Implications of progressive multifocal leukoencephalopathy and JC virus for the etiology of MS

Identification of viral-mediated pathogenic mechanisms in neurodegenerative diseases using network-based approaches

During the course of a viral infection, virus-host protein-protein interactions (PPIs) play a critical role in allowing viruses to replicate and survive within the host. These interspecies molecular interactions can lead to viral-mediated perturbations of the human interactome causing the generation of various complex diseases. Evidences suggest that viral-mediated perturbations are a possible pathogenic etiology in several neurodegenerative diseases (NDs). These diseases are characterized by chronic progressive degeneration of neurons, and current therapeutic approaches provide only mild symptomatic relief; therefore, there is unmet need for the discovery of novel therapeutic interventions. In this paper, we initially review databases and tools that can be utilized to investigate viral-mediated perturbations in complex NDs using network-based analysis by examining the interaction between the ND-related PPI disease networks and the virus-host PPI network. Afterwards, we present our theoretical-driven integrative network-based bioinformatics approach that accounts for pathogen-genes-disease-related PPIs with the aim to identify viral-mediated pathogenic mechanisms focusing in multiple sclerosis (MS) disease. We identified seven high centrality nodes that can act as disease communicator nodes and exert systemic effects in the MS-enriched Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways network. In addition, we identified 12 KEGG pathways, 5 Reactome pathways and 52 Gene Ontology Immune System Processes by which 80 viral proteins from eight viral species might exert viral-mediated pathogenic mechanisms in MS. Finally, our analysis highlighted the Th17 differentiation pathway, a disease communicator node and part of the 12 underlined KEGG pathways, as a key viral-mediated pathogenic mechanism and a possible therapeutic target for MS disease.

Characterization of Jc Virus Dna Amplified from Urine of Chronic Progressive Multiple Sclerosis Patients

Thirty-seven chronic progressive multiple sclerosis (MS) patients, 20 of whom were taking cyclosporine, were examined for excretion of JC virus (JCV) in the urine. Polymerase chain reaction (PCR) amplification of DNA in urinary cell extracts detected JCV in 30% of the MS urines. In the cyclosporine treated group four of 20 (20%) excreted JCV, whereas in the untreated group seven of 17 (41%) excreted JCV. Thus, cyclosporine treatment did not enhance urinary excretion of the virus. A control group consisting of an unselected series of 89 patients donating urine in a general medical clinic and 16 healthy volunteers showed 41% with detectable urinary JCV. Thirty-three percent of the control females excreted JCV (18154), as did 49% of the control males (25151). Although the percentage of MS patients excreting detectable virus was not increased compared to the control group, the presence of JCV in the urine provides or convenient source of the virus for further characterization. Genotyping of DNA fragments amplified from the VPI region indicates mainly the presence of JCV Type 1 in these chronic progressive MS patients. This is also the type that predominates in the control group. An apparent recombinant between Type 1 and Type 3 (African) within the VPI region, tentatively designated Type 113 (or Type 4), was found in both the MS group and the controls. A larger series of MS patients that includes relapsing/remitting disease will be required to determine whether the genotype profile of JCV excreted in the urine of MS patients differs significantly from controls.

The Enigmatic Role of Viruses in Multiple Sclerosis: Molecular Mimicry or Disturbed Immune Surveillance?

Multiple sclerosis (MS) is a T cell driven autoimmune disease of the central nervous system (CNS). Despite its association with Epstein-Barr Virus (EBV), how viral infections promote MS remains unclear. However, there is increasing evidence that the CNS is continuously surveyed by virus-specific T cells, which protect against reactivating neurotropic viruses. Here, we discuss how viral infections could lead to the breakdown of self-tolerance in genetically predisposed individuals, and how the reactivations of viruses in the CNS could induce the recruitment of both autoaggressive and virus-specific T cell subsets, causing relapses and progressive disability. A disturbed immune surveillance in MS would explain several experimental findings, and has important implications for prognosis and therapy.

A huge body of evidence suggests that viral infections promote MS; however, no single causal virus has been identified. Multiple viruses could promote MS via bystander effects.

Molecular mimicry is an established pathogenic mechanism in selected autoimmune diseases. It is also well documented in MS, but its contribution to MS pathogenesis is still unclear.

Bystander activation upon viral infection could be involved in the generation of the autoreactive and potentially encephalitogenic T helper (Th)-1/17 central memory (Th1/17_CM) cells found in the circulation of patients with MS.

Autoreactive Th1/17_CM cells could expand at the cost of antiviral Th1_CM cells in patients with MS, in particular in those undergoing natalizumab therapy, because these cells are expected to compete for the same homeostatic niche.

