Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “persistent”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 703 records · Page 39Linked to original sources
PubMed2004

Asymmetric dimethyl arginine and symmetric dimethyl arginine levels in infants with persistent pulmonary hypertension of the newborn.

OBJECTIVE: We investigated whether infants with persistent pulmonary hypertension had elevated levels of asymmetric dimethyl arginine, an endogenous inhibitor of nitric oxide synthase, and symmetric dimethyl arginine, a regioisomer. DESIGN: Prospective observational cohort study. SETTING: A 10-bed neonatal intensive care unit in a tertiary referral center. PATIENTS: Forty five infants >34 wks gestation and <2 wks old admitted to our intensive care unit. INTERVENTIONS: Samples of urine on days 1, 3, and 5 were analyzed by high-performance liquid chromatography to determine asymmetric dimethyl arginine and symmetric dimethyl arginine levels. The clinical progression and treatment of the infants were noted. MEASUREMENTS AND MAIN RESULTS: Twenty-nine infants had a clinical diagnosis of persistent pulmonary hypertension confirmed on echocardiography, and there were 16 control infants. Median asymmetric dimethyl arginine levels on day 1 were significantly higher in the persistent pulmonary hypertension group (n = 29), 14.8 (10.3-21.7) mmol.mmol creatinine(-1).L(-1), compared with controls (n = 16), 3.6 (1.4-5.2) mmol.mmol creatinine(-1).L(-1) (p < .001). Asymmetric dimethyl arginine levels decreased to control levels by day 5 (p = .33). Symmetric dimethyl arginine levels were significantly higher than controls on day 1, 31.0 (21.7-65.9) vs. 14.7 (4.1-20.2) mmol.mmol creatinine(-1).L(-1) (p = .001) and day 3, 34.7(20.3-42.5) mmol.mmol creatinine(-1).L(-1) (p = .0001) and by day 5 had decreased significantly (p = .007) back to 16.7 (12.3-23.8) mmol.mmol creatinine(-1).L(-1), which was not significantly different than the control group values. CONCLUSIONS: These results support the hypothesis that asymmetric dimethyl arginine and symmetric dimethyl arginine levels are elevated in patients with persistent pulmonary hypertension. Thus, endogenous inhibition of nitric oxide synthase by asymmetric dimethyl arginine may be responsible for the development of persistent pulmonary hypertension, suggesting novel therapeutic options in persistent pulmonary hypertension.

Arginine↗
PubMed1976

Persistent herpes simplex virus infections established in two Burkitt lymphoma derived cell lines.

Examination of P3HR-I cells (Epstein-Barr virus [EBV] producer) persistently infected with the MAL strain of herpes simplex virus type I (HSV-I) suggested that only a few cells were actively producing a virus indistinguishable from HSV-I (MAL) despite the presence of immunofluorescent HSV-I antigens associated with the majority of cells. EBV-specific immunofluorescence was not altered in HSV-I persistently infected P3HR-I cells. HSV-I persistently infected cells, labelled for 72 h with 14C-thymidine, incorporated approx. 8% of the label into cell associated HSV-I DNA as resolved by caesium chloride gradients. Values greater than 8% of the total were suggested by hybridization of gradient fractions with 3H-HSV-I DNA. To determine whether the establishment of HSV persistent infections in Burkitt lymphoma derived cells was a general phenomenon, six strains of HSV-I (MAL, KOS, Patton, Syn R, BF and SYN V) and two strains of type 2 (333 and MS) were used to infect the P3HR-I and Raji (EBV non-producer) cell lines derived from Burkitt lymphomas. In P3HR-I cells, persistent infections were established with all strains of HSV-I but not with HSV-2. In Raji cells, persistent infections were established with all strains of HSV-I, except Syn V, and with both strains of HSV-2. No external support was required to maintain these infections.

Adsorption↗
PubMed1980

Persistent Theiler's murine encephalomyelitis virus infection in mice depends on plaque size.

