Effect of prolonged exposure of BM stromal cells to TGF-β 1 on SDF-1 expression. (A) MS-5 (left) or NIH-3T3 (right) cells were incubated for 3 days in the absence (–) or in the presence (+) of TGF-β 1, with the addition of this cytokine (2 ng/mL) every 24 hours. Cells were lysed and subjected to RT-PCR analysis using SDF-1 or β -actin primers, as described for Figure 1. (B) MS-5 cells were treated for 3 days as described in panel A, without (–) or with (+) TGF-β 1. Supernatants (left) and cell lysates (right) were subjected to Western blot using anti–SDF-1α antibodies. Recombinant SDF-1 (50 ng) was used as control.