non-self antigen in diabetic autoimmunity: molecules and mechanisms

In this article, we have summarized current facts, models and views of the autoimmunity that leads to destruction of insulin-producing beta-cells and consequent Type 1 (insulin-dependent) diabetes mellitus. The presence of strong susceptibility and resistance gene loci distinguishes this condition from other autoimmune disorders, but environmental disease factors must conspire to produce disease. The mapping of most of the genetic risk (or disease resistance) to specific alleles in the major histocompatibility locus (MHC class II) has direct functional implications for our understanding of autoimmunity in diabetes and directly implies that presentation of a likely narrow set of peptides is critical to the development of diabetic autoimmunity. While many core scientific questions remain to be answered, current insight into the disease process is beginning to have direct clinical impact with concerted efforts towards disease prevention or intervention by immunological means. In this process, identification of the critical antigenic epitopes recognized by diabetes-associated T cells has achieved highest priority.

Islet expression of interferon-alpha precedes diabetes in both the BB rat and streptozotocin-treated mice

The mechanism(s) leading to beta cell dysfunction in type I diabetes has not been defined. We have investigated whether islet expression of IFN alpha could be a cause of the lesions that are hallmarks of type I diabetes. Streptozotocin induces the expression of interferon-alpha by pancreatic islets prior to the diabetes induced by streptozotocin. Increased IFN alpha, induced by poly I/C or expressed from a transgene will exacerbate the diabetogenic effects of streptozotocin. In another rodent model of type I diabetes (the BB rat), islet expression of IFN alpha precedes lymphocytic infiltration and diabetes. As in the streptozotocin model, in the BB rats poly I/C will induce islet expression of IFN alpha and accelerate the onset of diabetes. These results are consistent with the hypothesis that islet expression of IFN alpha participates in causing type I diabetes.

Behavioral effects of persistent lymphocytic choriomeningitis virus infection in mice

Lymphocytic choriomeningitis virus (LCMV) is a nonlytic murine virus that provides a valuable model system for studying the behavioral correlates of CNS viral infection. Newborn or immunosuppressed mice infected with LCMV develop a persistent tolerant infection characterized by continuous viral production. Virus can be found in various body organs including lung, liver, kidney, and brain. In brain, neurons are the predominant CNS cells infected and the greatest number of persistently infected neurons are found in the cerebral cortex, hippocampus, other limbic structures and parts of the hypothalamus. Despite continuous infection throughout the animal's life, neurons show no structural injury or dropout. Mice from the DBA/2J strain were infected with LCMV (1000 plaque-forming units) within 18 h of birth and tested for behavioral function as adults. Plaque assays indicated persistent infection in virus-injected mice. Mice were tested for their ability to learn a Y-maze spatial discrimination to avoid the onset of a mild footshock (0.43 mA). The number of correct avoidance responses made during training was taken as a measure of acquisition performance. The virus-infected mice showed a deficit in acquisition of the Y-maze discrimination compared to that seen in vehicle-injected and noninjected controls. Following additional training to reach control levels of performance, the infected mice and the controls were injected with the cholinergic antagonist scopolamine. Scopolamine (2.0 mg/kg) disrupted the performance of the infected mice significantly more than control performance, suggesting that a cholinergic dysfunction accounted for some of the learning deficit. A separate group of virus-infected mice exhibited hypoactivity during the first exposure to a locomotor testing apparatus.(ABSTRACT TRUNCATED AT 250 WORDS)

