Fig 2: Effect of bacitracin, a PDI inhibitor, on ADE condition of DENV2 infection of U937 cells. The effect of bacitracin on cell viability is shown in (a). Three mM of bacitracin was found to be suitable for use in further drug treatment experiments, because it showed low effect on cell viability. The effect of bacitracin on viral titer in both intracellular (lysed cells) and extracellular viral particles (culture supernatants), as determined by FFU assay (b); and, viral protein production (DENV2 E and NS1), as determined by Western blot analysis (c). The effect of bacitracin on time-of-drug-addition in ADE condition of DENV2 infection in U937 cells was evaluated by viral titer as determined by FFU assay. Bacitracin was added at 0, 2, 4, 6, 8, 12, 18, and 24 h after ADE infection in U937 cells. At 24 h post-infection, culture supernatants (extracellular virus) were collected to determine viral titer by FFU assay (d). The effect of drug-addition showed dramatically decreased viral titer during 0–6 h. The results of 3 independent experiments are shown as mean ± SEM (* p < 0.05).

Fig 3: Western blot analysis of PDI protein. Whole cell extract of 24 h post-infection DENV2-infected cells under ADE infection and isotype control were resolved by 1D-PAGE and Western blot analysis. The intensity of PDI was stained with specific antibody, and the intensity of PDI was calculated and normalized with ß-actin as a loading control (a,b). The infection of ADE condition was determined by Western blot analysis of DENV2 E protein (envelope protein) and NS1 protein, with GAPDH used as a control (c). The results of 3 independent experiments are shown as mean ± SEM.