Antigen and superantigen presentation as defined by the MHCII-accessory proteins and associated-peptides

MHCII molecules expose a weave of antigens, which send survival or activation signals to T lymphocytes. The ongoing process of peptide binding to the MHC class II groove implicates three accessory molecules: the invariant chain, DM and DO. The invariant chain folds and directs the MHCII molecules to the endosomal pathway. Then, DM exchanges the CLIP peptide, which is a remnant of the degraded invariant chain, for peptides of better affinity. Expressed in highly specialized antigen presenting cells, DO competes with MHCII molecules for DM binding and favors the presentation of receptor-internalized antigens. Altogether, these molecules exhibit potential immunomodulatory properties that can be exploited to increase the potency of peptide vaccines. DO requires DM for maturation and to exit the ER. Interestingly, it is possible to monitor this interaction through a conformation change on DOβ that is recognized by the Mags.DO5 monoclonal antibody. Using Mags.DO5, we showed that DM stabilizes the interactions between the DO α1 and β1 chains and that DM influences DO folding in the ER. Thus, the Mags.DO5+ conformation correlates with DO egress from the ER. To further evaluate this conformation change, directed evolution was applied to DO. Of the 41 unique mutants obtained, 25% were localized at the DM-DO binding interface and 12% are at the solvent-exposed β1 domain, which is thought to be the Mags.DO5 epitope. In addition, I used the library to test the ability of HLA-DO to inhibit HLA-DM and sorted for the amount of CLIP. Interestingly, most of the mutants showed a decrease inhibitory effect, supporting the notion that the intrinsic instability of DO is a required for its function. Finally, these results support the model in which DO competes against classical MHCII molecules by sequestering DM chaperone’s function. MHCII molecules are also characterized by their ability to present superantigens, a group of bacterial or viral toxins that coerces MHCII-TCR binding in a less promiscuous fashion than what is observed in a canonical setting. While the mechanism of how bacterial superantigens form trimeric complexes with TCR and MHCII is well understood, the mouse mammary tumor virus superantigens (vSAG) are poorly defined. In the absence of a crystal structure, I chose a functional approach to examine the relation between vSAG, MHCII and TCR with the goal of uncovering the overall trimolecular architecture. I showed that TCR concomitantly binds both the MHCII α chain and the vSAG and that TCR-MHCII docking is almost canonical when coerced by vSAGs. Because many peptides may be tolerated in the MHCII groove, the pressure exerted by vSAG seems to tweak conventional TCR-MHCII interactions. Furthermore, my results demonstrate that vSAG binding to MHCII molecules is conformation-dependent and abrogated by the CLIP amino-terminal residues extending outside the peptide-binding groove. In addition, they also suggest that vSAGs cross-link adjacent MHCIIs and activate T cells via a TGXY motif.Les molécules du CMH présentent une panoplie d'antigènes qui, lorsque reconnus par un lymphocyte T spécifique, indique à ce dernier de survivre ou de s'activer. Le processus menant à la liaison d'un peptide à la poche du CMH de classe II, implique trois molécules accessoires, soit la chaine invariante, DM et DO. La chaine invariante replie et dirige les molécules du CMHII jusqu'à la voie endosomale. Ensuite, DM échange CLIP, peptide découlant de la dégradation de la chaine invariante, pour d'autres ayant une meilleure affinité. Exprimé seulement chez certaines cellules présentatrices, DO compétitionne avec les molécules du CMHII pour la liaison à DM et ainsi favorise la présentation d'antigènes internalisés par des récepteurs membranaires. Ensemble, ces protéines ont un potentiel immunomodulatoire pouvant être exploité afin d'augmenter l'efficacité de vaccin peptidique. DO requiert DM pour arriver à maturité et sortir du RE. Cette interaction, qui induit un changement de conformation dans la chaine β de DO, peut être sondée à l'aide de l'anticorps monoclonal Mags.DO5. En utilisant cet anticorps, nous avons montré que DM stabilise l'interaction entre les domaines α1 et β1 de DO et influence son repliement dans le RE. Donc, la conformation qui révèle l’épitope Mags.DO5 corrèle avec la migration de DO hors du RE. Afin d'étudier plus précisément ce changement de conformation, DO fut contraint à une ronde d’évolution dirigée. Des 41 mutants obtenus, 25% se retrouvent à l'interface DO- DM et 12% se retrouvent à la surface exposée au solvant du domain β1, région hypothétique de l'épitope Mags.DO5. De plus, la bibliothèque de mutants a été testée pour son habileté à inhiber l'activité de DM. La plupart des mutants montre une activité inhibitrice diminuée, ce qui supporte le model où DO compétionne les molécules du CMHII en séquestrant le rôle chaperon de DM. Les molécules du CMHII ont l'unique habileté de présenter les superantigènes, une famille de toxines virales et bactériennes qui force l'interaction CMHII-TCR de façon beaucoup moins spécifique qu'en contexte canonique. Alors que la façon dont les superantigènes bactériens s'assemblent avec le CMHII et le TCR soit bien comprise, la nature du complexe trimoléculaire découlant des superantigènes du virus de la tumeur mammaire de la souris (vSAG) reste mal définie. En l'absence d'une structure cristalline, une approche fonctionnelle a été choisie pour examiner la relation des vSAGs avec le CMHII et le TCR avec le but de dévoiler l'architecture de ce multi-complexe protéique. Je montre que le TCR lie parallèlement la chaine α du CMHII et vSAG, ce qui résulte en une interaction presque canonique. Puisque différents peptides peuvent être tolérés lors de cet ancrage, il semble que vSAG ajuste les interactions CMHII-TCR conventionnelles. En outre, mes résultats montrent que vSAG reconnait un épitope conformationnel et que cette liaison peut être abrogée par l'extension amino-terminale du peptide CLIP, laquelle s'étend en deçà de la niche. Finalement, mes résultats suggèrent que vSAG peut réticuler plusieurs CMHII adjacents et active les cellules T via son motif TGXY

