Distinct cell-specific control of autoimmunity and infection by FcγRIIb

Fc gamma RIIb is an inhibitory Fc receptor expressed on B cells and myeloid cells. It is important in controlling responses to infection, and reduced expression or function predisposes to autoimmunity. To determine if increased expression of Fc gamma RIIb can modulate these processes, we created transgenic mice overexpressing Fc gamma RIIb on B cells or macrophages. Overexpression of Fc gamma RIIb on B cells reduced the immunoglobulin G component of T-dependent immune responses, led to early resolution of collagen-induced arthritis (CIA), and reduced spontaneous systemic lupus erythematosus (SLE). In contrast, overexpression on macrophages had no effect on immune responses, CIA, or SLE but increased mortality after Streptococcus pneumoniae infection. These results help define the role of Fc gamma RIIb in immune responses, demonstrate the contrasting roles played by Fc gamma RIIb on B cells and macrophages in the control of infection and autoimmunity, and emphasize the therapeutic potential for modulation of Fc gamma RIIb expression on B cells in inflammatory and autoimmune disease.