Autoreactive Th1/17 cells and antiviral Th1 cells are recruited to the CSF of patients with MS following attacks, suggesting that viral reactivations in the CNS induce the recruitment of pathogenic Th1/17 cells. Autoreactive Th1/17 cells in the CNS might also induce de novo viral reactivations in a circuit of self-induced inflammation.

JC Virus Replication at the First Symptoms of Multiple Sclerosis: A Case Report

Multiple sclerosis (MS) is an autoimmune, demyelinating disorder of unknown etiology, in which viruses have been suggested as etiological/triggering agents. The attention to the association between viruses and MS has been rekindled by the development of progressive multifocal leukoencephalopathy in natalizumab-treated MS patients. Here we report the case of a woman with JC virus (JCV) replication in the cerebrospinal fluid, blood and urine collected at the first symptoms of MS and during several follow-up visits. This observation shows that JCV can be associated with MS without a relation with natalizumab treatment, although the triggering role of JCV in some cases of MS will require further studies.

The long and evolving relationship between viruses and multiple sclerosis

Multiple sclerosis (MS) is a demyelinating disorder of unknown etiology, possibly caused by a virus or is virus-triggered. Several viruses, including herpesviruses, were suggested as etiologic agents or risk factors for exacerbation in the course of illness but none have been shown to be irrefutably linked. Recently the interest of researchers and clinicians in the association between viruses and MS was reawakened by the development of progressive multifocal leukoencephalopathy, a demyelinating and fatal disease caused by JC polyomavirus replication, in natalizumab-treated MS patients. In this review, we will illustrate the evidence underlying the viral hypothesis for MS pathogenesis and will review the main features of the potential viral candidates. We will also describe the risks associated with newer MS therapies and with viral/bacterial vaccinations.

JC virus in cerebrospinal fluid samples of multiple sclerosis patients at the first demyelinating event

Objective To evaluate the possible involvement of JC virus (JCV) in the aetiology of multiple sclerosis (MS), through the comparison of DNA prevalences and viral loads of JCV in cerebrospinal fluid (CSF) of MS patients at the first demyelinating event and subjects suffering from other neurological diseases (OND).

Methods Seventy-three CSF samples (43 from MS patients at the first demyelinating event, and 30 from patients with OND) were collected; all MS cases were followed up from 1 to 6.7 years after they were diagnosed with clinically definite MS. DNA was extracted and analysed by real-time PCR for the detection of JCV genomes.

Results We found JCV DNA in the CSF of two MS patients (4.7%) with a mean viral load of 2.1 and 6.7 copies/mL of CSF. Among the patients of the OND group we did not find any positive sample. We did not find any difference in the course of the disease between MS patients with and without JCV genomes in their CSF along the follow up.

Conclusion JCV seems to be only a bystander in the pathology of MS, and the presence of cell-free viral particles could be related to the immunological activation of the disease, mainly during relapses. Multiple Sclerosis 2007; 13: 590-595. http://msj.sagepub.com

Increased prevalence of varicella zoster virus DNA in cerebrospinal fluid from patients with multiple sclerosis

In order to investigate the possible involvement of viruses in Multiple Sclerosis (MS), the study evaluated the presence of viral genomic sequences in cerebrospinal fluid (CSF), as markers of viral replication within the central nervous system (CNS). A total of 85 CSF samples were collected from 38 MS patients, 28 patients with other neurological diseases and 19 subjects without neurological diseases. Using nested-PCR, the investigation focused on the presence of human herpes virus DNA, including herpes simplex virus 1 (HSV-1) and 2 (HSV-2), the Epstein-Barr virus (EBV), varicella zoster virus (VZV), human cytomegalovirus (HCMV), human herpes virus 6 (HHV-6) and JC virus (JCV). All the CSF samples from the individuals without neurological diseases were negative for viral DNA. Genomic sequences of HSV-1, HCMV, EBV, HHV6, and JCV were found in patients with MS and other neurological diseases without significant differences between the two groups. VZV DNA was detected more frequently (P < 0.05) in the MS group (31.6%), particularly among the relapsing-remitting MS patients (43.5%), compared with patients with other neurological diseases (10.7%). In addition, the results indicated that JCV and HHV-6 were replicating actively in the CNS of a small, but significant number of patients with MS and other neurological diseases. Most importantly, the study revealed a high frequency of VZV DNA in the CSF of patients with MS, suggesting a possible role of this virus in the pathogenesis of MS.

