156 research outputs found
Structural and Electronic Properties of Small Neutral (MgO)n Clusters
Ab initio Perturbed Ion (PI) calculations are reported for neutral
stoichiometric (MgO)n clusters (n<14). An extensive number of isomer structures
was identified and studied. For the isomers of (MgO)n (n<8) clusters, a full
geometrical relaxation was considered. Correlation corrections were included
for all cluster sizes using the Coulomb-Hartree-Fock (CHF) model proposed by
Clementi. The results obtained compare favorably to the experimental data and
other previous theoretical studies. Inclusion of correlaiotn is crucial in
order to achieve a good description of these systems. We find an important
number of new isomers which allows us to interpret the experimental magic
numbers without the assumption of structures based on (MgO)3 subunits. Finally,
as an electronic property, the variations in the cluster ionization potential
with the cluster size were studied and related to the structural isomer
properties.Comment: 24 pages, LaTeX, 7 figures in GIF format. Accepted for publication in
Phys. Rev.
Structural Transitions and Global Minima of Sodium Chloride Clusters
In recent experiments on sodium chloride clusters structural transitions
between nanocrystals with different cuboidal shapes were detected. Here we
determine reaction pathways between the low energy isomers of one of these
clusters, (NaCl)35Cl-. The key process in these structural transitions is a
highly cooperative rearrangement in which two parts of the nanocrystal slip
past one another on a {110} plane in a direction. In this way the
nanocrystals can plastically deform, in contrast to the brittle behaviour of
bulk sodium chloride crystals at the same temperatures; the nanocrystals have
mechanical properties which are a unique feature of their finite size. We also
report and compare the global potential energy minima for (NaCl)NCl- using two
empirical potentials, and comment on the effect of polarization.Comment: extended version, 13 pages, 8 figures, revte
Phosphorylation of Serine 248 of C/EBPα Is Dispensable for Myelopoiesis but Its Disruption Leads to a Low Penetrant Myeloid Disorder with Long Latency
BACKGROUND: Transcription factors play a key role in lineage commitment and differentiation of stem cells into distinct mature cells. In hematopoiesis, they regulate lineage-specific gene expression in a stage-specific manner through various physical and functional interactions with regulatory proteins that are simultanously recruited and activated to ensure timely gene expression. The transcription factor CCAAT/enhancer binding protein α (C/EBPα) is such a factor and is essential for the development of granulocytic/monocytic cells. The activity of C/EBPα is regulated on several levels including gene expression, alternative translation, protein interactions and posttranslational modifications, such as phosphorylation. In particular, the phosphorylation of serine 248 of the transactivation domain has been shown to be of crucial importance for granulocytic differentiation of 32Dcl3 cells in vitro. METHODOLOGY/PRINCIPAL FINDINGS: Here, we use mouse genetics to investigate the significance of C/EBPα serine 248 in vivo through the construction and analysis of Cebpa(S248A/S248A) knock-in mice. Surprisingly, 8-week old Cebpa(S248A/S248A) mice display normal steady-state hematopoiesis including unaltered development of mature myeloid cells. However, over time some of the animals develop a hematopoietic disorder with accumulation of multipotent, megakaryocytic and erythroid progenitor cells and a mild impairment of differentiation along the granulocytic-monocytic lineage. Furthermore, BM cells from Cebpa(S248A/S248A) animals display a competitive advantage compared to wild type cells in a transplantation assay. CONCLUSIONS/SIGNIFICANCE: Taken together, our data shows that the substitution of C/EBPα serine 248 to alanine favors the selection of the megakaryocytic/erythroid lineage over the monocytic/granulocytic compartment in old mice and suggests that S248 phosphorylation may be required to maintain proper hematopoietic homeostasis in response to changes in the wiring of cellular signalling networks. More broadly, the marked differences between the phenotype of the S248A variant in vivo and in vitro highlight the need to exert caution when extending in vitro phenotypes to the more appropriate in vivo context
Critical Role of Constitutive Type I Interferon Response in Bronchial Epithelial Cell to Influenza Infection
