Analysis of IFN signaling from conditioned medium (cMed) in homologous and heterologous cells. HeLa and MDBK cells were mock infected (Un) or infected and with 7,000 and 700 PFU of HSV-1 per well (1 and 2 in each set of assays). Medium from these cells was harvested 2 days after infection and applied to uninfected homologous and heterologous cells as indicated. Cells were harvested 1 h later and lysed, and cell aliquots were probed for the induction of pStat1. (a) MDBK > MDBK. Conditioned medium samples from uninfected MDBK cells (lane 3) or HSV-infected MDBK cells (lanes 4 and 5) were applied to fresh uninfected MDBK cells, and these cells were assayed 1 h later for pStat1. In each case, cells were also treated or untreated with 1,000 U of uIFN/ml as positive and negative controls (lanes 1 and 2, respectively). (b) MDBK > HeLa. Medium samples from uninfected MDBK cells (lane 8) or HSV-infected MDBK cells (lanes 9 and 10) were applied to fresh uninfected HeLa cells in parallel with positive and negative controls with uIFN (lanes 6 and 7). (c) HeLa > HeLa. Medium samples from uninfected (lane 11) or HSV-infected HeLa cells (lanes 12 and 13) were applied to fresh HeLa monolayers. (d) HeLa > MDBK. Medium samples from uninfected (lane 14) or HSV-infected HeLa cells (lanes 15 and 16) were applied to fresh MDBK monolayers. +, present; −, absent.