Detection of JC virus DNA in cerebrospinal fluid from multiple sclerosis patients

JC virus (JCV), the causative agent of progressive multifocal leukoencephalopathy (PML), has been proposed as a possible aetiopathogenic factor in multiple sclerosis (MS). We performed a study to search the LT region of JCV genome by nested PCR in cerebrospinal fluid (CSF), peripheral blood mononuclear cell (PBMC) and urine samples collected from 121 MS patients, 24 patients with other neurological disorders (OND), 30 non neurological patients (NND) and in PBMCs and urine of 40 healthy subjects. JCV DNA has been found in the CSF of 11 MS patients (9%) while all the CSFs from the 24 OND and the 30 NND cases were negative. No significant differences have been observed as regard to the frequency of JCV DNA detection in PBMCs and urine between the MS patients and the control groups. Nucleotide sequences analysis of seven JCV CSF isolates showed that five strains were identical the prototypal strain, while the other two had a base mutation (T-->C) in 4286 nucleotide (nt). The finding of JCV DNA in the CSF of MS patients suggest that JCV could play a role in the triggering and/or in the maintenance of MS aetiopathogenic process, and therefore it should be taken in consideration when monitoring this disease.

Human T-cell lymphotropic virus tax and Epstein-Barr virus DNA in peripheral blood of multiple sclerosis patients during acute attack

OBJECTIVES

A study was performed to determine whether persistent or latent viruses are reactivated during the acute attack in relapsing remitting multiple sclerosis (MS).

MATERIAL AND METHODS

DNA of herpes simplex virus type 1 and 2 (HSV-1 and -2), human cytomegalovirus (HCMV), Epstein-Barr virus (EBV), JC virus (JCV) and HTLV-I was searched, using nested polymerase chain reaction (PCR), in peripheral blood mononuclear cells (PBMCs) collected from 14 MS patients on the first day and, twice a week, during an acute attack of the disease.

RESULTS

Viral DNA was detected, in at least one PBMC sample, in all the patients. Interestingly, EBV DNA was found in 42.8% of the patients on the first day, while a sharp increase of the HTLV tax-rex DNA frequency (35.7%) was observed on the tenth day.

CONCLUSIONS

In MS relapse EBV DNA detection is an early, frequent event, while the finding of tax-rex, but not of other HTLV-I genomic regions, is a secondary phenomenon, suggesting that these two factors could interact in the pathogenesis of MS relapses.

Progressive multifocal leucoencephalopathy

Progressive multifocal leucoencephalopathy (PML) is a rarely occurring demyelinating disease of the central nervous system caused by a neurotropic papovavirus named JC virus (JCV). The most frequently affected affected regions are the cerebral hemispheres, especially the parietooccipital region, followed by the cerebellum and brain stem. The disease occurs predominantly in individuals with an immunocompromised state and impaired cellular mediated immunity (CMI) due to other underlying illness. More extensive use of irradiation and immunosuppressive therapy in relation to increased transplantational activities as well as treatment of autoimmune diseases and malignancies, in addition to the appearance of the acquired immunodeficiency syndrome (AIDS) as a consequence of infection with the human immunodeficiency virus (HIV), has caused a considerable increase in the occurrence of PML. The course of the disease is still most often rapidly progressive and fatal, but several cases with prolonged survival and even remission have been reported, and various antiviral treatments have been tried. The only drug that until now has shown favourable results is cytosine arabinoside. In HIV-infected PML-patients immunomodulation with AZT/zidovudine may alleviate the course and improve the prognosis in some patients. Suspicion of PML should lead to an extensive immunological investigation before considering of brain biopsy, which is still the only specific test. On the basis of the increased frequency of PML in relation to HIV-infection, it is likely that our knowledge of the pathogenetic aspects will increase, which, hopefully, may lead to an effective therapeutic strategy.

The role of chemical, physical, or viral exposures and health factors in neurocarcinogenesis: implications for epidemiologic studies of brain tumors

This review highlights some future prospects and implications for epidemiologic research on the etiology of nervous system tumors. It reviews some points regarding physiology of the nervous system, in connection with mechanisms of neurocarcinogenesis, and experimental studies in animals. The results of epidemiologic studies are summarized in the light of the biological and experimental observations. The following aspects are particularly emphasized: (i) higher susceptibility of the developing nervous system to neurocarcinogenic agents (in the fetus and after birth); (ii) possible implications of knowledge about mechanisms of neurocarcinogenesis regarding crossing of the blood-brain barrier, activation of oncogenes and inactivation of anti-oncogenes, relationship between chemical structure and neurocarcinogenic action; (iii) necessity of further investigation concerning the occurrence of nitrosoureas and their precursors in the environment, and the potential role of nitroso compounds in the development of human brain tumors; (iv) lack of information about promoting or inhibiting neurocarcinogenic effects, and co-carcinogenesis--among others, interaction between X-irradiation and exposure to neurocarcinogenic nitrosoureas; (v) need for studying the potential neurocarcinogenic risk of polyomaviruses BKV, JCV, and SV40 to humans.

