B cell depletion in immune thrombocytopenia reveals splenic long-lived plasma cells.

International audiencePrimary immune thrombocytopenia (ITP) is a disorder caused by autoantibody-mediated platelet destruction and decreased platelet production. Rituximab, a B cell-depleting agent, has become the first-line treatment for ITP; however, patients with refractory disease usually require splenectomy. We identified antibody-secreting cells as the major splenic B cell population that is resistant to rituximab. The phenotype, antibody specificity, and gene expression profile of these cells were characterized and compared to those of antibody-secreting cells from untreated ITP spleens and from healthy tissues. Antiplatelet-specific plasma cells (PC) were detected in the spleens of patients with ITP up to 6 months after rituximab treatment, and the PC population displayed a long-lived program similar to the one of bone marrow PC, thus explaining for most of these patients the absence of response to rituximab and the response to splenectomy. When analyzed by multiplex PCR at the single-cell level, normal splenic PC showed a markedly different gene expression profile, with an intermediate signature, including genes characteristic of both long-lived PC and proliferating plasmablasts. Surprisingly, long-lived PC were not detected in untreated ITP spleens. These results suggest that the milieu generated by B cell depletion promotes the differentiation and settlement of long-lived PC in the spleen

Étude de la réactivité d’anticorps vis-à-vis de leurs antigènes adsorbés à une interface solide/solution - Aspects dynamiques de processus interfaciaux

The aim of this thesis is to study the reactivity and exchange phenomena between proteins at a solid/liquid interface. It includes a description of the different aspects related to the proteins used (physicochemical characteristics of fibrinogen and immunoglobulin G, structure, function) and to the structure of the adsorbent (silica). It summarises some important properties of adsorption, desorption and exchange of proteins at the interface, and discusses all the experimental techniques and methods used. The last three chapters concern (1) the study of the reactivity of antibodies towards their antigens, when the latter are adsorbed directly on a solid surface, (2) the study of the reactivity of the same antigen/antibody systems, when the antigen is adsorbed by an exchange process on a pre-adsorbed protein layer, and (3) a dynamic and quantitative analysis of the heterogeneous exchange process between adsorbed immunoglobulin G and fibrinogen in solution.Le but de cette thèse est d'étudier les phénomènes de réactivité et d'échange entre des protéines à une interface solide/liquide. Elle comprend une description des différents aspects liés aux protéines utilisées (caractéristiques physicochimiques du fibrinogène et des immunoglobulines G, structure, fonction) et à la structure de l'adsorbant (silice). Elle résume certaines propriétés importantes concernant l'adsorption, la désorption et l'échange de protéines à l'interface, et présente la liste de toutes les techniques et méthodes expérimentales utilisées. Les trois derniers chapitres concernent (1) l'étude de la réactivité d'anticorps vis-à-vis de leurs antigènes, lorsque ces derniers sont adsorbés directement sur une surface solide, (2) l'étude de la réactivité des mêmes systèmes antigène/anticorps, lorsque l'antigène est adsorbé par un processus d'échange sur une couche protéique pré-adsorbée, et (3) une analyse dynamique et quantitative du processus d'échange hétérogène entre des immunoglobulines G adsorbées et du fibrinogène en solution

Etude du code neuronal sous-tendant la perception de signaux de communication acoustique

Un des objectifs des neurosciences computationelles consiste à élucider le code neuronal utilisé dans le système nerveux central pour représenter l information et élaborer des réponses adaptées à ces stimuli. Tandis que le taux de décharge des neurones reste très utilisé dans les travaux explorant les relations entre activité neuronale et fonctions cognitives, de plus en plus de recherches montrent que les aspects temporels des décharges neuronales pourraient constituer un code rapide et efficace de l information. J ai étudié des enregistrements électrophysiologiques collectés dans une structure du cerveau de canaris impliquée dans la perception et la production des chants. Alors qu une minorité de ces neurones sont sélectifs pour le propre chant de l oiseau en terme de taux de décharge, les réponses d une majorité d entre eux portent l information nécessaire à la discrimination entre le propre chant et son inverse, cette information étant majoritairement portée par les aspects temporels des décharges. Nous avons ensuite analysé des enregistrements obtenus dans le système thalamocortical de cobayes lors de la présentation de vocalisations conspécifiques. Alors que ces stimuli déclenchent des réponses similaires du point de vue du nombre de PA, la quantité d information transmise par l organisation temporelle des PA est importante. Tant dans le système thalamocortical que dans un noyau sensorimoteur, les neurones semblent donc émettre des séquences de PA dont l organisation temporelle est bien mieux corrélée avec les stimuli que le nombre de PA. Cette propriété dynamique de l activité neuronale pourrait donc être impliquée dans la perception de stimuli naturels.A major goal in computational neuroscience is to understand the neural code used to represent perceptual information and elaborate appropriate motor responses. Whereas most of the researches about relationships between neural activity and cognitives functions still focus on the discharge rate, a growing number of studies show that spike timing could constitute a rapid and efficient neural code. We studied spike trains recorded in the HVC nucleus, brain s structure involved in the perception and the production of songs in songbirds. Whereas a minority of neurons were selective in terms of spike rate, it appeared that spike timing carried the information required to disriminate between the bird s own song and its reverse. We then studied auditory thalamocortical spike trains recorded during the presentation of conspecific vocalizations. In that case also, spike timing conveys information allowing the discrimination between vocalizations and their time-reversed versions whereas spike rate was similar for both stimuli. An analysis of the first 100ms of the spike trains revealed that first spike latency conveyed twice more information that spike count for a discrimination between vocalizations in their natural version. Therefore, in the thalamocortical auditory system as well as in a sensorimotor nucleus, neurons seem to emit temporal patterns of spikes that better correlate with sensory stimuli than spike count does. This dynamic property of neural activity may thus be involved in the perception of naturalistic stimuli.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Many human peripheral VH5-expressing IgM+ B cells display a unique heavy-chain rearrangement.

