The Inhibitory Fc[gamma] Receptor is Unnecessary for IVIG Efficacy

Intravenous gamma globulin (IVIG) is used as an effective therapy for many different autoimmune and inflammatory diseases. The current paradigm for the mechanism underpinning anti-inflammatory effects links IVIG administration to increased expression and activity of the inhibitory Fc[gamma] receptor (Fc[gamma]RIIB) on splenic macrophages. This hypothesis has been disputed in the literature. Here we show that IVIG administered in the context of passive antibody-mediated thrombocytopenia to be therapeutically efficacious in both splenectomized and unmanipulated Balb/c mice despite no upregulation of Fc[gamma]RIIB mRNA in the spleen. Moreover, IVIG effectively ameliorated immune thrombocytopenia (ITP) in Fc[gamma]RIIB-deficient Balb/c mice, but not in Fc[gamma]RIIB-/- or Fc[gamma]RIIB+/+ control mice with a C57BL6/129S background. Our results demonstrate that Fc[gamma]RIIB is not relevant to the beneficial effects of IVIG. We anticipate that investigators will now shift their research focus away from Fc[gamma]RIIB and seek out other possible mechanism(s) to explain the plethora of diseases and conditions treatable with IVIG