Single-cell assays confirmed that CD45 expression and proliferation are IL-6–induced effects. CD45⁻ U-266 were flow-sorted, diluted, and plated at 1 cell per well in 96-well plate. Cells were cultured for 28 days with or without IL-6 (2 ng/mL). At the end of the culture period, cells were harvested from wells containing enough cells for flow cytometric analysis, stained with PE-CD45 monoclonal antibody, and analyzed. Representative flow cytograms from cells cultured with IL-6 are shown. The percentage of CD45⁺ cells is shown on each flow cytogram.