Activin A expression profile, proliferative rate, and immunosuppressive characteristics of MPCs from different tissue sources. (a) ELISA quantification of secreted activin A. Results are expressed as the mean of secretion in 48-hour supernatants of three cell cultures (mean ± S.D.). (b) Activin A:follistatin ratio by real-time RT-PCR. (c) Cell-proliferation rate determined by using CCK-8. BM-MPCs, T-MPCs, M-MPCs, and DP-MPCs were plated in 96-well plates at 1 × 104 cells per well and cultured in growth medium for 48, 96, 144, and 240 hours. (d) Proliferative activity of T cells stimulated with PHA. Responding PBMCs were stimulated with PHA at 5 μg/ml in the presence or absence of 5 × 104 MPCs. The proliferative response of T cells is represented as a percentage of PHA control (mean ± SD of triplicates). *P ≤ 0.05, versus BM-MPCs; **P ≤ 0.05 versus PHA.