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H L Lipton

Publications and source records attributed to H L Lipton.

At least 19 recordsLinked to original sources
PubMed2001

UDP-galactose transporter is required for Theiler's virus entry into mammalian cells.

Theiler's murine encephalomyelitis viruses (TMEV) are divided into two groups: high-neurovirulence strains, such as GDVII, cause fatal encephalitis, while low-neurovirulence strains, such as BeAn and DA, cause persistent infection and demyelination in mice. Cell surface sialic acid is bound by the low-neurovirulence DA and BeAn viruses, but not by the high-neurovirulence GDVII virus. We have identified a clone from a BHK-21 cell cDNA library that mediates TMEV entry and infection by viruses of both TMEV groups in a receptor-negative BHK-21 cell variant (R26). The sequence of this clone is 96.4% identical to the human UDP-galactose transporter (UGT), which belongs to a family of nucleotide-sugar transporter proteins involved in the biosynthesis of complex carbohydrate structures in the trans-Golgi network. UGT mRNA from R26 cells was found to have a 490-nucleotide deletion involving the C-terminal amino acids 255 to 392 and 81 nucleotides of the 3' noncoding region. These results suggest two possibilities by which UGT may mediate TMEV entry and infection. The most likely one relates to the transporter function of adding galactose to another receptor protein. This possibility suggests the requirement for a specific glycoprotein interaction for GDVII virus cell binding and entry, e.g., galactose for GDVII and sialic acid for BeAn. Alternatively, UGT might be a TMEV receptor itself, acting via UGT cycling to the cell surface.

Amino Acid Sequence↗
PubMed2001

Serological evidence that Mus musculus is the natural host of Theiler's murine encephalomyelitis virus.

Theiler's murine encephalomyelitis virus (TMEV) infection is maintained in mouse colonies by fecal-oral spread (with no apparent role for persistent central nervous system infection) from an acutely infected animal to another. Therefore, serological methods offer the principal way to assess infection in mice and related rodent populations. Infection of mouse colonies with TMEV appears to be worldwide, yet no systematic serologic studies have been reported. In this study, enzyme-linked immunoassay and neutralization analysis of sera from feral Mus musculus obtained from four locations in the United States and one in Russia revealed antibodies to purified TMEV and two linear viral peptide epitopes in more than 50% of the sera derived from the five different locations. A similar analysis of sera from 26 species of related rodents trapped at multiple locations in North America and Europe indicated the presence of anti-TMEV antibodies only in a small proportion of water and bank voles that belong to a different subfamily. These results indicate that Mus musculus is the natural host of TMEV.

Amino Acid Sequence↗
PubMed2001

Theiler's murine encephalomyelitis virus induces apoptosis in gamma interferon-activated M1 differentiated myelomonocytic cells through a mechanism involving tumor necrosis factor alpha (TNF-alpha) and TNF-alpha-related apoptosis-inducing ligand.

Infection of susceptible mice with the low-neurovirulence Theiler's murine encephalomyelitis virus strain BeAn results in an inflammatory demyelinating disease similar to multiple sclerosis. While the majority of virus antigen is detected in central nervous system macrophages (Mphis), few infiltrating Mphis are infected. We used the myelomonocytic precursor M1 cell line to study BeAn virus-Mphi interactions in vitro to elucidate mechanisms for restricted virus expression. We have shown that restricted BeAn infection of M1 cells differentiated in vitro (M1-D) results in apoptosis. In this study, BeAn infection of gamma interferon (IFN-gamma)-activated M1-D cells also resulted in apoptosis but with no evidence of virus replication or protein expression. RNase protection assays of M1-D cellular RNA revealed up-regulation of Fas and the p55 chain of the tumor necrosis factor alpha (TNF-alpha) receptor transcripts with IFN-gamma activation. BeAn infection of activated cells resulted in increased caspase 8 mRNA transcripts and the appearance of TNF-alpha-related apoptosis-inducing ligand (TRAIL) 4 h postinfection. Both unactivated and activated M1-D cells expressed TRAIL receptors (R1 and R2), but only activated cells were killed by soluble TRAIL. Activated cells were also susceptible to soluble FasL- and TNF-alpha-induced apoptosis. The data suggest that IFN-gamma-activated M1-D cell death receptors become susceptible to their ligands and that the cells respond to BeAn virus infection by producing the ligands TNF-alpha and TRAIL to kill the susceptible cells. Unactivated cells are not susceptible to FasL or TRAIL and require virus replication to initiate apoptosis. Therefore, two mechanisms of apoptosis induction can be triggered by BeAn infection: an intrinsic pathway requiring virus replication and an extrinsic pathway signaling through the death receptors.

Apoptosis↗
PubMed2001

High numbers of viral RNA copies in the central nervous system of mice during persistent infection with Theiler's virus.

