A snapshot of electrified nanodroplets

We investigate the size distribution of electrically charged nanodroplets. The droplets were generated using nano- and micro- scale silicon tips. A brief voltage pulse results in a "snapshot" of charged nanodroplets on a metal surface. Atomic force microscopy (AFM) of the snapshot revealed that certain droplet diameters are favored suggesting droplet fission due to Rayleigh instability at nanometer length scales. The most occurring droplet diameters are 85.9(4.1) nm and 167.1 nm (9.7 nm) and for nano- and micro- scale tips respectively indicating that the tip size determines deposition resolution

Step-to-step reproducibility and asymmetry to study gait auto-optimization in healthy and cerebral palsied subjects

AbstractObjectiveThe purpose of our study was to compare plantar pressure asymmetry and step-to-step reproducibility in both able-bodied persons and two groups of hemiplegics. The relevance of the research was to determine the efficiency of asymmetry and reproducibility as indexes for diagnosis and rehabilitation processes.Material and methodThis study comprised 31 healthy young subjects and 20 young subjects suffering from cerebral palsy hemiplegia assigned to two groups of 10 subjects according to the severity of their musculoskeletal disorders. The peaks of plantar pressure and the time to peak pressure were recorded with an in-shoe measurement system. The intra-individual coefficient of variability was calculated to indicate the consistency of plantar pressure during walking and to define gait stability. The effect size was computed to quantify the asymmetry and measurements were conducted at eight footprint locations.ResultsResults indicated few differences in step-to-step reproducibility between the healthy group and the less spastic group while the most affected group showed a more asymmetrical and unstable gait.ConclusionFrom the concept of self-optimisation and depending on the neuromotor disorders the organism could make priorities based on pain, mobility, stability or energy expenditure to develop the best gait auto-optimisation

Les cellules B de la zone marginale chez l'homme (un lignage NOTCH 2 dépendant)

Les lymphocytes B de la zone marginale (MZB) dérivent d une voie de différenciation indépendante du centre germinatif chez la souris, mais cette question reste controversée chez l homme. Chez la souris, la différenciation de ces cellules s effectue dans la rate en utilisant la voie Notch2. Un précurseur lymphoïde murin a été identifié, et sa différenciation en MZB par des signaux Notch2 a été démontrée in vitro. Nous avons cherché un tel précurseur dans le compartiment B IgD+ CD27- splénique chez l homme. Sur la base de sa capacité à acquérir in vitro les marqueurs des cellules MZB en réponse à un signal donné par le ligand de Notch, Delta Like One (Dll1), nous avons identifié dans la rate humaine deux populations de cellules B potentiellement précurseurs. La première présente un taux de mutations somatiques se rapprochant du taux des MZB et semble engagée dans une voie de différenciation plus mature qui reste à préciser ; la deuxième très peu mutée parait être un précurseur très précoce des MZB. In vitro cette population acquière un programme qui la rapproche des MZB, ce qui est confirmé par l induction de gènes que nous avons identifié comme spécifiquement exprimés par les MZB (comme le facteur de transcription SOX7) comparés aux cellules B mémoires. Cette population est majoritairement présente durant l enfance puis diminue fortement. Nous avons aussi identifié, dans la rate de jeunes enfants, des cellules non-lymphoïdes exprimant DLL1 à la périphérie de la zone marginale. Pour confirmer ces résultats, nous avons analysés le sang de trois patients présentant une mutation génétique invalidant un des deux allèles du gène NOTCH2 (Syndrome d Alagille). Contrairement aux contrôles sains, ces patients présentent un taux de cellules MZB dans le sang 2 à 3 fois diminué en comparaison du taux de cellules B mémoires. Ce phénotype rappelle celui des souris haploinsuffisantes pour Notch2, ce qui semble bien confirmer que, chez l homme comme chez la souris, la population zone marginale représente un lignage cellulaire spécifique dont la mise en place est indépendante du centre germinatif.Marginal zone B cell (MZB) is a specific B cell lineage in mice. The existence of such a lineage in human remains controversial. In mice, MZB differentiation takes place in the spleen and is under the control of a Notch2 signal. A marginal zone B cell precursor (MZP) has been identified in mice and its in vitro differentiation into MZB cell requires a Notch2 signaling. We have looked for such a precursor among IgD+ CD27- splenic B cell compartment in human. Based on its ability to acquire MZB cell markers in vitro after a Notch signaling, provided by the Notch ligand Delta Like One (Dll1), we identified in human spleen two B cell subsets that could be putative precursors. One shows a mutational rate close to the rate found in MZB and seems already engaged in an unidentified mature differentiation stage. The second population appears almost unmutated and seems to be a very early precursor for MZB. In vitro, this population acquires a transcriptional program resembling the MZB program. This is confirmed by the induction of genes specifically expressed by MZB (like SOX7) compared to B cell memory. Putative MZP is found in a higher proportion in children compared to adults and we also identified in children spleen non-lymphoid cells expressing DLL1 at the marginal zone border. To confirm all these results, we analyzed blood samples of three patients that are mutated in one of the two NOTCH2 alleles and suffering from the Alagille syndrome. Contrarily to healthy controls, the 3 Alagille patients showed a 2 to 3 fold decrease in MZB level compared to memory B cell level. Interestingly this phenotype is similar to mice showing a Notch2 haploinsufficiency, thus confirming that MZB population is, as in mice, a specific B cell lineage in human.PARIS5-Bibliotheque electronique (751069902) / SudocSudocFranceF

IL-4Rα Signaling in Keratinocytes and Early IL-4 Production Are Dispensable for Generating a Curative T Helper 1 Response in Leishmania major-Infected C57BL/6 Mice.

