Fig. 4

Pre-treatment of Naïve Recipient Human Monocytes with EXi-RVFV Significantly Reduces Viral Replication in the Cells during Subsequent Infection. A Naïve U937 cells were treated with either EXu or EXi-RVFV for 24 or 48 h, and cell counts and viability reads were subsequently performed using acridine orange/propidium iodide (AO/PI) staining. For each treatment condition and time point assayed, mean values ± SEM from three biological replicates are shown. B Plaque assays were performed to measure viral load in naïve U937 cells that had been pretreated with either EXu or EXi-RVFV and subsequently infected with RVFV. Both the 6 h p.i. and the 24 h pi. time points were analyzed. For each treatment condition and time point assayed, mean values ± SEM from three biological replicates are shown. C Plaque assays were performed to measure viral uptake by U937 cells post treatment with either EXu or EXi-RVFV for 24 h and subsequent infection with RVFV. Untreated cells were also included as control. At 1 h p.i., the cells were lysed and intracellular viral loads were determined by plaque assay. For cell lysis, three freeze–thaw cycles were performed in an ethanol-dry ice bath to release the intracellular virus, and quantitative lysis of the cells was verified through microscopic visualization of the sample. Mean values ± SEM from three biological replicates are shown. **P ≤ 0.01; ***P ≤ 0.005