Selective uptake of QDs by microglia in mixed primary cortical cultures. A. In mixed primary cortical cultures from rats, QDs (red) were internalized primarily by microglia labeled with anti-CD11b (green) or anti-Iba-1 (green) antibodies. Nuclei were labeled with DAPI (blue). Scale bar, 50 μm. Inset, higher magnification of a QD-containing microglia cell labeled with Iba-1 antibody. B, C. QDs (red) were not found in astrocytes labeled with anti-GFAP (green, B) or in neurons labeled with anti-MAP2 (green, C). Scale bar, 50 μm. D. Fluorescence intensity of QDs in microglia increased with time of incubation. n = 30-100 cells from 5-6 independent images measured with Metamorph analyses. * P < 0.05 (24 h vs. 48 h), *** P < 0.001 (3 h vs. 8 h, and 8 h vs. 24 h); one-way ANOVA with Tukey-Kramer posthoc analyses. Error bars represent SEM. E. QDs (red) were not detected in apoptotic or necrotic cells labeled with Annexin V/Sytox green (green). Scale bar, 50 μm. F. Microglial internalization of QD655 conjugated with polyethylene glycol (QD655-PEG), PEG-streptavidin (QD655-PEG-Strep), or -COO- (QD655-Carboxyl) in mixed cortical cultures. Red: QDs; green: Iba-1-positive microglia. Scale bar, 50 μm.