bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Single Amino Acid in the Reverse Transcriptase Domain of Hepatitis B Virus Affects Virus Replication Efficiency
Authors: Lin Xu , Yuan Zheng-Hong , Wu Li , Ding Jian-Ping , Wen Yu-Mei 
Published: July 2002

ABSTRACT
To explore functional domains in the hepatitis B virus (HBV) polymerase, two naturally occurring HBV isolates (56 and 2-18) with 98.7% nucleic acid sequence homology but different replication efficiencies were studied. After transfection into HepG2 cells, HBV DNA isolated from intracellular virus core particles was much higher in 56-transfected cells than in cells transfected with 2-18. The structural basis for the difference in replication efficiency between these two isolates was studied by functional domain gene substitution. The complete polymerase (P) gene and its gene segments coding for the terminal protein (TP), spacer (SP), reverse transcriptase (RT), and RNase H in 2-18 were separately replaced with their counterparts from 56 to construct full-length chimeric genomes. Cell transfection analysis revealed that substitution of the complete P gene of 2-18 with the P gene from 56 slightly enhanced viral replication. The only chimeric genome that regained the high replication efficiency of the original 56 isolate was the one with substitution of the RT gene of 2-18 with that from 56. Within the RT region, amino acid differences between isolates 2-18 and 56 were located at positions 617 (methionine versus leucine), 652 (serine versus proline), and 682 (valine versus leucine). Point mutation identified amino acid 652 as being responsible for the difference in replication efficiency. Homologous modeling studies of the HBV RT domain suggest that the mutation of residue 652 from proline to serine might affect the conformation of HBV RT which interacts with the template-primer, leading to impaired polymerase activity.
Characterization of the CD154-Positive and CD40-Positive Cellular Subsets Required for Pathogenesis in Retrovirus-Induced Murine Immunodeficiency
Authors: Green Kathy A. , Noelle Randolph J. , Durell Brigit G. , Green William R. 
Published: July 2002

ABSTRACTGenetically susceptible C57BL/6 (B6) mice that are infected with the LP-BM5 isolate of murine retroviruses develop profound splenomegaly, lymphadenopathy, hypergammaglobulinemia, terminal B-cell lymphomas, and an immunodeficiency state bearing many similarities to the pathologies seen in AIDS. Because of these similarities, this syndrome has been called murine AIDS (MAIDS). We have previously shown that CD154 (CD40 ligand)-CD40 molecular interactions are required both for the initiation and progression of MAIDS. Thus, in vivo anti-CD154 monoclonal antibody (MAb) treatment inhibited MAIDS symptoms in LP-BM5-infected wild-type mice when either a short course of anti-CD154 MAb treatment was started on the day of infection or a course was initiated 3 to 4 weeks after LP-BM5 administration, after disease was established. Here, we further characterize this required CD154-CD40 interaction by a series of adoptive transfer experiments designed to elucidate which cellular subsets must express CD154 or CD40 for LP-BM5 to induce MAIDS. Specifically with regard to CD154 expression, MAIDS-insusceptible B6 nude mice reconstituted with highly purified CD4+T cells from wild-type, but not from CD154 knockout, B6 donors displayed clear MAIDS after LP-BM5 infection. In contrast, nude B6 recipients that received CD8+T cells from wild-type B6 donors did not develop MAIDS after LP-BM5 infection. B6 CD40 knockout mice, which are also relatively resistant to LP-BM5-induced MAIDS, became susceptible to LP-BM5-induced disease after reconstitution with highly purified wild-type B cells but not after receiving purified wild-type dendritic cells (DC) or a combined CD40+population composed of DC and macrophages obtained from B6 SCID mouse donors. Based on these and other experiments, we thus conclude that the cellular basis for the requirement for CD154-CD40 interactions for MAIDS induction and progression can be accounted for by CD154 expression on CD4+T cells and CD40 expression on B cells.
Rev-Independent Simian Immunodeficiency Virus Strains Are Nonpathogenic in Neonatal Macaques
Authors: von Gegerfelt Agneta S. , Liska Vladimir , Li Pei-Lin , McClure Harold M. , Horie Kyoji , Nappi Filomena , Montefiori David C. , Pavlakis George N. , Marthas Marta L. , Ruprecht Ruth M. , Felber Barbara K. 
Published: July 2002

