Antibody-enhanced DENV infection and autophagosome formation in KU812 cells.

<p>(A and B) Cells were inoculated with medium alone (Mock), with DENV alone (MOI = 1), or with DENV in the presence of a sub-neutralizing dilution (1∶10,000) of dengue patient sera at 4°C for 1.5 h. After washing, cells were resuspended in fresh medium and incubated at 37°C for 24 h. The DENV E protein (A) and NS4B protein (B) were detected by flow cytometry. Infection of UV-inactivated DENV (iDENV) was served as negative control. The means of three independent experiments ± SD are shown. (C and D) After 24 h post-infection, the culture supernatant (C) and the mixture of cell and culture supernatant (D) were collected to determine viral titers by plaque assay. The means ± SD of three independent experiments are shown. (E) After infection for 24 h, cells were fixed and observed under TEM. We analyzed five cells by TEM in each condition including mock, DENV alone, and ADE. One section per cell was obtained to quantify the autophagosome vesicles. The black square areas in the left panels were amplified (×40000) and shown in right panels. The arrowheads indicate the autophagosomes. Cy: cytoplasm; N: nucleus. (F) The quantification of autophagosome numbers in each section from (E) is shown. The means ± SD of three independent experiments are shown. **<i>P</i><0.01.