NP-IDV synthesis, cell uptake, and release. Images were captured with a Hitachi H7500 Transmission Electron Microscope (TEM) or a Hitachi S3000N variable pressure Scanning Electron Microscope (SEM). (A) SEM analysis (magnification, ×12 000) showed smooth surfaces of NPs with sizes of approximately 1.6 μm. (B) TEM (original magnification, ×20 000) demonstrated uptake of NP-IDV into BMMs (arrowhead). (C) BMM cytoplasm appeared dark by light microscopic examination due to uptake and concentration of NPs after culture in the presence of NP-IDV for 12 hours. (D) Fluorescence microscopy of BMMs cocultured with rDHPE-NP-IDV (red) confirmed intracellular localization of NP-IDV. Ingested NPs appeared as red fluorescent dots and showed intensity located within cytoplasm. (E) Levels of IDV were assayed by HPLC from lysates of cultured BMMs sampled at specified times. (F) After single washout, extracellular (media) and intracellular (BMM) IDV levels were determined. (G) With subsequent media changes, intracellular and extracellular levels of IDV progressively diminished until reaching a nadir at day 6, when IDV levels fell below the limit of detection.