Flavivirus induces MHC antigen on human myoblasts: a model of autoimmune myositis?

Gestational Viral Infections: Role of Host Immune System

Viral infections in pregnancy are major causes of maternal and fetal morbidity and mortality. Infections can develop in the neonate transplacentally, perinatally, or postnatally (from breast milk or other sources) and lead to different clinical manifestations, depending on the viral agent and the gestational age at exposure. Viewing the peculiar tolerogenic status which characterizes pregnancy, viruses could exploit this peculiar immunological status to spread or affect the maternal immune system, adopting several evasion strategies. In fact, both DNA and RNA virus might have a deep impact on both innate and acquired immune systems. For this reason, investigating the interaction with these pathogens and the host's immune system during pregnancy is crucial not only for the development of most effective therapies and diagnosis but mostly for prevention. In this review, we will analyze some of the most important DNA and RNA viruses related to gestational infections.

Professor Cristobal G dos Remedios mentorship

As a non-English-speaking PhD student without previous scientific skills, I have been so lucky to be supervised and mentored by Professor Cristobal dos Remedios. In this commentary, I have commented my experience in dos Remedios laboratory. Finally, I would like to express my greatest appreciation to Professor dos Remedios for his kindness and mentorship over the last 31 years. His continuous support, which continues to the present, has been instrumental for the achievement of my current position.

Arboviruses and Muscle Disorders: From Disease to Cell Biology

Infections due to arboviruses (arthropod-borne viruses) have dramatically increased worldwide during the last few years. In humans, symptoms associated with acute infection of most arboviruses are often described as "dengue-like syndrome", including fever, rash, conjunctivitis, arthralgia, and muscular symptoms such as myalgia, myositis, or rhabdomyolysis. In some cases, muscular symptoms may persist over months, especially following flavivirus and alphavirus infections. However, in humans the cellular targets of infection in muscle have been rarely identified. Animal models provide insights to elucidate pathological mechanisms through studying viral tropism, viral-induced inflammation, or potential viral persistence in the muscle compartment. The tropism of arboviruses for muscle cells as well as the viral-induced cytopathic effect and cellular alterations can be confirmed in vitro using cellular models. This review describes the link between muscle alterations and arbovirus infection, and the underlying mechanisms.

The role of viral infections in the development of autoimmune diseases

The exact aetiology of most autoimmune diseases remains unknown, nonetheless, several factors contributing to the induction or exacerbation of autoimmune reactions have been suggested. These include the genetic profile and lifestyle of the affected individual in addition to environmental triggers such as bacterial, parasitic, fungal and viral infections. Infections caused by viruses usually trigger a potent immune response that is necessary for the containment of the infection; however, in some cases, a failure in the regulation of this immune response may lead to harmful immune reactions directed against the host's antigens. The autoimmune attack can be carried out by different arms and components of the immune system and through different possible mechanisms including molecular mimicry, bystander activation, and epitope spreading among others. In this review, we examine the data available for the involvement of viral infections in triggering or exacerbating autoimmune diseases in addition to discussing the mechanisms by which these viral infections and the immune pathways they trigger possibly contribute to the development of autoimmunity.

Longitudinally extensive transverse myelitis in a patient infected with West Nile virus

Until now, longitudinally extensive transverse myelitis (LETM) was reported in association with various viral infections. We describe the case in which a diagnosis of LETM was established as a clinical manifestation of West Nile virus (WNV) infection. We report a 39-year old man with WNV infection and LETM. In neurological examination, there was a left periscapular hypotrophy, moderate weakness of left arm, decreased left brachioradialis reflex, tandem instability and gait ataxia. Cervical spine MRI showed enhancing intramedullary lesion extending from C3-C7 level. According to the neurological, EMG and MRI findings, a diagnosis of LETM, with affection of anterior horn cells of the cervical spinal cord, induced by WNV infection was established. The patient was treated with antibiotics, acyclovir and high dose-steroids, methylprednisolone (MP) 1 g/daily in intravenous infusion, for 5 consecutive days, followed by tapering doses of prednisone during the next four months. Six weeks after onset of symptoms, previously described lesion on cervical spine MRI resolved, and the patient gradually clinically improved.

