Rôle des macrophages dans l'homéostasie du côlon

Une des principales fonctions du côlon est d`abriter la plus large proportion de microorganismes du corps humain, ainsi que d`absorber les fluides issus de la digestion. Ainsi, la muqueuse du côlon doit constamment affronter l`arrivée de produits potentiellement dangereux. Un des objectifs de mon étude est de déterminer comment le système immunitaire périphérique du côlon assure la surveillance des fluides absorbés. Il a été montré que les macrophages ont des spécificités distinctes dans les différentes portions de l`intestin et représentent l`un des acteurs majeurs du système immunitaire intestinal. Nous proposons que ces différents types de macrophages associés à la muqueuse épithéliale participent au maintien des fonctions des régions proximales et distales du côlon. J`ai observé que les macrophages des régions distales possèdent des protrusions trans-épithéliales uniques, que nous appelons « baloon-like protrusions », ou BLP, qui traversent la lame basale et contactent les cellules épithéliales. J`ai montré que la formation des BLP est fortement dépendante de la quantité d`eau absorbée au niveau du côlon, ainsi que de la présence des microorganismes intestinaux. La prolifération fongique non-contrôlée libère des métabolites qui provoquent l`apoptose des cellules intestinales. En rejoignant la circulation sanguine, ces métabolites sont responsables d`une septicémie létale chez l`Homme. Notre hypothèse de travail propose que les BLPs des macrophages servent de senseurs évaluant les fluides absorbés et contrôlant le niveau d`absorption de l`épithelium intestinal, afin d`éviter que des métabolites fongiques potentiellement dangereux puissent atteindre la circulation.The colon is primarily responsible for absorbing fluids. It contains a large number of microorganisms including fungi, which are enriched in its distal segment. The colonic mucosa must therefore tightly regulate fluid influx to control absorption of fungal metabolites, which can be toxic to epithelial cells and lead to barrier dysfunction. How this is achieved remains unknown. Here, we describe a mechanism by which the innate immune system allows rapid quality-check of absorbed fluids to avoid intoxication of colonocytes. This mechanism relies on a population of distal colon macrophages that are equipped with "balloon-like" protrusions (BLPs) inserted in the epithelium, which sample absorbed fluids. In the absence of macrophages or BLPs, epithelial cells keep absorbing fluids containing fungal products, leading to their death and subsequent loss of epithelial barrier integrity. These results reveal an unexpected and essential role of macrophages in the maintenance of colon-microbiota interactions in homeostasis

SPICE‐Met : profiling and imaging energy metabolism at the single‐cell level using a fluorescent reporter mouse

International audienceThe regulation of cellular energy metabolism is central to most physiological and pathophysiological processes. However, most current methods have limited ability to functionally probe metabolic pathways in individual cells. Here, we describe SPICE-Met (Single-cell Profiling and Imaging of Cell Energy Metabolism), a method for profiling energy metabolism in single cells using flow cytometry or imaging. We generated a transgenic mouse expressing PercevalHR, a fluorescent reporter for cellular ATP:ADP ratio. Modulation of PercevalHR fluorescence with metabolic inhibitors was used to infer the dependence of energy metabolism on oxidative phosphorylation and glycolysis in defined cell populations identified by flow cytometry. We applied SPICE-Met to analyze T-cell memory development during vaccination. Finally, we used SPICE-Met in combination with real-time imaging to dissect the heterogeneity and plasticity of energy metabolism in single macrophages ex vivo and identify three distinct metabolic patterns. Functional probing of energy metabolism with single-cell resolution should greatly facilitate the study of immunometabolism at a steady state, during disease pathogenesis or in response to therapy

Macrophages Maintain Epithelium Integrity by Limiting Fungal Product Absorption

International audienc

Transient microfluidic compartmentalization using actionable microfilaments for biochemical assays, cell culture and organs-on-chip

International audienceWe report here a simple yet robust transient compartmentalization system for microfluidic platforms. Cylindrical microfilaments made of commercially available fishing lines are embedded in a microfluidic chamber and employed as removable walls, dividing the chamber into several compartments. These partitions allow tight sealing for hours, and can be removed at any time by longitudinal sliding with minimal hydrodynamic perturbation. This allows the easy implementation of various functions, previously impossible or requiring more complex instrumentation. In this study, we demonstrate the applications of our strategy, firstly to trigger chemical diffusion, then to make surface co-coating or cell co-culture on a two-dimensional substrate, and finally to form multiple cell-laden hydrogel compartments for three-dimensional cell co-culture in a microfluidic device. This technology provides easy and low-cost solutions, without the use of pneumatic valves or external equipment, for constructing well-controlled microenvironments for biochemical and cellular assays

Galectin-8 Favors the Presentation of Surface-Tethered Antigens by Stabilizing the B Cell Immune Synapse

International audienceComplete activation of B cells relies on their capacity to extract tethered antigens from immune synapses by either exerting mechanical forces or promoting their proteolytic degradation through lysosome secretion. Whether antigen extraction can also be tuned by local cues originating from the lymphoid microenvironment has not been investigated. We here show that the expression of Galectin-8-a glycan-binding protein found in the extracellular milieu, which regulates interactions between cells and matrix proteins-is increased within lymph nodes under inflammatory conditions where it enhances B cell arrest phases upon antigen recognition in vivo and promotes synapse formation during BCR recognition of immobilized antigens. Galectin-8 triggers a faster recruitment and secretion of lysosomes toward the B cell-antigen contact site, resulting in efficient extraction of immobilized antigens through a proteolytic mechanism. Thus, extracellular cues can determine how B cells sense and extract tethered antigens and thereby tune B cell responses in vivo