ABSTRACTThe viral protein Rev is essential for the export of the subset of unspliced and partially spliced lentiviral mRNAs and the production of structural proteins. Rev and its RNA binding site RRE can be replaced in both human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) by the constitutive RNA transport element CTE of the simian type D retroviruses. We used neonatal macaques as a sensitive animal model to evaluate the pathogenicity of a pair of SIV mutant strains generated from Rev-independent molecular clones of SIVmac239 which differ only in the presence of thenefopen reading frame. After high primary viremia, all animals remained persistently infected at levels below the threshold of detection. All macaques infected as neonates developed normally, and none showed any signs of immune dysfunction or disease during follow-up ranging from 2.3 to 4 years. Therefore, the Rev-RRE regulatory mechanism plays a key role in the maintenance of high levels of virus propagation, which is independent of the presence ofnef. These data demonstrate that Rev regulation plays an important role in the pathogenicity of SIV. Replacement of Rev-RRE by the CTE provides a novel approach to dramatically lower the virulence of a pathogenic lentivirus. These data further suggest that antiretroviral strategies leading to even a partial block of Rev function may modulate disease progression in HIV-infected individuals.
The Liver Is a Major Organ for Clearing Simian Immunodeficiency Virus in Rhesus Monkeys
Authors: Zhang Linqi , Dailey Peter J. , Gettie Agegnehu , Blanchard Jim , Ho David D. 
Published: July 2002

ABSTRACTInfection with human or simian immunodeficiency virus (SIV) is characterized by the rapid turnover of both viral particles and productively infected cells. It has recently been reported that the clearance of SIV in vivo is exceedingly fast, with half-lives on the order of minutes. The underlying mechanism or site responsible for this rapid clearance, however, remains unknown. To investigate this issue, we chose to infuse infectious SIVmac239 grown from autologous peripheral blood mononuclear cells that were radioactively labeled by [35S]methionine and [35S]cysteine. This approach eliminates from the viral membrane alloantigens that may have a significant impact on viral clearance. In addition, this approach also permits identification of the sites of viral clearance by measuring the radioactive intensity, even if degradation of SIV RNA occurs in tissues. We now report that the half-life of infused SIV in blood is extremely close to estimates from a previous study, in which unlabeled SIV grown in a heterologous cell line was used. The allogeneic effect due to the presence of human antigens on the surfaces of virions may, therefore, play a minimal role in the high rate of virion clearance. Moreover, close to 30% of infused radioactivity was found in the liver and measureable amounts were detected in the lungs (5.4%), lymph nodes (3.0%), and spleen (0.4%). The detection of a significant proportion of infused virus in the liver suggests that viral clearance from circulation is mediated by a common, nonspecific mechanism, such as the phagocytic functions of the reticuloendothelial system. The rapid clearance and degradation of exogenously infused virions may pose a major obstacle for gene therapy with viral vectors, unless strategies to overcome the rapid in vivo elimination of these particles are developed.
Evolution of Bacteriophage in Continuous Culture: a Model System To Test Antiviral Gene Therapies for the Emergence of Phage Escape Mutants
Authors: Lindemann Björn F. , Klug Christian , Schwienhorst Andreas 
Published: July 2002

ABSTRACTThe emergence of viral escape mutants is usually a highly undesirable phenomenon. This phenomenon is frequently observed in antiviral drug applications for the treatment of viral infections and can undermine long-term therapeutic success. Here, we propose a strategy for evaluating a given antiviral approach in terms of its potential to provoke the appearance of resistant virus mutants. By use of Qβ RNA phage as a model system, the effect of an antiviral gene therapy, i.e., a virus-specific repressor protein expressed by a recombinantEscherichia colihost, was studied over the course of more than 100 generations. In 13 experiments carried out in parallel, 12 phage populations became resistant and 1 became extinct. Sequence analysis revealed that only two distinct phage mutants emerged in the 12 surviving phage populations. For both escape mutants, sequence variations located in the repressor binding site of the viral genomic RNA, which decrease affinity for the repressor protein, conferred resistance to translational repression. The results clearly suggest the feasibility of the proposed strategy for the evaluation of antiviral approaches in terms of their potential to allow resistant mutants to appear. In addition, the strategy proved to be a valuable tool for observing virus-specific molecular targets under the impact of antiviral drugs.
Both R5 and X4 Human Immunodeficiency Virus Type 1 Variants Persist during Prolonged Therapy with Five Antiretroviral Drugs
Authors: van Rij Ronald P. , Visser Janny A. , van Praag Rieneke M. E. , Rientsma Ronald , Prins Jan M. , Lange Joep M. A. , Schuitemaker Hanneke 
Published: July 2002