Immune and myodegenerative pathomechanisms in inclusion body myositis

Inclusion Body Myositis (IBM) is a relatively common acquired inflammatory myopathy in patients above 50 years of age. Pathological hallmarks of IBM are intramyofiber protein inclusions and endomysial inflammation, indicating that both myodegenerative and inflammatory mechanisms contribute to its pathogenesis. Impaired protein degradation by the autophagic machinery, which regulates innate and adaptive immune responses, in skeletal muscle fibers has recently been identified as a potential key pathomechanism in IBM. Immunotherapies, which are successfully used for treating other inflammatory myopathies lack efficacy in IBM and so far no effective treatment is available. Thus, a better understanding of the mechanistic pathways underlying progressive muscle weakness and atrophy in IBM is crucial in identifying novel promising targets for therapeutic intervention. Here, we discuss recent insights into the pathomechanistic network of mutually dependent inflammatory and degenerative events during IBM.

Antiviral macrophage responses in flavivirus encephalitis

Mosquito-borne flaviviruses are a major current and emerging threat, affecting millions of people worldwide. Global climate change, combined with increasing proximity of humans to animals and mosquito vectors by expansion into natural habitats, coupled with the increase in international travel, have resulted in significant spread and concomitant increase in the incidence of infection and severe disease. Although neuroinvasive disease has been well described for some viral infections such as Japanese Encephalitis virus (JEV) and West Nile virus (WNV), others such as dengue virus (DENV) have recently displayed an emerging pattern of neuroinvasive disease, distinct from the previously observed, systemically-induced encephalomyelopathy. In this setting, the immune response is a crucial component of host defence, in preventing viral dissemination and invasion of the central nervous system (CNS). However, subversion of the anti-viral activities of macrophages by flaviviruses can facilitate viral replication and spread, enhancing the intensity of immune responses, leading to severe immune-mediated disease which may be further exacerbated during the subsequent infection with some flaviviruses. Furthermore, in the CNS myeloid cells may be responsible for inducing specific inflammatory changes, which can lead to significant pathological damage during encephalitis. The interaction of virus and cells of the myeloid lineage is complex, and this interaction is likely responsible at least in part, for crucial differences between viral clearance and pathology. Recent studies on the role of myeloid cells in innate immunity and viral control, and the mechanisms of evasion and subversion used by flaviviruses are rapidly advancing our understanding of the immunopathological mechanisms involved in flavivirus encephalitis and will lead to the development of therapeutic strategies previously not considered.

Neuromuscular manifestations of west nile virus infection

The most common neuromuscular manifestation of West Nile virus (WNV) infection is a poliomyelitis syndrome with asymmetric paralysis variably involving one (monoparesis) to four limbs (quadriparesis), with or without brainstem involvement and respiratory failure. This syndrome of acute flaccid paralysis may occur without overt fever or meningoencephalitis. Although involvement of anterior horn cells in the spinal cord and motor neurons in the brainstem are the major sites of pathology responsible for neuromuscular signs, inflammation also may involve skeletal or cardiac muscle (myositis, myocarditis), motor axons (polyradiculitis), and peripheral nerves [Guillain–Barré syndrome (GBS), brachial plexopathy]. In addition, involvement of spinal sympathetic neurons and ganglia provides an explanation for autonomic instability seen in some patients. Many patients also experience prolonged subjective generalized weakness and disabling fatigue. Despite recent evidence that WNV may persist long-term in the central nervous system or periphery in animals, the evidence in humans is controversial. WNV persistence would be of great concern in immunosuppressed patients or in those with prolonged or recurrent symptoms. Support for the contention that WNV can lead to autoimmune disease arises from reports of patients presenting with various neuromuscular diseases that presumably involve autoimmune mechanisms (GBS, other demyelinating neuropathies, myasthenia gravis, brachial plexopathies, stiff-person syndrome, and delayed or recurrent symptoms). Although there is no specific treatment or vaccine currently approved in humans, and the standard remains supportive care, drugs that can alter the cascade of immunobiochemical events leading to neuronal death may be potentially useful (high-dose corticosteroids, interferon preparations, and intravenous immune globulin containing WNV-specific antibodies). Human experience with these agents seems promising based on anecdotal reports.