Experimental infection with the protozoan parasite Leishmania major has been extensively used to understand the mechanisms involved in T helper cell differentiation. Following infection, C57BL/6 mice develop a small self-healing cutaneous lesion and they are able to control parasite burden, a process linked to the development of T helper (Th) 1 cells. The local presence of IL-12 has been reported to be critical in driving Th1 cell differentiation. In addition, the early secretion of IL-4 was reported to potentially contribute to Th1 cell differentiation. Following infection with L. major, early keratinocyte-derived IL-4 was suggested to contribute to Th1 cell differentiation. To investigate a putative autocrine role of IL-4 signaling on keratinocytes at the site of infection, we generated C57BL/6 mice deficient for IL-4Rα expression selectively in keratinocytes. Upon infection with L. major, these mice could control their inflammatory lesion and parasite load correlating with the development of Th1 effector cells. These data demonstrate that IL-4 signaling on keratinocytes does not contribute to Th1 cell differentiation. To further investigate the source of IL-4 in the skin during the first days after L. major infection, we used C57BL/6 IL-4 reporter mice allowing the visualization of IL-4 mRNA expression and protein production. These mice were infected with L. major. During the first 3 days after infection, skin IL-4 mRNA expression was observed selectively in mast cells. However, no IL-4 protein production was detectable locally. In addition, early IL-4 blockade locally had no impact on subsequent Th1 cell differentiation and control of the disease. Taken together, the present data rule out a major role for skin IL-4 and keratinocyte IL-4Rα signaling in the development of a Th1 protective immune response following experimental infection with L. major

Critical role of WASp in germinal center tolerance through regulation of B cell apoptosis and diversification

This project was supported by grant 310030-179251 from the Suisse National Science Foundation (SNF) (to F.C.), funds from the BLACKSWAN Foundation (BSF-005) (to M.D.), and the Wellcome Trust (to A.J.T.).A main feature of Wiskott-Aldrich syndrome (WAS) is increased susceptibility to autoimmunity. A key contribution of B cells to development of these complications has been demonstrated through studies of samples from affected individuals and mouse models of the disease, but the role of the WAS protein (WASp) in controlling peripheral tolerance has not been specifically explored. Here we show that B cell responses remain T cell dependent in constitutive WASp-deficient mice, whereas selective WASp deletion in germinal center B cells (GCBs) is sufficient to induce broad development of self-reactive antibodies and kidney pathology, pointing to loss of germinal center tolerance as a primary cause leading to autoimmunity. Mechanistically, we show that WASp is upregulated in GCBs and regulates apoptosis and plasma cell differentiation in the germinal center and that the somatic hypermutation-derived diversification is the basis of autoantibody development.Publisher PDFPeer reviewe

Critical role of WASp in germinal center tolerance through regulation of B cell apoptosis and diversification

A main feature of Wiskott-Aldrich syndrome (WAS) is increased susceptibility to autoimmunity. A key contribution of B cells to development of these complications has been demonstrated through studies of samples from affected individuals and mouse models of the disease, but the role of the WAS protein (WASp) in controlling peripheral tolerance has not been specifically explored. Here we show that B cell responses remain T cell dependent in constitutive WASp-deficient mice, whereas selective WASp deletion in germinal center B cells (GCBs) is sufficient to induce broad development of self-reactive antibodies and kidney pathology, pointing to loss of germinal center tolerance as a primary cause leading to autoimmunity. Mechanistically, we show that WASp is upregulated in GCBs and regulates apoptosis and plasma cell differentiation in the germinal center and that the somatic hypermutation-derived diversification is the basis of autoantibody development

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

AKT activity orchestrates marginal zone B cell development in mice and humans.

The signals controlling marginal zone (MZ) and follicular (FO) B cell development remain incompletely understood. Here, we show that AKT orchestrates MZ B cell formation in mice and humans. Genetic models that increase AKT signaling in B cells or abolish its impact on FoxO transcription factors highlight the AKT-FoxO axis as an on-off switch for MZ B cell formation in mice. In humans, splenic immunoglobulin (Ig) D <sup>+</sup> CD27 <sup>+</sup> B cells, proposed as an MZ B cell equivalent, display higher AKT signaling than naive IgD <sup>+</sup> CD27 <sup>-</sup> and memory IgD <sup>-</sup> CD27 <sup>+</sup> B cells and develop in an AKT-dependent manner from their precursors in vitro, underlining the conservation of this developmental pathway. Consistently, CD148 is identified as a receptor indicative of the level of AKT signaling in B cells, expressed at a higher level in MZ B cells than FO B cells in mice as well as humans

A highly potent antibody effective against SARS-CoV-2 variants of concern.

Control of the ongoing SARS-CoV-2 pandemic is endangered by the emergence of viral variants with increased transmission efficiency, resistance to marketed therapeutic antibodies, and reduced sensitivity to vaccine-induced immunity. Here, we screen B cells from COVID-19 donors and identify P5C3, a highly potent and broadly neutralizing monoclonal antibody with picomolar neutralizing activity against all SARS-CoV-2 variants of concern (VOCs) identified to date. Structural characterization of P5C3 Fab in complex with the spike demonstrates a neutralizing activity defined by a large buried surface area, highly overlapping with the receptor-binding domain (RBD) surface necessary for ACE2 interaction. We further demonstrate that P5C3 shows complete prophylactic protection in the SARS-CoV-2-infected hamster challenge model. These results indicate that P5C3 opens exciting perspectives either as a prophylactic agent in immunocompromised individuals with poor response to vaccination or as combination therapy in SARS-CoV-2-infected individuals