Search PubMed⌕ Search

Biomedical subjects

C Letellier

Publications and source records attributed to C Letellier.

At least 19 recordsLinked to original sources
PubMed2001

Characterization of monoclonal antibodies directed against the bovine herpesvirus-1 glycoprotein E and use for the differentiation between vaccinated and infected animals.

A panel of seven monoclonal antibodies (MAbs) directed against the bovine herpesvirus-1 (BHV-1) glycoprotein E (gE) was obtained. For that purpose, mice were either tolerized to BHV-1 gE-negative virus and then immunized with wild type BHV-1 or immunized with plasmid DNA expressing the gE and gI glycoproteins. The MAbs were characterized by their reactivity with the gE protein or the gE/gI complex and by competition experiments. Results showed that the MAbs were directed against three antigenic domains, two located on the gE glycoprotein and one on the gE/gI complex. Blocking experiments were performed with sera from experimentally vaccinated and infected cattle. A competition was observed between gE-positive bovine sera and six of the seven MAbs. The bovine sera thus recognized two of the three antigenic sites. Field sera were then tested in blocking enzyme-linked immunosorbent assay using one horseradish peroxidase-conjugated MAb. A specificity of 98.2% and a sensitivity of 98.2% compared to the commercially available test were observed.

Animals↗
PubMed2001

Ansatz library for global modeling with a structure selection.

The information contained in a scalar time series and its time derivatives is used to obtain a global model for the underlying dynamics. This model provides a description of the time evolution of the system studied in a space spanned by the time series and its successive time derivatives which is expected to be equivalent to the original phase space. Differential models are, in general, very complicated and do not necessarily capture all properties of the original dynamics. The possibility of choosing a form among an ansatz library for the original system which allows a structure selection for the differential model is considered. It allows for the reduction of the complexity of the model and the recovery of the right property when the differential model is transformed back into the space associated with the ansatz.

Journal Article↗
PubMed2001

Experimental evidence for a torus breakdown in a glow discharge plasma.

A global bifurcation scenario for a two-frequency torus breakdown depicted by Baptista and Caldas [Physica D 132, 325 (1999)] is observed on a glow-discharge experiment. The torus is broken through a crisis with an unstable periodic orbit. The torus section before the bifurcation is a sided polygon that has a number of edges equal to the period of the unstable orbit. Since the discharge is an extended system the two-frequency torus breakdown is shown to be a possible way to space-time chaos.

Journal Article↗
PubMed2001

Diversity among bovine pestiviruses.

Bovine viral diarrhoea virus (BVDV) isolates are characterized by an important genetic, antigenic and pathogenic diversity. The emergence of new hypervirulent BVDV strains in North America has provided clear evidence of pathogenic differences between BVDV strains. The origin of BVDV diversity is related to high mutation rate occurring in RNA viruses but the consequences of mutations obviously depend on the genes which are involved. Mutations in genes encoding for structural proteins of immunological importance may have practical implications. Knowledge of BVDV diversity is important for understanding the wide variety of pathogenesis of diseases caused by the virus, for monitoring the epidemiology of the different types and for the design of optimum laboratory tests and vaccines. This review focuses on the origin and consequences of BVDV diversity with regard to pathogenesis, biotypes, and antigenic and genetic variations.

Animals↗
PubMed2000

Covering dynamical systems: twofold covers.

We study the relation between a dynamical system, which is unchanged (equivariant) under a discrete symmetry group G and another locally identical dynamical system with no residual symmetry. We also study the converse mapping: lifting a dynamical system without symmetry to a multiple cover, which is equivariant under G. This is done in R3 for the two element rotation and inversion groups. Comparisons are done for the equations of motion, the strange attractors that they generate, and the branched manifolds that classify these strange attractors. A dynamical system can have many inequivalent multiple covers, all equivariant under the same symmetry group G. These are distinguished by the value of a certain topological index. Many examples are presented. A new global bifurcation, the "peeling bifurcation," is described.

Journal Article↗
PubMed2000

Differences in experimental virulence of bovine viral diarrhoea viral strains isolated from haemorrhagic syndromes.

In the late 1980s, a new hypervirulent and epidemic form of bovine viral diarrhoea virus (BVDV) infection appeared in North America. A similar but sporadic syndrome was later reported in Europe. To compare the pathogenic characters of the North American and European hypervirulent strains, we inoculated BVDV naïve calves with BVDV strains isolated from haemorrhagic syndromes originating in Belgium, France and the USA. The experimental procedure comprised daily clinical examination and measurement of blood and virological parameters. The American BVD890/256 strain induced severe thrombocytopaenia, profuse diarrhoea and pneumonia in all calves, indicating that hypervirulent BVDV could be the primary infectious agent of pneumonia. Interestingly, a strong correlation was observed between the intense viraemia and a decreased platelet count. None of the European strains tested induced significant pathological signs, although isolated from cases presenting haemorrhagic syndrome.

