Role of spontaneous IL-6 production in activating STAT3 and promoting cell proliferation. (A) Western blot analysis of STAT3 and selected cell cycle regulators in BCL-6^-/- macrophages that had been treated with either IL-6-neutralizing antibody (α-IL-6) or control IgG (ctrl Ab). (B) Cell proliferation measured by 3H-thymidine incorporation assays after antibody-mediated neutralization of IL-6 or chemokines MCP-1 and MIP-1α. Error bars indicate SD. Results are representative of 2 independent experiments.