PMA induces a dose-dependent selective downregulation of CCR2. (a). THP-1 cells were either untreated (lanes 1, 5 and 9) or treated with PMA at 1 nM (lanes 2, 6 and 10), 10 nM (lanes 3, 7 and 11) or 50 nM (lanes 4, 8 and 12) for 48 hours. Messenger RNA was then prepared and RT-PCR performed using primers for CCR1 (lanes 1–4), CCR2 (lanes 5–8) and GAPDH (lanes 9–12). M is a 100 bp DNA ladder. Similar results were obtained in seven other experiments. (b). THP-1 cells were either left untreated or stimulated with PMA (50 nM) for the times indicated. Subsequently the cells were introduced into a FACScan flow cytometer to measure cell surface expression of CCR1 (left panel) or CCR2 (right panel).