An approach to understanding the mechanisms of poliovirus persistence in infected cells of neural or non-neural origin

Enterovirus and Encephalitis

Enterovirus-induced infection of the central nervous system (CNS) results in acute inflammation of the brain (encephalitis) and constitutes a significant global burden to human health. These viruses are thought to be highly cytolytic, therefore normal brain function could be greatly compromised following enteroviral infection of the CNS. A further layer of complexity is added by evidence showing that some enteroviruses may establish a persistent infection within the CNS and eventually lead to pathogenesis of certain neurodegenerative disorders. Interestingly, enterovirus encephalitis is particularly common among young children, suggesting a potential causal link between the development of the neuroimmune system and enteroviral neuroinvasion. Although the CNS involvement in enterovirus infections is a relatively rare complication, it represents a serious underlying cause of mortality. Here we review a selection of enteroviruses that infect the CNS and discuss recent advances in the characterization of these enteroviruses with regard to their routes of CNS infection, tropism, virulence, and immune responses.

Post-poliomyelitis syndrome as a possible viral disease

This review summarizes current concepts on post-polio syndrome (PPS), a condition that may arise in polio survivors after partial or complete functional recovery followed by a prolonged interval of stable neurological function. PPS affects 15-20 million people worldwide. Epidemiological data are reported, together with the pathogenic pathways that possibly lead to the progressive degeneration and loss of neuromuscular motor units. As a consequence of PPS, polio survivors experience new weakness, generalized fatigue, atrophy of previously unaffected muscles, and a physical decline that may culminate in the loss of independent life. Emphasis is given to the possible pathogenic role of persistent poliovirus infection and chronic inflammation. These factors could contribute to the neurological and physical decline in polio survivors. A perspective is then given on novel anti-poliovirus compounds and monoclonal antibodies that have been developed to contribute to the final phases of polio eradication. These agents could also be useful for the treatment or prevention of PPS. Some of these compounds/antibodies are in early clinical development. Finally, current clinical trials for PPS are reported. In this area, the intravenous infusion of normal human immunoglobulins appears both feasible and promising.

Current understanding of ovarian aging

The reproductive system of human female exhibits a much faster rate of aging than other body systems. Ovarian aging is thought to be dominated by a gradual decreasing numbers of follicles, coinciding with diminished quality of oocytes. Menopause is the final step in the process of ovarian aging. This review focuses on the mechanisms underlying the ovarian aging involving a poor complement of follicles at birth and a high rate of attrition each month, as well as the alternated endocrine factors. We also discuss the possible causative factors that contribute to ovarian aging, e.g., genetic factors, accumulation of irreparable damage of microenvironment, pathological effect and other factors. The appropriate and reliable methods to assess ovarian aging, such as quantification of follicles, endocrine measurement and genetic testing have also been discussed. Increased knowledge of the ovarian aging mechanisms may improve the prevention of premature ovarian failure.

Viral and host factors that contribute to pathogenicity of enterovirus 71

The single-stranded RNA virus enterovirus 71 (EV71), which belongs to the Picornaviridae family, has caused epidemics worldwide, particularly in the Asia–Pacific region. Most EV71 infections result in mild clinical symptoms, including herpangina and hand, foot and mouth disease. However, serious pathological complications have also been reported, especially for young children. The mechanisms of EV71 disease progression remain unclear. The pathogenesis of adverse clinical outcomes may relate to many factors, including cell tropism, cell death and host immune responses. This article reviews the recent advances in the identification of factors determining EV71 cell tropism, the associated mechanisms of viral infection-induced cell death and the interplay between EV71 and immunity.

Persistent infection of human intestinal Caco-2 cell line by Coxsackieviruses B

Coxsackieviruses B (CV-B, Picornaviridae family, genus Enterovirus) are characterized by their ability to cause cytopathic effects in tissue culture. These viruses are considered highly cytolytic, but can establish persistence/latency in susceptible cells, indicating that a regulatory mechanism may exist to shut off viral protein synthesis and replication under certain situations. The persistence of coxsackieviral B RNA is of great interest because of its implication in the pathogenesis of several chronic human diseases. However, a few studies have dealt with the persistence of these viruses at the intestinal level. The aim of this study is to test the capacity of the six CV-B serotypes to establish persistent infection in human intestinal Caco-2 cell line. Ten CV-B isolates, including CV-B3 prototype strain (Nancy) and a recombinant isolate (B3-B4), were tested. Six CV-B isolates were found to establish persistent infections in Caco-2 cell line. Persistent replication was proved by the detection of viral RNA from cell cultures, VP1 capsid protein detection by immunofluorescence (IF) staining, and the release of infectious particles up to two months and a half after infection without any obvious cytolysis. In addition, our results suggest that the establishment of a persistent infection is serotype-independent.

