Trafficking of fluorescently tagged IL-6. Macrophages were transfected with IL-6–GFP and activated with LPS and IFN for 4 h. (A) Epifluorescence image shows the localization of IL-6–GFP to the Golgi complex and in vesicular structures. (B) Secretion of IL-6 from transfected macrophages in the absence (control) and presence (+LPS) of LPS stimulation as measured by cytokine-specific ELISA. Error bars represent SEM of triplicate transfections in a single experiment. (C and D) Live imaging of transfected macrophages showing IL-6–GFP exiting the Golgi complex in both vesicular (C) and tubular (D) structures. In C, an intensity-based color display pallet was used to emphasize vesicular structures. In the enlarged images (magnified images of boxed areas), arrows are used to highlight single trafficking events or tubules. Bars, 10 μm.