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F Rousset

Publications and source records attributed to F Rousset.

At least 55 records · Page 3Linked to original sources
PubMed1996

Equilibrium values of measures of population subdivision for stepwise mutation processes.

Expected values of WRIGHT's F-statistics are functions of probabilities of identity in state. These values may be quite different under an infinite allele model and under stepwise mutation processes such as those occurring at microsatellite loci. However, a relationship between the probability of identity in state in stepwise mutation models and the distribution of coalescence times can be deduced from the relationship between probabilities of identity by descent and the distribution of coalescence times. The values of FIS and FST can be computed using this property. Examination of the conditional probability of identity in state given some coalescence time and of the distribution of coalescence times are also useful for explaining the properties of FIS an FST at high mutation rate loci, as shown here in an island model of population structure.

Alleles↗
PubMed1996

Testing differentiation in diploid populations.

We examine the power of different exact tests of differentiation for diploid populations. Since there is not necessarily random mating within populations, the appropriate hypothesis to construct exact tests is that of independent sampling of genotypes. There are two categories of tests, FST-estimator tests and goodness of fit tests. In this latter category, we distinguish "allelic statistics", which account for the nature of alleles within genotypes, from "genotypic statistics" that do not. We show that the power of FST-estimator tests and of allelic goodness of fit tests are similar when sampling is balanced, and higher than the power of genotypic goodness of fit tests. When sampling is unbalanced, the most powerful tests are shown to belong to the allelic goodness of fit group.

Alleles↗
PubMed1996

Molecular identification of a Wolbachia endosymbiont in a Tetranychus urticae strain (Acari: Tetranychidae).

Wolbachia, a maternally inherited bacterium, is involved in alterations of arthropod sexuality. Reproductive incompatibilities are often observed in miles, but the existence of this microorganism in their cytoplasm has not yet been demonstrated. We identified the presence of Wolbachia in a strain of the spider mite Tetranychus urticae based on the amplification and sequencing of part of the 16S rDNA and ftsZ genes. In order to establish the phylogenetic relationships between Wolbachia found in T. urticae and in other arthropods, we aligned the resulting sequences with already published ones. For both 16S and ftsZ genes the Wolbachia carried by T. urticae clustered together with Wolbachia found in other arthropods.

Animals↗
PubMed1995

Evolution of single and double Wolbachia symbioses during speciation in the Drosophila simulans complex.

Maternally inherited bacteria of the genus Wolbachia are responsible for the early death of embryos in crosses between uninfected females and infected males in several insect species. This phenomenon, known as cytoplasmic incompatibility, also occurs between strains infected by different symbionts in some species, including Drosophila simulans. Wolbachia was found in two species closely related to D. simulans, Drosophila mauritiana, and Drosophila sechellia, and shown to cause incompatibility in the latter species but not in D. mauritiana. Comparison of bacterial and mtDNA history clarifies the origins of bacterial and incompatibility polymorphisms in D. simulans. Infection in D. mauritiana is probably the result of introgression of an infected D. simulans cytoplasm. Some D. simulans and D. sechellia cytoplasmic lineages harbor two bacteria as a consequence of a double infection which probably occurred in a common ancestor. The descendant symbionts in each species are associated with similar incompatibility relationships, which suggests that little variation of incompatibility types has occurred within maternal lineages beyond that related to the density of symbionts in their hosts.

Animals↗
PubMed1995

Endogenous IL-6 and IL-10 contribute to the differentiation of CD40-activated human B lymphocytes.

