Dual virus etiology of age-dependent poliomyelitis of mice. A potential model for human motor neuron diseases

The human endogenous retrovirus link between genes and environment in multiple sclerosis and in multifactorial diseases associating neuroinflammation

Endogenous retroviruses represent about 8% of the human genome and belong to the superfamily of transposable and retrotransposable genetic elements. Altogether, these mobile genetic elements and their numerous inactivated "junk" sequences represent nearly one half of the human DNA. Nonetheless, a significant part of this "non-conventional" genome has retained potential activity. Epigenetic control is notably involved in silencing most of these genetic elements but certain environmental factors such as viruses are known to dysregulate their expression in susceptible cells. More particularly, embryonal cells with limited gene methylation are most susceptible to uncontrolled activation of these mobile genetic elements by, e.g., viral infections. In particular, certain viruses transactivate promoters from endogenous retroviral family type W (HERV-W). HERV-W RNA was first isolated in circulating viral particles (Multiple Sclerosis-associated RetroViral element, MSRV) that have been associated with the evolution and prognosis of multiple sclerosis. HERV-W elements encode a powerful immunopathogenic envelope protein (ENV) that activates a pro-inflammatory and autoimmune cascade through interaction with Toll-like receptor 4 on immune cells. This ENV protein has repeatedly been detected in MS brain lesions and may be involved in other diseases. Epigenetic factors controlling HERV-W ENV protein expression then reveal critical. This review addresses the gene-environment epigenetic interface of such HERV-W elements and its potential involvement in disease.

Human endogenous retrovirus (HERV)-W ENV and GAG proteins: Physiological expression in human brain and pathophysiological modulation in multiple sclerosis lesions

Antigen expression of a human endogenous retrovirus family, HERV-W, in normal human brain and multiple sclerosis lesions was studied by immunohistochemistry by three independent groups. The HERV-W multicopy family was identified in human DNA from the previously characterized multiple sclerosis-associated retroviral element (MSRV). A panel of antibodies against envelope (ENV) and capsid (GAG) antigens was tested. A physiological expression of GAG proteins in neuronal cells was observed in normal brain, whereas there was a striking accumulation of GAG antigen in axonal structures in demyelinated white matter from patients with MS. Prominent HERV-W GAG expression was also detected in endothelial cells of MS lesions from acute or actively demyelinating cases, a pattern not found in any control. A physiological expression of ENV proteins was detected in microglia in normal brain; however,a specific expression in macrophages was apparently restricted to early MS lesions. Thus, converging results from three groups confirm that GAG and ENV proteins encoded by the HERV-W multicopy gene family are expressed in cells of the central nervous system under normal conditions. Similar to HERV-W7q ENV (Syncitin), which is expressed in placenta and has been shown to have a physiological function in syncytio-trophoblast fusion, HERV-W GAG may thus also have a physiological function in human brain. This expression differs in MS lesions, which may either reflect differential regulation of inherited HERV-W copies, or expression of "infectious" MSRV copies. This is compatible with a pathophysiological role in MS, but also illustrates the ambivalence of such HERV antigens, which can be expressed in cell-specific patterns, under physiological or pathological conditions.

Lactate dehydrogenase-elevating virus induces apoptosis in cultured macrophages and in spinal cords of C58 mice coincident with onset of murine amyotrophic lateral sclerosis

Age-dependent poliomyelitis (ADPM) or murine amyotrophic lateral sclerosis (ALS) is a murine paralytic disease triggered in immunosuppressed genetically-susceptible mice by infection with the arterivirus lactate dehydrogenase-elevating virus (LDV). This disease provides an animal model for ALS, affecting anterior horn neurons and resulting in neuroparalysis 2-3 weeks after LDV infection. We have tested the hypothesis that spinal cord apoptosis is a feature of the LDV-induced murine ALS, since apoptosis is postulated to be a causal factor in human ALS. Gene microarray analyses of spinal cords from paralyzed animals revealed upregulation of several genes associated with apoptosis. Spinal cord apoptosis was investigated further by TUNEL and activated caspase-3 assays, and was observed to emerge concurrent with paralytic symptoms in both neuronal and non-neuronal cells. Caspase-3-dependent apoptosis was also triggered in cultured macrophages by neurovirulent LDV infection. Thus, virus-induced spinal cord apoptosis is a pre-mortem feature of ADPM, which affects both neuronal and support cells, and may contribute to the pathogenesis of this ALS-like disease.

