Burst induction by IVIg required prestimulation with TNFα. (A) Gray curve indicates PBS only; black curve, PBS + TNFα. (B) Gray curve indicates PBS; black curve, PBS + IVIg (batch A4). (C) Gray curve indicates PBS; black curve, PBS + TNFα + IVIg (batch A4). IVIg concentration 2.5 mg/mL, incubation time 80 minutes.