Theiler's murine encephalomyelitis virus (TMEV) is an enteric pathogen of mice which causes acute and chronic neurological disorders in the natural host. When brain-derived stocks of TMEV isolates are adapted to cell culture they predominantly form either large or small plaques. In this study the type of central nervous system (CNS) infection (acute versus chronic) and the associated disease occurring in mice inoculated intracerebrally with large and small plaque strains of TMEV was investigated. Large and small plaque strains of TMEV were found to vary in virulence, type of neurological disease produced and ability to establish persistent CNS infection in mice. Two large plaque strains, GDVII and FA viruses, were highly virulent, produced acute encephalitis, but were cleared from the nervous systems of surviving animals. Therefore, it appears that these large plaque variants do not cause persistent CNS infection in mice. In contrast, five small plaque strains, DA, WW, TO4, Yale and BeAn8386 viruses, were relatively avirulent, usually produced no illness during the first month after inoculation, but readily established persistent CNS infection in mice. Persistently infected mice later developed demyelinating disease. Having identified strains of TMEV that differ regarding their ability to persist, we now hope to be able to exploit this difference in elucidating the basic mechanism(s) of TMEV persistence.

Animals↗
PubMed1981

Establishment of persistent infection in mouse cells by Sindbis virus and its temperature-sensitive mutants.

The ability of wild-type (wt) Sindbis virus and six temperature-sensitive (ts) mutants to establish persistent infection in mouse L cells and a line of mouse embryo (ME) cells was determined. The wt established persistent infection in both ME cells and L cells at 39 degrees C. At 30 degrees C the wt established persistent infection in L cells but not ME cells, which did not recover from the initial infection. For the ts mutants, both cell lines survived the initial infection at 39 degrees C (the restrictive temperature) but the virus was eventually eliminated. At 30 degrees C (the permissive temperature) in L cells all mutants established persistent infection. In ME cells at 30 degrees C, RNA- mutants (unable to synthesize virus-specified RNA at 39 degrees C) established persistent infection whereas the cells did not recover from infection with RNA+ mutants (able to synthesize virus-specified RNA at 39 degrees C). The wt virus was less cytopathic in L cells than in BHK or ME cells. Interferon was produced by both L and ME cells at 30 degrees C and 39 degrees C, but its activity could not be detected in either cell line at 30 degrees C. It is proposed that establishment of persistent infection is dependent on reduced cytopathogenicity in the early stage of infection, and that further evolution of the virus then occurs to a less cytopathic form. Elimination of the virus at 39 degrees C is probably due to the action of interferon.

Animals↗
PubMed1981

Persistent infection of Vero cells with Tacaribe virus.

Persistently infected cultures have been established from Vero cells surviving primary infection with Tacaribe virus (Vero-T). The growth rate and morphological characteristics of the persistently infected cells were indistinguishable from normal Vero cells. Virus release declined during the first 6 passages, a cyclical pattern was observed between passages 6 and 16, and subsequently no virus infectivity could be detected. Co-cultivation with normal RK-13 or Vero cells enhanced virus yield from virus-producing cultures of Vero-T cells (passage 15), but the addition of susceptible cells had no effect on non-producer Vero-T cultures (passage 19). Only a small proportion (less than 1%) of the persistently infected cells tested during the first 16 passages produced infectious virus. The virus released during the early stages of persistence was temperature-sensitive if grown at 40 degree C, more thermolabile at 50 degree C than parental virus, and unable to initiate a persistent infection in Vero cells. Vero-T cells consistently showed refractoriness to homotypic Tacaribe virus superinfection and a selective graded resistance to other arenavirus replication. The possible use of viral susceptibility of persistently infected cultures as marker of antigenic relationship among Tacaribe complex viruses if considered.

Animals↗
PubMed1988

Deleted viral RNAs and lymphocytic choriomeningitis virus persistence in vitro.

Lymphocytic choriomeningitis virus (LCMV) infection of most tissue culture cell lines results in a non-cytopathic persistent infection. Persistent infections in vitro share many characteristics with persistent LCMV infection of mice; both are associated with decreased titres of infectious virus, restricted accumulation of viral glycoproteins at the surface of infected cells and the generation of interfering particles. We have used gel electrophoresis and hybridization techniques to analyse LCMV gene expression during persistent infection of a number of tissue culture cell lines. Our study has demonstrated that, although deleted viral RNAs can be detected during persistent LCMV infection in vitro, there may not be an obligatory association between deleted RNAs and persistence. In addition, we have found that LCMV interfering activity can be produced in the apparent absence of deleted intracellular viral RNAs.

