The pCFG5-EGZ retroviral vector used for transfection [72] as well as the constructs to express dominant negative MKK6 (MKK6Ala) or IKK2 (IKK2KD) have been described earlier [52, 73] . The Phoenix amphotropic retroviral producer cells (a gift from G. Nolan, Stanford, CA) [74] were cultured in Dulbecco's modified Eagle's medium containing 10% fetal bovine serum, 100 units/ml penicillin and 100 mg/ml streptomycin. Generation of MKK6Ala or IKKKD expressing producer cells as well as transduction of A549 cells to stably express these transgenes was performed as previously described [52, 53] . Figure S1 Infection of HUVEC results in inhibition of STAT1 phosphorylation and IFNb independent SOCS-3 gene transcription. HUVEC were infected with PR8 (MOI = 5) (A, B, D) or stimulated with 100 U/ml IFNb (E) for time points indicated. To assess the mRNA levels of SOCS-3 (A, E), IFNb (B) and MxA (E) RNA was reverse transcribed and cDNA was subjected to quantitative real time PCR. Equivalent mRNA amounts were normalized to endogenous GAPDH and calculated as n-fold of untreated cells that were arbitrarily set as 1. To assess the amount of phosphorylated STAT1 (B) A549 cells were infected with PR8 (MOI = 5) for time points indicated. Total cells lysate was subjected to Western Blot analysis using anti-phospho-STAT1, anti-STAT1 antibodies. To assess effective viral replication viral NS1 was detected using an anti-NS1 antibody. (C) Quantification of relative band intensities of (B) using AIDA software and 2D densitometry (Fuji). Figure S2 IL1b and TNFa do not affect induction of SOCS-3 gene transcription. A549 wt cells were stimulated with 100 U/ml IL1b (A), 20 ng/ml TNFa (B) or infected with PR8 (MOI = 5) (C) for time points indicated. Cells were lysed, and RNA was subjected to reverse transcription. cDNA was analyzed in quantitative real time PCR to assess mRNA amounts of SOCS-3 and IL6 (A and B) or IL1b (C). Equivalent mRNA amounts were normalized to GAPDH mRNA levels and calculated as n-fold of the levels of untreated cells that were arbitrarily set as 1.