Effect of state of differentiation of mononuclear phagocytes on CCR5 expression. Untreated mononuclear phagocytes from adult blood (n = 2) and cord blood (n = 3) were examined for CCR5 expression immediately after isolation, at 48 hours postisolation, and at 8 days postisolation. Monocytes at 24 hours postisolation and MDM at 7 days postisolation were also incubated with IFN-γ (500 U/mL for 24 hours), and CCR5 expression was studied in IFN-γ–treated cells at 48 hours and 8 days postisolation. Results are shown as the percentage of cells staining positive for CCR5 expression by flow cytometry (mean ± SEM). Similar changes were seen in mean fluorescence intensity (data not shown).