For quantification of infectious VSV in organs, mice were anesthetized with pentobarbital (150 mg/kg) and blood was removed from organs by cardiac perfusion with 10 ml of PBS. Organs were snap-frozen in liquid nitrogen, weighed, pestle/tubehomogenized (Kimble/Kontes) in 1 ml of PBS per brain or peripheral organ or 0.1 ml per pair of olfactory bulbs, and virus was titered in 10-fold serial dilutions on Vero cells by plaque assay. Results are expressed as plaque-forming units (pfu) per gram of tissue. For quantification of infectious VSV yields in MEF, cells (2/+IFN-b pretreatment as indicated) were infected with VSV inoculum for 1 h, and after another 12 h, cells were freeze/ thawed, and cleared supernatants of lysates were assayed for VSV by plaque assay on Vero cells.