B cell activation is regulated by the stiffness properties of the substrate presenting the antigens (P1152)

Abstract

Abstract B lymphocytes are activated upon the sensing of antigens by BCRs. The substrate presenting the antigens can show different degree of stiffness. However it is not clear if B cells can respond to substrate stiffness changes. In this report, we use high resolution, high speed live cell imaging techniques to capture the early events in B cell activation shortly after the recognition of antigens tethered to polyacrylamide gel substrates with variable degrees of stiffness as quantified by Young’s modulus (2.6-22.1 kPa). We show that the initiation of B cell activation is extremely sensitive to substrate stiffness. B cells exhibit much stronger activation responses when encountering antigens tethered to substrates with a high degree of stiffness as measured by the accumulation of BCRs, pSyk and pTyr molecules into B cell immunological synapse. Moreover, BCR and pSyk microclusters induced by antigens on stiffer substrate are more prominent and show significantly enhanced colocalization compared to activation with antigens on softer substrate. As a result, the expression of the B cell activation marker CD69 is greatly enhanced in B cells encountering antigens on stiffer substrate. Using a series of cytoskeleton inhibitors, we determine that the mechanosensing capability of B cell is strictly dependent on microtubules, and only mildly linked to actin cytoskeleton. These results suggest the importance of mechanical properties mediated by substrate stiffness in B cell activation.