Inclusion body myositis: laser microdissection reveals differential up-regulation of IFN-γ signaling cascade in attacked versus nonattacked myofibers

Sporadic inclusion body myositis (IBM) is a muscle disease with two separate pathogenic components, degeneration and inflammation. Typically, nonnecrotic myofibers are focally surrounded and invaded by CD8(+) T cells and macrophages. Both attacked and nonattacked myofibers express high levels of human leukocyte antigen class I (HLA-I) molecules, a prerequisite for antigen presentation to CD8(+) T cells. However, only a subgroup of HLA-I(+) myofibers is attacked by immune cells. By using IHC, we classified myofibers from five patients with sporadic IBM as attacked (A(IBM)) or nonattacked (N(IBM)) and isolated the intracellular contents of myofibers separately by laser microdissection. For comparison, we isolated myofibers from control persons (H(CTRL)). The samples were analyzed by microarray hybridization and quantitative PCR. HLA-I up-regulation was observed in A(IBM) and N(IBM), whereas H(CTRL) were negative for HLA-I. In contrast, the inducible chain of the interferon (IFN) γ receptor (IFNGR2) and several IFN-γ-induced genes were up-regulated in A(IBM) compared with N(IBM) and H(CTRL) fibers. Confocal microscopy confirmed segmental IFNGR2 up-regulation on the membranes of A(IBM), which positively correlated with the number of adjacent CD8(+) T cells. Thus, the differential up-regulation of the IFN-γ signaling cascade observed in the attacked fibers is related to local inflammation, whereas the ubiquitous HLA-I expression on IBM muscle fibers does not require IFNGR expression.

Immunopathology of flavivirus infections

With the recent emergence of the flavivirus, West Nile virus (WNV), in particular, the New York strain of Lineage I WNV in North America in 1999, there has been a significant increase in activity in neurotropic flavivirus research. These viruses cause encephalitis that can result in permanent neurological sequelae or death. Attempts to develop vaccines have made progress, but have been variably successful, despite considerable commercial underwriting. Thus, the discovery of ways and means to combat disease is no less urgent. As such, most recent work has been directed towards dissecting and understanding the pathogenesis of disease, as a way of informing possible approaches to abrogation or amelioration of illness. Whether inherent to flaviviruses or because humans are incidental, dead-end hosts, it is clear that these viruses interact with their human hosts in extremely complex ways. This occurs from the cellular level, at which infection must be established to produce disease, to its interaction with the adaptive immune response, which may result in its eradication, with or without immunopathological and consequent neurological sequelae. As human proximity to and contact with flavivirus insect vectors and amplifying hosts cannot practically be eliminated, our understanding of the pathogenesis of flavivirus-induced diseases, especially with regard to possible targets for treatment, is imperative.

Rhabdomyolysis in patients with west nile encephalitis and meningitis

Since 1999, more than 6,500 cases of West Nile virus neuroinvasive disease (WNND) have been reported in the United States. Patients with WNND can present with muscle weakness that is often assumed to be of neurological origin. During 2002, nearly 3,000 persons with WNV meningitis or encephalitis (or both) were reported in the United States; in suburban Cook County, Illinois, with 244 persons were hospitalized for WNV illnesses. The objective of this investigation was to describe the clinical and epidemiological features of identified cases of WNV neuroinvasive disease and rhabdomyolysis. Public health officials investigated patients hospitalized in Cook County, and identified a subset of WNV neuroinvasive disease patients with elevated creatine kinase levels. Cases were defined as hospitalized persons with a WNV infection, encephalitis or meningitis, and rhabdomyolysis. Retrospective medical record reviews were conducted and data was abstracted with a standardized data collection instrument. Eight patients with West Nile encephalitis and one with West Nile meningitis were identified with rhabdomyolysis. Median age of the nine patients was 70 years (range, 45-85 years), and eight were men. For all nine patients, the peak CK level was documented a median of 2 days after hospitalization (range, 1-24 days). Median CK level during hospitalization for all case-patients was 3,037 IU (range, 1,153-42,113 IU). Six patients had history of recent falls prior to admission. Although the temporal relationship of rhabdomyolysis and neurological WNV illness suggested a common etiology, these patients presented with complex clinical conditions which may have led to development of rhabdomyolysis from other causes. The spectrum of WNV disease requires further investigation to describe this and other clinical conditions associated with WNV infection.