Innate antiviral responses in bronchial epithelial cells (BECs) provide the first line of defense against respiratory viral infection and the effectiveness of this response is critically dependent on the type I interferons (IFNs). However the importance of the antiviral responses in BECs during influenza infection is not well understood. We profiled the innate immune response to infection with H3N2 and H5N1 virus using Calu-3 cells and primary BECs to model proximal airway cells. The susceptibility of BECs to influenza infection was not solely dependent on the sialic acid-bearing glycoprotein, and antiviral responses that occurred after viral endocytosis was more important in limiting viral replication. The early antiviral response and apoptosis correlated with the ability to limit viral replication. Both viruses reduced RIG-I associated antiviral responses and subsequent induction of IFN-β. However it was found that there was constitutive release of IFN-β by BECs and this was critical in inducing late antiviral signaling via type I IFN receptors, and was crucial in limiting viral infection. This study characterizes anti-influenza virus responses in airway epithelial cells and shows that constitutive IFN-β release plays a more important role in initiating protective late IFN-stimulated responses during human influenza infection in bronchial epithelial cells
Enterovirus 71 3C Protease Cleaves a Novel Target CstF-64 and Inhibits Cellular Polyadenylation
Identification of novel cellular proteins as substrates to viral proteases would provide a new insight into the mechanism of cell–virus interplay. Eight nuclear proteins as potential targets for enterovirus 71 (EV71) 3C protease (3Cpro) cleavages were identified by 2D electrophoresis and MALDI-TOF analysis. Of these proteins, CstF-64, which is a critical factor for 3′ pre-mRNA processing in a cell nucleus, was selected for further study. A time-course study to monitor the expression levels of CstF-64 in EV71-infected cells also revealed that the reduction of CstF-64 during virus infection was correlated with the production of viral 3Cpro. CstF-64 was cleaved in vitro by 3Cpro but neither by mutant 3Cpro (in which the catalytic site was inactivated) nor by another EV71 protease 2Apro. Serial mutagenesis was performed in CstF-64, revealing that the 3Cpro cleavage sites are located at position 251 in the N-terminal P/G-rich domain and at multiple positions close to the C-terminus of CstF-64 (around position 500). An accumulation of unprocessed pre-mRNA and the depression of mature mRNA were observed in EV71-infected cells. An in vitro assay revealed the inhibition of the 3′-end pre-mRNA processing and polyadenylation in 3Cpro-treated nuclear extract, and this impairment was rescued by adding purified recombinant CstF-64 protein. In summing up the above results, we suggest that 3Cpro cleavage inactivates CstF-64 and impairs the host cell polyadenylation in vitro, as well as in virus-infected cells. This finding is, to our knowledge, the first to demonstrate that a picornavirus protein affects the polyadenylation of host mRNA
Characterisation of secreted exosomes from the intestinal nematode Heligmosomoides polygyrus
The parasite secretome has been shown to play a key role in both pathogenicity and
the regulation of host defence, allowing pathogens, such as helminths, to establish a
chronic infection within the host. The recently discovered presence of extracellular
vesicles within parasite-derived excretory-secretory products introduces a new
mechanism of potential cross-species communication. Extracellular vesicles (EVs),
such as exosomes, facilitate cellular communication through the transfer of small
RNAs, lipids and proteins between cells and organisms across all three kingdoms of
life. In addition to their roles in normal physiology, EVs also transport molecules
from pathogens to hosts, presenting parasite antigens and transferring infectious
agents.
Here, I examine secreted vesicles from the murine gastrointestinal nematode
Heligmosomoides polygyrus, and their potential role in the host-helminth
interactions. Transmission electron microscopy reveals vesicle-like structures of 50-
100 nM in the ultracentrifuged secretory product, and potential evidence of multi-vesicular
bodies in the worm intestine. This, coupled with information from the
exoproteome, helped support the hypothesis that exosomes originate from the
parasite intestinal tract.
