Effects of 1,25(OH)₂D₃ on U937 cells. (A) Proliferation assay. Early log-phase growing U937 cells were treated with 1 × 10⁻⁷ mol/L 1,25(OH)₂D₃ or ethanol (no ligand control) for 0 to 72 hours. At the indicated timepoints, cells were harvested and incubated with MTS/PMS and absorbance at 490 nm determined, as described in Materials and Methods. All time points were assayed in triplicate and expressed as the percentage of inhibition relative to untreated controls. (B) Differentiation assay. 1,25(OH)₂D₃- or ethanol-treated cells were harvested after 72 hours and incubated with PE-conjugated CD11b or CD14 antibodies and analyzed for positive staining by FACS. Mean fluorescent intensities for each antibody are shown at the bottom of the graphs.