Neuromuscular Manifestations of Human West Nile Virus Infection

Physicians in areas with active West Nile virus (WNV) transmission should be aware that WNV infection can present as a polio-like syndrome and that the spectrum of neuromuscular signs and symptoms may range from acute flaccid paralysis in the absence of fever or meningoencephalitis to subjective weakness and disabling fatigue. This awareness will help to avoid less tenable diagnoses and the morbidity associated with inappropriate treatment. Although anterior horns are the major site of spinal cord pathology, inflammatory changes also may involve spinal sympathetic neurons and ganglia, providing an explanation for the autonomic instability seen in some patients with WNV infection. However, the role that autonomic dysfunction plays in the morbidity and mortality of human WNV infection has to be elucidated. Another unresolved issue with important neuromuscular implications is whether WNV infection may lead to autoimmune disease. Support for this contention arises from reports of WNV patients presenting with various neuromuscular diseases that have a presumed autoimmune mechanism, including Guillain-Barre syndrome, other demyelinating neuropathies, myasthenia gravis, brachial plexopathies, and stiff-person syndrome. Although there is no specific treatment or vaccine currently approved for WNV infection in humans, and the standard is supportive care only, several drugs that can alter the cascade of immunobiochemical events leading to neuronal death may be potentially useful. Among these agents, minocycline (a semisynthetic derivative of tetracycline), interferon alpha, and high-dose corticosteroids are candidate therapies, although human experience is limited. In addition, passive immunization with intravenous immune globulin containing WNV-specific antibodies seems promising, based on anecdotal human reports.

West Nile virus encephalitis with myositis and orchitis

This report documents the hospital course and autopsy findings of a 43-year-old man with a renal allograft who died of West Nile virus (WNV) encephalitis. Central nervous system (CNS) findings were those of severe necrotizing and hemorrhagic encephalitis affecting gray matter regions limited to the diencepahlon, rhombencephalon, spinal cord, and limbic system. The bilateral process exhibited preferential involvement of motor neurons. Brain imaging obtained 6 days before death demonstrated an unusual pattern of involvement corresponding with the autopsy findings, confirming that imaging may be a specific diagnostic guide in WNV encephalitis. Extra-CNS findings include myositis with T-lymphocyte infiltration of nerve fibers, suggesting that the virus may reach the CNS via peripheral nerves. Orchitis with dense T-lymphocyte infiltration and syncytial cell formation thought to be due to WNV were also noted.

Manipulation of cell surface macromolecules by flaviviruses

Cell surface macromolecules play a crucial role in the biology and pathobiology of flaviviruses, both as receptors for virus entry and as signaling molecules for cell–cell interactions in the processes of vascular permeability and inflammation. This review examines the cell tropism and pathogenesis of flaviviruses from the standpoint of cell surface molecules, which have been implicated as receptors in both virus–cell as well as cell–cell interactions. The emerging picture is one that encompasses extensive regulation and interplay among the invading virus, viral immune complexes, Fc receptors, major histocompatibility complex antigens, and adhesion molecules.

Immune modulation by flaviviruses

Flaviviruses cause pleomorphic disease with significant morbidity and mortality worldwide. Interestingly, in contrast to most viruses, which subvert or avoid host immune systems, members of the neurotropic Japanese encephalitis serocomplex cause functional changes associated with increased efficacy of the immune response. These viruses induce increased cell surface expression of immune recognition molecules, including class I and II major histocompatibility complex (MHC) and various adhesion molecules. Increases are functional: infected cells are significantly more susceptible to both virus- and MHC-specific cytotoxic T cell lysis. Induced changes are modulated positively or negatively by Th1 and Th2 cytokines, as well as by cell cycle position and adherence status at infection. Infection also increases costimulatory molecule expression on Langerhans cells in the skin. Local interleukin-1 beta production causes accelerated migration of phenotypically altered Langerhans cells to local draining lymph nodes, where initiation of antiviral immune responses occur. The exact mechanism(s) of upregulation is unclear, but changes are associated with NF-kappa B activation and increased MHC and ICAM-1 gene transcription, independently of interferon (IFN) or other proinflammatory cytokines. Increased MHC and adhesion molecule expression may contribute to the pathogenesis of flavivirus encephalitis. Results from a murine model of flavivirus encephalitis developed in this laboratory suggest that fatal disease is immunopathological in nature, with IFN-gamma playing a crucial role. We hypothesize that these viruses may decoy the adaptive immune system into generating low-affinity T cells, which clear virus poorly, as part of their survival strategy. This may enable viral growth and immune escape in cycling cells, which do not significantly upregulate cell surface molecules.

