Aminoacyl tRNA Synthetase–Interacting Multifunctional Protein 1 Acts as a Novel B Cell–Activating Factor In Vitro and In Vivo

Abstract

Endogenous B cell–activating factors play pivotal roles in defense mechanisms by regulating B cell responses. We previously reported that aminoacyl tRNA synthetase–interacting multifunctional protein 1 (AIMP1) functions as a novel proinflammatory cytokine that activates macrophages and dendritic cells. However, roles of AIMP1 in B cell responses have not been studied. In this study, we investigated the effects of AIMP1 on B cell responses and their underlying mechanisms. AIMP1 induced the expression of surface activation markers on murine B cells and the proliferation of B cells. Additionally, AIMP1 increased the expression of activation-induced deaminase and class switch recombination in B cells. AIMP1 also had synergistic effects on B cell activation when combined with CD40 stimulus. Intracellular signaling experiments showed that AIMP1 activated B cells through a protein kinase C/NF-κB signaling pathway. Importantly, i.v. injection of AIMP1 into mice increased the expression of CD69 on splenic B cells and significantly enhanced Ag-specific Ab production. Taken together, our results show that AIMP1 acts as a novel B cell–activating factor. AIMP1-mediated B cell activation and the involvement of AIMP1 in diseases will provide additional information for therapeutic strategies.