BAFF increases B-cell chemotaxis through interactions with BAFF-R. (A) Surface expression of BCMA, TACI, and BAFF-R was analyzed by flow cytometry on freshly isolated B cells (0 hours) and on B cells incubated for 16 hours with medium. MFI of specific staining (positive minus IgG control) was 17 (BCMA), 17 (TACI), and 55 (BAFF-R) at 0 hours and 28 (BCMA), 32 (TACI), and 67 (BAFF-R) at 16 hours. Data are representative of 4 separate experiments. (B) Similarly, the ability of BAFF-FLAG and APRIL-FLAG to bind B cells was analyzed by flow cytometry using both freshly isolated B cells (0 hours) and B cells incubated for 16 hours with medium. MFI of specific staining was 7 (APRIL) and 39 (BAFF) at 0 hours and 44 (APRIL) and 121 (BAFF) at 16 hours. Data are representative of 4 separate experiments. (C) B cells were incubated for 16 hours with medium (□), 10 μg/mL anti–BAFFR Ab (■), 25 ng/mL BAFF (▫), or 10 μg/mL anti–BAFF-R mAb and 25 ng/mL BAFF (▤). B cells were analyzed for migration to 250 ng/mL CCL21, 250 ng/mL CXCL12, and 500 ng/mL CXCL13. The experiment was performed with samples from 3 different donors and results are expressed as the percentage plus or minus SD of specific chemotaxis. *P < .05.