Animals↗
PubMed1988

Establishment and characterization of St Louis encephalitis virus persistent infections in Aedes and Culex mosquito cell lines.

Persistent infections with St Louis encephalitis (SLE) virus were established in three mosquito cell lines (Aedes albopictus, A. dorsalis and Culex tarsalis) and were maintained for over 2 years. All three persistently infected cell cultures shared two features: (i) no overt cytopathic effect and (ii) a relatively high proportion of cells infected (41 to 85%). The Aedes persistently infected cultures were resistant to superinfection with the homologous virus but not heterologous viruses. Two significant differences were observed between the Aedes and C. tarsalis persistently infected cell cultures: (i) viral titres in the A. albopictus and A. dorsalis cell cultures decreased slowly over time (the decrease was particularly marked in the A. albopictus cell cultures), whereas titres in the C. tarsalis cell cultures remained relatively constant and (ii) the addition of anti-SLE virus antibody led to decreased virus production in the C. tarsalis cell cultures (one of two cultures was cured of infection), whereas antibody had no effect on the persistently infected Aedes cell cultures. These results suggest that there may be significant differences in the regulation of viral replication and the maintenance of flavivirus persistent infections in mosquito cell lines of different origins.

Aedes↗
PubMed1995

Theiler's murine encephalomyelitis virus 3D RNA polymerase: its expression in the CNS and the specific immune response generated in persistently infected mice.

Intracerebral inoculation of the neurotropic murine picornavirus, Theiler's murine encephalomyelitis virus (TMEV), results either in an acute encephalitis (GDVII strain) or in the establishment of a persistent infection with the development of demyelinating lesions (BeAn strain). In this article, the expression of the viral RNA polymerase was studied in the central nervous system of both acutely and persistently infected mice and in infected cells in tissue culture. Similar numbers of acutely infected glial cells (80-85%) expressed both viral polymerase and structural proteins in vitro while a much smaller proportion of persistently infected glial cells (0.6-0.9%) expressed these proteins. Following infection of mice with GDVII, many cells in the brain were found to express polymerase. However, in the spinal cord of mice persistently infected with BeAn, very few cells were found to express the polymerase while many more cells showed the presence of viral structural proteins. This suggests that a restriction in viral replication, possibly at the level of polymerase expression, may be a feature of the persistent infection. However, enough polymerase was expressed to maintain a polymerase-specific antibody response in a number of infected animals as late as 21 months post-infection. Mechanisms that may be involved in the establishment and maintenance of TMEV persistence are discussed with reference to these findings.

Animals↗
PubMed1998

Quasispecies evolution of a hypervariable region of the feline calicivirus capsid gene in cell culture and in persistently infected cats.

Feline calicivirus (FCV) is a respiratory pathogen of cats that is capable of causing persistent infections. This study examined the evolution of a hypervariable region of the FCV capsid gene both during 90 passages in cell culture and during replication in persistently infected cats. This region of the capsid protein is known to contain neutralization epitopes and may be a target for immune evasion during virus persistence in the host. Sequence analysis showed that FCV exists as a quasispecies which evolved both in cell culture and in persistently infected cats. Changes involved both loss of sequence present in the infecting isolate and a gain of both synonymous and non-synonymous nucleotide substitutions to generate sequences not detected within earlier isolates. Overall, these changes led to a reduction in population heterogeneity over time. Where virus populations were highly homogeneous allowing a consensus sequence to be determined, evolution rates for the consensus sequence ranged from 0.10-1.07 substitutions per nucleotide per year. Marked changes in virus neutralization profiles were seen in isolates obtained sequentially from a persistently infected cat. This was not the case with cell culture passaged virus, suggesting that the individual amino acid changes found only in virus from persistently infected cats may significantly alter the antigenic profile of FCV, and may be the result of immune selection.

Amino Acid Sequence↗
PubMed2005

Porins limit the intracellular persistence of Mycobacterium smegmatis.

