Protein contents of cell lysate were quantified with the Bio-Rad DC protein assay (Bio-Rad, Hercules, CA, USA), and an equal amount of total protein was loaded in each lane. Samples for IRF-3 dimerization assay were run on a polyacrylamide gel under non-denaturing conditions (35) . Other samples were denatured and separated by sodium dodecyl sulfate polyacrylamide gelelectrophoresis (SDS-PAGE). Proteins were then transferred onto a nitrocellulose membrane and stained with the appropriate antibodies with the SNAP i.d. TM system (Millipore, Worcester, MA, USA) according to the manufacturer's instructions.