Fig. 6.

Biological activity of BMP7-aAB. IgG preparations from BMP7-aAB positive and negative serum samples were analyzed using the BRE-luciferase reporter system. NIH3T3 cells were transfected with BRE reporter construct and pSEAP2 for normalization. (A) Transfected cells react to stimulation with 0.5 nM rhBMP7 by firefly luciferase expression. The wells were co-incubated with either a monoclonal BMP7-antibody (BMP7ab) as positive control, or IgG preparations from BMP7-aAB positive (pos 11, 13, 14) or negative (neg 1, 5, 6, 7) serum samples. Co-incubation with BMP7-aAB positive IgG preparations blocked the signal in all three cases, as does the monoclonal BMP7ab. Co-incubation with IgG preparations from BMP7-aAB negative subjects had no effect on BMP7 signaling. (B) Using the same cell culture BMP reporter system, co-incubation with BMP2 induced a luciferase signal which was inhibited by co-incubation with a polyclonal BMP2-antibody (BMP2ab). Co-incubation of BMP2 with IgG from BMP7-aAB positive samples suppressed the BMP2 signal in one (IgG 11) of three cases. No effect on the reporter activity was detected for the other two BMP7-aAB positive or the BMP7-aAB negative preparations. n = 6 (BMP7); n = 3 (BMP2); mean + SD; Student's t-test; ***, P < 0.0001.