Effect of RA on antigen expression analyzed by flow cytometry. MO were cultured on teflon foils with or without 10⁻⁷ mol/L 9-cis-RA. After 4 days, cells were harvested and stained according to the Materials and Methods. Data represent the difference in fluorescence intensity between cultures with or without RA (mean ± SEM for at least 3 experiments with different donors).