Fig. 3.

Binding to and uptake of 100-nm SiO₂ NPs by human adherent PBMCs, which are mainly monocytes. NPs (arrow) are initially adsorbed to the cell surface (a). Bar indicates 1 μm. b Some NPs, on the outside of the cell, lay within an invagination (arrow) of the cell surface; such invagination is an early step in phagocytosis. The cell is a negative control (no NEM; thus no gold particles; see “Methods and materials”). M mitochondrium. Bar indicates 1 μm. c Two 100-nm NPs are within a vacuole (V), presumably a phagolysosome; GSH distribution is indicated by the 10-nm gold particles. d An apoptotic cell (Ap) bound (start of efferocytosis) to a monocyte with NPs is shown. The 100-nm NPs are in V, either phagosomes or phagolysosomes. One of these V contains material other than silica particles, indicating that it is an autophagolysosome (Au); N nucleus. The apoptotic cell contains no silica NPs and may have started the process of apoptosis before being exposed to the silica NPs. Bar indicates 1 μm