Enterovirus infections of the central nervous system

Enteroviruses (EV) frequently infect the central nervous system (CNS) and induce neurological diseases. Although the CNS is composed of many different cell types, the spectrum of tropism for each EV is considerable. These viruses have the ability to completely shut down host translational machinery and are considered highly cytolytic, thereby causing cytopathic effects. Hence, CNS dysfunction following EV infection of neuronal or glial cells might be expected. Perhaps unexpectedly given their cytolytic nature, EVs may establish a persistent infection within the CNS, and the lasting effects on the host might be significant with unanticipated consequences. This review will describe the clinical aspects of EV-mediated disease, mechanisms of disease, determinants of tropism, immune activation within the CNS, and potential treatment regimes.

Update on current and emerging treatment options for post-polio syndrome

Post-polio syndrome (PPS) refers to the clinical deterioration experienced by many polio survivors several decades after their acute illness. The symptoms are new muscle weakness, decreased muscle endurance, fatigue, muscle pain, joint pain, cold intolerance, and this typical clinical entity is reported from different parts of the world. The pathophysiology behind PPS is not fully understood, but a combination of distal degeneration of enlarged motor units caused by increased metabolic demands and the normal aging process, in addition to inflammatory mechanisms, are thought to be involved. There is no diagnostic test for PPS, and the diagnosis is based on a proper clinical workup where all other possible explanations for the new symptoms are ruled out. The basic principle of management of PPS lies in physical activity, individually tailored training programs, and lifestyle modification. Muscle weakness and muscle pain may be helped with specific training programs, in which training in warm water seems to be particularly helpful. Properly fitted orthoses can improve the biomechanical movement pattern and be energy-saving. Fatigue can be relieved with lifestyle changes, assistive devices, and training programs. Respiratory insufficiency can be controlled with noninvasive respiratory aids including biphasic positive pressure ventilators. Pharmacologic agents like prednisone, amantadine, pyridostigmine, and coenzyme Q10 are of no benefit in PPS. Intravenous immunoglobulin (IVIG) has been tried in three studies, all having positive results. IVIG could probably be a therapeutic alternative, but the potential benefit is modest, and some important questions are still unanswered, in particular to which patients this treatment is useful, the dose, and the therapeutic interval.

Elevated serum inflammatory markers in post-poliomyelitis syndrome

OBJECTIVES

To determine (i) whether serum inflammatory markers TNFalpha, IL-1beta. IL-6, and leptin are increased in post-poliomyelitis syndrome (PPS) compared to healthy controls; and (ii) whether an association exists between elevated inflammatory markers and clinical parameters in PPS. The cause of PPS is unknown, but abnormal inflammatory responses have been implicated in several small studies.

METHODS

Serum inflammatory markers were measured (by Luminex) in 51 PPS patients and 26 normal controls. Clinical parameters assessed included disease duration, muscle strength (Medical Research Council sumscore), fatigue (Fatigue Severity Scale and Multidimensional Fatigue Inventory), and pain (visual analog scale scores).

RESULTS

In PPS, TNFalpha levels, as well as IL-6 and leptin were significantly increased compared to controls (Wilcoxon rank-sum test, p=0.03 for TNFalpha, p=0.03 for IL-6, p=0.01 for leptin). The elevated TNFalpha levels in PPS were associated with increased pain due to illness (Spearman correlation coefficient r=0.36, 95% C.I. 0.09 to 0.57) and specifically, with muscle pain (r=0.38, 95% C.I. 0.11 to 0.59). There were no correlations between inflammatory markers in PPS and joint pain, muscle strength, fatigue, or disease duration.

CONCLUSIONS

Serum TNFalpha, IL-6 and leptin levels are abnormally increased in PPS patients. Elevated TNFalpha levels appear to be specifically associated with increased muscle pain.

Intravenous immunoglobulin for post-polio syndrome: a randomised controlled trial

BACKGROUND

Survivors of poliomyelitis often develop increased or new symptoms decades after the acute infection, known as post-polio syndrome. Production of proinflammatory cytokines within the CNS indicates an underlying inflammatory process, accessible for immunomodulatory treatment. We did a multicentre, randomised, double-blind, placebo-controlled study of intravenous immunoglobulin in post-polio syndrome.