Diabetes mellitus due to viruses--some recent developments

Many different viruses belonging to several genera have the potential to damage beta cells. The mechanisms they employ are varied, and infection may result in either a direct destruction of islets and rapid insulin deficiency, or in a more gradual loss of functioning islets with the onset of diabetes many years later. Several case histories involving extensive cytolysis of beta cells can be directly linked to viral infection, whilst an example of diabetes occurring many years after viral infection is found in individuals who had a congenital infection with rubella virus. Here, the virus induces an autoimmune reaction against beta cells. Autoimmune phenomena have also been observed in islets following infections with viruses other than rubella, and thus activation of autoimmune mechanisms leading to beta-cell destruction may be a relatively frequent occurrence. Recent evidence shows that picornaviruses are not exclusively lytic, and can induce more subtle, long-term changes in beta cells, which may be important in the aetiology of diabetes. The exact mechanisms involved are not known, but it is clear that several viruses can directly inhibit insulin synthesis and induce the expression of other proteins such as interferons, and the HLA antigens. Strain differences in viruses are important since not all variants are tropic for the beta cells. Several laboratories are in the process of identifying the genetic determinants of tropism and diabetogenicity, especially amongst the Coxsackie B (CB) virus group. The sequence of one such diabetogenic CB4 strain virus has been determined.(ABSTRACT TRUNCATED AT 250 WORDS)

Human cytomegalovirus in the pancreas of patients with type 2 diabetes: is there a relation to clinical features, mRNA and protein expression of insulin, somatostatin, and MHC class II?

Human cytomegalovirus (HCMV) was recently demonstrated in the pancreas of about half the patients with type 2 diabetes mellitus in the absence of mumps, rubella or Coxsackie B virus. The present study addresses the question as to whether type 2 diabetes with an HCMV-positive pancreas differs from those with HCMV-negative pancreases with respect to age, sex, treatment, duration of disease, volume densities of B-cells and D-cells, mRNA levels of insulin and somatostatin, islet amyloid peptide deposits and major histocompatibility complex (MHC) class I and class II gene transcription, and protein expression. HCMV-positive type 2 diabetic patients showed a tendency towards a shorter duration of disease and significantly increased levels of MHC class II on RNA. In addition, expression of MHC class II product (HLA-DR) was identified in duct epithelial cells and/or islet cells in 9 diabetic pancreases and in 2 non-diabetic glands. No MHC class I expression could be detected. No other clinical differences between HCMV-positive and HCMV-negative glands were found. All 10 HCMV-positive diabetics showed a strong expression of MHC class II mRNA in the pancreas. By immunocytochemistry, 4 of 10 demonstrated expression on the islets; three of ten also expressed MHC DR beta on ductal cells. This finding might be related to the viral infection, as only 2 of the 9 HCMV-negative patients were HLA-DR beta positive and none of the non-diabetic controls showed increased levels of MHC class II mRNA. These data suggest that HCMV infection in the pancreas is associated with type 2 diabetes. However, no conclusions as to a role of this virus in the aetiopathology of type 2 diabetes can be drawn at present.

Virus infection triggers insulin-dependent diabetes mellitus in a transgenic model: role of anti-self (virus) immune response

We investigated the potential association between viruses and insulin-dependent (type 1) diabetes (IDDM) by developing a transgenic mouse model. By inserting into these mice a unique viral protein that was then expressed as a self-antigen in the pancreatic islets of Langerhans, we could study the effect on that expressed antigen alone, or in concert with an induced antiviral (i.e., autoimmune) response manifested later in life in causing IDDM. Our results indicate that a viral gene introduced as early as an animal's egg stage, incorporated into the germline, and expressed in islet cells does not produce tolerance when the host is exposed to the same virus later in life. We observed that the induced anti-self (viral) CTL response leads to selective and progressive damage of beta cells, resulting in IDDM.

Viruses as therapeutic agents. II. Viral reassortants map prevention of insulin-dependent diabetes mellitus to the small RNA of lymphocytic choriomeningitis virus

