Characterization of SARS-CoV S DNA vaccine (pci-S)-PEI complexes. (A) Transmission electron micrographic image of PEI/pci-S complexes at N/P ratio 10. Scale bar represents 0.5 μm. (B) Size distribution of complexes prepared at N/P ratio 10. (C) The cell uptake of PEI/pci-S complexes was observed by confocal laser scanning microscope. Upper left, intracellular distribution of rhodamine-labeled PEI/pci-S (red). Upper right, cell nuclei by DAPI staining. Lower left, differential interference images of RAW 264.7 cells. Lower right, overlapping image of nuclei and rhodamine-labeled PEI/pci-S. (D) Expression of S mRNA in RAW 264.7 cells transfected with PEI/pci-S complexes was detected by RT-PCR. (E) S protein in RAW 264.7 cells with PEI/pci-S complexes was detected by Western blot.