To better understand the effect of increased OPN expression on viral yield during RSV infection and to validate that OPN expression is sufficient for the increase in viral titer seen in HEK-293 cells, we used varying concentrations of human rOPN (0, -1, 10, -50, 100 and 200 ng/ml) to pretreat HEK-293 cells four hours before infection with 0.1 MOI of RSV-L19F. Here, SPP1 is linked to infection.