Biomedical subjects

F Rousset

Publications and source records attributed to F Rousset.

At least 19 recordsLinked to original sources

PubMed1999

Genetic differentiation in populations with different classes of individuals.

I formulate and analyse a model of population structure with different classes of individuals. These different classes may be age classes, other demographic classes, or different types of habitats homogeneously distributed over a geographical area. The value of population differentiation under an island model of dispersal and the increase of differentiation with geographical distance in one- and two-dimensional "isolation by distance" models are then obtained for a generalization of the FST measure of population structure, as a function of "effective" mutation, migration, and population size parameters. The relevant effective subpopulation size is related to the "mutation effective population size" of a single isolated subpopulation and, in models of age-structured populations, to the inbreeding effective population size.

Age Factors↗

PubMed1999

Wolbachia infections are distributed throughout insect somatic and germ line tissues.

Wolbachia are intracellular microorganisms that form maternally-inherited infections within numerous arthropod species. These bacteria have drawn much attention, due in part to the reproductive alterations that they induce in their hosts including cytoplasmic incompatibility (CI), feminization and parthenogenesis. Although Wolbachia's presence within insect reproductive tissues has been well described, relatively few studies have examined the extent to which Wolbachia infects other tissues. We have examined Wolbachia tissue tropism in a number of representative insect hosts by western blot, dot blot hybridization and diagnostic PCR. Results from these studies indicate that Wolbachia are much more widely distributed in host tissues than previously appreciated. Furthermore, the distribution of Wolbachia in somatic tissues varied between different Wolbachia/host associations. Some associations showed Wolbachia disseminated throughout most tissues while others appeared to be much more restricted, being predominantly limited to the reproductive tissues. We discuss the relevance of these infection patterns to the evolution of Wolbachia/host symbioses and to potential applied uses of Wolbachia.

Animals↗

PubMed1999

Interleukin-10 in Epstein-Barr virus-associated post-transplant lymphomas.

We used enzyme-linked immunosorbent assays (ELISA) to investigate the presence of interleukin-10 (IL-10) in the serum of patients developing post-transplant lymphomas. Serum IL-10 was detected in 14 out of 19 cases with a lymphoma or Hodgkin's disease, with higher values being observed in patients who had developed a lymphoma within the first few months post-transplantation, and who had an aggressive form of the disease. Eleven out of the 14 patients in whom IL-10 was detected had Epstein Barr virus-positive tumors. And 11 out of 14 patients died of lymphomas. In most of the patients who had detectable IL-10 at the time of diagnosis of the lymphoma, the IL-10 had not been present previously, but it was found in the serum of 7 out of 9 dialysis patients, and in 8 out of 17 stable transplant patients. We conclude that IL-10 plays a role in the development of the more severe forms of post-transplant lymphomas, and may be secreted by tumor cells. However. data from patients with chronic renal failure or patients undergoing immunosuppressive therapy must be treated with caution.

Burkitt Lymphoma↗

PubMed1999

A stable triple Wolbachia infection in Drosophila with nearly additive incompatibility effects.

Drosophila simulans strains infected with three different Wolbachia strains were generated by experimental injection of a third symbiont into a naturally double-infected strain. This transfer led to a substantial increase in total Wolbachia density in the host strain. Each of the three symbionts was stably transmitted in the presence of the other two. Triple-infected males were incompatible with double-infected females. No evidence was obtained for interference between modification effects of the different Wolbachia strains in males. Some incompatibility was observed between triple-infected males and females. However, this incompatibility reaction is not a specific property of triple-infected flies, because it was also observed in double-infected strains.

Animals↗

PubMed1999

Genetic differentiation within and between two habitats.

We investigate the usefulness of analyses of population differentiation between different ecological types, such as host races of parasites or sources and sink habitats. To that aim, we formulate a model of population structure involving two classes of subpopulations found in sympatry. Extensions of previous results for Wright's F-statistics in island and isolation-by-distance models of dispersal are given. It is then shown that source and sinks cannot in general be distinguished by F-statistics nor by their gene diversities. The excess differentiation between two partially isolated classes with respect to differentiation within classes is shown to decrease with distance, and for a wide range of parameter values it should be difficult to detect. In the same circumstances little differentiation will be observed in "hierarchical" analyses between pools of samples from each habitat, and differences between levels of differentiation within each habitat will only reflect differences between levels of gene diversity within each habitat. Exceptions will indicate strong isolation between the different classes or habitat-related divergent selection.