Multiple sclerosis retrovirus particles and recombinant envelope trigger an abnormal immune response in vitro, by inducing polyclonal Vbeta16 T-lymphocyte activation

A retroviral element (MSRV) defining a family of genetically inherited endogenous retroviruses (HERV-W) has recently been characterized in cell cultures from patients with multiple sclerosis (MS). To address the possible relationship with MS, direct detection of circulating virion RNA was proposed but revealed technically difficult to perform in standardized conditions, in the face of multiple endogenous HERV-W copies. A parallel approach has evaluated MSRV potential pathogenicity in relation to characteristic features of multiple sclerosis, in particular, T-lymphocyte-mediated immunopathology. We report here that MSRV particles induce T-lymphocyte response with a bias in the Vbeta16 chain usage in surface receptor, whatever the HLA DR of the donor. A recombinant MSRV envelope-but not core-protein reproduced similar nonconventional activation. Molecular analysis of Vbeta CDR3 showed that Vbeta16 expansions are polyclonal. Our results thus provide evidence that MSRV envelope protein can trigger an abnormal immune response with similar characteristics to that of superantigens.

Inhibition of virus-induced age-dependent poliomyelitis by interferon-gamma

Age-dependent poliomyelitis (ADPM) is a neuroparolytic disease which results from combined infection of susceptible mice with lactate dehydrogenase-elevating virus (LDV) and murine leukemia virus (MuLV). The present study examined the effects of interferon-gamma (IFN-gamma) treatment on the incidence of ADPM, replication of LDV and MuLV and anti-LDV immunity. IFN-gamma treatment of ADPM-susceptible C58/M mice protected them from paralytic disease, but had no detectable effect on the IgG anti-LDV response or LDV viremia. IFN-gamma-mediated protection from ADPM correlated with reduced expression of LDV RNA, but not MuLV RNA, in the spinal cords of C58/M mice. These results confirm that spinal cord LDV replication is the determinant of ADPM and demonstrate that cytokine-mediated inhibition of LDV replication in the central nervous system prevents neuroparalytic disease.

Retroviral synthetic peptide serum antibodies in human sporadic amyotrophic lateral sclerosis

We examined 101 sera from 32 adult sporadic amyotrophic lateral sclerosis (ALS) patients, including nine with positive enzyme-linked immunosorbent assay (ELISA) serum antibodies against human spuma retrovirus (HSRV) [human foamy virus (HFV)] envelope (env) and/or capsid (gag) proteins, for peptide seroreactivity. Synthetic peptides 10 to 14 amino acids in length were selected from HSRV (3), maedi-visna virus (1), human nerve growth factor-beta (1), and human amyloid-beta sequences (1). Eighteen of 101 ALS sera compared with six of 144 control sera reacted to any of the sequences (p < 0.01) (i.e., 8/32 ALS patients and 2/93 control patients bound to a synthetic peptide, p < 0.01). Peptide VLA- [NGF beta(1-14)] was reproducibly recognized by one of the 93 neurologic controls, and one of the 32 ALS patients reproducibly reacted to synthetic peptides [EET-, HSRVenv/NGF beta(55-61)] and [GSN-, beta-amyloid(25-35)] simultaneously. This amyloid-A(25-35) peptide corresponds to the neurotoxic and neurotrophic tachykinin homology sequence described by Yanker. Only ALS patients (no controls) reacted with the visna/CNTF peptide SMC- and HSRVbcl-1/amyloid(740-751) peptide EGP-. Testing a total of 245 sera from 125 patients, three reproducible reactivities (two ALS, one OND) were observed both with and without glutaraldehyde linkage. Of the four peptides recognized either by more than one serum from the same patient with ALS or by sera from ALS patients only (EET-, GSN-, SMC-, EGP-), two share a circumscript homology with maedi-visna virus envelope glycoprotein (Table 1).(ABSTRACT TRUNCATED AT 250 WORDS)

Do endogenous retroviruses have etiological implications in inflammatory and degenerative nervous system diseases?