The genus Mycobacterium comprises highly pathogenic as well as opportunistic or apathogenic species exhibiting a great variability with respect to their ability to persist or multiply within monocytic host cells. The impact of the permeability of the mycobacterial outer membrane on intracellular persistence was studied. For this purpose, a Mycobacterium smegmatis mutant with a deletion of the major porin gene mspA and a second mutant lacking mspA and the homologous porin gene mspC were used. Deletion of mspA together with mspC significantly enhanced intracellular persistence in murine bone marrow macrophages, the mouse macrophage cell line J774A.1 and Acanthamoeba castellanii. Complementation of mspA in the porin mutant strains resulted in restoration of the wild-type phenotype with respect to intracellular persistence. This is the first report to show that the deletion of porins of mycobacteria results in improved persistence in eukaryotic cells, demonstrating that the intracellular persistence of M. smegmatis depends upon the permeability of the outer membrane.

Acanthamoeba castellanii↗
PubMed2006

A mouse model of persistent brain infection with recombinant Measles virus.

Measles virus (MV) nucleocapsids are present abundantly in brain cells of patients with subacute sclerosing panencephalitis (SSPE). This invariably lethal brain disease develops years after acute measles as result of a persistent MV infection. Various rodent models for MV infection of the central nervous system (CNS) have been described in the past, in which the detection of viral antigens is based on histological staining procedures of paraffin embedded brains. Here, the usage of a recombinant MV (MV-EGFP-CAMH) expressing the haemagglutinin (H) of the rodent-adapted MV-strain CAM/RB and the enhanced green fluorescent protein (EGFP) is described. In newborn rodents the virus infects neurons and causes an acute lethal encephalitis. From 2 weeks on, when the immune system of the genetically unmodified animal is maturating, intracerebral (i.c.) infection is overcome subclinically, however, a focal persistent infection in groups of neurons remains. The complete brain can be analysed in 50 or 100 microm slices, and infected autofluorescent cells are readily detected. Seven and 28 days post-infection (p.i.) 86 and 81% of mice are infected, respectively, and virus persists for more than 50 days p.i. Intraperitoneal immunization with MV 1 week before infection, but not after infection, protects and prevents persistence. The high percentage of persistence demonstrates that this is a reliable and useful model of a persistent CNS infection in fully immunocompetent mice, which allows the investigation of determinants of the immune system.

Age Factors↗
PubMed2001

Numerical study of persistence in models with absorbing states.

Extensive Monte Carlo simulations are performed in order to evaluate both the local (straight theta(l)) and global (straight theta(g)) persistence exponents in the Ziff-Gulari-Barshad (ZGB) [Phys. Rev. Lett. 56, 2553 (1986)] irreversible reaction model. At the second-order irreversible phase transition (IPT) we find that both the local and the global persistence exhibit power-law behavior with a crossover between two different time regimes. On the other hand, at the ZGB first-order IPT, active sites are short lived and the persistence decays more abruptly; it is not clear whether it shows power-law behavior or not. In order to analyze universality issues, we have also studied another model with absorbing states, the contact process, and evaluated the local persistence exponent in dimensions from 1 to 4. A striking apparent superuniversality is reported: the local persistence exponent seems to coincide in both one- and two-dimensional systems. Some other aspects of persistence in systems with absorbing states are also analyzed.

Journal Article↗
PubMed2001

Persistence in the one-dimensional A+B--> Ø reaction-diffusion model.

The persistence properties of a set of random walkers obeying the A+B--> Ø reaction, with equal initial density of particles and homogeneous initial conditions, is studied using two definitions of persistence. The probability P(t) that an annihilation process has not occurred at a given site has the asymptotic form P(t) approximately const+t(-straight theta), where straight theta is the persistence exponent (type I persistence). We argue that, for a density of particles rho>>1, this nontrivial exponent is identical to that governing the persistence properties of the one-dimensional diffusion equation, partial differential(t)straight phi= partial differential(xx)straight phi, where straight theta approximately 0.1207 [S. N. Majumdar, C. Sire, A. J. Bray, and S. J. Cornell, Phys. Rev. Lett. 77, 2867 (1996)]. In the case of an initial low density, rho(0)<<1, we find straight theta approximately 1/4 asymptotically. The probability that a site remains unvisited by any random walker (type II persistence) is also investigated and found to decay with a stretched exponential form, P(t) approximately exp(-constxrho(1/2)(0)t(1/4)), provided rho(0)<<1. A heuristic argument for this behavior, based on an exactly solvable toy model, is presented.