International audienceThe immunoscope methodology has proven useful to analyze T-cell repertoires in mice and humans. We adapted it to the analysis of VH chains of human peripheral B cells by setting up a quantification of various VH and JH segments and the profiling of IgM-, IgG-, IgA- and IgE-expressing B cells. We then tested the hypothesis that the human B-cell and T-cell repertoires have a similar diversity of VH and V-beta rearrangements. We studied in more detail the VH5 family because it is not abundantly used, which facilitated the analysis. The data showed that the number of distinct VH5 rearrangements in all samples studied is close to the number of cells in the sample. This contrasts with T cells in which we previously showed that distinct V-beta rearrangements amount to a few percent of the number of T cells because each V-beta chain is on the average paired with approximately 25 alpha chains. Thus, in the VH5 family, the light chains add little quantitative diversity to that produced by the heavy chain alone. Whether this feature can be generalized to other VH chains is discussed

A Bregman-proximal point algorithm for robust non-negative matrix factorization with possible missing values and outliers - application to gene expression analysis

BackgroundNon-Negative Matrix factorization has become an essential tool for feature extraction in a wide spectrum of applications. In the present work, our objective is to extend the applicability of the method to the case of missing and/or corrupted data due to outliers.ResultsAn essential property for missing data imputation and detection of outliers is that the uncorrupted data matrix is low rank, i.e. has only a small number of degrees of freedom. We devise a new version of the Bregman proximal idea which preserves nonnegativity and mix it with the Augmented Lagrangian approach for simultaneous reconstruction of the features of interest and detection of the outliers using a sparsity promoting ℓ 1 penality.ConclusionsAn application to the analysis of gene expression data of patients with bladder cancer is finally proposed.KeywordsFeature extraction Non-negative matrix factorization Gene expression analysis Outliers and missing dat

Citrulline enhances myofibrillar constituents expression of skeletal muscle and induces a switch in muscle energy metabolism in malnourished aged rats

We are grateful to Florence Blandel for carbonylated protein analysis. We would like to thank Morgane Le-Gall, Guilhem Clary, and Cedric Broussard for their help in the DIGE experiments and MS analysis. We also thank Professor E. Fontaine for helpful discussion.Citrulline (Cit) actions on muscle metabolism remain unclear. Those latter were investigated using a proteomic approach on Tibialis muscles from male Sprague-Dawley rats. At 23 months of age, rats were either fed ad libitum (AL group) or subjected to dietary restriction for 12 weeks. At the end of the restriction period, one group of rats was euthanized (R group) and two groups were refed for one week with a standard diet supplemented with nonessential amino acids group or Cit (CIT group). Results of the proteomic approach were validated using targeted Western blot analysis and assessment of gene expression of the related genes. Maximal activities of the key enzymes involved in mitochondrial functioning were also determined. Cit supplementation results in a significant increase in the protein expression of the main myofibrillar constituents and of a few enzymes involved in glycogenolysis and glycolysis (CIT vs. AL and R, p < 0.05). Conversely, the expression of oxidative enzymes from Krebs cycle and mitochondrial respiratory chain was significantly decreased (CIT vs. AL, p < 0.05). However, maximal activities of key enzymes of mitochondrial metabolism were not significantly affected, except for complex 1 which presented an increased activity (CIT vs. AL and R, p < 0.05). In conclusion, Cit supplementation increases expression of the main myofibrillar proteins and seems to induce a switch in muscle energy metabolism, from aerobia toward anaerobia