Vertebrates carry large numbers of endogenous retroviruses (ERVs) and related sequences in their genomes. These retroviral elements are inherited as Mendelian traits. Generally, ERVs are defective without the ability of being expressed as viral particles. However, ERV sequences often have a potential for expression of at least some proteins. So far, the possible biological significance of ERVs is not clear. Nonetheless, there are observations suggesting a connection between ERVs and various diseases. This is the case with murine lupus and a spinal cord disease of certain mouse strains. In the present review, we discuss possible mechanisms by which ERVs could contribute to the development of human degenerative and inflammatory nervous system diseases, including direct effects on nervous system cells and immune cells. Interactions between ERVs and infectious viruses are also discussed. Finally, we review a possible retroviral etiology of multiple sclerosis.

Lactate dehydrogenase-elevating virus (LDV): subgenomic mRNAs, mRNA leader and comparison of 3'-terminal sequences of two LDV isolates

The 3'-terminal 1314 nucleotides of the genome of one isolate of lactate dehydrogenase-elevating virus, LDV-P, has been derived by sequence analyses of cDNAs from several genomic libraries and compared to that of another LDV isolate, LDV-C (Godeny et al. (1990) Virol. 177, 768-771). The 3'-non-coding segment of 80 nucleotides of the two LDV genomes is identical, whereas marked, but varying nucleotide and amino acid divergence is apparent in the three upstream overlapping open reading frames (ORF). The third ORF from the 3'-end exhibits only 82% nucleotide and 90% amino acid identity, whereas the 3'-terminal ORF, which encodes the nucleocapsid protein, exhibits approximately 99% amino acid identity. The second 3'-terminal ORF encodes an 18.8 kDa protein which lacks N-glycosylation sites but possesses 2 or 3 potential transmembrane helices in the N-terminal half of the molecule. A similar membrane organization is observed for the corresponding protein of equine arteritis virus and the M protein of mouse hepatitis virus. The sequence analyses combined with Northern hybridization analyses of RNA from LDV-infected macrophages and spleens of LDV-infected mice indicate that the three ORFs encoded by the 3'-terminal end of the LDV genome are expressed via the three smallest mRNAs (mRNAs 6-8) of the seven subgenomic mRNAs of LDV (mRNAs 2-8), which range in size from about 0.8 to 3.6 kb. All mRNAs have been shown to carry poly(A)-tracts and a common leader sequence. The seven mRNAs were produced in infected macrophage cultures concomitantly with genomic LDV RNA. Maximum LDV RNA synthesis was observed between 6 and 8 h post-infection. The same seven subgenomic mRNAs were detected in macrophages infected with three different isolates of LDV, but different relative amounts of some of the mRNAs were produced. The relative proportions of molecules of mRNAs 1-8 present in 6 h LDV-P-infected macrophages were about 13, 5, 5, 8, 6, 11, 11 and 27% of the total, respectively.

Lactate dehydrogenase-elevating virus, equine arteritis virus, and simian hemorrhagic fever virus: a new group of positive-strand RNA viruses

The last comprehensive reviews of nonarbotogaviruses included discussions on pestiviruses, rubella virus, lactate dehydrogenase-elevating virus (LDV), equine arteritis virus (EAV), simian hemorrhagic fever virus (SHFV), cell fusion agent, and nonarboflaviviruses. The inclusion of all these viruses in the family Togaviridae was largely based on the similarities in morphological and physical–chemical properties of these viruses, and in the sizes and polarities of their genomes. In the intervening years, considerable new information on the replication strategies of these viruses and the structure and organization of their genomes has become available that has led to the reclassification or suggestions for reclassification of some of them. The replication strategy of EAV resembles that of the coronaviruses, involving a 3'-coterminal nested set of mRNAs. Therefore, EAV has been suggested to be included in a virus superfamily, along with coronaviruses and toroviruses. Recent evidence indicates that LDV not only resembles EAV in morphology, virion and genome size, and number and size of their structural proteins, but also in genome organization and replication via a 3'-coterminal set of mRNAs. SHFV, although not fully characterized, exhibits properties resembling those of LDV and EAV, and the recent evidence suggest that it may possess the same genome organization as these viruses. The three viruses may, therefore, represent a new family of positive-strand RNA viruses and are reviewed together in this chapter. In this chapter, emphasis is on the recent information concerning their molecular properties and pathogenesis in vitro and in vivo and on the host immune responses to infections by these viruses.

