Long-term time course of IFN production in infected MDBK cells. MDBK cells were infected with 2,000 PFU of HSV-1 [V44] per 60-mm-diameter dish. The medium was harvested every day for 14 days and filtered. In parallel, in a set of infected cells, medium was removed at day 11 and replaced with fresh medium, which was then harvested at 11, 12, 13, and 14 days (11r, 12r, 13r, and14r). The conditioned medium (cMed) samples harvested each day without any replacement (lanes 1 to 11 and 13, 15, and 17) and conditioned medium samples replaced at day 11 and harvested at 11, 12, 13, and 14 days (lanes 12, 14, 16, and 18) were then applied to fresh uninfected MDBK cells for 1 h and assayed for Stat1 phosphorylation as before. d.p.i., days postinfection.