Cell apoptosis and viability assay
To determine apoptosis, cultured B cells were double-stained with an annexin V-FITC conjugate and propidium iodide (PI) using TACS annexin V kits (Oncogene) according to the manufacturer’s instructions. The stained B cells were analysed using a FACS Calibur flow cytometer (BD Biosciences) within 30 min.