Protein identification and relative quantitation was performed using ProteinPilot 2.0.1 software (AB Sciex). Data files from both technical replicates of an iTRAQ sample set were processed together. The search database was a self-built combination of Uniprot human protein sequences and Uniprot ssRNA negativestrand viruses sequences (both form the release 55.0, 02/08). The search criteria were: cysteine alkylation with MMTS, trypsin digestion, biological modifications allowed, thorough search and detected protein threshold of 95% confidence (Unused ProtScore  .1,3) . Additionally, automatic bias correction was used for intracellular fractions to correct for uneven protein loading. ProteinPilot identification and quantitation results were also manually checked: for each identified protein at least two unique peptides with good quality MS/MS data were required, and MS/ MS spectra with all reporter ion peak heights below 10 counts were manually removed from quantitation results. False discovery rates were calculated using a concatenated normal and reversed sequence database and a previously reported method [54] .