7,559 research outputs found
A well-conserved Plasmodium falciparum var gene shows an unusual stage-specific transcript pattern
No full textThe var multicopy gene family encodes Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) variant antigens, which, through their ability to adhere to a variety of host receptors, are thought to be important virulence factors. The predominant expression of a single cytoadherent PfEMP1 type on an infected red blood cell, and the switching between different PfEMP1 types to evade host protective antibody responses, are processes thought to be controlled at the transcriptional level. Contradictory data have been published on the timing of var gene transcription. Reverse transcription-polymerase chain reaction (RT-PCR) data suggested that transcription of the predominant var gene occurs in the later (pigmented trophozoite) stages, whereas Northern blot data indicated such transcripts only in early (ring) stages. We investigated this discrepancy by Northern blot, with probes covering a diverse var gene repertoire. We confirm that almost all var transcript types were detected only in ring stages. However, one type, the well-conserved varCSA transcript, was present constitutively in different laboratory parasites and does not appear to undergo antigenic variation. Although varCSA has been shown to encode a chondroitin sulphate A (CSA)-binding PfEMP1, we find that the presence of full-length varCSA transcripts does not correlate with the CSA-binding phenotype
The role of Plasmodium falciparum var genes in malaria in pregnancy
No full textSequestration of Plasmodium falciparum-infected erythrocytes in the placenta is responsible for many of the harmful effects of malaria during pregnancy. Sequestration occurs as a result of parasite adhesion molecules expressed on the surface of infected erythrocytes binding to host receptors in the placenta such as chondroitin sulphate A (CSA). Identification of the parasite ligand(s) responsible for placental adhesion could lead to the development of a vaccine to induce antibodies to prevent placental sequestration. Such a vaccine would reduce the maternal anaemia and infant deaths that are associated with malaria in pregnancy. Current research indicates that the parasite ligands mediating placental adhesion may be members of the P. falciparum variant surface antigen family PfEMP1, encoded by var genes. Two relatively well-conserved subfamilies of var genes have been implicated in placental adhesion, however, their role remains controversial. This review examines the evidence for and against the involvement of var genes in placental adhesion, and considers whether the most appropriate vaccine candidates have yet been identified
Virulence of malaria is associated with differential expression of Plasmodium falciparum var gene subgroups in a case-control study
No full textPlasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) is a major pathogenicity factor in falciparum malaria that mediates cytoadherence. PfEMP1 is encoded by approximately 60 var genes per haploid genome. Most var genes are grouped into 3 subgroups: A, B, and C. Evidence is emerging that the specific expression of these subgroups has clinical significance. Using field samples from children from Papua New Guinea with severe, mild, and asymptomatic malaria, we compared proportions of transcripts of var groups, as determined by quantitative polymerase chain reaction. We found a significantly higher proportion of var group B transcripts in children with clinical malaria (mild and severe), whereas a large proportion of var group C transcripts was found in asymptomatic children. These data from naturally infected children clearly show that major differences exist in var gene expression between parasites causing clinical disease and those causing asymptomatic infections. Furthermore, parasites forming rosettes showed a significant up-regulation of var group A transcripts
Identification of Plasmodium falciparum var1CSA and var2CSA domains that bind IgM natural antibodies
No full textMalaria in pregnancy is responsible for maternal anaemia, low-birth-weight babies and infant deaths. Plasmodium falciparum infected erythrocytes are thought to cause placental pathology by adhering to host receptors such as chondroitin sulphate A (CSA). CSA binding infected erythrocytes also bind IgM natural antibodies from normal human serum, a process that may facilitate placental adhesion or promote immune evasion. The parasite ligands that mediate placental adhesion are thought to be members of the variant erythrocyte surface antigen family P. falciparum erythrocyte membrane protein 1 (PfEMP1), encoded by the var genes. Two var gene sub-families, var1CSA and var2CSA, have been identified as parasite CSA binding ligands and are leading candidates for a vaccine to prevent pregnancy-associated malaria. We investigated whether these two var gene subfamilies implicated in CSA binding are also the molecules responsible for IgM natural antibody binding. By heterologous expression of domains in COS-7 cells, we found that both var1CSA and var2CSA PfEMP1 variants bound IgM, and in both cases the binding region was a DBL epsilon domain occurring proximal to the membrane. None of the domains from a control non-IgM-binding parasite (R29) bound IgM when expressed in COS-7 cells. These results show that PfEMP1 is a parasite ligand for non-immune IgM and are the first demonstration of a specific adhesive function for PfEMP1 epsilon type domains
Hvordan påvirker ISIL sine tap av ressurser, gruppens evne til å bruke propaganda og sosiale medier som strategi for å nå sine målsetninger?
