CD45⁺ cells proliferated in response to IL-6 stimulation. Growth curves of flow-sorted CD45⁻cells (dotted lines) cultured in medium alone (○) or in the presence of IL-6 (2 ng/mL; •), and CD45⁺ cells (solid lines) cultured in medium alone (□) or in the presence of IL-6 (▪). Cells were cultured for the indicated period of time, and cell counts were performed as described in Materials and Methods.