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Search Results: 1 - 10 of 67 matches for " Jurg;Druilhe "
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Mechanisms of immune protection in the asexual blood stage infection by Plasmodium falciparum: analysis by in vitro and ex-vivo assays
Gysin, Jurg;Druilhe, Pierre;Silva, Luiz Pereira da;
Memórias do Instituto Oswaldo Cruz , 1992, DOI: 10.1590/S0074-02761992000900023
Abstract: mechanisms of immune protection against the asexual blood stage infection by plasmodium falciparum are reviewed. recent studies of two independent lines of research developed at the institute pasteur, in humans and primate infections clearly indicate an obligatory interaction of antibodies and effector cells to express the anti-parasitic effect.
Analysis of Ringing and Noise in FE and FDTD Calculated Acoustic Pulse Profiles  [PDF]
Arthur Every, Laurent Aebi, Jurg Dual
Applied Mathematics (AM) , 2012, DOI: 10.4236/am.2012.330191
Abstract: Ringing, i.e. the emergence of an oscillatory tail behind a wave pulse as it propagates through a medium, is a pervasive artefact in FE and FDTD calculated waveforms. It is known to be a consequence of numerical dispersion arising from the discretization of the equations of motion. The use of an irregular mesh in a FE code has the further consequence of rendering the displacement field increasingly noisy with distance behind the wave front. In this paper these effects are illustrated using the commercial FE package ABAQUS with square and irregular triangular meshes to calculate the progress of a longitudinally polarized Ricker pulse along the axis of a cylindrically shaped aluminium specimen. We are able to give a precise analytical account of the evolution of ringing on the basis of a low order approximation for the dispersion relation of the discretized equations of motion. A qualitative account is provided of the generation of noise in the use of an irregular triangular mesh.
The malaria candidate vaccine liver stage antigen-3 is highly conserved in Plasmodium falciparum isolates from diverse geographical areas
Eric Prieur, Pierre Druilhe
Malaria Journal , 2009, DOI: 10.1186/1475-2875-8-247
Abstract: The whole 4680 bp genomic sequence of lsa-3 was amplified by polymerase chain reaction and sequenced. The clinical isolate sequences were aligned on the sequence of the laboratory reference P. falciparum strain 3D7.The non-repeated sequence of lsa-3 was very well conserved with only a few allelic variations scattered along the sequence. Interestingly, a formerly identified immunodominant region, employed for the majority of pre-clinical vaccine development, was totally conserved at the genetic level. The most significant variations observed were in the number and organization of tetrapeptide repeated units, but not in their composition, resulting in different lengths of these repeated regions. The shorter repeated regions were from Brazilian origin. A correlation between the geographical distribution of the parasites with single nucleotide polymorphisms was not detected.The lack of correlation between allelic polymorphisms with a specific transmission pressure suggests that LSA-3 is a structurally constrained molecule. The unusual characteristics of the lsa-3 gene make the molecule an interesting candidate for a subunit vaccine against malaria.The human malaria parasite Plasmodium falciparum is responsible for 300-500 million clinical cases and 1-2 million deaths every year mainly among young African children [1]. The incidence of malaria among travellers from non-endemic areas is on the rise [2]. The emergence and spread of resistances against anti-malarial drugs makes the development of a vaccine an urgent need. Na?ve volunteers immunized with radiation-attenuated sporozoites [3], the form of the parasite injected in the host by a mosquito bite, but not killed parasites, were protected from a challenge with wild-type parasites. This observation suggests that the partial intra-hepatic development of the parasite was necessary to confer protection against the pre-erythrocytic (PE) stages of P. falciparum as it has been further verified with recently developed geneti
Conformal Field Theory and Geometry of Strings
Jurg Frohlich,Krzysztof Gawedzki
Physics , 1993,
Abstract: What is quantum geometry? This question is becoming a popular leitmotiv in theoretical physics and in mathematics. Conformal field theory may catch a glimpse of the right answer. We review global aspects of the geometry of conformal fields, such as duality and mirror symmetry, and interpret them within Connes' non-commutative geometry. Extended version of lectures given by the 2nd author at the Mathematical Quantum Theory Conference, Vancouver, Canada, August 4 to 8, 1993
Immune mechanisms underlying the premunition against Plasmodium falciparum malaria
Pérignon, Jean Louis;Druilhe, Pierre;
Memórias do Instituto Oswaldo Cruz , 1994, DOI: 10.1590/S0074-02761994000600013
Abstract: the most unique characteristic of a parasite when it is in its normal host is the ability to make itself tolerated, which clearly indicates that it has sophisticated means to ensure the neutrality of its host. this is true also in the case of plasmodium falciparum, since after numerous malaria attacks an equilibrium is reached with a chronic stage of infection, characterized by a relatively low parasitemia, and low or no disease (sergent & parrot 1935). we shall briefly review the main characteristics of this state of "premunition", and present data suggesting that the underlying mechanisms of defense rely on the cooperation between cell and antibodies, leading to an antibody dependent cellular inhibition of the intra-erythrocytic growth of the parasite.
