alpha v integrins engage autophagy components to regulate B cell immune response

Signaling through Toll-like receptors (TLR) has been implicated in activation of immune cell populations such as B lymphocytes. TLR ligands associated with self-antigens can drive increased self-reactive B cell responses however TLR ligands present in pathogenic products or vaccines can also enhance protective antibody responses. Our recent work has identified a novel mechanism by which αv integrins, a family of adhesion molecules and the autophagy proteins limit excessive B cell TLR signaling. Specifically, we have found that αvβ3 integrin regulates TLR signaling (NFKB and IRF7 activation) by directing maturation of TLR containing endosomes, through activation of components of the autophagy pathway (LC3 and Atg5). B cells lacking either αv integrins or autophagy components show enhanced TLR signaling and increased proliferative responses to TLR ligands. Mice with disruption in this pathway develop increased autoantibodies with age and develop accelerated autoimmunity in murine lupus models. Therefore, we propose that αv-mediated regulation of TLR signaling exists to limit excessive B cell responses to self-antigens. In addition, we find that mice in which αv is specifically deleted from B cells mount stronger antibody responses when immunized with exogenous antigens containing TLR-ligand adjuvants. Immune responses to these antigens are characterized by increased expansion of germinal center cells, increased somatic hyper-mutation and higher levels of high-affinity class-switched antibodies. Therefore this αv mediated regulation of TLR signaling not only regulates B cell responses to self-antigens but it is also important for regulating germinal center B cell responses and production of high-affinity antibodies.