Fig. 1.

CpG-siRNA is actively internalized by scavenger receptor-mediated endocytosis in RAW 264.7 macrophages. (A) Transmission electron microscopy on fixed cells treated for 30 min using CpG-Stat3 siRNA^5′SS-FITC. Sections of flash-frozen cell pellets were incubated with FITC-specific antibodies and then detected using secondary antibodies coupled to 10 nm gold nanoparticles. Intracellular localization of CpG-siRNA is shown with arrowheads. Scale bars: 1 μm (left) and 100 nm (right). (B) CpG-siRNA uptake is mediated by scavenger receptors. Cells were pre-treated with dextran sulfate (DS, scavenger receptor ligand) or chondroitin sulfate (CS, negative control) for 2 h, then incubated with 500 nM CpG-Stat3 siRNA^5′SS-Cy3 for 1 h and then analyzed by flow cytometry. Shown are representative results of one of three independent experiments.