Paolo Pierobon (Institut Curie, Paris). Biophysics seminar ENS-ESPCI.

2 June 2017 13:00 » 14:00 — ESPCI, Amphi Urbain, Ground Floor, Staircase N

Mechanics and force patterning at the immune synapse.

In order to establish an efficient immune response, hence to produce high affinity antibodies, B cell have to internalize the antigen presented on the surface of neighboring cells in the lymph node (typically follicular dendritic cells and subcapsular macrophages). This leads to the formation of a signalling platform, the immune synapse, where cytoskeleton rearrangement are essential for the antigen extraction, internalization and processing. Two models have been proposed for extraction of surface-tethered antigens by B cells: (1) spreading and contraction; (2) mechanical pulling on BCR-Ag complexes. The role of Myosin II is debated and a unifying model is missing. By using traction force microscopy we reconcile these findings and describe the existence of both global contractile forces at the periphery of the synapse and of local forces at the center of the synapse. Peripheral contractile forces depend on centripetal flow of Myosin II whereas central pulling forces are generated by F-actin patches that form in a Myosin II-dependent manner. By linking forces to antigen extraction, our results open interesting perspectives on the role of mechanics in the acquisition of specific antigen and more generally on receptor internalization.