This study was initiated to explore the contribution of endogenous cytokines to CD40-induced B cell proliferation and differentiation. First, both CD40 and Ag receptor (AgR) cross-linking induced purified tonsillar human B lymphocytes to secrete the same pattern of cytokines, including IL-1 beta, IL-6, IL-10, granulocyte-macrophage-CSF, and TNF-alpha, whereas IL-1 alpha, IL-2, IL-3, IL-4, IL-5, IL-7, granulocyte (G)-CSF, or IFN-gamma were not detected. Second, cotriggering of CD40 and AgR resulted in additive secretion of both IL-6 and IL-10. Addition of IL-4 to CD40-activated B cells increased IL-6 levels but decreased IL-10 levels. In contrast, exogenous IL-10 diminished IL-6 levels. Neutralization of IL-6 and IL-10 using blocking Abs did not alter CD40-induced B cell growth. In contrast, IL-6 neutralization markedly inhibited the IL-4-induced IgE secretion (57 +/- 10%) as well as the IgG and IgM production resulting from AgR and CD40 cotriggering (49 +/- 16.5 and 29.5 +/- 4.5%, respectively). Blocking IL-10 inhibited the IgA secretion (25 +/- 2.7%) obtained after CD40 activation and the production of IgG, IgA, and IgM (24.1 +/- 5.6, 25 +/- 8, and 42 +/- 6.5%, respectively) by B lymphocytes undergoing dual ligation of CD40 Ag and AgR. Simultaneous neutralization of both endogenous IL-6 and IL-10 resulted in an increased inhibition of Ig secretion for B cells cotriggered by CD40 Ag and AgR (65-75%). Thus, endogenously produced IL-6 and IL-10 are involved in the differentiation of CD40-activated B cell.

Antigens, CD↗
PubMed1995

Anti-CD40 plus interleukin-4-activated human naive B cell lines express unmutated immunoglobulin genes with intraclonal heavy chain isotype variability.

Combination of anti-CD40 antibody and interleukin-4 (IL-4) induces B cell clonal expansion reminiscent of the T-dependent proliferation following antigenic challenge in vivo. We have analyzed the usage of CH genes and the presence or absence of somatic mutations within the progeny of a single human naive B cell activated with anti-CD40 + IL-4. To address this issue, single-cell cultures of naive (sIgD+) tonsillar B lymphocytes expressing the VH1-restricted G8 idiotype were set up. After culture and RNA extraction, VH1+ Ig mRNA were reverse-transcribed, amplified by polymerase chain reaction and sequenced. A single sIgD+ B cell could generate clones expressing mu, gamma 1, gamma 3, or epsilon, illustrating that the progeny of a single cell can express different isotypes in response to the same stimulus in vitro. The rate of somatic mutations affecting the immunoglobulin variable heavy chain gene was indistinguishable from the background of errors introduced by Taq polymerase.

Antibodies, Anti-Idiotypic↗
PubMed1995

Testing heterozygote excess and deficiency.

Currently used tests of Hardy-Weinberg proportions do not take into account the nature of the alternative hypothesis, which is generally a heterozygote deficiency. Different exact tests, appropriate for small sample size and large number of alleles, are proposed in this perspective, and their properties are evaluated by power comparisons. Some tests are found to be close to optimal for the detection of inbreeding or heterozygote excess, one of which is a score test closely related to Robertson and Hill's estimator of the inbreeding coefficient. This test is also easily applied to multiple samples. Such tests are not always the most appropriate if alternative hypotheses differ from those considered here.

Alleles↗
PubMed1995

Long-term cultured CD40-activated B lymphocytes differentiate into plasma cells in response to IL-10 but not IL-4.

We compared the effects of IL-10 and IL-4 on the functions of B lymphocytes triggered through their CD40. During the initial phase, IL-10 was as potent as IL-4 in inducing the expansion of viable B cells. Then, cellular expansion slowed down and after approximately 3 weeks the number of B cells started to decline. While the combination of IL-10 and IL-4 was synergistic during the first 2 weeks of culture, B cell recovery declined after 3 weeks, indicating that IL-10 prevails over IL-4. Those effects were not restricted to a specific B cell subset as both sIgD+ B cells and sIgD- B cells behaved in a similar way, though the latter population responded with a slightly accelerated kinetic. Inverted microscope examination and scanning electron microscopy showed that in response to IL-10, CD40-activated B cell cultures were heterogeneous with loose aggregates of cells as well as free floating large ovoid cells. In contrast, in the presence of IL-4, CD40-activated B cell cultures were essentially composed of tight cell clumps. IL-10 progressively induced all B cells to differentiate into non-replicating cells with intracytoplasmic Ig that secreted Ig at a high rate. Cytologic analysis indicated that IL-10 cultured cells display a basophilic cytoplasm with an arcoplasm and a low nucleus/cytoplasm ratio. Transmission electron microscopy demonstrated that when IL-10 was added to the culture, B cells displayed structures for excretion with extended endoplasmic reticulum and dilated cisternae containing paracrystalline structures, typical of plasmablasts cells. Taken together, these results indicate that IL-10 acts as a plasma cell differentiation factor for CD40-activated B cells.