Mode of neutralization of lactate dehydrogenase-elevating virus by polyclonal and monoclonal antibodies

Neutralization of the infectivity of [3H]uridine-labeled lactate dehydrogenase-elevating virus (LDV) by polyclonal mouse or rabbit antibodies to the envelope glycoprotein of LDV, VP-3, or by neutralizing monoclonal antibodies (mAb) that recognize a different epitope on VP-3 than the polyclonal antibodies correlated with an increase in the sedimentation rate of LDV from 230 S to greater than or equal to 270 S. Incubation of LDV with normal mouse plasma or non-neutralizing mAbs to LDV VP-3 had no effect on its sedimentation rate. Similarly, incubation of a neutralization escape variant of LDV with the mAb used in its selection had no effect on its sedimentation rate, whereas neutralization of this variant by polyclonal mouse or rabbit anti-VP3 antibodies increased the sedimentation rate. Neutralization of LDV infectivity was only observed at high antibody/virion ratios and often was followed by loss of the viral RNA. The results suggest that neutralization of LDV infectivity results from binding of multiple antibody molecules that recognize specific epitopes on the viral envelope glycoprotein and ultimately leads to disintegration of the virions.

A nested set of eight RNAs is formed in macrophages infected with lactate dehydrogenase-elevating virus

Total RNA was extracted from primary cultures of mouse macrophages isolated from 10-day-old mice 6 to 12 h postinfection with lactate dehydrogenase-elevating virus (LDV). Poly(A)+ RNA was extracted from spleens of 18-h LDV-infected mice. The RNAs were analyzed by Northern (RNA) blot hybridization with a number of LDV-specific cDNAs as probes. A cDNA representing the nucleocapsid protein (VP-1) gene located at the 3' terminus of the viral genome (E. K. Godeny, D. W. Speicher, and M. A. Brinton, Virology 177:768-771, 1990) hybridized to viral genomic RNA of about 13 kb plus seven subgenomic RNAs ranging in size from about 1 to about 3.6 kb. Two other cDNA clones hybridized only to the four or five largest subgenomic RNAs, respectively. In contrast, two cDNAs encoding continuous open reading frames with replicase and zinc finger motifs hybridized only to the genomic RNA. The replicase motif exhibited 75% amino acid identity to that of the 1b protein of equine arteritis virus (EAV) and 44% amino acid identity to those of the 1b proteins of coronaviruses and Berne virus. Combined, the results indicate that LDV replication involves formation of a 3'-coterminal-nested set of mRNAs as observed for coronaviruses and toroviruses as well as for EAV, with which LDV shares many other properties. Overall, LDV, like EAV, possesses a genome organization resembling that of the coronaviruses and toroviruses. However, EAV and LDV differ from the latter in the size of their genomes, virion size and structure, nature of the structural proteins, and symmetry of the nucleocapsids.

Monoclonal antibody protection from age-dependent poliomyelitis: implications regarding the pathogenesis of lactate dehydrogenase-elevating virus