Genetic Variation↗

PubMed1998

Phylogeny and PCR-based classification of Wolbachia strains using wsp gene sequences.

Wolbachia are a group of intracellular inherited bacteria that infect a wide range of arthropods. They are associated with a number of different reproductive phenotypes in their hosts, such as cytoplasmic incompatibility, parthenogenesis and feminization. While it is known that the bacterial strains responsible for these different host phenotypes form a single clade within the alpha-Proteobacteria, until now it has not been possible to resolve the evolutionary relationships between different Wolbachia strains. To address this issue we have cloned and sequenced a gene encoding a surface protein of Wolbachia (wsp) from a representative sample of 28 Wolbachia strains. The sequences from this gene were highly variable and could be used to resolve the phylogenetic relationships of different Wolbachia strains. Based on the sequence of the wsp gene from different Wolbachia isolates we propose that the Wolbachia pipientis clade be initially divided into 12 groups. As more sequence information becomes available we expect the number of such groups to increase. In addition, we present a method of Wolbachia classification based on the use of group-specific wsp polymerase chain reaction (PGR) primers which will allow Wolbachia isolates to be typed without the need to clone and sequence individual Wolbachia genes. This system should facilitate future studies investigating the distribution and biology of Wolbachia strains from large samples of different host species.

Animals↗

PubMed1998

Comparative analysis of microsatellite and allozyme markers: a case study investigating microgeographic differentiation in brown trout (Salmo trutta).

A comparative study between microsatellite and allozyme markers was conducted on natural populations of resident brown trout (Salmo trutta) sampled over a reduced geographical scale and on hatchery strains. The higher level of polymorphism observed at microsatellite loci resulted in higher power of statistical tests for differentiation among population samples and for genotypic linkage disequilibrium. Genetic distances of Cavalli-Sforza and Edwards were on average two times larger for microsatellites than for allozymes but multilocus FST estimates computed over the entire set of populations were not significantly different for both categories of markers. Assignment tests of individual fish to the set of sampled populations demonstrated a much higher efficiency of microsatellites compared to allozymes. Pairwise multilocus FST estimates were significantly correlated to waterway distances and there was a significant tendency for the incorrectly classified individuals to be assigned to one of the nearest populations, indicating that isolation-by-distance acted significantly on brown trout populations. This increase of differentiation with distance was higher for allozymes than for microsatellites. Traditional measures of genetic differentiation (Cavalli-Sforza and Edwards' chord distance and FST) were compared for microsatellites to recently proposed statistics taking into account allele size differences (Goldstein's distance and PST). Using Goldstein's distance for neighbour-joining analysis did not improve the tree structure resolution. Multilocus estimates of PST and FST were not significantly different when computed over the entire set of populations but no significant correlation was detected between matrices of pairwise multilocus PST estimates and waterway distances.

Alleles↗

PubMed1998

Analysis of population structure in autotetraploid species.

Population structure parameters commonly used for diploid species are reexamined for the particular case of tetrasomic inheritance (autotetraploid species). Recurrence equations that describe the evolution of identity probabilities for neutral genes in an "island model" of population structure are derived assuming tetrasomic inheritance. The expected equilibrium value of FST is computed. In contrast to diploids, the correlation of genes between individuals within populations with respect to genes between populations (FST) may vary among loci due to the particular segregation patterns expected under tetrasomic inheritance and is consequently inappropriate for estimating demographic parameters in such populations. We thus define a new parameter (rho) and derive its relationship with Nm. This relationship is shown to be independent from both the selfing rate and the proportion of double reduction. Finally, the statistical procedure required to evaluate these parameters using data on gene frequencies distribution among autotetraploid populations is developed.

Chromosome Segregation↗

PubMed1997

Contrasting levels of variability between cytoplasmic genomes and incompatibility types in the mosquito Culex pipiens.

Reproductive incompatibilities called cytoplasmic incompatibilities are known to affect a large number of arthropod species and are mediated by Wolbachia, a maternally transmitted microorganism. The crossing relationships between strains of potential hosts define their incompatibility types and it is generally assumed that differences between strains of Wolbachia induce different crossing types. Among all the described host species, the mosquito, Culex pipiens, displays the greatest variability of cytoplasmic incompatibility crossing types. We analysed mitochondrial and bacterial DNA variability in Culex pipiens in order to investigate some possible causes of incompatibility crossing type variability. We sequenced fragments of the ftsZ gene, and the A + T-rich control region of the mtDNA. We also sequenced the second subunit of the mitochondrial cytochrome oxidase (COII) gene, in Culex pipiens and a closely related species, C. torrentium, in order to verify the usefulness of the A + T-rich region for the present purposes. No variability was found in the Wolbachia ftsZ gene fragment, and very limited variation of the mitochondrial marker whatever the compatibility type or the origin of the host. A low variability was found in the A + T-rich region and comparison of divergence of the A + T-rich region and COII gene between C. pipiens and C. torrentium did not reveal any special constraints affecting this region. In contrast to observations in other host species, variability of incompatibility crossing types is not due to multiple infections by distantly related Wolbachia strains.