Journal Article↗
PubMed2003

Joint persistence of transformation products in chemicals assessment: case studies and uncertainty analysis.

The joint persistence (JP) quantifies the environmental persistence of a parent compound and a selection of relevant transformation products. Here, the importance as well as the uncertainty of the JP in comparison to the persistence of the parent compound alone (primary persistence, PP) are investigated. To demonstrate the effect of transformation products on the environmental persistence of organic chemicals, three case studies of parent compounds (nonylphenol ethoxylates, perchloroethylene, atrazine) and transformation products are investigated in detail with a multimedia fate model. Comparison of the PP and JP values shows that transformation products can significantly increase the persistence. In addition to the point estimates of PP and JP, the associated uncertainties are investigated. For each of the case studies, the chemical-specific input parameters of all compounds are varied and the corresponding variance of the PP and JP is determined by Monte Carlo simulations. Interestingly, the higher number of input parameters required for the JP does not necessarily increase the uncertainty of the JP as compared to that of the PP alone. An exact mathematical expression specifying the contribution of each transformation product to the JP is given. When transformation products are grouped in different generations, it becomes discernible that the first generation increases the JP most; the later generations are of decreasing importance. Finally, the effect of incomplete knowledge of the transformation products and their properties on the JP results is discussed. For reliable JP estimates, knowledge of the first generation transformation products and their degradation rate constants is required.

Journal Article↗
PubMed1988

Persistent infection with herpes simplex virus type 1 in an Ia antigen-positive murine macrophage cell line.

The interaction of herpes simplex virus type 1 (HSV-1) with murine macrophage cell lines was examined. The cell lines appeared to be moderately permissive for HSV-1 replication, though the yield of the virus was limited compared with that in Vero cells. Furthermore, the murine macrophage cell line SL-1, bearing Ia antigen, was persistently infected with HSV-1 for over one year, and was designated SL-1/KOS. Persistent infection could not be established in an Ia antigen-negative macrophage cell line, SL-4. In the SL-1/KOS culture, there was a small number of infected cells as revealed by infectious center assay. Treatment with monoclonal antibody against HSV-1 cured the persistent infection. Therefore maintenance of the persistent infection is considered to be due to a carrier culture consisting of a minority of infected cells and a majority of uninfected cells. In the SL-1/KOS cultures a low level of interferon (IFN) was found. When a large amount of exogenous recombinant murine IFN-beta (10(5)-10(6) international units/ml) was added to the culture, virus production diminished to undetectable levels. These results suggest that IFN plays an important role in the maintenance of persistent infection. In long-term persistently infected cultures, syncytium formation appeared and the virus from such cultures had a different DNA structure from that of the virus originally used for infection as revealed by restriction endonuclease analysis.

Animals↗
PubMed1993

Transient and persistent expansions of large granular lymphocytes (LGL) and NK-associated (NKa) cells: the Yorkshire Leukaemia Group Study.

A survey of 870 different adult blood samples (primarily from patients with non-haematological disorders) found that 269 (31%) had increased proportions (> 25%) and/or absolute numbers (> 1.0 x 10(9)/l) of morphologically-defined large granular lymphocytes (LGL), and/or phenotypically-defined NK-associated (NKa) cells. Of these, 112 were re-analysed at least 6 months after initial presentation and were classified as 'persistent' (92/112) or 'transient' (20/112) according to whether or not the original abnormality was still present. Lymphocyte counts in most patients with persistent abnormalities were within normal limits (18/92) or slightly increased (68/92), with only six having a lymphocytosis exceeding 10.0 x 10(9)/l. With the exception of five persistent LGL expansions in which the granular lymphocytes did not express NKa determinants (designated LGL+NKa-), the remaining 87 cases could be phenotypically grouped according to their primary abnormality as CD8+NKa+ (n = 33), CD4+ NKa+ (n = 14), CD8dim+NKa+ (n = 7) or CD8-NKa+ (n = 33). TCR genotypic studies in 58 patients showed that the 16 patients with rearranged TCR components were restricted to the CD8+NKa+ group and that, in most of these, the CD8+ fraction showed abnormal relative CD16/CD56 expression. Persistent neutropenia (n = 15) also appeared to be associated with primary abnormalities of CD8+NKa+ cells (12/15), with 10 of these additionally showing rearranged TCR genes. In contrast, persistently increased CD8dim+NKa+ and CD8-NKa+ components did not appear to phenotypically differ from their corresponding 'counterparts' in normal bloods or in patients with transient LGL/NKa+ abnormalities. This survey has therefore established that persistent LGL/NKa+ abnormalities are considerably more common than suggested in published work, that a high proportion of patients with expanded CD8+NKa+ components, with quite diverse clinical histories, show evidence of clonal lymphoid populations, and that the clonal nature of such disorders appears to be associated with abnormal NKa phenotypic patterns.