METHODS

142 patients at four university clinics were randomly assigned infusion of either 90 g in total of intravenous immunoglobulin (n=73) or placebo (n=69) during 3 consecutive days, repeated after 3 months. Seven patients were withdrawn from the study. Thus, 135 patients were assessed per protocol. Primary endpoints were muscle strength in a selected study muscle and quality of life as measured with the SF-36 questionnaire (SF-36 PCS). Secondary endpoints were 6-minute walk test (6MWT), timed up and go (TUG), muscle strength in muscles not chosen as the study muscle, physical activity scale of the elderly (PASE), visual analogue scale (VAS) for pain, multidimensional fatigue inventory (MFI-20), balance, and sleep quality. Outcome tests were done immediately before the first infusion and 3 months after the second infusion. This study is registered with , number NCT00160082.

FINDINGS

Compared with baseline, median muscle strength differed by 8.3% between patients receiving intravenous immunoglobulin and placebo, in favour of the treatment group (p=0.029). SF-36 PCS did not differ significantly between the groups after treatment (p=0.321). Differences in the subscale vitality score (p=0.042) and PASE (p=0.018) favoured the active treatment group. MFI-20, TUG, muscle strength in the muscles not chosen as the study muscle, 6MWT, balance, and sleep quality did not differ between groups. For the whole study population there was no significant change in pain, as determined by VAS. Nevertheless, patients who reported pain at the study start improved in the intervention group but not in the placebo group (p=0.037). Intravenous immunoglobulin was well tolerated.

INTERPRETATION

Intravenous immunoglobulin could be a supportive treatment option for subgroups of patients with post-polio syndrome. Further studies on responding subgroups, long-term effects, and dosing schedules are needed.

Establishment and characterization of a novel genetic hybrid cell line for propagation of four pathogens

Chromosomal DNAs were purified from human epidermoid carcinoma (HEP-2) cells and transfected into human embryonic lung (HEL) cells to establish a genetic hybrid cell line susceptible to infections by toxoplasma, rubella virus, cytomegalovirus, and herpes simplex virus. Karyotype analysis showed that the resultant hybrid cells, designated D3, had a chromosome number of 96, which was stable after passage for 100 generations. Direct microscopy and immunofluorescence showed that the D3 cells could be infected by the four pathogens with overt cytopathic effects. The toxoplasma and three viruses were purified from infected D3 cells by sucrose gradient centrifugation and used as the antigens for detection of specific IgG and/or IgM in serum samples from pregnant women with suspicious infections by the four pathogens, the results of which were consistent with those of commercial kits. These data indicate that a stable genetic hybrid cell line has been generated, which is a valuable tool for the isolation of the four intrauterine pathogens and for the preparation of antigens for serological tests.

Failure to detect enterovirus in the spinal cord of ALS patients using a sensitive RT-PCR method

OBJECTIVE

To assess the association of enteroviruses (EV) with ALS by applying a sensitive seminested reverse transcription (RT) PCR protocol to the detection of enteroviral RNA in a blinded set of archived tissues from ALS and control cases.

METHODS

The specimen set consisted of 24 frozen spinal cord samples from ALS cases, 17 frozen spinal cord samples from negative control (non-ALS) cases, and 5 frozen spinal cord positive control samples. The positive controls were two human spinal cord samples spiked with poliovirus (PV) and three spinal cords from PV-infected transgenic mice. A sensitive, EV-specific, seminested RT-PCR assay was used to detect EV genome in RNA extracted from the specimens and controls.

RESULTS

The assay detected EV RNA in a 10(-5) dilution of infected mouse tissue. EV RNA was not detected in the ALS specimens or in specimens from control cases, despite the presence of amplifiable RNA as assessed by amplification with control primers, whereas all of the positive control specimens yielded the expected PV amplification product.

CONCLUSION

The reported association between EV infection and ALS was not confirmed by testing this set of specimens with these sensitive methods.

Restriction of poliovirus RNA replication in persistently infected nerve cells

The aetiology of post-polio syndrome may involve persistence of poliovirus (PV) in the CNS. PV persists in the CNS of infected paralysed mice for over a year after the acute phase of paralytic poliomyelitis. However, infectious PV particles cannot be recovered from homogenates of CNS from paralysed mice after the acute phase of disease, indicating that PV replication is restricted. To identify the molecular mechanism by which PV replication is limited, PV RNA synthesis was analysed by estimating the relative level of genomic (plus-strand) and complementary (minus-strand) PV RNA in the CNS of persistently infected mice. PV RNA replication decreased during the 6 months following onset of paralysis, due mainly to inhibition of plus-strand RNA synthesis. Thus, restriction of PV RNA synthesis may contribute to persistence by limiting virus replication in the mouse CNS. Interestingly, viral RNA replication was similarly inhibited in neuroblastoma IMR-32 cell cultures persistently infected with PV. This in vitro model thus shows that cellular factors play a role in the inhibition of viral RNA synthesis.

