Membrane cholesterol depletion differentially affects endocytosis of MPS and PS NPs. RBL cells (30,000/cm 2 ) adherent on cover-slips were pulse-labeled for 5 minutes with 10 μg of MPS or 75 μg of PS NPs or both in complete or serum-free medium as indicated. Parallel cultures were preincubated for 1 hour, with 5 mM <t>MbCD</t> in serum-free medium used to assess the involvement of cholesterol-dependent mechanisms in the uptake of NPs. After this, cells were washed and imaged under the fluorescence microscope. Representative images of two independent experiments in triplicate are shown. Abbreviations: MbCD, <t>methyl-β-cyclodextrin;</t> MPS, mesoporous silica; NPs, nanoparticles; RBL, rat basophilic leukemia; PS, polystyrene. 