Adult↗
PubMed2005

Prevalence of persistent pain after endodontic treatment and factors affecting its occurrence in cases with complete radiographic healing.

AIMS: To (i) determine the prevalence of persistent dento-alveolar pain following nonsurgical and/or surgical endodontic treatment conducted in a teaching dental hospital and (ii) identify the risk factors associated with persistent pain after apparently successful root canal treatment. STUDY DESIGN: A total of 175 patients/teeth were reviewed 12-59 months following treatment. The patients were examined clinically and radiographically and a detailed pain history obtained. Multiple logistic regression analysis was used to investigate the association between potential risk factors and persistent pain after successful endodontic treatment. RESULTS: The prevalence of persistent pain after successful root canal treatment was 12% (21/175). Treatment success was determined by the absence of clinical and radiographic signs of dental disease. The factors that were significantly (P < 0.05) associated with persistent pain following endodontic treatment were: 'duration of preoperative pain' [odds ratio (OR) = 8.6], 'preoperative pain from the tooth' (OR = 7.8), 'preoperative tenderness to percussion' (OR = 7.8), 'previous chronic pain problems' (OR = 4.5), 'gender' (OR = 4.5) and 'history of painful treatment in the orofacial region' (OR = 3.8). 'Type of treatment received (surgical or nonsurgical treatment)' showed borderline significance at the 10% level. CONCLUSIONS: The presence and duration of preoperative pain from the tooth site, lasting at least 3 months, a positive history of previous chronic pain experience or painful treatment in the orofacial region, and female gender were important risk factors associated with persistent pain after successful endodontic treatment.

Adolescent↗
PubMed2006

Treatment persistence: a comparison among patients with schizophrenia who were initiated on atypical antipsychotic agents.

BACKGROUND: Although clinical trials have demonstrated the efficacy of atypical antipsychotic agents in reducing symptoms of schizophrenia, the likelihood of sustaining control of schizophrenic symptoms may depend on treatment persistence. OBJECTIVE: In this study, we compared treatment persistence between patients who were initiated on risperidone or olanzapine, the two most widely prescribed atypical antipsychotic agents. METHOD: We identified patients with schizophrenia by ICD-9-CM codes (> or =1 inpatient or > or =2 outpatient ICD-9-CM codes > or =7 days apart) between 1 July 1998 and 30 June 1999. We further selected those who were prescribed the target drug during 1 April 1999 through 31 March 2000 provided that they were not on any antipsychotic agents during the prior 6 months. Using event history analysis, we compared the treatment persistence in terms of hazard ratio between olanzapine and risperidone initiators, adjusting for patient's sociodemographic and clinical characteristics. RESULTS: Following the initiation of the target drug, more patients switched from risperidone to olanzapine than vice versa. However, among patients with schizophrenia who had comorbid diabetes, there were more patients who made a switch from olanzapine to risperidone; whereas among those who used anxiolytics, there were more patients who switched from risperidone to olanzapine. Finally, olanzapine initiators had decreased hazards of discontinuation by 14% (unadjusted; P < 0.001) and 12% (adjusted; P = 0.002), respectively, than risperidone initiators. CONCLUSIONS: Compared with risperidone, olanzapine seems to be better tolerated by patients as indicated by better treatment persistence. As such, initiation of olanzapine may increase the likelihood of sustaining control of symptoms of schizophrenia. Future research needs to provide a more comprehensive assessment of treatment persistence by considering other antipsychotic agents in the study and developing models to assess treatment persistence and switching as two interdependent competing risks.

Adolescent↗