Dose- and time-dependent effect of BAFF on B-cell chemotaxis. (A) B cells were incubated for 16 hours with medium (□), 25 ng/mL (▫) or 100 ng/mL (■) BAFF, and 25 ng/mL (▤) or 100 ng/mL () APRIL, and were then tested for migration to 250 ng/mL CCL21, 250 ng/mL CXCL12, or 500 ng/mL CXCL13. Basal migration of B cells was 5% (± 1.4%, medium-treated), 4.7% (± 1.1%, 25 ng/mL BAFF–treated), 5.4% (± 0.5%, 100 ng/mL BAFF–treated), 4.3% (± 2%, 25 ng/mL APRIL–treated), and 5% (± 3%, 100 ng/mL APRIL–treated) Results are expressed as the mean percentage plus or minus SD of cells specifically migrating in response to each chemokine. (B) B cells were incubated for up to 48 hours with medium or 25 ng/mL BAFF. Mock-treated (□) and BAFF-treated (■) B cells were analyzed for migration to 500 ng/mL CXCL13. The experiment was performed using samples from 4 different donors, and basal migration ranged from 3% to 4% and 3.3% to 4.7% for mock- and BAFF-treated B cells, respectively. Results are expressed as the percentage plus or minus SD of specific chemotaxis. *P < .05; **P < .005. (C) B cells were treated for 16 hours with medium (□) or 25 ng/mL BAFF (▫) and analyzed for their migration to 250 ng/mL CCL21, 250 ng/mL CXCL12, and 500 ng/mL CXCL13. Basal migration was 4.4% (± 1.2%) and 4.3% (± 1.1%) for mock- and BAFF-treated B cells, respectively. Results are expressed as the mean percentage plus or minus SD of specifically migrating cells obtained for each donor. *P < .05; **P < .005. (D) B cells were treated for 16 hours with medium (data not shown), 25 ng/mL BAFF (▫), or 100 ng/mL CD40MGL (■) and analyzed for their migration to 250 ng/mL CCL21, 250 ng/mL CXCL12, and 500 ng/mL CXCL13. The experiment was performed using samples from 3 different donors, and basal migration was 3.3% (± 2.1%), 2.3% (± 1.5%), and 1.3% (± 0.6%) for mock-, BAFF-, and CD40MGL-treated B cells, respectively. Results are expressed as mean fold increase plus or minus SD. (E) The percentage of B-cell recovery after overnight culture with medium or 25 ng/mL BAFF was calculated for each donor. Results are expressed as median values obtained from 28 independent experiments. Error bars correspond to 95% confidence intervals about the median. (F) B cells from 3 different donors were incubated for 16 hours at 37°C with medium (□) or 25 ng/mL BAFF (▫) and then incubated for 60 minutes at 37°C with medium or 100 ng/mL chemokines. Cells were washed in ice-cold medium and stained with PE-conjugated CCR7, CXCR4, or CXCR5 mAb for 30 minutes at 4°C. The mean channel fluorescence intensity (MFI) values for mock-treated cells were between 57 and 123 for CCR7, 356 and 1067 for CXCR4, and 64 and 81 for CXCR5. Each of these individual values was considered as 100% expression. Data are expressed as the mean plus or minus SD percentage of MFI values for remaining surface expression.