No full textTerrorgruppen kjent som blant annet den Islamske staten i Irak og Levanten
(ISIL), erobret på sitt toppunkt et område på størrelse med Storbritannia.
23 mars 2019 erklærte den kurdisk ledede frie arme, at de hadde tatt den siste ISIL kontrollerte byen Baghuz i Syria (BBC, monitoring, 2019 23.mars). Med dette mistet ISIL kontrollen over sine kjerneområder i Syria og Irak, og dermed viktige ressurser. Oppgavens hovedtema vil være ISIL sin bruk av propaganda og sosiale medier i en digital strategi for å nå målsetninger. Oppgaven vil se på om ressursene gruppen disponerte gjorde at ISIL kunne bruke denne strategien mer effektivt, eller om tap av ressurser ikke påvirker dette. Når ISIL var på topp politisk, økonomisk og militært, kontrollerte gruppen ressurser ingen annen terrorgruppe har hatt tidligere. Dette var i form av territorielle, finansielle og menneskelige ressurser. Oppgaven vil forsøke å vise, hvordan disse ressursene muliggjorde for ISIL å bygge opp et statslignende apparat med ulike departementer, også innenfor media og kommunikasjon. ISIL benyttet seg til det fulle av mulighetene innenfor teknologi, internett, sosiale medier og propaganda i en vellykket medieoperasjon. Oppgaven vil se om den gradvise svekkelsen av gruppen og tap av ressurser har svekket denne medieoperasjonen eller ikke. Noen av funnene i oppgaven tyder på at suksessen bak ISIL sin medieoperasjon, lå i ressursene i kalifatet, spesielt evnen til å holde på territorium, som gav handlingsrom til produksjon og koordinering av propaganda. Andre funn tyder på at det er elementer ved ISIL sin organisasjonsstruktur som kan hjelpe gruppen til å nå sine målsetninger, selv om ISIL mister sine ressurser. ISIL sin hovedmålsetning er opprettelsen av kalifatet her og nå, noe de gjorde i 2014. Opprettelsen av kalifatet er å anse som gruppens hovedmålsetning. Ettersom gruppen nå er bekjempet i kjerneområdene, vil gruppen forsøke en reetablering av det fysiske kalifatet som oppgaven vil definere innenfor hovedmålsetningen. ISIL vil også gjøre strategiske grep for å overleve, dette vil oppgaven definere som et delmål . Oppgaven vil se på hvordan ISIL sin medieoperasjon herunder bruk av propaganda og sosiale medier støtter oppunder disse definerte målsetningene, ved å sammenligne ISIL sin bruk av propaganda og sosiale medier i 2 perioder. Hvor den ene blir definert som en periode med tilgang på ressurser og den andre med tap av ressurser. Dette vil forhåpentligvis kunne bidra til å se om ISIL sin effektive medieoperasjon var knyttet til ressursene i kalifatet, eller om de effektivt kan bruke propaganda og sosiale medier selv om ressursene som lå i kjerneområdene er tapt
Response of Venezuelan output to monetary policy, deficit spending, and currency depreciation: a VAR model
No full textThis study applies the VAR model to find possible responses of real GDP to selected macroeconomic variables in Venezuela. Based on an annual sample during 1961 - 2001, the author finds that the real GDP responds positively to a shcock to real M2 , goverment déficit spending, exchange rate depreciation, and the lagged output and negatively to a shick to the inflation rate during some of the time periods. Except for the lagged output, government deficit spending and the inflation rate are the most influential variable in the first year, and real M2 and the real exchange rate are more influential and have longer - term after the first year.Modelo VAR, política monetaria, déficit
Modelling and Forecasting Dynamic VaR Thresholds for Risk Management and Regulation
No full textThe paper presents methods of estimating Value-at-Risk (VaR) thresholds utilising two calibrated models and three conditional volatility or GARCH models. These are used to estimate and forecast the VaR thresholds of an equally-weighted portfolio, comprising: the S & P500, CAC40, FTSE100 a Swiss market index (SMI). On the basis of the number of (non-)violations of the Basel Accord thresholds, the best performing model is PS-GARCH, followed by VARMA-AGARCH, then Portfolio-GARCH and the RiskmetricsTM -EWMA models, both of which would attract a penalty of 0.5. The worst forecasts are obtained from the standard normal method based on historical variances.Value at Risk (VaR) modelling, forecasting risk thresholds, Portfolio Spillover-Garch, risk management and regulation Acknowledgements: The authors wish to thank Felix Chan, Suhejla Hoti, Alex Zsimayer and seminar participants at the Institute of Economics, Academia Sinica, Taiwan, Ling Tung Institute of Technology, Griffith University, Queensland University of Technology, and University of Queensland for helpful comments and suggestions. The first and second authors wish to thank the Australian Research Council for financial support. The third author wishes to acknowledge a University Postgraduate Award and an International Postgraduate Research Scholarship at the University of Western Australia.