Viruses, virulence and pathogenicity

Pathogenicity is a complex process with stringent requirements of both the host cell and the infecting virion. Among these requirements are a port of entry into host cells, a means of replication for the virus, and a means by which infection damages host cells. Damage to the host can result from multiple mechanisms including transformation, suppression of cellular metabolism, apoptosis, autoimmune responses directed against infected or uninfected tissues, or by molecular mimicry. In the attempt to identify new associations between viral infection and disease, investigators should be mindful that variable host factors as well as viral infection may be required for pathogenesis. Efforts to associate specific viral infections with specific diseases may be obscured by final common pathways through which multiple agents damage host cells in similar ways.

Polyomavirus models of brain infection and the pathogenesis of multiple sclerosis

Multiple sclerosis (MS) is generally considered to be an autoimmune disorder with myelin as the target and with several unidentified viruses playing ancillary roles, possibly through molecular mimicry. Although this paradigm has led to important progress on potential mechanisms of myelin loss, neither a target antigen in myelin nor a triggering mechanism has yet been identified, leaving the etiology of MS still unknown. Animal models of viral demyelination and studies showing that JC virus (JCV), the polyomavirus which causes progressive multifocal leukoencephalopathy (PML), may be latent in some normal human brains suggest another possibility. A host immune response targeting proteins expressed at low levels from viral DNA latent in the central nervous system (CNS) might underlie a focal demyelinating disease such as MS. A shift from autoimmunity to a latent-virus model is not a trivial substitution of target antigens. This shift would expand the search for a definitive laboratory test for MS and could lead to improved therapeutic and preventive approaches.

JC virus and multiple sclerosis: a refutation?

Polyomavirus JC (JCV) has been implicated in the etiology of multiple sclerosis (MS), because it causes progressive multifocal leukoencephalopathy (PML), a multifocal demyelinating disease with many microscopical similarities to MS. During childhood, the virus establishes a latent infection in the kidneys, which can be reactivated in immunocompromised patients. During reactivation, the virus is shed in the urine. The kidney is the only known site of latent infection and reactivation. Therefore, excretion of the virus in the urine of MS patients is to be expected, if reactivated JCV is involved in the etiology of MS. We studied urine samples of 53 patients with definitive MS and of 53 controls matched for age and sex. We found no evidence of active JCV infection in MS. The hypothesis of a polyomaviral etiology of MS is not supported by the results of this study.

Lack of JC viral genomic sequences in multiple sclerosis brain tissue by polymerase chain reaction

With DNA extracted from brain specimens from 19 multiple sclerosis, 5 progressive multifocal leukoencephalopathy, 1 Alzheimer's disease, and 8 nonneurological control subjects, polymerase chain reaction was performed using nested sets of primer pairs amplifying segments of the large T and VP1 antigen-encoding sequences of JC virus. Both sequences were detected in each of the 5 brain specimens of progressive multifocal leukoencephalopathy but in none of the 19 multiple sclerosis, 1 Alzheimer's disease, or the 8 control brain specimens.

Identification of a 58-kDa antigen with increased immunoreactivity in the cerebella of multiple sclerosis patients

An increase in immunoreactivity associated with a 58-kDa antigen was found in a majority of MS cerebellar homogenates examined by Western blot analysis using antisera obtained by selective immunization of rabbits with autopsy cerebella. Two-dimensional immunoblotting demonstrated that the majority of the increased immunoreactivity observed in MS cerebella was associated with the highest apparent pI of three immunoreactive species at 58 kDa. Immuno-crossreaction with rat cerebellar homogenates demonstrated that the 58-kDa antigen was developmentally regulated, showing the greatest immunoreactivity at embryonic day 15. The 58-kDa cerebellar antigen may represent a membrane protein which is re-expressed as part of the onset of MS.

PAb 2000 specifically recognizes the large T and small t proteins of JC virus

A monoclonal antibody, PAb 2000, has been derived which recognizes the large T protein of JC virus (JCV), but not the corresponding proteins of the related polyomaviruses BK virus (BKV) and SV40. The epitope bound by PAb 2000 was localized to the amino-terminal 81 amino acids of this multifunctional protein. As observed previously with several monoclonal antibodies that bind a similar region of SV40 large T antigen, PAb 2000 was found to interact with the small t antigen and the denatured form of large T antigen. This monoclonal antibody recognized a subpopulation of T protein, the abundance of which varied in different species of cells transformed by JCV. The availability of PAb 2000, the first JCV T antigen-specific monoclonal antibody, will facilitate the purification and biochemical characterization of the JCV oncoproteins.