Activation is required for BLP-mediated reduction of CCR5 transcript levels. (A) Bone marrow-derived macrophages from WT mice were stimulated with 20 ng/mL BLP and CCR transcript levels determined. CCR1 (B) and CCR2 (C) transcript reduction was similar and dose-dependent in both WT and D6-deficient macrophages. (D) CCR5 transcripts were greater in resting D6-deficient macrophages and BLP stimulation reset these levels to those seen in WT macrophages. (E) Treatment with 10 ng/mL of IFN-γ for 24 hours induced CCR5 up-regulation in WT macrophages was reset by 4 hours of BLP stimulation to the lower level observed in resting WT cells. Marked bars are statistically different from unstimulated cells (Student t test; *P = .02).