FCGR2B encodes the inhibitory Fc gamma receptor IIb, which serves as a critical negative regulator of immune responses by binding to immunoglobulin G immune complexes 1. This receptor plays a central role in controlling autoantibody generation and their effector functions through multiple mechanisms, including regulation of B-cell activation, germinal center responses, and dendritic cell migration 1. FCGR2B functions as an inhibitory checkpoint that downregulates immune cell activation triggered by antigen receptors or other Fc receptors 1. The receptor mediates therapeutic effects through immune complex interactions, as demonstrated by anti-citrullinated protein antibodies that bind citrullinated α-enolase and engage FCGR2B on macrophages, resulting in increased IL-10 secretion and reduced osteoclastogenesis 2. FCGR2B also regulates innate immunity by inhibiting Toll-like receptor and complement receptor-mediated activation 1. In cancer immunotherapy, FCGR2B deletion enhances CD8 T cell stemness and improves anti-PD-1 therapy responses by promoting tumor-specific memory T cells with high stemness characteristics 3. Polymorphisms in FCGR2B are associated with autoimmune diseases including IgA nephropathy and systemic lupus erythematosus 4. The receptor's expression correlates with immune microenvironment characteristics and serves as a prognostic marker in gliomas 5.