IL-6–induced proliferation was abrogated by vanadate. Flow-sorted CD45⁺ U-266 cells were cultured in medium alone; in medium +IL-6 (2 ng/mL); or in medium + IL-6 + either 50 μmol/L Na₃VO₄; 10 ng/mL okadaic acid; or DMSO. Cell counts were performed after 1 and 2 days after treatment. Only vanadate could abrogate IL-6–induced proliferation after 2 days.