TGF-β1 down-regulates SDF-1 mRNA expression. MS-5 stromal cell monolayers were incubated for the indicated times with 2 ng/mL TGF-β 1 (A, left) for 8 hours with different concentrations of TGF-β 1 (A, middle) or for 8 hours with 2 ng/mL TGF-β 1 in the presence or absence of anti–TGF-β 1 antibodies (A, right). RNA from cell lysates was reverse transcribed, and amplification of SDF-1 mRNA was performed by PCR using SDF-1–specific primers. Also shown is control PCR amplification of each sample using β -actin–specific primers. (B) Kinetics of induction of SDF-1 promoter activity by TGF-β 1 in MS-5 cells. Fold induction values indicate relative luciferase activity per microgram protein in TGF-β 1–treated cells divided by the values of untreated cells. Data represent the mean ± SD of triplicate samples from a representative result of 4 experiments. Reduction was significant (**P < .005; *P < .05) according to the Student 2-tailed t test.