HSV-2 ability to infect human monocyte cell line U937 relies on their differentiation level. A) HSV-2 replication in undifferentiated U937 cells. The U937 cell line was infected with two different MOI of HSV-2, as reported in the graph legend. Vero cells were infected as a control. HSV-2 titre in the cellular supernatants was measured by plaque assay, at different times post-infection (p.i.). B) Effect of TPA treatment of U937 cells on CD14 expression. The effect of TPA treatment on U937 cell differentiation state was analyzed by CD14 FACS analysis. The percentage of positive cells is reported. C) HSV-2 replication in TPA-treated U937 cells. Undifferentiated or TPA-treated U937 cells were infected with HSV-2 (MOI of 1 PFU/cell). HSV-2 titre in the cellular supernatant was measured by plaque assay. In all cases, the reported values represent the mean of four independent experiments. The error bars represent the standard deviation.