Antibodies in falciparum malaria: what matters most, quantity or quality?
Bouharoun-Tayoun, Hasnaa;Druilhe, Pierre;
Memórias do Instituto Oswaldo Cruz , 1992, DOI: 10.1590/S0074-02761992000700038
Abstract: in view of the recent demonstration that antibodies that are protective agains plasmodium falciparum malaria may act in collaboration with blood monocytes, we have investigated the isotype content of sera from individuals with defined clinical states of resistance or susceptibility to malaria. profound differences in the distribution of each ig subclass and particulary in the ratio of cytophilic versus noncytophilic antibodies were found. in protected subjects, two cytophilic isotypes, igg1 and igg3 were found to predominate. in non-protected subjects, i.e. children and primary attack adults, three different situations were encountered: a) an imbalance in which igg2, a non-cytophilic class, predominated (mostly seen in primary attacks); b) imbalance in which mostly igm antibodies predominated (a frequent event in children) or c) less frequently, an overall low level of antimalarial antibodies. of 33 non immune subjects studied all, except one, had one of the above defects. the function of total ig presenting such an isotype imbalance was studied in vitro in antibody-dependent -cellular-inhibition assays. not only did igg from protected subjects cooperate efficiently with blood monocytes, whilst igg from non-protected groups did not, but moreover the latter inhibit the in vitro effect of the former: in competition assays whole igg from primary attack cases with increased igg2 content, competed with igg from immune adults, thus suggesting that non-protected subjects had antibodies to epitopes critical for protection, but that these antibodies are non functional.
Multilocus association mapping using generalized ridge logistic regression
Zhe Liu, Yuanyuan Shen, Jurg Ott
BMC Bioinformatics , 2011, DOI: 10.1186/1471-2105-12-384
Abstract: Within each sliding window, we apply a forward model selection procedure using generalized ridge logistic regression for model fitness in each step. In power simulations, we compare the performance of our method with that of five other methods in current use. Averaging power over all the conditions considered, our method dominates the others. We also present two published datasets where our method is useful in causal SNP identification.Our method can automatically combine genetic information in local genomic regions and allow for linkage disequilibrium between SNPs. It can overcome some defects of the scan statistics approach and will be very promising in genome-wide case-control association studies.In genome-wide association studies (GWAS), it is generally accepted that multilocus methods can obtain better power than single-locus approaches that test only one single-nucleotide polymorphism (SNP) at a time [1-3]. Among a large number of mathematical and statistical approaches considering many predictors simultaneously, scan statistics [4] serve as a useful multilocus analytical means for combining genetic information on multiple contiguous SNPs. In this method, the whole genome is scanned by a sliding window with estimated size, and the moving sum for each window is computed as the sum of suitable single-locus statistics. Then the scan statistic, defined as the largest moving sum, is calculated and its associated empirical p-value is evaluated by permutation tests.Despite its remarkable advantages, the scan statistics method has two drawbacks that can restrict its practical use: (I) linkage disequilibrium (LD) within local genomic regions is not taken into account, which can result in an inflated type I error rate; (II) all contiguous SNPs within a genomic region (window) are selected simultaneously, which can bring excess noise and increase the false discovery rate (FDR).During the last decade, various advances based on the framework of scan statistics have been de
Combining identity by descent and association in genetic case-control studies
Qingrun Zhang, Shuang Wang, Jurg Ott
BMC Genetics , 2008, DOI: 10.1186/1471-2156-9-42
