Figure 6

The effects of infecting Cf2Th cells with the three different BIV versions. The three BIV variants (WT and the two dUTPase mutants- D48E/N57S and Δ36) were used to infect the Cf2Th cells, as described in Methods. The infection of the cells by BIV was monitored by the formation of multi-cell syncytia after 10 passages. Since in Cf2Th cells, background syncytia of up to 10 nuclei per multinucleated cell could be occasionally observed, we have considered as BIV-specific only syncytia with more than 15 nuclei. A. The syncytia were visualized by phase contrast microscopy and by Hoechst dye for fluorescent staining of cell nuclei. The large, multinucleated giant cell syncytia are highlighted in red. B. A quantitative presentation of the average number of syncytia in a ×20 magnification microscopic field of the Cf2Th cells that were infected with WT and dUTPase mutated BIV. The control was performed with growth medium (marked- DMEM). Syncytia, obtained in three independent experiments and in 10 different microscopic fields from each, were counted.