Animals↗

PubMed1997

CD40 ligation of human keratinocytes inhibits their proliferation and induces their differentiation.

While CD40-CD40 ligand interactions are known to regulate B cell proliferation and differentiation, much less is known about the role this receptor plays on other cell types, especially those of nonhemopoietic origin. We report here that CD40 is expressed in normal human epidermis in situ, especially on the basal cell layer, and that it is maintained on cultured epidermal basal cells. Immunoprecipitation and SDS-PAGE analysis confirms that CD40 expressed by epidermal basal cells is immunologically related to the B cell CD40. IFN-gamma up-regulates CD40 expression on cultured keratinocytes, whereas other proinflammatory cytokines, such as IL-1 or TNF-alpha, have little effects. Using CD40-ligand-transfected L cells (CD40Lc), we demonstrated that CD40 triggering results in an enhanced secretion of both IL-8 and TNF-alpha by cultured epidermal basal cells, suggesting that CD40-CD40L interactions may play a role in amplifying the cutaneous inflammatory reactions. More importantly, we found that keratinocyte proliferation was significantly inhibited when the cells were grown on CD40Lc, as compared with CD32-transfected, or nontransfected, L cells. This inhibitory effect can be reversed substantially by pretreatment of keratinocytes with anti-CD40 mAb. In addition, inhibition of proliferation could be obtained by adding a soluble form of CD40 ligand to the keratinocyte cultures. Interestingly, inhibition of keratinocyte proliferation on CD40Lc correlates with differentiation of the cells, as assessed by morphologic analysis and increased profilaggrin content. Collectively, these results demonstrate that CD40 is expressed and functional on human epidermal basal cells and that, on these cells, CD40 ligation may be a signal for limitation of cell growth and induction of differentiation.

Animals↗

PubMed1997

B-cell-derived IL-10: production and function.

In vitro and in vivo studies identify IL-10 as a key cytokine that inhibits cell-mediated immunity and inflammation while promoting humoral responses. The present review summarizes our studies regarding the ability of B cells to secrete IL-10. When established lines are considered, the production of human IL-10 is restricted to mature B-cell lines and correlates with Epstein-Barr Virus (EBV) expression. Accordingly, EBV infection induces purified tonsil B lym phocytes to produce high levels of human IL-10, whereas viral IL-10 (encoded by EBV) remains undetectable. Exogenous IL-10 enhances EBV-induced B-cell growth, while a neutralizing anti-IL-10 antibody inhibits it, suggesting that IL-10 acts as an autocrine growth factor for EBV-infected B lymphocytes. Normal B lymphocytes secrete lower levels of human IL-10 following activation through B-cell receptor or CD40 antigen. While addition of exogenous IL-4 diminishes CD40-induced secretion of IL-10, addition of Staphyloccocus aureus Cowan I (SAC) particles increases it. Neutralization of endogenous IL-10 does not alter growth of CD40-activated B cells but inhibits their IgG, IgA, and IgM secretion, especially when costimulated with SAC particles. Finally, the simul taneous blocking of both endogenous IL-10 and IL-6 inhibits two-thirds of the production of the three isotypes when B cells were triggered through CD40 in the presence of SAC particles, suggesting that IL-10 synergizes with IL-6 to sustain differentiation of CD40-activated B lymphocytes. Overexpression of B-cell-derived IL-10 is likely to contribute in vivo to different pathologies such as B-lymphoproliferative disorders and autoimmune diseases.

Antibodies↗

PubMed1997

Pleiotropy of adaptive changes in populations: comparisons among insecticide resistance genes in Culex pipiens.

