Lastly, we examined lung endothelial cells following acute cHV68 infection in vivo. Our in vitro studies revealed that viable, infected endothelial cells were not latently infected, but uniformly supported a lytic viral program (Fig. 2C, Fig. 3C and 3D ). Because persistent viral infection and lytic viral antigen expression is likely to be cleared by an intact immune response, we analyzed endothelial cell infection in lung tissues of immune-deficient CD8-alpha null mice. At six days post-intranasal infection, lung cells enriched for those bearing the endothelial cell marker CD31 were analyzed alongside the remaining CD31 depleted lung cells. Given the possibility that a small percentage of non-endothelial cells can transiently express CD31 (i.e. macrophages and neutrophils), we depleted the CD31 positive cell population of these potential contaminating cells and analyzed resultant cell populations by flow cytometry (Fig. S5B ). PCR analysis with single copy sensitivity for cHV68 gene50 (Rta) was performed to determine the frequency of viral genome positive cells in the CD31-enriched and remaining CD31-depleted lung cell populations (Fig. 8C) . Data from this analysis revealed that approximately 1/102 CD31-enriched cells were viral genome positive, whereas 1/525 remaining CD31depleted lung cells contained viral DNA. Thus, these data support that a surprisingly large proportion of lung endothelial cells were viral genome positive following in vivo infection.