I have completed a series of studies looking at the fundamental properties of
exosome-cell interactions, providing comparative studies between mammalian and
H. polygyrus-derived exosomes. I have determined some of the key factors
influencing exosome uptake, including time of incubation, cell type and exosome
origin. Through microarray analysis of H. polygyrus exosome-treated small
intestinal epithelial cells, we see significant gene expression changes, including those
involved in the regulation of signalling and the immune response, such as DUSP1
(dual-specificity phosphatase) and IL1RL1 (the receptor for IL-33). The modest
reduction of inflammatory cytokine responses by exosomes in small intestinal cell
lines was amplified in immune cells, such as macrophages. Exosomes can
significantly reduce expression of classical activation markers, as well as
inflammatory cytokine production in the macrophage cell line RAW 264.7, and this
is further supported by similar responses in bone marrow-derived macrophages.
Owing to their suppressive nature, I demonstrate that immunization of mice
with an exosome/alum conjugate generates significant protection from a subsequent
H. polygyrus larval challenge, as seen through a reduction in egg counts and worm
burden.
I have investigated the role of the IL33 receptor (IL-33R); a key molecule
associated with parasitic resistance that is suppressed by exosomes in type-2
associated immune responses. Uptake of H. polygyrus-derived exosomes by
alternatively activated macrophages caused the suppression of type 2
cytokine/protein release and the reduction of key genes associated with this
phenotype. In addition, there was also significant repression of both transcript and
surface T1/ST2, a subunit of the IL-33R). Using a model of lung inflammation, in
vivo studies demonstrate that, in both prophylactic and co-administration
experiments, exosomes modulate the innate cellular response. This is represented by
changes in the number of innate lymphoid cells (ILCs), bronchoalveolar lavage
eosinophils and type-2 cytokine output. In this system, the expression of T1/ST2 on
type 2 ILCs was also significantly reduced.
I have extended the investigation on exosome-IL-33R responses by using
T1/ST2 knockout mice. Despite generating strong antibody responses, vaccination
against exosomes could not protect T1/ST2 knockout mice against a subsequent
infection.
This work suggests that exosomes secreted by nematodes could mediate the
transfer and uptake of parasite products into host cells, establishing cross-species
communication to suppress the host ‘danger’ or inflammatory response
Trichomonas vaginalis: Clinical relevance, pathogenicity and diagnosis
Trichomonas vaginalis is the etiological agent of trichomoniasis, the most prevalent non-viral sexually transmitted disease worldwide. Trichomoniasis is a widespread, global health concern and occurring at an increasing rate. Infections of the female genital tract can cause a range of symptoms, including vaginitis and cervicitis, while infections in males are generally asymptomatic. The relatively mild symptoms, and lack of evidence for any serious sequelae, have historically led to this disease being under diagnosed, and under researched. However, growing evidence that T. vaginalis infection is associated with other disease states with high morbidity in both men and women has increased the efforts to diagnose and treat patients harboring this parasite. The pathology of trichomoniasis results from damage to the host epithelia, caused by a variety of processes during infection and recent work has highlighted the complex interactions between the parasite and host, commensal microbiome and accompanying symbionts. The commercial release of a number of nucleic acid amplification tests (NAATs) has added to the available diagnostic options. Immunoassay based Point of Care testing is currently available, and a recent initial evaluation of a NAAT Point of Care system has given promising results, which would enable testing and treatment in a single visit
SARS in Taiwan:an overview and lessons learned
SummaryObjectives:This report aims to describe the epidemiology of severe acute respiratory syndrome (SARS) in Taiwan between March and July 2003, and to examine the public health response.Methods:Surveillance for SARS was initiated on 14 March 2003. Response activities are described for the isolation of patients; contact tracing; quarantine of contact persons; fever screening for inbound and outbound passengers at the airport; and hospital infection control as assessed by mobile SARS containment teams.Results:Between 14 March and 30 July 2003 a total of 668 probable cases of SARS were reported. Of the 668 cases, 181 (27%) were fatal. Compared to the survivors, fatal cases were more likely to be older (p<0.001), male (p<0.05), exposed through hospital contact (p<0.001), and have a coexisting medical disorder (p<0.001). Between 28 March and 30 July a total of 151,270 persons were quarantined. Among them, 46 (3.0/10,000) were subsequently classified as being probable SARS cases. At the time of the mobile team assessments, 46 (53%) hospitals had implemented WHO infection control recommendations.Conclusions:In this outbreak, an emergency plan consisted of patient isolation and strict hospital infection control
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