Nonobese diabetic (NOD) mice are the experimental prototype of type 1 insulin-dependent diabetes mellitus (IDDM). These mice develop a characteristic autoimmune lesion in the pancreatic islets of Langerhans, where infiltrating lymphocytes destroy beta cells, resulting in hypoinsulinemia, hyperglycemia, ketoacidosis, and death. This IDDM, which closely resembles that in humans, is prevented by infecting NOD mice with particular strains of lymphocytic choriomeningitis virus (LCMV), including Armstrong 53b, Traub, WE, and Pasteur. In contrast, the LCMV Armstrong 53b variant, Clone 13, fails to abort IDDM. Hence, although Clone 13 establishes a persistent infection that endures throughout the life spans of NOD mice, their hyperglycemia, hypoinsulinemia, and lymphocytic infiltration into the islets of Langerhans still occur. Genetic reassortant viruses generated between the IDDM therapeutic strain of LCMV Pasteur and the nontherapeutic variant, LCMV Clone 13, were used to treat NOD mice. By using such reassortants and both parental strains of virus to infect NOD mice, the prevention of IDDM was mapped to the S RNA segment of LCMV Pasteur.

Viruses as therapeutic agents. I. Treatment of nonobese insulin-dependent diabetes mice with virus prevents insulin-dependent diabetes mellitus while maintaining general immune competence

A situation in which virus can be used as a therapeutic agent to prevent a lethal autoimmune disease is explored. Nonobese insulin-dependent diabetes (NOD) mice spontaneously develop insulin-dependent diabetes mellitus (IDDM), characterized by lymphocytic infiltration into the islets of Langerhans and beta cell destruction, resulting in hypoinsulinemia, hyperglycemia, ketoacidosis, and death. Infection of NOD mice with lymphocytic choriomeningitis virus (LCMV) aborts the autoimmune manifestations and resultant IDDM. The viruses' effect is on a subset of CD4+ lymphocytes. Ablating this autoimmune diabetes does not significantly alter immune responses to a variety of non-LCMV antigens that require CD4+ lymphocyte participation. The prevention of IDDM associated with viral therapy is maintained throughout the life spans of NOD mice.

The role of viruses and environmental factors in the induction of diabetes

The development of IDDM results from the destruction of pancreatic beta cells. Genetic factors, various immune system alterations, and environmental factors have been studied as the possible causes of IDDM. The concordance rate for developing IDDM between monozygotic twins approaches 50%, suggesting that genetic factors are necessary, but nongenetic factors such as various immune system alterations and environmental factors also influence the clinical expression of genetic susceptibility. Environmental factors (e.g., viruses, chemicals, and diet) affecting the induction of diabetes may act as primary injurious agents which damage pancreatic beta cells or as triggering agents of autoimmunity. Certain viruses including EMC-D and Mengo virus 2T can directly infect pancreatic beta cells and replicate in the cells. The replication of viruses in the beta cells results in the destruction of the cells within 3 days, and the infected mice develop a diabeteslike syndrome in 3-4 days without the involvement of autoimmunity. In contrast, rubella virus appears to be somewhat weakly associated with autoimmune IDDM in hamsters. In addition, endogenous retrovirus expressed in pancreatic beta cells is clearly associated with the development of insulitis and diabetes in NOD mice. In man, there appears to be no correlation between the detection of islet cell autoantibodies and anti-Coxsackie B viral antibodies in newly diagnosed IDDM. In contrast, persistent infection of CMV and rubella virus appears to be associated with the presence of autoantibodies in newly diagnosed IDDM patients. It is particularly noteworthy that human CMV can induce islet cell autoantibodies that react specifically with a 38 kDa islet cell protein which may represent islet cell-specific antigens in a proportion of CMV-associated IDDM cases. These observations suggest that the association of diabetes with Coxsackie B viruses might be due to cytolytic infection of the beta cells with no link to autoimmunity, while both rubella virus and CMV are probably associated with autoimmune IDDM. A number of structurally diverse chemicals including alloxan, streptozotocin, chlorozotocin, Vacor, and cyproheptadine are diabetogenic mainly in rodents and sometimes in man. Possible mechanisms for beta cell destruction by these chemicals include (a) generation of oxygen free radicals and alteration of endogenous scavengers of these reactive species; (b) breakage of DNA and a consequent increase in the activity of poly-ADP-ribose synthetase, an enzyme depleting nicotinamide adenine dinucleotide in beta cells; and (c) inhibition of active calcium transport and calmodulin-activated protein kinase activity. (ABSTRACT TRUNCATED AT 400 WORDS)