Interaction of flaviviruses with cells of the vertebrate host and decoy of the immune response

Flaviviruses cause endemic and epidemic disease with significant morbidity and mortality throughout the world. In contrast to viruses that avoid the host immune response by down-regulating cell surface major histocompatibility complex expression, infection by members of the neurotropic Japanese encephalitis serogroup induce virus-directed functional increases in expression of class I and II major histocompatibility complex and various adhesion molecules, resulting in increased susceptibility to both virus- and major histocompatibility complex-specific cytotoxic T lymphocyte lysis. These changes are comodulated by T1 and T2 cytokines, as well as by cell cycle position and adherence status at infection. Infected skin dendritic (Langerhans) cells also show increased costimulatory molecule expression and local interleukin-1beta production causes accelerated migration of Langerhans cells to local draining lymph nodes, where initiation of antiviral immune responses occur. The exact mechanism(s) of up-regulation is unclear, but changes are associated with NF-kappaB activation and increased MHC and ICAM-1 gene transcription, independently of interferon or other pro-inflammatory cytokines. We hypothesize that these viruses may decoy the adaptive immune system into generating low-affinity, self-reactive T cells which clear virus poorly, as part of their survival strategy. This may enable viral growth and immune escape in cycling cells, which do not significantly up-regulate cell surface molecules. A possible side-effect of this might be immunopathology, caused by 'autoimmune' cross-reactive damage of uninfected high major histocompatibility complex and adhesion molecule-expressing cells, with consequent exacerbation of encephalitic disease. Results from a murine model of flavivirus encephalitis developed in this laboratory further suggest that interferon-gamma plays a crucial role in fatal immunopathology.

MHC class I up-regulation by flaviviruses: Immune interaction with unknown advantage to host or pathogen

In contrast to many other viruses that escape from cytotoxic T cell recognition by down-regulating major histocompatibility complex class I-restricted antigen presentation, flavivirus infection of mammalian cells up-regulates cell surface expression of major histocompatibility complex class I molecules. Two putative mechanisms for flavivirus-induced major histocompatibility complex class I up-regulation, one via activation of the transcription factor NF-kappaB, the second by augmentation of peptide import into the lumen of the endoplasmic reticulum, are reviewed, and the biological effect of the flavivirus-mediated phenomenon on target cell recognition by natural killer and cytotoxic T cells is addressed. Finally, we speculate on the physiological role of flavivirus-mediated modulation of major histocompatibility complex class I antigen presentation in the context of the biology of flavivirus transmission between the vertebrate host and arthropod vector and suggest that it may represent a strategy for immune evasion from the natural killer cell response or, alternatively, that up-regulation of major histocompatibility complex class I is a by-product of flavivirus replication without significance for virus growth.

Regulation of immune recognition molecules by flavivirus, West Nile

We have shown the flaviviruses can up-regulate the cell surface expression of the immune recognition molecules, major histocompatability complex class-I and class-II (MHC-I, MHC-II), ICAM-1, VCAM, and E-selectin, in an interferon-independent and tumor necrosis factor-independent manner. This up-regulation is associated with an increased transcription of the relevant genes and is due to activation of the transcription factor, nuclear factor-kappa B. The level of up-regulation is determined in part by the cell cycle position of the cell when infected with the flavivirus, as quiescent cells show a greater increase in the level of expression of the immune recognition molecules, MHC-I and ICAM-1, than cells in other phases of the cell cycle. The resultant increased cell surface expression is functional with the increased expression resulting in increased recognition by flavivirus-specific and allo-specific cytotoxic T cells.

Transfection of single-stranded hepatitis A virus RNA activates MHC class I pathway

Although infection of single-stranded RNA viruses can enhance expression of major histocompatibility complex (MHC) class I genes, the mechanism underlying this process remains unclear. Recent studies have indicated that exposure of non-immune cells to double-stranded deoxyribonucleic acid (DNA) or ribonucleic acid (RNA) of viral origin can directly increase the expression of MHC class I and related molecules without immune cell interaction. In this report, we show that transfection of single-stranded hepatitis A virus RNA into cultured hepatocytes results in the induction of genes for MHC class I, LMP2 and transporter for antigen processing (TAP1), in addition to the generation of viral proteins. We suggest that this stimulatory effect is due to the double-stranded RNA formed during replication of single-stranded viral RNA, and involves both double-stranded, RNA-dependent protein kinase PKR and the secretion of IFNbeta.