ABSTRACTA viral reservoir of human immunodeficiency virus type 1 (HIV-1)-infected, resting CD4+T cells persists despite suppression of plasma viremia by combination antiretroviral therapy. In a longitudinal analysis of three patients treated with a five-drug regimen, both R5 and X4 HIV-1 variants persisted in the cellular reservoir for up to 3 years.
Stable Replication of Papillomavirus Genomes in
Saccharomyces cerevisiae
Authors: Angeletti Peter C. , Kim Kitai , Fernandes Fiona J. , Lambert Paul F. 
Published: July 2002

ABSTRACT

Papillomaviruses normally replicate in stratified squamous epithelial tissues of their mammalian hosts, in which the viral genome is found as a nuclear plasmid. Two viral proteins, E1, a helicase, and E2, a transcriptional activator and plasmid maintenance factor, are known to contribute to the episomal replication of the viral genome. Recently, our laboratory discovered that papillomaviruses can also replicate in an E1-independent manner in mammalian cells (K. Kim and P. F. Lambert, Virology, in press; K. Kim and P. F. Lambert, submitted for publication). In this study, we describe experiments investigating the capacity of the human papillomavirus type 16 (HPV16) genome to replicate in yeast (
Saccharomyces cerevisiae
). The full-length HPV16 genome, when linked in
cis
to a selectable yeast marker gene, either
TRP1
or
URA3
, could replicate stably as an episome in yeast. The replication of papillomavirus genomes in yeast is not limited to HPV16. Bovine papillomavirus type 1 and HPV6b, -11, -16, -18, and -31 were all capable of replicating in short-term assays over a period of 20 cell doublings. The long-term persistence of viral episomes did not require any one viral gene, as mutant genomes defective in single genes also replicated episomally. These results indicate that the viral episome can replicate in the absence of the E1 DNA helicase. Similarly, E2 was also not required for replication in yeast, and E2 mutant viral genomes were stably maintained in the absence of selection, indicating the existence of an E2-independent mechanism for plasmid maintenance. The episomal replication of papillomavirus genomes in yeast provides a genetically manipulatable system in which to investigate cellular factors required for episomal replication and may provide a novel means for generating infectious papillomavirus.
Functional instability in non-contact ankle ligament injuries
Authors: Rose Alison , Lee Robert J , Williams Rachel M , Thomson Lindsay C , Forsyth Anne 
Published: July 2002

Objectives—To measure objectively functional standing balance in the acute stages of non-contact ankle sprain, and to compare patients with controls.Methods—A Chattanooga balance machine was used to measure postural stability in patients with acute ankle sprain and uninjured controls over a two week period, in one and two legged stance, with eyes open and closed. Participants also completed the Olerud and Molander questionnaire to provide a subjective measure of ankle function.Results—There was a highly significant improvement in questionnaire scores for the patients during the study period (p<0.0001). Patients appeared to be less stable than controls in all balance tests, although the difference did not reach significance. There was evidence of improvement over time in the number of tests successfully completed on the injured leg in single legged stance with eyes closed (p = 0.043) between visits 1 and 3.Conclusions—The patient group showed a subjective improvement, which supports clinical experience of treating acute ankle injuries. There is some evidence that on average the patient group appeared to be less stable than controls in all balance tests, although the difference did not reach statistical significance, even on the uninjured leg. There is a need to carry out further studies to confirm the results found in this pilot study and to investigate the hypotheses generated. It would be useful to evaluate a simple test that could be used clinically to monitor progress after ankle injury, and also to identify athletes with decreased functional stability, who may be more at risk of sustaining ankle injury.
Hormone levels of world class cyclists during the Tour of Spain stage race
Authors: Lucía A , Díaz B , Hoyos J , Fernández C , Villa G , Bandrés F , Chicharro J L 
Published: July 2002

