Key Points Antibodies causing FNAIT have decreased Fc fucosylation, unlike in refractory thrombocytopenia. Decreased Fc fucose increases affinity to FcγRIIIa/b, enhances platelet phagocytosis, and correlates with increased disease severity.

Key Points Phagocytosis of IgG-opsonized blood cells by human macrophages is inhibited by intravenous immunoglobulins. This inhibition is independent of IgG-Fc sialylation but improves with IgG preparations that bind FcγRs more avidly.