The low-neurovirulence Theiler's murine encephalomyelitis viruses (TMEV), such as BeAn virus, cause a persistent infection of the central nervous system (CNS) in susceptible mouse strains that results in inflammatory demyelination. The ability of TMEV to persist in the mouse CNS has traditionally been demonstrated by recovering infectious virus from the spinal cord. Results of infectivity assays led to the notion that TMEV persists at low levels. In the present study, we analyzed the copy number of TMEV genomes, plus- to minus-strand ratios, and full-length species in the spinal cords of infected mice and infected tissue culture cells by using Northern hybridization. Considering the low levels of infectious virus in the spinal cord, a surprisingly large number of viral genomes (mean of 3.0 x 10(9)) was detected in persistently infected mice. In the transition from the acute (approximately postinfection [p.i.] day 7) to the persistent (beginning on p.i. day 28) phase of infection, viral RNA copy numbers steadily increased, indicating that TMEV persistence involves active viral RNA replication. Further, BeAn viral genomes were full-length in size; i.e., no subgenomic species were detected and the ratio of BeAn virus plus- to minus-strand RNA indicated that viral RNA replication is unperturbed in the mouse spinal cord. Analysis of cultured macrophages and oligodendrocytes suggests that either of these cell types can potentially synthesize high numbers of viral RNA copies if infected in the spinal cord and therefore account for the heavy viral load. A scheme is presented for the direct isolation of both cell types directly from infected spinal cords for further viral analyses.

Animals↗
PubMed2000

Mutation of predicted virion pit residues alters binding of Theiler's murine encephalomyelitis virus to BHK-21 cells.

Theiler's murine encephalomyelitis virus (TMEV), a natural pathogen of mice, is a member of the genus Cardiovirus in the family Picornaviridae. Structural studies indicate that the cardiovirus pit, a deep depression on the surface of the virion, is involved in receptor attachment; however, this notion has never been systematically tested. Therefore, we used BeAn virus, a less virulent TMEV, to study the effect of site-specific mutation of selected pit amino acids on viral binding as well as other replicative functions of the virus. Four amino acids within the pit, V1091, P1153, A1225 and P3179, were selected for mutagenesis to evaluate their role in receptor attachment. Three amino acid replacements were made at each site, the first a conservative replacement, followed by progressively more radical amino acid changes in order to detect variable effects at each site. A total of seven viable mutant viruses were recovered and characterized for their binding properties to BHK-21 cells, capsid stability at 40 degrees C, viral RNA replication, single- and multistep growth kinetics, and virus translation. Our data implicate three of these residues in TMEV-cell receptor attachment.

Animals↗
PubMed1999

Restricted Theiler's murine encephalomyelitis virus infection in murine macrophages induces apoptosis.

Increasing evidence suggests that macrophages (M(phi)s) are necessary for persistence of Theiler's murine encephalomyelitis virus (TMEV) in the mouse central nervous system. Analysis of BeAn virus infection in the Mphi cell lines P388D1, J774A.1 and PU5-1.8, which are intermediate in their state of differentiation and resemble multifunctional resident M(phi)s, revealed restricted TMEV growth. As a result of the restricted infection, these Mphi cell lines were induced to undergo apoptosis as demonstrated by cellular morphology, DNA fragmentation, caspase protease activity, and in individual cells, by terminal deoxytransferase dUTP nick-end labelling (TUNEL).

Animals↗
PubMed1999

Differentiation of M1 myeloid precursor cells into macrophages results in binding and infection by Theiler's murine encephalomyelitis virus and apoptosis.

Infection of susceptible mouse strains with BeAn, a less virulent strain of Theiler's murine encephalomyelitis virus (TMEV), results in immune system-mediated demyelinating lesions in the central nervous system (CNS) similar to those in multiple sclerosis. Since macrophages appear to carry the major detectable antigen burden in vivo, and purification of sufficient cell numbers from the CNS for detailed analysis is difficult, macrophage-like cell lines provide an accessible system with which to study virus-macrophage interactions. The myeloid precursor cell line M1 differentiates in response to cytokines and expresses many characteristics of tissue macrophages. Incubation of TMEV with undifferentiated M1 cells produced neither infection nor apoptosis, whereas differentiated M1 (M1-D) cells developed a restricted virus infection and changes indicative of apoptosis. Virus binding and RNA replication as well as cellular production of alpha/beta interferons increased with differentiation. Although the amount of infectious virus was highly restricted, BeAn-infected M1-D cells synthesized and appropriately processed virus capsid proteins at levels comparable to those for permissive BHK-21 cells. Analysis of Bcl-2 protein family expression in undifferentiated and differentiated cells suggests that susceptibility of M1-D cells to apoptosis may be controlled, in part, by expression of the proapoptotic alpha isoform of Bax and Bak. These data suggest that macrophage differentiation plays a role in susceptibility to TMEV infection and apoptosis.