Inflationary effects of oil prices and domestic gasoline prices: Markov-switching-VAR analysis
No full textThe purpose of this study is to contribute to the literature by studying the effects of sudden changes both on crude oil import price and domestic gasoline price on inflation for Turkey, an emerging country. Since an inflation targeting regime is being carried out by the Central Bank of Turkey, determination of such effects is becoming more important. Therefore empirical evidence in this paper will serve as guidance for those countries, which have an inflation targeting regime. Analyses have been done in the period of October 2005-December 2012 by Markov-switching vector autoregressive (MS-VAR) models which are successful in capturing the nonlinear properties of variables. Using MS-VAR analysis, it is found that there are 2 regimes in the analysis period. Furthermore, regime changes can be dated and the turning points of economic cycles can be determined. In addition, it is found that the effect of the changes in crude oil and domestic gasoline prices on consumer prices and core inflation is not the same under different regimes. Moreover, the sudden increase in gasoline price is more important for consumer price inflation than crude oil price shocks. Another finding is the presence of a pass-through effect from oil price and gasoline price to core inflation
The Specification of the Regime Structure in Turkish Economy with MS-VAR
No full textThe Specification of the Regime Structure in Turkish Economy with MS-VAR The structural changes in Turkey's economy which began in 1980, ended at the beginnings of 1990 by the completion of the process, then stepped in a term during which economy is frequently faced to face crises with the effect of internal and external shocks and serious fluctuations is observed. In this term, the general situation of economy can be explained shortly as spiral of high real interest rates, entries of hot money, low value of national currency as a result of frequent and huge devaluations in the value of national currency. Since 2002, transition to the strong economy program has been put into practice as a result of crises with the effect of crises experienced at the end of 1990 and at the beginning of 2000. Short summary of this term points out that various structures are the case in Turkish economy. The aim of this paper is to present the regime structure of Turkey's economy in the period from the beginning of 1990 to 2007, in other words, determination of regime change periods. In this study, Markov switching vector autoregressive (MS-VAR) models are used in determining the regime structure. Analyses are done for the period 1992:01-2007:03 by using current account, GDP growth rate, ratio of import coverage by export and interest rate series which are important and continuously observed macroeconomic variables and findings of this analyze exhibit the existence of three different regimes in this time period. This study's findings, especially related to the particular characteristics of pre-crisis period, contribute to reduce uncertainty and guide for decision makers in money and financial markets
The taxonomic status of Bryum arachnoideum C. Müll. and B. lanatum (P. Beauv.) Brid.
No full textA study of an isotype of Bryum arachnoideum C. Müll., a poorly understood species described from tropical Africa, revealed that this species is distinct from B. argenteum Hedw. var. lanatum (P. Beauv.) Hampe. The differences between both species are listed. All specimens from tropical Africa named as B. arachnoideum by the author must be attributed to B. argenteum var. lanatum. The differences between B. argenteum var. argenteum and var. lanatum, both morphologically and ecologically, are so important that it is proposed to treat var. lanatum on a species level as B. lanatum (P. Beauv.) Brid
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