For silencing SOCS-3 mRNA, A549 cells were transfected with 150 nM human SOCS-3 siRNA 48 h before infection using Hiperfect (Qiagen) according to manufacturer's instructions. In brief, 150 nM siRNA was added to a mixture of D-MEM without FCS/antibiotics and Hiperfect and incubated for 10 min at room temperature. For transfection 400 ml of this mixture were added to the cells. Subsequently cells were subjected to plaque assay analysis or Western blot analysis. Control siRNA was purchased from Qiagen. The sequences for the human SOCS-3 siRNA in use are: human SOCS-3 siRNA sense 59-CCA AGA ACC UGC GCA UCC AdTdT-39, human SOCS-3 siRNA anti-sense 59 -UGG AUG CGC AGG UUC UUG GdTdT-39 ) (see Table 1 for accession number of the human SOCS-3 gene).