BAFF receptor expression in human B cells. (A) Cells were stained with 3 × FLAG-sBAFF supernatant followed by anti-FLAG M2 mAb with FITC-labeled antimouse IgG1 Ab, or anti-IgM Ab followed by FITC-labeled antigoat Ab, or directly PE-labeled anti-CD19 mAb. Expression was analyzed by FACS. (B) The expression of BAFF receptors was evaluated by real-time quantitative RT-PCR for TACI, BCMA, and BAFF-R, as described in Figure 3B. The amount of transcription was normalized to the level of β-actin and designated as a relative quantity. Data shown are representative of 3 different experiments.