Antibody-Producing Cells↗
PubMed1994

Human monoclonal autoantibodies specific for the bullous pemphigoid antigen 1 (BPAg 1).

Bullous pemphigoid (BP) is an acquired blistering skin disease associated with the production of IgG autoantibodies to the 230-kDa BP Ag (BPAg1). To better characterize the epitopes of BPAg1, we generated immortalized B cell lines secreting human mAbs (HumAbs) to BPAg1 from two BP patients whose sera reacted with native BPAg1 but not with a recombinant BP55 carboxyl-terminal peptide. Ab-producing B cell lines were established by EBV infection of CD40-activated PBMCs. Three independent clonal lines were obtained that secreted IgG HumAbs, including one IgG1 kappa (BP3) and two distinct IgG4 kappa (BP1 and BP2). These three HumAbs immunoprecipitated BPAg1. Blocking immunofluorescence experiments and phylogenetic studies showed that these Abs recognize different epitopes of BPAg1. This analysis with HumAbs further extends the serologic demonstration of the wide variety of epitopes recognized by BPAg1 autoantibodies which contrasts with the limited number of epitopes recognized by thyroid peroxidase monoclonal autoantibodies.

Antibodies, Monoclonal↗
PubMed1994

Regulatory effects of prostaglandin E2 on the growth and differentiation of human B lymphocytes activated through their CD40 antigen.

We have studied the effects of prostaglandin E2 (PGE2) on the growth and differentiation of human tonsillar B lymphocytes cultured in the CD40 system with or without IL-4 or IL-10. PGE2 (10(-9) to 10(-6) M) enhanced proliferation of B cells activated through their CD40 Ag, but not their Ig secretion. PGE2 further potentiated both IL-4- and IL-10-induced B cell growth as determined by [3H]TdR uptake and cellular enumeration. The IL-10-induced IgM, IgG, and IgA secretion was enhanced twofold to fourfold after addition of PGE2, whereas IL-4-induced IgG and IgE secretion was inhibited. The IgE production was particularly sensitive as an approximately 90% inhibition was obtained for 10(-7) M PGE2. In addition, PGE2 inhibited IgE production by naive surface IgD+ B cells cultured in the CD40 system, suggesting that PGE2 may interact with mechanisms involved in IgE switching. PGE2 displayed similar effects on cytokine-induced proliferation and Ig secretion of B cells activated by anti-CD40 Abs used in a soluble form. Finally, the PGE2 effects were mimicked by agents increasing cAMP, indicating that the PGE2 activities are likely to depend on the activation of the cAMP pathway. Altogether, the present data indicate that PGE2 stimulates human CD40-activated B cell growth, but differently modulates cytokine-induced differentiation. Thus, in microenvironments supporting the development of an immune response, the secretion of PGE2 by competent cells such as macrophages may participate in the regulation of the humoral response.

Antigens, CD↗
PubMed1994

CD40-activated surface IgD-positive lymphocytes constitute the long term IL-4-dependent proliferating B cell pool.

In vitro, B cells undergo long term proliferation when triggered through their CD40 surface molecule and in the presence of IL-4. Here, we show that cells that proliferate in this culture system lose their germinal center (GC) features and acquire or maintain non-GC markers. When separated by the magnetic cell separation system, both sIgD+ and sIgD- B cells can proliferate in this culture system, sIgD+ B cells exhibiting a higher rate of growth than sIgD- cells. Simultaneous flow cytometric measurement of sIgD and DNA content revealed that B lymphocytes can keep their sIgD after entry into cell cycle. Experiments using G8 Id-positive B lymphocytes allowed us to follow the evolution of sIgD+ and sIgD- cells in a reconstituted B cell population. Long term proliferating cells are sIgD+/sIgM(+)-derived B lymphocytes whereas the initial sIgD-/sIgM- cells are lost. Taken together, these data show that anti-CD40 + IL-4 activated sIgD+ B blasts express non-GC characteristics and that sIgD+ B cells preferentially proliferate in the CD40 system. The possible in vivo role of IL-4 + CD40 signaling is discussed.