Scrapie-induced diabetes mellitus in hamsters

Scrapie-infected hamsters had slightly elevated non-fasting plasma glucose levels, markedly abnormal glucose tolerance tests, and impaired release of insulin in response to a glucose load. Plasma cortisol levels were essentially the same in infected and uninfected animals. Histological examination of the pancreas revealed no morphological changes in infected animals with no alteration in distribution of cells secreting insulin, glucagon and somatostatin. In contrast, brains of scrapie-infected animals had the diffuse vacuolation typical of spongiform encephalopathy. These experiments suggest that scrapie-induced diabetes mellitus in hamsters may result from damage to the central nervous system.

The arginine-stimulated insulin response is impaired in congenital duck hepatitis B virus infection

Duck hepatitis B virus (DHBV) infects both A (glucagon-containing) and B (insulin-containing) islet cells. To examine the effect of this infection on islet cell function, baseline and secretagogue-augmented plasma insulin and glucagon levels as well as the pancreatic content of insulin and glucagon were compared in congenitally DHBV- and noninfected ducks. No difference in baseline plasma levels or the pancreatic content of insulin or glucagon was detected. However, the magnitude of the second phase of the biphasic arginine-stimulated insulin response was markedly diminished in infected ducks.

Insulin mRNA content in pancreatic beta cells of coxsackievirus B4-induced diabetic mice

Molecular hybridization was used to measure poly(A)-containing mRNA and insulin mRNA, and to evaluate viral persistence, in pancreatic beta cells of coxsackievirus B4-induced diabetic mice. Cellular RNA was hybridized with [3H]poly(U) to measure poly(A)-containing total mRNA, 32P-labeled preproinsulin I and II probes to measure insulin mRNA, and a 32P-labeled virus-specific probe to evaluate persistence. The infected mice (80-90%) showed subnormal blood glucose at 72 h postinfection and were hyperglycemic at 6 and 8 weeks. Poly(A)-containing total mRNA decreased by about 26% at 72 h and 6 weeks and by 49% at 8 weeks, while preproinsulin I mRNA by 30% and preproinsulin II by 46% at 8 weeks postinfection compared to control. Viral sequences were abundant at 72 h and in fair amounts later. It appears that persistent viral infection produces a pathological state, which impairs beta cell function to reduce insulin mRNA and consequently insulin synthesis apparently leading to hyperglycemia.

Potential detrimental effects of rodent viral infections on long-term experiments

Healthy animals are of paramount importance in obtaining meaningful, reliable scientific results. Viral infections of rodents often have a significant impact on various types of biomedical research. Laboratory animal specialists and researchers must be aware of the possible consequences associated with the use of infected animals. The objective of the paper is a discussion of the frequently encountered viral infections that can complicate or invalidate the interpretation of results by altering the host's response.

Persistent infection with a nontransforming RNA virus leads to impaired growth factor receptors and response

The potential role of viral persistence with nontransforming viruses on cellular growth and cellular function has received little attention. We found that when infected with type 3 reovirus (five plaque-forming units (PFU/cell), balb/C 3T3 cells (a mouse embryo fibroblast cell line) undergo a limited lytic phase. The surviving cells, about 90% of the original cells, appear morphologically normal by light microscopy and exhibit normal growth patterns in serum-supplemented medium but are persistently infected by electron microscopy. These persistently infected cells shed infectious virus in the culture medium (1.6-60 X 10(6) PFU per 10(6) cells per 24 h). In comparison to control uninfected 3T3 cells, the persistently infected cells exhibit a 70-90% decrease in receptor number for epidermal growth factor (EGF). This occurs without production of any EGF-like material and is associated with a parallel decrease in EGF-stimulated DNA synthesis. By contrast, insulin receptors are increased in number three-fold and insulin and serum stimulated DNA synthesis are comparable to control uninfected cells. These results suggest that persistent infection with a nontransforming virus may lead to major alteration in control of cell growth by specific growth factors.