For the isolation of CD19 and CD20 B-cells, 40 ml whole blood from EDTA tubes was collected and PBMCs were isolated by using a Ficoll-Paque™ gradient (Amersham). CD19 and CD20 B-cells were prepared by positive selection from the PBMCs by incubation with magnetic anti-CD19 or CD20 mAb-coated microbeads (MACS, Miltenyi Biotec). For the isolation of PBMCs from whole blood, BD Vacutainer® CPT Mononuclear Cell Preparation Tubes (Becton and Dickinson) were used. Total RNA was isolated from 5 ml of whole blood samples with the PAXGene Blood RNA system (QIAGEN) and samples were left at room temperature for 24 hours before processing according to manufacturer's instructions.