Early E-selectin, VCAM-1, ICAM-1, and late major histocompatibility complex antigen induction on human endothelial cells by flavivirus and comodulation of adhesion molecule expression by immune cytokines

Expression of E-selectin (ELAM-1, CD62E) on human umbilical vein endothelial cells significantly increased 30 min postinfection with the flavivirus West Nile virus (WNV), was maximal by 2 h postinfection, and declined to baseline levels within 24 h. Expression of ICAM-1 (CD54) and VCAM-1 (CD106) was significantly increased by 2 h and maximal at 4 h after infection. P-selectin (CD62P) expression was unaffected by WNV. Upregulation occurred earlier than that caused by tumor necrosis factor alpha (TNF-alpha) or interleukin 1 (IL-1) and could not be inhibited by neutralizing TNF-alpha, IL-1alpha, or alpha/beta interferon (IFN-alpha/beta) antibodies, suggesting a direct, virus-mediated phenomenon. TNF-alpha significantly enhanced WNV-induced increases in E-selectin, P-selectin, ICAM-1, and VCAM-1 expression, while IFN-gamma enhanced WNV-induced ICAM-1 expression. In contrast, IL-4 abrogated WNV-induced E-selectin expression increases but acted in synergy with WNV to increase P-selectin and VCAM-1 expression. WNV increased the expression of class I and II major histocompatibility complex antigens (MHC-I and MHC-II, respectively) at 24 and 72 h, respectively. IFN-gamma, TNF-alpha, or IL-1 acted in synergy with WNV to produce greater increases in MHC-I expression than WNV or cytokines alone, while IFN-alpha/beta or IL-4 had no effect. MHC-II induction in cytokine-treated, WNV-infected cells was similar to that caused by cytokines alone. Neutralizing IFN-alpha/beta antibody inhibited WNV-induced MHC-I expression by 30% at 24 h and by 100% by 72 h. The differential kinetics of modulation suggest sequential adhesion of leukocyte subpopulations to infected endothelial cells, which may be important in initial viral spread in vivo.

Genetic determinants of susceptibility to coxsackievirus B1-induced chronic inflammatory myopathy: effects of host background and major histocompatibility complex genes

Infection of outbred CD-1 mice with the Tucson strain of coxsackievirus B1 (CVB1T) leads to the development of chronic hind limb weakness and associated inflammatory muscle disease. Host factors that influence susceptibility have not been studied in this mouse model of chronic inflammatory myopathy (IM). Therefore, the pathogenesis was examined by using different inbred strains of mice. Initially, seven strains of mice with either the H-2d or H-2b major histocompatibility complex (MHC) haplotype were evaluated. All strains showed similar levels of acute mortality caused by viral infection, but chronic weakness or inflammation did not develop in two strains with the B6 background, regardless of their MHC haplotype. In susceptible mice, weakness was more likely to develop in the H-2d strains than in mice with the H-2b haplotype. Based on these results, H-2 congenic strains of the susceptible B10 background (C57BL/10 and B10.D2) and the resistant B6 background (C57BL/6 and B6.C-H2d) were examined in greater detail. During acute infection, the kinetics and degree of viral replication in hind limb muscle were similar among B6 and B10 strains. By 4 weeks after infection, more intense chronic muscle inflammation and pathology were observed in susceptible B10 mice of the H-2d haplotype than in those of the H-2b haplotype. Resistant B6 mice did not show signs of inflammation or calcification, but they did exhibit some myopathic features, including centralized nuclei and variations in myofiber size and shape. These changes were less common in resistant B6 mice than in B10 strains but were significant when compared with changes in uninfected controls. Viral RNA persistence and elevated titers of antiviral IgG were more prevalent in but not restricted to susceptible strains. These studies demonstrate that host background genes confer resistance to chronic IM but also that MHC genes influence disease severity. They also reveal that susceptibility to acute CVB1T infection is under different genetic control than that which mediates development of chronic post-viral IM.

