Prospective single center study with an observational phase (phase A) and a randomized intervention-phase (phase B), monitoring adverse events and complement activation after IVIG infusion. Patients would be enrolled at the Out-patient Clinic of the Division of Hematology at the Department of Internal Medicine at the University Hospital Basel (USB). Based on the number of patients receiving IVIG at the Division of Hematology of the USB we expect to be able to complete data accrual within 8-10 months.