Animals↗
PubMed1999

Pharmacy benefit management companies: dimensions of performance.

Research on pharmacy benefit management companies focuses on descriptive accounts of the organizations and the scope of their services. This review provides a critical analysis of publicly available research on contemporary issues surrounding the operations and effects of pharmacy benefit management companies. There has been very little systematic, empirical research on these issues; major questions concerning the impact of pharmacy benefit management companies on quality, costs, and patient outcomes remain unanswered. We analyze what is known and what needs to be known, and we explore major research challenges that lie ahead in the assessment of the pharmacy benefit management company's role in the health care system and in improving the public's health.

Drug Industry↗
PubMed1998

Attenuation of neurovirulence of Theiler's murine encephalomyelitis virus strain GDVII is not sufficient to establish persistence in the central nervous system.

Virus recombinants constructed from Theiler's murine encephalomyelitis virus (TMEV) strain GDVII, which causes a rapidly fatal encephalitis in mice, and the less virulent BeAn, which persists in the murine central nervous system (CNS) and causes inflammatory demyelination, and a GDVII mutant deleted of 46 of 76 leader protein amino acids were analysed for virus persistence in the CNS. The two recombinant and mutant viruses principally contain GDVII sequences including the nucleotides encoding the polyprotein and 3' untranslated region. These viruses were found to replicate in the CNS of mice but they did not produce acute encephalitis or paralysis, i.e. they were attenuated in neurovirulence compared to the GDVII parent. More important, none of the viruses persisted in the mouse CNS nor caused chronic demyelination. Thus, attenuation of GDVII neurovirulence alone is not sufficient to establish TMEV persistence. This result is discussed in the context of a genomic determinant for persistence.

Animals↗
PubMed1998

Characterization of and functional antigen presentation by central nervous system mononuclear cells from mice infected with Theiler's murine encephalomyelitis virus.

We examined the phenotype and function of cells infiltrating the central nervous system (CNS) of mice persistently infected with Theiler's murine encephalomyelitis virus (TMEV) for evidence that viral antigens are presented to T cells within the CNS. Expression of major histocompatibility complex (MHC) class II in the spinal cords of mice infected with TMEV was found predominantly on macrophages in demyelinating lesions. The distribution of I-As staining overlapped that of the macrophage marker sialoadhesin in frozen sections and coincided with that of another macrophage/microglial cell marker, F4/80, by flow cytometry. In contrast, astrocytes, identified by staining with glial fibrillary acidic protein, rarely expressed detectable MHC class II, although fibrillary gliosis associated with the CNS damage was clearly seen. The costimulatory molecules B7-1 and B7-2 were expressed on the surface of most MHC class II-positive cells in the CNS, at levels exceeding those found in the spleens of the infected mice. Immunohistochemistry revealed that B7-1 and B7-2 colocalized on large F4/80(+) macrophages/microglia in the spinal cord lesions. In contrast, CD4(+) T cells in the lesions expressed mainly B7-2, which was found primarily on blastoid CD4(+) T cells located toward the periphery of the lesions. Most interestingly, plastic-adherent cells freshly isolated from the spinal cords of TMEV-infected mice were able to process and present TMEV and horse myoglobin to antigen-specific T-cell lines. Furthermore, these cells were able to activate a TMEV epitope-specific T-cell line in the absence of added antigen, providing conclusive evidence for the endogenous processing and presentation of virus epitopes within the CNS of persistently infected SJL/J mice.

Amino Acid Sequence↗
PubMed1998

A determinant for central nervous system persistence localized in the capsid of Theiler's murine encephalomyelitis virus by using recombinant viruses.

The demyelinating process in Theiler's murine encephalomyelitis virus (TMEV) infection in mice requires virus persistence in the central nervous system. Using recombinant TMEV assembled between the virulent GDVII and less virulent BeAn virus cDNAs, we now provide additional evidence supporting the localization of a persistence determinant to the leader P1 (capsid) sequences. Further, recombinant viruses in which BeAn sequences progressively replaced those of GDVII within the capsid starting at the leader NH2 terminus suggest that a conformational determinant requiring homologous sequences in both the VP2 puff and VP1 loop regions, which are in close contact on the virion surface, might underlie persistence.

Animals↗
PubMed1997

Role of sialyloligosaccharide binding in Theiler's virus persistence.