Objectives—To evaluate the hormonal response to strenuous endurance exercise performed by elite athletes.Methods—Nine professional cyclists (mean (SD) age 28 (1) years; mean (SD) Vo2max75.3 (2.3) ml/kg/min) who participated in a three week tour race (Vuelta a España 1999) were selected as subjects. Morning urinary levels of 6-sulphatoxymelatonin (aMT6s) and morning serum levels of testosterone, follicle stimulating (FSH), luteinising hormone (LH), and cortisol were measured in each subject at t0(before the competition), t1(end of first week), t2(end of second week), and t3(end of third week). Urine samples of aMT6s were also evaluated in the evening at t0, t1, t2, and t3.Results—Mean urinary aMT6s levels had increased significantly (p<0.01) during the day after each stage (1091 (33)v683 (68) ng/ml at t1; 955 (19)v473 (53) ng/ml at t2; 647 (61)v337 (47) ng/ml at t3). Both morning and evening aMT6s levels decreased significantly during the study. A similar pattern was observed for morning serum levels of cortisol and testosterone.Conclusions—The results suggest that the basal activity of the pineal gland, adrenal glands, and testis may be decreased after consecutive days of intense, long term exercise.
Gastrointestinal cell proliferation and crypt fission are separate but complementary means of increasing tissue mass following infusion of epidermal growth factor in rats
Authors: Berlanga-Acosta J , Playford R J , Mandir N , Goodlad R A 
Published: July 2002

BACKGROUND AND AIMSEpidermal growth factor (EGF) is a potent mitogen for the gastrointestinal tract and also influences the number of new crypts formed by crypt fission. The time course of these events and possible linkage between these two complementary mechanisms is however poorly understood. We therefore examined the temporal relationship of proliferation and fission in rats treated with EGF.METHODSOsmotic minipumps were implanted subcutaneously into male Wistar rats to infuse EGF continuously (60 μg/rat/day) for periods of 1–14 days. Proliferation and crypt branching were quantified following vincristine induced metaphase arrest and morphometric assessment of microdissected tissue.RESULTSIn the small intestine, EGF significantly increased epithelial cell proliferation and crypt and villus area after 24 hours of EGF, although maximal effects were only reached following six days of infusion. EGF also resulted in an approximate 30% reduction in crypt fission in the small bowel. In the colon, EGF caused a twofold increase in epithelial cell proliferation one day after infusion, from 15.3 (2.3) to 29.6 (3.5) metaphases per crypt (p<0.01). Maximal effects were seen in rats receiving EGF for seven days. For all time points, colonic crypt size increased in response to EGF. The amount of branching increased following one day of infusion with EGF (from 15.3 (1.9) to 32.4 (5.5)%; p<0.001) but was significantly lower (approximately 25% of control values) following longer periods of infusion. Crypt fission did not correlate with crypt area.CONCLUSIONEGF has profound effects on cell proliferation and also altered crypt fission, with its actions on crypt fission most pronounced in the colon where it first increased and then decreased fission. EGF can thus be a potent stimulus for crypt fission during short term infusion and may reduce the number of branched crypts present in a resting or quiescent stage. Growth factors can alter cell mass by two separate but linked mechanisms, namely altered cell production and crypt fission.
Balancing rationalities: gatekeeping in health care
Authors: Willems Dick L 
Published: July 2002

Physicians are increasingly confronted with the consequences of allocation policies. In several countries, physicians have been assigned a gatekeeper role for secondary health care. Many ethicists oppose this assignment for several reasons, concentrating on the harm the intrusion of societal arguments would inflict on doctor-patient relations. It is argued that these arguments rest on a distinction of spheres of values and of rationality, without taking into account the mixing of values and rationalities that takes place in everyday medical practice. If medical practice, then, does not follow a single, pure rationality, can it also incorporate the societal rationality of the gatekeeper role?Using a case from general practice, I try to show how physicians may integrate societal arguments into their practice in a morally acceptable way. A version of the model of reflective equilibrium and especially Beauchamp and Childress's safeguards, may be helpful both to analyse and teach such balancing of values and rationalities.
In vitro toxicology of respirable Montserrat volcanic ash
Authors: Wilson Martin R , Stone Vicki , Cullen Richard T , Searl Alison , Maynard Robert L , Donaldson Kenneth 
Published: July 2002

