(a) Internalization of uncoated and PMDV-coated Si particles in phagocytic cells. FITC-labeled Si particles were incubated with PMA-differentiated THP-1 at particle-to-cell ratios of 5:1 and 10:1. Cells with internalized particles were quantified by flow cytometry after removal of surface bound particles by trypsin. Results are presented as the mean ± SEM, n=3; **, p<0.01. (b) Representative flow cytometry histograms of phagocytic THP-1 cells with internalized Si particles. (c) Representative images of phagocytic THP-1 cells with internalized Si particles. After removing surface bound Si particles by trypsin, cells were cytospun onto glass slides. Nuclei were stained by DAPI (blue). Arrows: Si particles; arrowheads: nuclei. (d) Differential opsonization of human IgG to the surface of uncoated and PMDV-coated Si particles. After 30 min incubation with human serum, washed particles were stained with FITC-labeled anti-hIgG Fc. Particles were imaged through green fluorescent and DIC channels. (e) CD47 was partially responsible for reduced phagocytosis of PMDV-coated Si particles. FITC-labeled PMDV-coated Si particles were preincubated with anti-CD47 blocking antibody and subsequently added to PMA-differentiated THP-1 cells. Cells with internalized particles were quantified by flow cytometry. Results are presented as the mean ± SEM; n=3; *, p<0.05; **, p<0.01.