Flavivirus-induced up-regulation of MHC class I antigens; implications for the induction of CD8+ T-cell-mediated autoimmunity

Infection of a wide variety of cells of human, mouse and other species' origin by flaviviruses such as WNV, YF, Den, MVE, KUN and JE, increases the cell-surface expression of MHC class I. This MHC class I up-regulation is not due to increased MHC class I synthesis per se, but the result of increased peptide availability in the ER for MHC class I assembly. This is most likely due to the interaction of the viral polyprotein with the ER membrane during viral replication. Flavivirus infection can overcome peptide deficiency in TAP-deficient or non-permissive cell lines such as RMA-S and Syrian hamster cells, BHK and NIL-2. The consequence of this increased MHC class I expression manifests itself in reduced susceptibility to NK cells and augmented lysis by Tc cells. In mice, long-term flavivirus-immune Tc cell memory formation is impaired, following the appearance of strong anti-self Tc cell reactivity observed in in vitro cultures from splenocytes of flavivirus-primed animals. We hypothesize that flavivirus-induced MHC class I up-regulation leads to transient T-cell autoimmunity, followed by down-regulation of both autoimmunity and virus-specific Tc cell memory. Furthermore, we speculate that flavivirus infections of humans in the tropics may be responsible for the observed lower incidence of overt autoimmunity in these geographic regions than in temperate climates where flaviviruses are not endemic.

Antigen processing and presentation by a murine myoblast cell line

The ability of non-professional antigen-presenting cells (APC) to process and present antigen to the immune system has been the subject of debate in autoimmunity and tumour immunology. The role of muscle cells in the processing and presentation of antigen to T cells via class I and class II MHC pathways is of increasing interest. Muscle cells are the targets of autoimmune attack in the inflammatory muscle diseases, and direct intramuscular injection of antigen-expressing DNA constructs is under scrutiny as a means of vaccination. Furthermore, the immunological properties of muscle cells are of relevance in attempts to transfer myoblasts as replacement cells in dystrophic diseases or as depot cells for the secretion of certain molecules in deficiency states. Using class I and class II MHC transfectant clones of the C2C12 myoblast cell line, myoblasts have been shown to be capable of presenting antigen to, and stimulating secretion of IL-2 by, T cell hybridomas via both of these pathways. The epitopes which are dominantly presented by professional APC after processing of native antigens were also presented by the myoblast cell line after processing of either ovalbumin (class I) or hen egg lysozyme (class II). Further, antigen processing and presentation via the class II pathway were enhanced by pretreatment of the myoblasts with interferon-gamma (IFN-gamma). Up-regulation of invariant chain expression by this treatment may have contributed to this enhanced presentation, but an effect of IFN-gamma on the expression of other molecules such as H-2 DM may have also played a role. The demonstration of the antigen-presenting properties of these myoblasts is of relevance to all three areas mentioned above. In each situation myoblasts comprise a significant population within muscle. In the case of inflammatory muscle diseases the process of muscle degeneration and regeneration is on-going, while in the vaccination procedure some muscle damage occurs, and vaccination is more effective when muscle damage has preceded inoculation.

Adherence status regulates the primary cellular activation responses to the flavivirus West Nile

Increases in cell-surface intercellular adhesion molecule-1 (ICAM-1; CD54) and major histocompatibility complex antigen class I (MHC-I) and class II (MHC-II) expression during flavivirus infection of murine macrophages was strongly dependent on adherence status. CD54 and MHC expression was significantly increased during infection with the flavivirus West Nile (WNV) on adherent, but not on non-adherent, macrophages. In contrast, increased CD54 and MHC-I expression was induced by interferon-gamma (IFN-gamma) in both cultures but was significantly greater on adherent cells than non-adherent cells. Adherent status was also important in human embryonic fibroblasts (HEF), adherent cells of non-immune origin. Similar to macrophages, WNV induced increased CD54 or MHC-I expression on adherent but not non-adherent HEF. Again, induction of these antigens by IFN-gamma occurred in both cultures but was significantly greater on adherent cells than non-adherent cells. Macrophages or HEF that aggregated when cultured at high density under non-adherent conditions, responded to WNV and IFN-gamma in a manner similar to adherent cells. Unresponsive non-adherent cells infected with WNV or treated with IFN-gamma under non-adherent conditions for 24 or 48 hr recovered if transferred to adherent culture conditions for 24 or 48 hr. Moreover, these cells expressed significantly higher cell-surface CD54 and MHC-I concentrations, compared to similarly treated HEF cultured under adherent conditions during the entire culture period. WNV infection also induced significant nitric oxide production in macrophages, and adherence status was similarly important in this response, with adherent cells producing higher amounts of nitrite/nitrate than non-adherent cells. These results suggest that adherent status may be critical for effective antiviral immune responses involving macrophages.

