Substrate Stiffness Regulates B-cell Activation, Proliferation, Class Switch And T Cell-independent Antibody Responses

B cells use B-cell receptors(BCRs) to sense a variety of diverse antigens and then initiate the activation which is followed by proliferation and differentiation into plasma cells and memory B cells. It is known that the antigens encountered by B cells in vivo are usually presented on substrates with various stiffness features. However it is not known how substrate stiffness affects B-cell proliferation, class switch and in vivo antibody responses.We addressed these questions using poly-dimethylsiloxane(PDMS) substrates with different stiffness(20 kPa or 1100 kPa) to present antigens. Live cell imaging experiments suggested that antigens on stiffer substrates more efficiently trigger the synaptic accumulation of BCR and pSyk molecules compared with antigens on softer substrates.In vitro expansion of mouse primary B cells shows different preferences for substrate stiffness when stimulated by different types of stimuli. LPS equally drives B-cell proliferation on stiffer or softer substrates. Anti-CD40 antibodies enhance B-cell proliferation on stiffer substrates, while antigens enhance B-cell proliferation on softer substrates through a mechanism involving the enhanced phosphorylation of PI3 K, Akt and FoxO1. In vitro class switch differentiation of B cells prefers softer substrates. Lastly, NP67-Ficoll on softer substrates accounted for an enhanced antibody response in vivo.Thus substrate stiffness regulates B-cell activation, proliferation, class switch and T cell-independent antibody responses in vivo, suggesting a sophisticated manipulation of B-cell mechanosensing and mechanotransducing. This study will likely help us to build better vaccines and cure diseases that are induced by hyper or hypo-B-cell activation, such as B cell tumors and certain types of autoimmune diseases.