Fig. 2

Internalization of nanomaterials by steady-state DCs. Immature DCs were incubated for 2 h at 37 °C with 250 μg ml⁻¹ SAS particles (13-nm primary diameter) and analyzed by TEM. a Representative steady-state DC showing emerging dendrites interacting with particles. N, nucleus; bar, 0.5 μm. Contrasted with uranyl acetate/lead citrate for 15 min; the rectangle indicates the area selected for higher magnification. b Magnified region of the DC near its cell surface to highlight membrane protrusions (arrowhead) in the process of engulfing SAS particles (asterisk). The two arrows indicate internalized particles within a vacuole (V). Scale bar, 0.2 μm. c Magnified region of a DC that visualizes the process by which SAS particles (asterisk) are engulfed into intracellular vacuoles. A small SAS aggregate is enclosed in a vacuole. Scale bar, 0.2 μm; contrasted with uranyl acetate/lead citrate for 1 min to improve particle visibility. d Analysis of a representative intracellular SAS particle aggregate and cytoplasmic background by energy-dispersive X-ray spectroscopy (EDX). Internalized FePO₄ and TiO₂ particles are shown in Additional file 1: Figure S5