Theiler's murine encephalomyelitis viruses (TMEVs) belong to the Picornaviridae family and are divided into two groups, typified by strain GDVII virus and members of the TO (Theiler's original) group. The highly virulent GDVII group causes acute encephalitis in mice, while the TO group is less virulent and causes a chronic demyelinating disease which is associated with viral persistence in mice. This persistent central nervous system infection with demyelination resembles multiple sclerosis (MS) in humans and has thus become an important model for studying MS. It has been shown that some of the determinants associated with viral persistence are located on the capsid proteins of the TO group. Structural comparisons of two persistent strains (BeAn and DA) and a highly virulent strain (GDVII) showed that the most significant structural variations between these two groups of viruses are located on the sites that may influence virus binding to cellular receptors. Most animal viruses attach to specific cellular receptors that, in part, determine host range and tissue tropism. In this study, atomic models of TMEV chimeras were built with the known structures of GDVII, BeAn, and DA viruses. Comparisons among the known GDVII, BeAn, and DA structures as well as the predicted models for the TMEV chimeras suggested that a gap on the capsid surface next to the putative receptor binding site, composed of residues from VP1 and VP2, may be important in determining viral persistence by influencing virus attachment to cellular receptors, such as sialyloligosaccharides. Our results showed that sialyllactose, the first three sugar molecules of common oligosaccharides on the surface of mammalian cells, inhibits virus binding to the host cell and infection with the persistent BeAn virus but not the nonpersistent GDVII and chimera 39 viruses.

Amino Acid Sequence↗
PubMed1997

Molecular pathogenesis of Theiler's murine encephalomyelitis virus-induced demyelinating disease in mice.

After an acute phase of virus growth in neurons (e.g. anterior horn cells), Theiler's murine encephalomyelitis virus (TMEV) persists as a chronic productive infection, largely in macrophages in the CNS white matter. TMEV replication in macrophages is highly restricted, probably as the result of host cell factors. The preponderance of evidence indicates that TMEV persistence leads to immunopathologic damage of myelin, mediated by major histocompatibility class II-restricted Th1 lymphocytes directed at a virus epitope(s) rather than host neuroantigens at least early in the infection. Analysis of TMEV recombinant and mutant viruses suggests that persistence requires a specific capsid conformation involving the VP2 puff and VP1 loops, which may influence persistence through virion receptor binding or attachment to host cells, e.g. macrophages.

Animals↗
PubMed1996

The structure of a highly virulent Theiler's murine encephalomyelitis virus (GDVII) and implications for determinants of viral persistence.

GDVII is a highly virulent Theiler's murine encephalomyelitis virus (TMEV) which causes acute encephalitis in mice, while the BeAn and DA strains are the less virulent TMEV which cause chronic demyelinating disease in the central nervous system as a result of persistent infection. Purified GDVII virus isolated from infected BHK-21 cells was crystallized and its structure was determined to 3.5-A resolution by X-ray crystallography. In contrast to other TMEV structures, the VP1 C-terminus of GDVII virus has an ordered conformation that forms a hook over the VP3 knob near the threefold axis. Comparisons with the atomic structures of the less virulent BeAn and DA viruses revealed significant structural variations in a major site (cluster B) on the protruding surface loop puff B of VP2. Puff B is located near the VP3 GH loop region which is structurally analogous to the host receptor attachment site of the major serogroup of human rhinoviruses. Mutations at residue 1101 in VP1 and residue 2141 in VP2, which are also near the VP3 GH loop and adjacent to cluster B, were previously shown to influence persistence of DA virus. These observations indicate that the characteristic interaction with the host receptor through these sites may potentially alter TMEV persistence.

Amino Acid Sequence↗
PubMed1996

Theiler's murine encephalomyelitis virus kills restrictive but not permissive cells by apoptosis.

Theiler's murine encephalomyelitis viruses (TMEV), genus Cardiovirus, family Picorniviridae, are natural enteric pathogens of mice which cause central nervous system demyelination similar to that seen in multiple sclerosis. TMEV can be classified into two groups based on neurovirulence: a highly virulent group, e.g., GDVII virus, and a less virulent group, e.g., BeAn virus. Both viruses, depending on the multiplicity of infection, produced cytopathology in BSC-1 cells similar to that in BHK-21 cells. Since apoptosis has been reported as a mechanism of cell death after infection with many viruses, we examined infected BHK-21 and BSC-1 cells for morphological and biochemical changes consistent with apoptosis. Only the restrictive BSC-1 cells showed evidence of nuclear morphology and internucleosomal DNA degradation indicative of apoptosis. Interestingly, the more virulent GDVII virus was at least 50-fold more efficient in inducing apoptosis than the less virulent BeAn virus. This difference was not due to greater GDVII viral RNA replication or production of infectious virus, since the two viruses were similarly restricted in BSC-1 cells. Apoptosis in BSC-1 cells appears to be triggered by a cytoplasmic event, since inactivation of GDVII viral RNA by UV light abolished the ability of the virus to induce apoptosis. The possible role of apoptosis in the pathogenesis of TMEV infection in mice, especially virus persistence in central nervous system macrophages, is discussed.

Animals↗