Abstract: Imposing the restriction, F ≥ 0, makes some of the genotype frequencies invalid thereby reducing noise. We propose a new statistical association test, the FP test, by focusing on allele frequency differences between case and control individuals while allowing for suitable IBD probabilities. Power calculations show that (1) the practice of generally carrying out two association tests (allele and genotype test) has an increased type I error and (2) our test is more powerful than conventional genotype and allele tests under recessive trait inheritance, and at least as powerful as these conventional tests under dominant inheritance.For dominant and recessive modes of inheritance, any apparent power gain by an allele test when carried out in conjunction with a genotype test tends to be purchased entirely by an increased rate of false positive results due to omission of a multiple testing correction. As an alternative to these two standard association tests, our FP test represents a convenient and more powerful alternative.In their well-known paper on homozygosity mapping published 20 years ago, Lander and Botstein [1] showed that fewer than a dozen unrelated inbred children should suffice to map a recessive trait given a dense map of genetic markers. They recommended that one should search for extended regions of homozygosity shared by a set of inbred individuals. The power of this approach was demonstrated by the mapping of a gene for a rare recessive trait in a genome-wide investigation of only three distantly related patients [2]: On chromosome 18, five of the six disease chromosomes shared a region of 19 cM in length.Even individuals seemingly collected at random from the population tend to exhibit extended regions of allele sharing [3], which may be interpreted as the consequence of the mating of (distantly) related individuals. Such homozygosity represents autozygosity, that is, the sharing of two alleles that are copies of a single ancestral allele [3].In recent y
AprioriGWAS, a New Pattern Mining Strategy for Detecting Genetic Variants Associated with Disease through Interaction Effects
Qingrun Zhang ,Quan Long ,Jurg Ott
PLOS Computational Biology , 2014, DOI: doi/10.1371/journal.pcbi.1003627
Abstract: Identifying gene-gene interaction is a hot topic in genome wide association studies. Two fundamental challenges are: (1) how to smartly identify combinations of variants that may be associated with the trait from astronomical number of all possible combinations; and (2) how to test epistatic interaction when all potential combinations are available. We developed AprioriGWAS, which brings two innovations. (1) Based on Apriori, a successful method in field of Frequent Itemset Mining (FIM) in which a pattern growth strategy is leveraged to effectively and accurately reduce search space, AprioriGWAS can efficiently identify genetically associated genotype patterns. (2) To test the hypotheses of epistasis, we adopt a new conditional permutation procedure to obtain reliable statistical inference of Pearson's chi-square test for the contingency table generated by associated variants. By applying AprioriGWAS to age-related macular degeneration (AMD) data, we found that: (1) angiopoietin 1 (ANGPT1) and four retinal genes interact with Complement Factor H (CFH). (2) GO term “glycosaminoglycan biosynthetic process” was enriched in AMD interacting genes. The epistatic interactions newly found by AprioriGWAS on AMD data are likely true interactions, since genes interacting with CFH are retinal genes, and GO term enrichment also verified that interaction between glycosaminoglycans (GAGs) and CFH plays an important role in disease pathology of AMD. By applying AprioriGWAS on Bipolar disorder in WTCCC data, we found variants without marginal effect show significant interactions. For example, multiple-SNP genotype patterns inside gene GABRB2 and GRIA1 (AMPA subunit 1 receptor gene). AMPARs are found in many parts of the brain and are the most commonly found receptor in the nervous system. The GABRB2 mediates the fastest inhibitory synaptic transmission in the central nervous system. GRIA1 and GABRB2 are relevant to mental disorders supported by multiple evidences.
Gravitational Forces with Strongly Localized Retardation
Thomas Chen,William D. Walker,Jurg Dual
Physics , 1996,
Abstract: We solve the linearized Einstein equations for a specific oscillating mass distribution and discuss the usual counterarguments against the existence of observable gravitational retardations in the "near zone", where d/r << 1 (d = oscillation amplitude of the source, r = distance from the source). We show that they do not apply in the region d/r \approx 1, and prove that gravitational forces are retarded in the immediate vicinity of the source. An experiment to measure this retardation is proposed, which may provide the first direct experimental observation of propagating gravitational fields.
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