Resistance to toxicants is a convenient model for investigating whether adaptive changes are associated with pleiotropic fitness costs. Despite the voluminous literature devoted to this subject, intraspecific comparisons among toxicant resistance genes are rare. We report here results on the pleiotropic effect on adult survival of Culex pipiens mutants involved in the same adaptation: the resistance to organophosphorus insecticides. This field study was performed in southern France where four resistance genes sequentially appeared and increased in frequency in response to intense insecticide control. By repeated sampling of overwintering females through winter, we analysed the impact of each of three resistance genes on adult survival. We showed that (i) the most recent gene seems to be of no disadvantage during winter, (ii) the oldest affects survival in some environmental conditions, and (iii) the third induces a constant, severe and dominant survival cost. Such variability is discussed in relation to the physiological changes involved in resistance.

Acetylcholinesterase↗

PubMed1997

Genetic differentiation and estimation of gene flow from F-statistics under isolation by distance.

I reexamine the use of isolation by distance models as a basis for the estimation of demographic parameters from measures of population subdivision. To that aim, I first provide results for values of F-statistics in one-dimensional models and coalescence times in two-dimensional models, and make more precise earlier results for F-statistics in two-dimensional models and coalescence times in one-dimensional models. Based on these results, I propose a method of data analysis involving the regression of FST/(1-FST) estimates for pairs of subpopulations on geographic distance for populations along linear habitats or logarithm of distance for populations in two-dimensional habitats. This regression provides in principle an estimate of the product of population density and second moment of parental axial distance. In two cases where comparison to direct estimates is possible, the method proposed here is more satisfactory than previous indirect methods.

Gene Frequency↗

PubMed1996

Interleukin (IL)-10 and IL-6 are produced in vivo by non-Hodgkin's lymphoma cells and act as cooperative growth factors.

The in vivo production of interleukin (IL)-10, IL-6, IL-2, and tumor necrosis factor (TNF)-alpha in tumor samples was investigated by immunohistochemistry in 54 non-Hodgkin's lymphomas (NHLs). Respectively, 55, 89, 23, and 29% of tumor samples were found positive for IL-10, IL-6, IL-2, and TNF-alpha expression by immunohistochemistry. Using reverse transcription-PCR, the mRNA of IL-10 and IL-6 were detectable in all samples tested and in 90 and 34% of the samples for TNF-alpha and IL-2, respectively. In 13 patients, fresh tumor tissue was available for B NHL cell purification with Dynabeads. IL-10, IL-6, IL-2, and TNF-alpha were detectable in the supernatant of 38, 100, 0, and 23% of purified tumor cell preparations (PTCPs), respectively. All patients with detectable IL-10 in culture had increased serum IL-10. IL-6 production by tumor cells and serum IL-6 levels were also found to be highly correlated (P < 0.0001). This suggests that tumor cells are a major source of serum IL-1O and IL-6 in these patients. Exogenous IL-10, IL-6, IL-2, and TNF-alpha significantly enhanced the [3H]thymidine uptake in 13 of 13 (100%), 5 of 13 (38%), 9 of 13 (69%), and 2 of 10 (20%) PTCPs costimulated with anti-CD40, respectively. IL-2, IL-6, and TNF-alpha synergized with IL-10 in 54, 23, and 30% of PTCPs. The combination of IL-10, IL-2, and IL-6 induced the maximal level of proliferation in 12 (92%) of 13 PTCPs. CD40 ligand mRNA expression was also detectable in vivo using reverse transcription-PCR in 28 of the 29 (97%) tumor samples tested, including 11 of those tested for [3H]thymidine incorporation. These results show that IL-1O, IL-6, IL-2, and TNF-alpha are produced in NHL tumors and may cooperate in vivo to increase NHL cell proliferation.

B-Lymphocytes↗

PubMed1996

Human IgG monoclonal antibodies that modulate the binding of specific IgE to birch pollen Bet v 1.

Birch pollen allergy is a very frequent pathology in Europe and North America. More than 95% of the tree pollen allergic patients display IgE reactivity against Bet v 1, the major birch pollen allergen. Starting with PBL from a patient desensitized by immunotherapy, we have generated five B cell lines (BAB1 to BAB5) that secrete human IgG mAbs of high affinity for Bet v 1. Although competition studies indicated that these human IgG mAb recognized different epitopes, broad cross-reactivity was found with Bet v 1 homologous allergens present in tree pollens and plant-derived foods. When tested for interference with allergic patients' IgE, BAB1 inhibited (by 80-100%) the binding of IgE to nitrocellulose-blotted Bet v 1, while BAB2 enhanced it. The biologic significance of the ability of BAB1 to interfere with patients' IgE binding is indicated by the finding that BAB1 completely inhibited Bet v 1-induced histamine release from allergic patients' basophils. Allergen-specific human IgG mAbs such as BAB1, which presents high blocking activity in both immunochemical and cellular IgE competition experiments, might have therapeutical application.

