Fig. 4.

Chemotactic recruitment of monocytic U937 cells and macrophage-like PMA-differentiated U937 cells by cell culture supernatants of infected and non-infected cells. Attraction of U937 cells (A) or PMA-differentiated U937 cells (B) towards cell culture supernatants of VACV-, CPXV- (strain BR) or mock-infected HeLa cells (6 h p.i.). Fresh media served as control (Ctrl.). Cell migration towards the cell culture supernatants was assessed by chemotaxis assay (5 μm pore size) over a period of 12 h (rfu, relative fluorescence units). Statistics: one-way ANOVA and Tukey's multiple comparison test. The asterisks indicate statistically significant results. **p = 0.001 to 0.01.