Antibodies, Monoclonal↗
PubMed1994

Expression of Bruton's tyrosine kinase protein within the B cell lineage.

Defects in the gene encoding Bruton's tyrosine kinase (Btk), normally expressed in B cells, cause X-linked agammaglobulinemia (XLA). The phenotype of XLA is characterized by a lack of circulating B cells and immunoglobulin. It has been suggested that B cell maturation from the pre-B cell stage to more mature stages is dependent on the appropriate expression of this gene. The Btk mRNA is expressed in B cells and myeloid cells, but protein expression in relation to B cell maturation has not been determined. Moreover, expression of the Btk protein has so far only been investigated in human Epstein-Barr virus-transformed B cell lines, and in murine splenocytes and B cell lines. We have developed an antiserum which recognizes the human Btk protein and shown that normal human tonsillar B cells, peripheral blood monocytes and myeloid cells express the protein, whereas tonsil-derived T cells do not. We also show that the protein is present in early and mature human B cell lines, but is absent in terminally differentiated plasma cell lines. Furthermore, expression is reduced or absent in three B lineage cell lines derived from two patients with defined genetic mutations in Btk and suffering from XLA.

Agammaglobulinaemia Tyrosine Kinase↗
PubMed1994

Molecular control of B lymphocyte growth and differentiation.

During antigen driven immune responses, antigen-specific naive B lymphocytes undergo a cascade of events including activation, expansion, mutations, isotype switch, selections and differentiation into either antibody secreting plasma cells or memory B cells. These antigen-dependent events, which we propose to call immunopoiesis, occur in different areas of secondary lymphoid organs, as well as other nonlymphoid organs. B cells interact with antigens and numerous cell types (T cells, dendritic cells, follicular dendritic cells and macrophages) through numerous cell surface molecules and cytokines. B cells costimulated through their antigen receptor and cytokines such as interleukin 2 (IL-2), IL-4 and IL-10 undergo limited proliferation and differentiation into immunoglobulin (Ig) secreting cells. In contrast, crosslinking of the B cell CD40 antigen, a member of the tumor necrosis factor (TNF) receptor family, results in major cellular activation further modulated by cytokines. In particular, IL-4 and IL-13 permit establishment of long-term factor-dependent B cell lines, as well as isotype switch towards the production of IgE and IgG4. Addition of IL-10 to CD40-activated B cells results in limited proliferation and remarkable differentiation into plasma cells. IL-10 also participates in isotype switch towards IgG1, IgG3 and IgA. The ligand for CD40, a member of the TNF family, is transiently expressed on activated T cells, and interrupted CD40/CD40-L interactions result in profoundly altered humoral immune responses.

Animals↗
PubMed1994

Properties of Drosophila simulans strains experimentally infected by different clones of the bacterium Wolbachia.

Maternally inherited bacteria of the genus Wolbachia are responsible for reproductive incompatibilities between strains of Drosophila simulans. Such incompatibilities are known in several types of crosses, including both directions of crossing between two types of infected strains, 'R' and 'S'. To determine whether the bidirectional incompatibility between R and S flies is due only to differences between their bacteria, flies from an uninfected strain have been experimentally infected with bacteria associated with each type. The incompatibility properties of experimental strains are close to those of original strains harbouring the same bacteria and therefore independent of nuclear background. Backcross experiments, however, show that the infection level of a strain depends on the nature of paternal ancestors. This is not explained by nuclear effects but is possibly the result of an interaction between the infection levels of both parents, in which the infection level of S strains is an equilibrium between a tendency for females to produce weakly infected offspring and selection of more infected eggs by sperm from infected males.

Animals↗