Ezrin tunes the magnitude of humoral immunity. (IRM8P.709)

Abstract

Abstract Ezrin is a member of the Ezrin-Radixin-Moesin (ERM) family of membrane-actin cytoskeleton crosslinkers that participate in a variety of cellular processes. In B cells, phosphorylation of ezrin at different sites regulates multiple processes such as lipid raft coalescence, BCR diffusion, microclustering, and endosomal JNK activation. In this study, we generated mice with conditional deletion of ezrin in the B cell lineage to investigate the physiological significance of ezrin’s function in antigen receptor-mediated B cell activation and humoral immunity. B cell development, as well as the proportion and numbers of major B cell subsets in peripheral lymphoid organs were unaffected by the loss of ezrin. Using super resolution imaging methods we show that in the absence of ezrin, BCRs respond to antigen binding by accumulating into larger and more stable signaling microclusters. Loss of ezrin led to delayed BCR capping and accelerated lipid raft coalescence. Although proximal signaling proteins showed stronger activation in the absence of ezrin, components of the distal BCR signaling components displayed distinct effects. Ezrin deficiency resulted in increased B cell proliferation and differentiation into antibody-secreting cells ex vivo, and stronger T cell-independent and -dependent responses to antigen in vivo. Overall, our data demonstrate that ezrin regulates amplification of BCR signals and tunes the strength of B cell activation and humoral immunity.