To further examine the proliferation observed during the first six days of culture, we stained MB114 cells with carboxyfluoroscein (CFSE) prior to infection. CFSE is a fluorescent molecule used to measure cell proliferation, in that each time a cell divides, the two daughter cells contain half the CFSE of the parent cell. S11 cells demonstrated a drop in CFSE signal intensity after six days in culture, consistent with cell division. At the time of harvest (day six post-infection), MB114 cells also demonstrated a drop in CFSE signal intensity consistent with multiple cell divisions (Fig. 5B ). After six more days in culture (12 days post-infection) CFSE signal intensity dropped further, consistent with continued cellular proliferation. Thus, endothelial cells which remained intact after cHV68 underwent multiple rounds of proliferation.