Animals↗
PubMed2000

Modeling maps by using rational functions

Rational functions are not very useful for obtaining global differential models because they involve poles that may eject the trajectory to infinity. In contrast, it is here shown that they allow one to significantly improve the quality of models for maps. In such a case, the presence of poles does not involve any numerical difficulty when the models are iterated. The models then take advantage of the ability of rational functions to capture complicated structures that may be generated by maps. The method is applied to experimental data from copper electrodissolution.

Journal Article↗
PubMed2000

Symbolic sequence statistical analysis for free liquid jets

Free liquid jets are investigated here as nonlinear dynamical systems. A scalar time series corresponding to the time evolution of the jet diameter is then used to investigate the underlying dynamics in terms of reconstructed phase portraits, Poincare sections, and first-return maps. Particular attention is paid to characterizing the behavior using symbolic sequence statistics that enable different atomization regimes to be distinguished. Such statistics are first applied on theoretical maps to support the results obtained on the jet dynamics.

Journal Article↗
PubMed2000

Determination of lipoprotein(a) concentrations and apolipoprotein(a) molecular weights in diabetic patients.

Lipoprotein(a) (Lp(a)) with atherogenic and thrombotic properties has been frequently studied in diabetes, because a high cardiovascular risk has been reported both in type 1 and type 2 diabetes. Few studies have considered genetic factors, especially the isoforms of apolipoprotein(a). The aim of this work is to determine the distribution of apo(a) phenotypes in the serum of 148 diabetic patients (59 type 1, 89 type 2) with or without vascular complications. Apo(a) phenotypes are determined using 4-15% sodium dodecyl sulfate polyacrylamide gel electrophoresis followed by immunoblotting (PhastSystem - Pharmacia). An inverse relationship is observed between Lp(a) serum concentration and the apparent molecular mass of apo(a) isoforms: type 1 r=- 0.61, p<0.01; type 2 r=- 0.55, p<0.01. The frequency of apo(a) isoforms is significantly different between type 1 and type 2 diabetes mellitus. A higher prevalence of isoforms of low molecular weight was observed in the type 2 diabetic population.

Adolescent↗
PubMed1999

Detection and genotyping of bovine diarrhea virus by reverse transcription-polymerase chain amplification of the 5' untranslated region.

A reverse-transcription polymerase chain reaction (RT-PCR) was developed to differentiate the bovine diarrhea virus (BVDV) from other pestiviruses, and to determine the genotype of the BVDV isolates. For this purpose, primer pairs were selected in the 5' untranslated region (5'UTR). The primers BE and B2 were located in highly conserved regions and were pestivirus-specific. Two primer pairs named B3B4 and B5B6 were specific of BVDV genotypes I and II, respectively. With this technique, an amplification product of the expected size was obtained with either the B3B4 or the B5B6 primer pairs for the 107 BVDV isolates tested but not for BDV or CSFV. For some isolates that were grouped in the genotype II, sequence analysis of the PCR fragments confirmed their classification into this genotype.

5' Untranslated Regions↗
PubMed1999

Susceptibility of bovine antigen-presenting cells to infection by bovine herpesvirus 1 and in vitro presentation to T cells: two independent events.

The aim of the present study was to develop an in vitro system for presentation of bovine herpesvirus 1 (BHV-1) antigens to bovine T lymphocytes and to characterize the antigen-presenting cells (APC) which efficiently activate CD4(+) T cells. Two approaches were used to monitor the infection of APC by BHV-1 as follows: (i) detection of viral glycoproteins at the cell surface by immunofluorescence staining and (ii) detection of UL26 transcripts by reverse transcription-PCR. The monocytes were infected, while dendritic cells (DC) did not demonstrate any detectable viral expression. These data suggest that monocytes are one site of replication, while DC are not. The capacities of monocytes and DC to present BHV-1 viral antigens in vitro were compared. T lymphocytes (CD2(+) or CD4(+)) from BHV-1 immune cattle were stimulated in the presence of APC previously incubated with live or inactivated wild-type BHV-1. DC stimulated strong proliferation of Ag-specific T cells, while monocytes were poor stimulators of T-cell proliferation. When viral attachment to the surface of the APC was inhibited by virus pretreatment with soluble heparin, T-cell proliferation was dramatically decreased. Unexpectedly, incubation of DC and monocytes with the deletion mutant BHV-1 gD-/-, which displays impaired fusion capacity, resulted in strong activation of T lymphocytes by both APC types. Collectively, these results indicate that presentation of BHV-1 antigens to immune T cells is effective in the absence of productive infection and suggest that BHV-1 gD-/- mutant virus could be used to induce virus-specific immune responses in cattle.

Animals↗