Over 90% of cyclophosphamide-treated, 6- to 7-month-old C58/M mice developed fatal paralytic disease after infection with a virulent strain of lactate dehydrogenase-elevating virus (LDV), with a mean onset of paralysis of about 16 days. Passive immunization with polyclonal antibodies or with a group of anti-LDV monoclonal antibodies (MAbs) with single-epitope specificity 1 day before or at the time of LDV infection prevented the development of paralytic disease without interfering with the replication of LDV in permissive macrophages, the primary host cells of LDV. In situ hybridization of spinal cord sections with an LDV-specific cDNA probe indicated that the MAb specifically prevented the cytocidal infection of motor neurons by LDV without blocking the infection of smaller nonneuronal cells in the spinal cord. The protective antibodies recognize at least two different epitopes on the glycoprotein of LDV, VP-3. Passive immunizations with other anti-LDV MAbs, which recognize at least three other epitopes on VP-3 of LDV, afforded no protection. In contrast to the protective effect of anti-LDV MAb injection before or at the time of LDV infection, their administration postinfection exerted relatively little protection, though it delayed the appearance of paralytic symptoms. However, repeated injections of MAbs until at least 7 days postinfection also afforded a high degree of protection. The results indicate that protective MAbs may interfere with two stages in the development of LDV-induced paralytic disease. When administered at the time of LDV infection, they prevent the initial infection of spinal cord motor neurons. After this initial event, repeated injections of MAb are required to inhibit the spread of LDV between neurons until the endogenous production of protective anti-LDV antibodies in these mice.

Polyclonal B cell activation of IgG2a and IgG2b production by infection of mice with lactate dehydrogenase-elevating virus is partly dependent on CD4+ lymphocytes

Concentrations of IgM and IgG isotypes were determined by capture ELISA in plasma of Swiss, BALB/c and C58/M mice. Plasma IgG isotype concentrations, especially of IgM, IgG1 and IgG2a, varied considerably between mouse strains, batches of mice of the same strain and individual mice and as a function of age. Infection of the mice with LDV, which is known to replicate primarily in a subpopulation of macrophages, consistently resulted in a rapid elevation of plasma IgG2a (or of IgG2b in some Swiss nu/+ mice), but no plasma IgG increases were observed in mice immunized with inactivated LDV. Plasma IgG2a elevation after LDV infection was greatly delayed and reduced by depletion of the mice of CD4+, but not of CD8+, T cells by administration of protein-G-purified anti-CD4 or anti-CD8 mAbs, and completely inhibited by repeated treatment of the mice with cyclophosphamide. Treatment with anti-CD4 mAbs, or cyclophosphamide also greatly reduced the production of anti-LDV antibodies, while not significantly affecting the replication of LDV in these mice. Nude Swiss mice also failed to produce anti-LDV antibodies, though supporting normal LDV replication. Plasma IgM, IgG1, IgG2a and IgG2b levels increased in LDV-infected nu/nu mice, but similar changes were observed in uninfected mice. The results indicate that the LDV-induced polyclonal activation of B cells requires productive LDV infection of mice and is, at least partly, dependent on functioning CD4+ cells. They suggest that productive infection of the LDV-permissive subpopulation of macrophages leads to the activation of CD4+ T lymphocytes of subset 1 and their Spleen cells from 5-day LDV-infected BALB/c mice incorporated [3H]thymidine 2-3 times more rapidly in vitro than spleen cells from companion uninfected mice, whereas their responses to concanavalin A and lipopolysaccharide were reduced 60-70%.

Persistent infection of mice by lactate dehydrogenase-elevating virus: transient virus replication in macrophages of the spleen

In order to assess whether the spleen is the major site of replication of lactate dehydrogenase-elevating virus (LDV) in mice during the acute phase of infection, LDV replication in the spleen was measured by electron microscopy and fluorescent antibody staining of tissue sections and northern hybridization of total spleen RNA with an LDV-specific cDNA probe, and the effect of splenectomy on LDV replication was determined. LDV RNA and antigens and infected cells, presumably macrophages, were present in the spleen in high concentrations 18-25 h post infection, but then rapidly disappeared to undetectable levels during the next 1-2 days. Thus, LDV clearly replicates in the spleen during the initial phase of infection, but LDV replication in the spleen is transient due to the cytocidal nature of LDV replication and destruction of all permissive macrophages in the spleen. Furthermore, spleen macrophages do not seem to represent the major source of LDV released into the circulation, since LDV viremia as well as anti-LDV antibody production were the same in splenectomized and control animals for at least 28 days postinfection.