Immune complex enhances tolerogenecity of immature dendritic cells via FcγRIIb and promotes FcγRIIb-overexpressing dendritic cells to attenuate lupus

A balance of inhibitory and activating signals determines the function of dendritic cells (DCs) in the immune response, which may be regulatory or stimulatory. Defects of inhibitory receptor Fc gamma RIIb are involved in the pathogenesis of autoimmune diseases such as systemic lupus erythematosus (SLE), in which high levels of circulating immune complexes (IC) exist. Our previous study showed that IC/Ig can suppress TLR4-triggered inflammatory responses in macrophages via Fc gamma RIIb. This led us to question whether IC/Ig can polarize Fc gamma RIIb-overexpressing DCs (DC-Fc gamma RIIb) to be tolerogenic, thus attenuating lupus progression once infused in vivo. First, we found that IC/Ig markedly inhibited LPS- or CpG-induced DC maturation, enhanced tolerogenicity of DCs via Fc gamma RIIb, and induced massive prostaglandin E2 (PGE2) secretion from DCs, both contributing to T-cell hyporesponsiveness. Endogenous Ig and lupus-derived IC also exhibited the same effect. DC-Fc gamma RIIb, transfected with recombinant adenovirus encoding Fc gamma RIIb, displayed enhanced tolerogenic function and produced more PGE2 in the presence of IC, thus further inhibiting T-cell responses. Importantly, in vivo infusion with DC-Fc gamma RIIb significantly reduced kidney damage and prolonged the survival of lupus-prone MRL/lpr mice either before or after the onset of clinic lupus. Therefore, administration of DC-Fc gamma RIIb may be a new approach to attenuate lupus progression.