Extreme faint flux imaging with an EMCCD

An EMCCD camera, designed from the ground up for extreme faint flux imaging, is presented. CCCP, the CCD Controller for Counting Photons, has been integrated with a CCD97 EMCCD from e2v technologies into a scientific camera at the Laboratoire d'Astrophysique Experimentale (LAE), Universite de Montreal. This new camera achieves sub-electron read-out noise and very low Clock Induced Charge (CIC) levels, which are mandatory for extreme faint flux imaging. It has been characterized in laboratory and used on the Observatoire du Mont Megantic 1.6-m telescope. The performance of the camera is discussed and experimental data with the first scientific data are presented.Comment: 33 pages, 17 figures, accepted for publication in PAS

Direct inscription of on-surface waveguides in polymers using a mid-ir fiber laser

A detailed study of photo-inscribed optical waveguides in PMMA and polycarbonate using a mid-IR laser is presented. The wavelength of the laser is tuned near the absorption peaks of stretching C-H molecular bonds and the focused beam is scanned onto the surface of planar polymer samples. For the first time, we report the formation of optical waveguides in both polymers through resonant absorption of the laser beam. The optical properties of the waveguides were thoroughly assessed. An elliptic Gaussian mode is guided at the surface of both polymers. Insertion losses of 3.1 dB for a 30 mm long on-surface waveguide inscribed in PMMA were recorded. Such waveguides can interact with the external medium through evanescent coupling. As a proof of concept, the surface waveguides are used as highly sensitive refractometric sensors. An attenuation dynamical range of 35 dB was obtained for a liquid that matches the index of the PMMA substrate. Our results pave the way for large scale manufacturing of low cost biocompatible photonic devices

A nanoparticle ink allowing the high precision visualization of tissue engineered scaffolds by MRI

Hydrogels are widely used as cell scaffolds in several biomedical applications. Once implanted in vivo, cell scaffolds must often be visualized, and monitored overtime. However, cell scaffolds appear poorly contrasted in most biomedical imaging modalities such as magnetic resonance imaging (MRI). MRI is the imaging technique of choice for high-resolution visualization of low-density, water-rich tissues. Attempts to enhance hydrogel contrast in MRI are performed with “negative” contrast agents that produce several image artifacts impeding the delineation of the implant’s contours. In this study, a magnetic ink based on ultra-small iron oxide nanoparticles (USPIONs; <5 nm diameter cores) is developed and integrated into biocompatible alginate hydrogel used in cell scaffolding applications. Relaxometric properties of the magnetic hydrogel are measured, as well as biocompatibility and MR-visibility (T1-weighted mode; in vitro and in vivo). A 2-week MR follow-up study is performed in the mouse model, demonstrating no image artifacts, and the retention of “positive” contrast overtime, which allows very precise delineation of tissue grafts with MRI. Finally, a 3D-contouring procedure developed to facilitate graft delineation and geometrical conformity assessment is applied on an inverted template alginate pore network. This proof-of-concept establishes the possibility to reveal precisely engineered hydrogel structures using this USPIONs ink high-visibility approach

The influence of multi-morbidity and self-reported socio-economic standing on the prevalence of depression in an elderly Hong Kong population