OBJECTIVESIn July 1995 the Soufriere Hills volcano on the island of Montserrat began to erupt. Preliminary reports showed that the ash contained a substantial respirable component and a large percentage of the toxic silica polymorph, cristobalite. In this study the cytotoxicity of three respirable Montserrat volcanic ash (MVA) samples was investigated: M1 from a single explosive event, M2 accumulated ash predominantly derived from pyroclastic flows, and M3 from a single pyroclastic flow. These were compared with the relatively inert dust TiO2and the known toxic quartz dust, DQ12.METHODSSurface area of the particles was measured with the Brunauer, Emmet, and Teller (BET) adsorption method and cristobalite content of MVA was determined byxray diffraction (XRD). After exposure to particles, the metabolic competence of the epithelial cell line A549 was assessed to determine cytotoxic effects. The ability of the particles to induce sheep blood erythrocyte haemolysis was used to assess surface reactivity.RESULTSTreatment with either MVA, quartz, or titanium dioxide decreased A549 epithelial cell metabolic competence as measured by ability to reduce 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT). On addition of mannitol, the cytotoxic effect was significantly less with M1, quartz, and TiO2. All MVA samples induced a dose dependent increase in haemolysis, which, although less than the haemolysis induced by quartz, was significantly greater than that induced by TiO2. Addition of mannitol and superoxide dismutase (SOD) significantly reduced the haemolytic activity only of M1, but not M2 or M3, the samples derived from predominantly pyroclastic flow events.CONCLUSIONSNeither the cristobalite content nor the surface area of the MVA samples correlated with observed in vitro reactivity. A role for reactive oxygen species could only be shown in the cytotoxicity of M1, which was the only sample derived from a purely explosive event. These results suggest that in general the bioreactivity of MVA samples in vitro is low compared with pure quartz, but that the bioreactivity and mechanisms of biological interaction may vary according to the ash source.
Risk of mesothelioma from exposure to crocidolite asbestos: a 1995 update of a South African mortality study
Authors: Kielkowski Danuta , Nelson Gillian , Rees David 
Published: July 2002

OBJECTIVETo find the risk of developing mesothelioma in a cohort born in 1916–36 in Prieska, Northern Cape Province, South Africa.METHODSA birth cohort mortality study was carried out in a small town in the Northern Cape Province, South Africa, with a history of crocidolite asbestos mining and milling. The cohort comprised all white births registered in the magisterial district of Prieska from 1916 to 1936, inclusive (2390). Causes of death due to mesothelioma and other cancers as recorded on medical certificates of cause of death were investigated. Person-years analysis was used to calculate mortalities due to mesothelioma, other respiratory cancers, and other non-respiratory cancers. Proportional cancer mortalities were also calculated for mesothelioma and other specific neoplasms.RESULTSThe follow up rate for the cohort was 74.3% in 1995, and 683 traced members (38.6%) had died. Cause of death was unknown for 6.4% of deaths. There were 118 cases of cancer, 28 of them from mesothelioma, giving a cause specific mortality for mesothelioma of 277 (170–384) per 106person-years. The rates for men and women were 366 and 172 per 106person-years, respectively. The mortality for lung cancer (29 deaths) was 287 (135–436) per 106person-years, and that for other non-respiratory cancers (60 deaths) was 593 (442–745). Two cases of laryngeal and four of colon cancer were observed. All cancer mortality, mesothelioma, and lung cancer proportional cancer mortality ratios were increased.CONCLUSIONThe mortality for mesothelioma in men was twice that in women, probably because men were more likely to have had both occupational and environmental exposure to asbestos. Nevertheless, the mortality in women was still high and is probably indicative of the environmental exposure as white women were rarely employed in the asbestos industry in the Prieska area. Due to the long latency from first exposure to diagnosis of the neoplasm, the cause specific mortality in this cohort could be expected to increase rapidly over the next 10 years.