CD45 expression was induced by IL-6 and lost on its withdrawal. (A) Flow-sorted CD45⁻ U-266 cells were cultured in medium alone (left) or in medium + IL-6 (2 ng/mL; right), and cells were analyzed by flow cytometry after staining with PE-Cy5-CD45 and FITC-CD38. The percentage of CD45⁺ cells is indicated on each flow cytogram. (B) CD45⁻IL-6–independent KMS-5 cells were cultured with or without exogenous IL-6 (2 ng/mL) and analyzed after staining by PE-Cy5-CD45 and FITC-CD38. (C) RT-PCR analysis of β-actin, CD45, and IL-6 of CD45⁻ U-266 cells cultured with IL-6. Lane M, ◊ X174/Hae III digest DNA size marker; lane 1, negative control without RT product; lanes 2, 3, 4, 5, and 6, IL-6–treated CD45⁻ cells at day 0, 2, 4, 6, and 8, respectively; lane 7, CD45⁺ U-266 cells. (D) Flow-sorted CD45⁺ U-266 cells were incubated in medium without IL-6. Cells were stained with PE-CD45 and FITC-CD38 and subjected to flow cytometric analysis as described in Materials and Methods. The percentage of CD45⁺ cells is indicated on each flow cytogram. (E) Flow-sorted CD45⁺ U-266 cells were cultured without exogenous IL-6 for 2 weeks (left), and only CD45⁺ fraction was sorted out and incubated with or without IL-6 (2 ng/mL) for another 2 weeks (middle). Both CD45⁺ and CD45⁻ fractions were separately sorted out and cultured for 5 days with and without IL-6 (right). The percentages of both CD45⁺ and CD45⁻ fractions are indicated on each flow cytogram.