CTL recognition of west Nile virus-infected fibroblasts is cell cycle dependent and is associated with virus-induced increases in class I MHC antigen expression

Confluent and non-confluent mouse embryo fibroblast (CMEF and NCMEF) monolayers were infected with West Nile virus (WNV) for 24 hr, and class I major histocompatibility complex antigen (MHC-I) concentrations measured by flow cytometry (FCM). Concentrations on CMEF increased significantly more than on NCMEF. This was not owing to differences in interferon-beta (IFN-beta)-mediated MHC induction, as the IFN-beta quantity secreted by each infected fibroblast was similar in each culture, and IFN-beta-mediated MHC-I induction on NCMEF was greater than on CMEF. Furthermore, despite neutralization of WNV-induced supernatant IFN-beta, CMEF increased MHC-I expression significantly more than NCMEF. Functionally, WNV-infected CMEF were lysed 10-fold better by WNV-specific and allospecific cytotoxic T cells, than infected NCMEF. FCM demonstrated 76% CMEF and 68% NCMEF distributed in G0/G1. This represented G0 in CMEF, and G1 in NCMEF, confirmed by ribonucleotide reductase M1 subunit labelling, where only 20% CMEF was labelled, compared to 84% NCMEF. The possible implications for antiviral immune responses are discussed.

Presentation of endogenous acetylcholine receptor epitope by an MHC class II-transfected human muscle cell line to a specific CD4+ T cell clone from a myasthenia gravis patient

Muscle or thymic myoid cells, if induced to express MHC class II in addition to endogenous acetylcholine receptor (AChR), might present epitopes derived from the AChR to specific CD4+ T cells. These T cells could in turn initiate or maintain the anti-AChR response that is responsible for AChR loss in myasthenia gravis (MG). We transfected the AChR+ TE671 (rhabdomyosarcoma) cells with HLA-DR4 and co-cultured them with the DR4-restricted, CD4+ T cell clone (PM-A1; raised from a hyperplastic thymus of an MG patient and previously shown to recognise all forms of the AChR that contain the sequence alpha 144-156). Significant T cell activation, demonstrated both by 3H-thymidine incorporation and by lysis of the TE671 cells, was found in the presence of added alpha 144-156 and, more importantly, in the absence of exogenous antigen. These results show that MHC class II-expressing muscle or other AChR-expressing cells could present endogenous AChR to pathogenic T cells. This process may be important in the aetiology of MG.

West Nile virus infection induces susceptibility of in vitro outgrown murine blastocysts to specific lysis by paternally directed allo-immune and virus-immune cytotoxic T cells

Day 3 post-coitum BALB/c and (BALB/c x CBA/H)F1 blastocysts were isolated and hatched in replicate wells. Some were treated with interferon-gamma (IFN-gamma). Whilst others were infected with West Nile Virus (WNV) at 100 plaque-forming units per cell, for 18 h. Controls were mock-treated. Gamma-irradiated (2000 rads) CBA/H, (paternal) WNV-specific and allo(CBA/H)-specific cytotoxic T (Tc) cells were then added to replicates of infected, mock-infected or IFN-gamma-treated cultures for 20 h. [3H]Thymidine was then added for a further 8 h. [3H]Thymidine incorporation was inhibited by 40-50% in WNV-infected cultures exposed to WNV-paternal-specific Tc cells and by 30-40% in WNV-infected cultures exposed to allo-paternal-specific Tc cells compared to similarly exposed, uninfected, or unexposed, WNV-infected, or unexposed, uninfected cultures. No significant differences in [3H]thymidine incorporation were found between these controls and IFN-gamma-treated cultures exposed to allo-paternal-specific Tc cells or IFN-gamma-treated cultures not exposed to Tc cells. Parallel exposure of L929 fibroblasts to the same Tc cells irradiated with 500-8000 rads in doubling doses, showed that irradiation did not alter the efficacy or specificity of the Tc cells. Relevance to maternal anti-viral immune responses during implantation is discussed.