Biophysical Society Thematic Meeting| Aussois 2019

Biology and Physics Confront Cell-Cell Adhesion

Monday Speaker Abstracts

OIL-IN-WATER EMULSION DROPLETS AND MICROFLUIDIC TOOLS TO STUDY B CELLS POLARIZATION AND MECHANICS OF IMMUNOLOGICAL SYNAPSE Léa Pinon 1,2,3 ; Judith Pineau 2 ; Olivier Mesdjian 1,3 ; Lorraine Montel 1,3 ; Paolo Pierobon 2 ; Jacques Fattaccioli 1,3 ; 1 Ecole Normale Supérieure, Chemistry, Paris, France 2 Institut Curie, U932, Paris, France 3 Institut Pierre Gilles de Gennes, Paris, France Right after a pathogen invasion, organism deploys two lines of defense: the innate and adaptive immunities. The first one is a short-term response providing pathogen destruction then antigen presentation promoted by Antigen Presenting Cells (APC). The latest ensures an important long- term response mostly thanks to B lymphocytes which promote high-affinity antibodies secretion and memory B cells differentiation. B cells either catch soluble antigens in the plasma or extract them onto the APC membrane. In the latest case, APC and B cells ensure the antigen transfer via a highly organized contact: the immunological synapse. To precisely understand the physicochemical mechanics involved in this synapse, we first model cell-cell contact by creating new APC-like substrates respecting crucial properties. Emulsion droplets properly mimic antigen mobility at the oil/water interface as observed on the cellular membrane; and due to low and controllable surface tension, droplets are as deformable as real APC. We determine the visco-elastic modulus of droplets and B cells thanks to glass microplates experiment. We so optimize emulsion properties to observe the cellular response of B lymphocytes. We also use microfluidic-trap devices to ease the observation of several isolated synapses simultaneously and follow their formation over time. Consequently, we temporally and spatially control the APC-like droplet/B cell synapse. By combining emulsion and microfluidic tools, the kinetic of lysosomes moving to the synapse area and the stress applied by the cell on the droplet are quantified. As preliminary results, we find the lysosomal recruitment only occurs during the synapse with stiff droplets: mechanical force is not enough to extract antigen. Moreover, we quantify the force applied by B cells on soft droplets. We here point out the role of APC rigidity during the immune synapse and show how droplets and microfluidic traps are promising tools to study the physicochemical parameters of cell-cell contact.

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