Verification of proliferating cells as monocytes. (A) Monocytes were grown for 8 days with immobilized CD137 protein and labeled for 60 minutes with 10 μmol/L BrdU (yellow). (B) Monocytes were cultured on immobilized CD137-Fc protein on chamber slides. After 10 days the cells were labeled for 60 minutes with 10 μmol/L BrdU (yellow). Monocytes were identified by staining for CD14 (red), and nuclei were visualized by Hoechst 33342 (blue). Similar results were obtained in 3 independent experiments for (A) and (B), respectively.