C3a generation in human serum by IVIG. A total of 100 μL of serial dilutions of the IVIG preparations in VBS⁺⁺ was incubated for 1 hour at 37°C with 100 μL of fresh human serum and the C3a contents of this incubation mixture immediately quantitated by a commercial ELISA. As controls, the baseline C3a content of the used serum and the C3a generation by heat-aggregated IVIgG are also depicted in the figure. Average values of duplicates are given with indication of the standard deviations (SD).