Figure 4.

Belimumab inhibits membrane-bound and residual soluble BAFF in furin-deficient U937 cells. (A,B) CFSE-labeled BAFFR:Fas reporter cells were exposed to (A) medium or to (B) a lethal dose of Fc-BAFF (50 ng/ml) in the presence of increasing concentrations of atacicept, belimumab or denosumab. Cell viability after overnight incubation was measured by flow cytometry. Mean of triplicates ± SEM. Experiment performed twice. (C,D) CFSE-labeled BAFFR:Fas reporter cells were co-cultured overnight with (C) BAFF-deficient (BAFF-ko) or (D) furin-deficient (furin-ko) U937 cells in the presence of atacicept, belimumab or denosumab at the indicated concentrations. Mean of triplicates ± SEM. Experiment performed twice. (E) BAFFR:Fas reporter cells were exposed to undiluted conditioned medium of the indicated U937 cells that were grown alone, but for the same time (17 h) and otherwise identical conditions to those of U937 cells used in panels C and D. Medium and Fc-BAFF at 50 ng/ml in medium pre-incubated alone for 17 h in the same conditions were used as controls. Viability of reporter cells was monitored with the PMS/MTS assay. Mean of triplicates ± SEM. Experiment performed twice.