Figure 1

BMP-6 inhibits proliferation of human B cells. A) CD19⁺ B cells were isolated from peripheral blood and stimulated in triplicates with anti-IgM (37.5 μg/ml) or anti-IgM and CD40 ligand (CD40L; 10 ng/ml) in the presence or absence of BMP-6 for 72 hours. DNA synthesis was measured by [3H]-thymidine incorporation for the last 18 hours. Data are given as relative proliferation obtained by normalizing the mean counts per minute (cpm) for each stimulation to the mean cpm obtained for anti-IgM stimulated cells ± SEM. (mean cpm = 25 352 for anti-IgM stimulated cells, *p ≤ 0.0002 (n = 8), **p ≤ 0.023 (n = 6). B) Dose dependent inhibition of BMP-6 of anti-IgM induced DNA-synthesis of CD19⁺ B cells (relative proliferation ± SEM, n = 3) and C) the Burkitt lymphoma cell line Ramos (relative proliferation ± SEM, n = 3). Ramos cells were cultured for 72 hours and [3H]-thymidine were added for the last 4 hours. D) Noggin (5 μg/ml) and BMP-6 (0,25 or 1 μg/ml) were preincubated for 1 h at 37°C and then added to the CD19⁺ B cells in the presence of anti-IgM(37.5 μg/ml). Cells were cultured for 72 h and DNA synthesis was measured by ³H-thymidine incorporation. One representative of three separate experiments is shown (mean cpm ± SD of triplicates). E) Highly purified CD19⁺CD27^- or CD19⁺CD27⁺ cells were obtained by cell sorting of CD19⁺ cells and stimulated with anti-IgM in the presence or absence of BMP-6, as indicated for 72 hours. DNA synthesis was measuredby [3H]-thymidine incorporation. Data are given as relative proliferation obtained by normalizing the mean cpm for each stimulation to the mean cpm obtained for anti-IgM stimulated cells (mean cpm = 18 221 for CD19⁺CD27^- naïve B cells, mean cpm = 8 930 for CD19⁺CD27⁺ memory B cells, n = 5; * p ≤ 0,004, **p ≤ 0.001).