Molecular Interactions Between Cd21/35 & The Actin Cytoskeleton In Follicular Dendritic Cells Are Regulated By Cell-Ecm Traction Forces

Follicular dendritic cells (FDCs) are stromal cells that reside in follicles of secondary and tertiary lymphoid organs and germinal centres. They provide structure to the tissue micro-environment and promote the proliferation, activation, and affinity maturation of B cells. FDCs express high levels of complement receptor 1/2 (CD21/35) on their surface to retain immune complexes for presentation to B cells. It has been suggested that the FDC actin cytoskeleton influences the sensitivity and specificity of B cell responses, but the underlying mechanisms are not clear. In this project we are investigating the interplay between CD21/35 clustering, diffusion, and cortical actin dynamics in mouse primary FDCs and how this interplay is influenced by traction forces exerted by the FDC onto extracellular matrix (ECM). Using a combination of drug inhibitors and activators, we show that filamentous actin regulates CD21/35 spatial organisation and mobility in the FDC membrane. Moreover, by culturing FDCs on polyacrylamide hydrogels of different stiffness to modulate FDC-ECM traction forces, we show that FDCs respond to changes in substrate stiffness by altering their size and filamentous actin structures, which impacts CD21/35 organisation and its association with actin. Overall, our data suggest that FDC-ECM traction forces influence CD21/35 interactions with actin, which may have implications for B cell activation in response to immune complexes presented on the FDC surface.