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Effect of combined treatment of RANKL, TRAIL and OPG on osteoclastic differentiation. Adherent PBMC were cultured with M-CSF alone for 6 days. Then cells were cultured for additional 14 days with the addition of RANKL in the absence or presence of TRAIL and/or OPG, as indicated. Cultures were analysed for osteoclastic differentiation by scoring the number of TRAP⁺ multinucleated cells (A), and measuring the levels of TRAP 5b (B), a specific marker of resorption activity, in culture supernatants by ELISA. Data represent the means ±SD of three different experiments performed in duplicate.