Adjuvants, Immunologic↗

PubMed1996

Inability to produce IL-6 is a functional feature of human germinal center B lymphocytes.

In response to Ag encounter, B lymphocytes undergo a complex maturation process yielding phenotypically distinct subpopulations that are located in highly organized compartments of secondary lymphoid organs. This study describes the patterns of cytokine secretion of naive, memory, and germinal center (GC) human tonsillar B lymphocytes, activated either through CD40 or B cell receptor or with Staphylococcus aureus Cowan I particles. The three B cell subpopulations produced comparable levels of IL-10 and TNF-alpha, regardless of the stimulation pathway. Interestingly, activated GC B lymphocytes fail to express IL-6, as determined both at mRNA and at protein levels, whereas both naive and memory B cells can be induced to secrete IL-6. Likewise, naive B lymphocytes undergoing dual ligation of CD40 and B cell receptor fail to express IL-6, since they acquire a GC-like phenotype. IL-6 receptors are up-regulated on both ex vivo-purified GC B lymphocytes and in vitro generated GC-like B cells, following CD40 activation. Consistent with this, addition of exogenous IL-6 sustains growth of CD40-stimulated GC B lymphocytes. Taken together, these results demonstrate that loss of IL-6 secretion is a functional characteristic of human GC B lymphocytes. The swap from an autocrine to a paracrine IL-6 response may permit a better control of B cell growth and differentiation during the germinal center reaction.

Antilymphocyte Serum↗

PubMed1996

Negative selection of human germinal center B cells by prolonged BCR cross-linking.

The antigen receptors on T and B lymphocytes can transduce both agonist and antagonist signals leading either to activation/survival or anergy/death. The outcome of B lymphocyte antigen receptor (BCR) triggering depends upon multiple parameters which include (a) antigen concentration and valency, (b) duration of BCR occupancy, (c) receptor affinity, and (d) B cell differentiation stages. Herein, using anti-immunoglobulin kappa and lambda light chain antibodies, we analyzed the response of human naive, germinal center (GC) or memory B cells to BCR cross-linking regardless of heavy chain Ig isotype or intrinsic BCR specificity. We show that after CD40-activation, anti-BCR (kappa + gamma) can elicit an intracellular calcium flux on both GC and non-GC cells. However, prolonged BCR cross-linking induces death of CD40-activated GC B cells but enhances proliferation of naive or memory cells. Anti-kappa antibody only kills kappa + GC B cells without affecting surrounding gamma + GC B cells, thus demonstrating that BCR-mediated killing of GC B lymphocytes is a direct effect that does not involve a paracrine mechanism. BCR-mediated killing of CD40-activated GC B cells could be partially antagonized by the addition of IL-4. Moreover, in the presence of IL-4, prestimulation through CD40 could prevent subsequent anti-Ig-mediated cell death, suggesting a specific role of this combination in selection of GC B cells. This report provides evidence that in human, susceptibility to BCR killing is regulated along peripheral B cell differentiation pathway.

Antibodies, Anti-Idiotypic↗

PubMed1996

Four IgG anti-islet human monoclonal antibodies isolated from a type 1 diabetes patient recognize distinct epitopes of glutamic acid decarboxylase 65 and are somatically mutated.

The selective destruction by an autoimmune process of the beta cells in the pancreas is the hallmark of the type 1 insulin-dependent diabetes mellitus. What triggers islet cell-specific autoreactive T and B cells, however, remains unclear. Identification of the targets of the anti-islet cell autoantibodies frequently found in insulin-dependent diabetes mellitus patients and analysis of their sequences should provide some insights into the nature of this disease. We have combined EBV transformation with CD40 activation of peripheral B cells from one patient with insulin-dependent diabetes mellitus to isolate four B cell clones that secrete islet cell-specific autoantibodies, These four human monoclonal autoantibodies are of the IgG1 isotype, and they each recognize a different epitope of the glutamic acid decarboxylase enzyme. Analysis of their variable gene sequences shows that, while clonally unrelated, three of the four human monoclonal autoantibodies use a member of the VH4 family, and two have rearranged the same delta light chain variable gene. The IgG1 isotype of the four autoantibodies as well as the presence of somatic mutations in both heavy and light chain genes provide concrete evidence for their derivation by a T cell-dependent immune response.

Adult↗