&lt;b&gt;Background&lt;/b&gt; There has been an increasing prevalence of both depression and chronic medical conditions globally but the relationship between depression and multi-morbidity is not well understood. The aim of the present study was to investigate the relationship between depression, multi-morbidity (number of chronic medical conditions, and measures of socioeconomic standing (SES) in an elderly Hong Kong population.&lt;p&gt;&lt;/p&gt; &lt;b&gt;Methods&lt;/b&gt; Cross sectional study. Information on clinically relevant depressive symptoms, measured by the Geriatric Depression Scale (GDS), and demographic and chronic medical conditions were collected using standardized questionnaires. Information collected on SES included educational status (ES), maximum ever income (MEI), and self-perceived social standing in local community (SES-COM) and in Hong Kong generally (SES-HK). Analysis was conducted using multiple logistic regression.&lt;p&gt;&lt;/p&gt; &lt;b&gt;Results&lt;/b&gt; Depression rates were similar in men and women (GDS caseness 8.1% vs 8.4%). Multi-morbidity of chronic medical conditions was common (40% of men and 46% of women had three or more). In the overall sample, the prevalence of depression was associated with the number of chronic medical conditions (OR 1.27; CI: 1.16–1.39). In addition, SES-HK and SES-COM were significant independent variables.&lt;p&gt;&lt;/p&gt; &lt;b&gt;Conclusion&lt;/b&gt; In this elderly Hong Kong population, depression prevalence rose markedly with number of chronic medical conditions and SES-HK and SES-COM

Gamma-ray and radio properties of six pulsars detected by the fermi large area telescope

We report the detection of pulsed γ-rays for PSRs J0631+1036, J0659+1414, J0742-2822, J1420-6048, J1509-5850, and J1718-3825 using the Large Area Telescope on board the Fermi Gamma-ray Space Telescope (formerly known as GLAST). Although these six pulsars are diverse in terms of their spin parameters, they share an important feature: their γ-ray light curves are (at least given the current count statistics) single peaked. For two pulsars, there are hints for a double-peaked structure in the light curves. The shapes of the observed light curves of this group of pulsars are discussed in the light of models for which the emission originates from high up in the magnetosphere. The observed phases of the γ-ray light curves are, in general, consistent with those predicted by high-altitude models, although we speculate that the γ-ray emission of PSR J0659+1414, possibly featuring the softest spectrum of all Fermi pulsars coupled with a very low efficiency, arises from relatively low down in the magnetosphere. High-quality radio polarization data are available showing that all but one have a high degree of linear polarization. This allows us to place some constraints on the viewing geometry and aids the comparison of the γ-ray light curves with high-energy beam models

Rare variant analysis of 4241 pulmonary arterial hypertension cases from an international consortium implicates FBLN2, PDGFD, and rare de novo variants in PAH

Abstract: Background: Pulmonary arterial hypertension (PAH) is a lethal vasculopathy characterized by pathogenic remodeling of pulmonary arterioles leading to increased pulmonary pressures, right ventricular hypertrophy, and heart failure. PAH can be associated with other diseases (APAH: connective tissue diseases, congenital heart disease, and others) but often the etiology is idiopathic (IPAH). Mutations in bone morphogenetic protein receptor 2 (BMPR2) are the cause of most heritable cases but the vast majority of other cases are genetically undefined. Methods: To identify new risk genes, we utilized an international consortium of 4241 PAH cases with exome or genome sequencing data from the National Biological Sample and Data Repository for PAH, Columbia University Irving Medical Center, and the UK NIHR BioResource – Rare Diseases Study. The strength of this combined cohort is a doubling of the number of IPAH cases compared to either national cohort alone. We identified protein-coding variants and performed rare variant association analyses in unrelated participants of European ancestry, including 1647 IPAH cases and 18,819 controls. We also analyzed de novo variants in 124 pediatric trios enriched for IPAH and APAH-CHD. Results: Seven genes with rare deleterious variants were associated with IPAH with false discovery rate smaller than 0.1: three known genes (BMPR2, GDF2, and TBX4), two recently identified candidate genes (SOX17, KDR), and two new candidate genes (fibulin 2, FBLN2; platelet-derived growth factor D, PDGFD). The new genes were identified based solely on rare deleterious missense variants, a variant type that could not be adequately assessed in either cohort alone. The candidate genes exhibit expression patterns in lung and heart similar to that of known PAH risk genes, and most variants occur in conserved protein domains. For pediatric PAH, predicted deleterious de novo variants exhibited a significant burden compared to the background mutation rate (2.45×, p = 2.5e−5). At least eight novel pediatric candidate genes carrying de novo variants have plausible roles in lung/heart development. Conclusions: Rare variant analysis of a large international consortium identified two new candidate genes—FBLN2 and PDGFD. The new genes have known functions in vasculogenesis and remodeling. Trio analysis predicted that ~ 15% of pediatric IPAH may be explained by de novo variants

La pratique de la bioéthique : quel horizon méthodologique?

This paper proposes to see the field of bioethics as a set of activities operating through two main modes of identification: the purpose of the activity (ethical issues raised by medicine, health and well-being) and the method of the activity. The paper summarizes some of the highlights of these two modes as they have historically and gradually contributed to differentiate bioethics. In so doing, the paper also suggests an original interpretation of the future of this field, in associating methodological concerns with a democratic agenda