Cell cycle status affects coxsackievirus replication, persistence, and reactivation in vitro

Enteroviral persistence has been implicated in the pathogenesis of several chronic human diseases, including dilated cardiomyopathy, insulin-dependent diabetes mellitus, and chronic inflammatory myopathy. However, these viruses are considered highly cytolytic, and it is unclear what mechanisms might permit their long-term survival. Here, we describe the generation of a recombinant coxsackievirus B3 (CVB3) expressing the enhanced green fluorescent protein (eGFP), which we used to mark and track infected cells in vitro. Following exposure of quiescent tissue culture cells to either wild-type CVB3 or eGFP-CVB3, virus production was very limited but increased dramatically after cells were permitted to divide. Studies with cell cycle inhibitors revealed that cells arrested at the G(1) or G(1)/S phase could express high levels of viral polyprotein and produced abundant infectious virus. In contrast, both protein expression and virus yield were markedly reduced in quiescent cells (i.e., cells in G(0)) and in cells blocked at the G(2)/M phase. Following infection with eGFP-CVB3, quiescent cells retained viral RNA for several days in the absence of infectious virus production. Furthermore, RNA extracted from nonproductive quiescent cells was infectious when transfected into dividing cells, indicating that CVB3 appears to be capable of establishing a latent infection in G(0) cells, at least in tissue culture. Finally, wounding of infected quiescent cells resulted in viral protein expression limited to cells in and adjacent to the lesion. We suggest that (i) cell cycle status determines the distribution of CVB3 during acute infection and (ii) the persistence of CVB3 in vivo may rely on infection of quiescent (G(0)) cells incapable of supporting viral replication; a subsequent change in the cell cycle status may lead to virus reactivation, triggering chronic viral and/or immune-mediated pathology in the host.

Laryngeal manifestations of postpoliomyelitis syndrome

Postpoliomyelitis syndrome (PPS) is a disease that may occur in survivors of acute poliomyelitis several decades after their initial infection. It can present as dysphonia, with vocal weakness and fatigue. Swallowing, respiratory, and other laryngopharyngeal symptoms may be manifestations of the disease or they may represent worsening of previously stable and compensated deficits. Three cases of laryngeal changes in PPS with videostroboscopic and laryngeal electromyography findings highlight the features of this disorder. We review possible etiologies of laryngeal PPS, diagnostic criteria, and treatment, as well as the current literature.

Molecular mechanisms of coxsackievirus persistence in chronic inflammatory myopathy: viral RNA persists through formation of a double-stranded complex without associated genomic mutations or evolution

Enterovirus infection and persistence have been implicated in the pathogenesis of certain chronic muscle diseases. In vitro studies suggest that persistent enteroviruses mutate, evolving into forms that are less lytic and display altered tropism, but it is less clear whether these mechanisms operate in vivo. In this study, persistent coxsackievirus RNA from the muscle of mice afflicted with chronic inflammatory myopathy (CIM) was characterized and compared with RNA from a virus that had established a persistent infection of G8 mouse myoblasts for 30 passages in vitro. Competitive strand-specific reverse transcription-PCR and susceptibility to RNase I treatment revealed that plus- and minus-strand viral RNAs were present at nearly equivalent levels in muscle and that they persisted in a double-stranded conformation. All regions of the viral genome persisted and were amplified as a series of seven overlapping fragments. Restriction endonuclease fingerprinting coupled with sequencing indicated that there was no evolution of the viral genome associated with its persistence in muscle. This contrasted with the productive persistent infection that was established in myoblast cultures, where plus-strand RNA predominated and persistent virus developed distinct mutations. In vitro persistence proceeded by a carrier culture mechanism and was completely dependent on production of infectious virus, since persistent viral RNA was not detected in cultures subjected to antibody-mediated curing. These experiments demonstrate that persistence of coxsackievirus RNA in muscle is not facilitated by distinct genetic changes in the virus that give rise to replication-defective forms but occurs primarily through production of stable double-stranded RNA that is produced as the acute viral infection resolves. The data suggest a mechanism for coxsackievirus persistence in myofibers and perhaps other nondividing cells whereby cells that survive infection could harbor persistent viral RNA for extended times without producing detectable levels of infectious virus.