FOSL1 and viral infectious disease: Because IRF3 is a transcription factor that plays a critical role in IFN-I responses to cytosolic RNA/DNA and virus infection (22, 23), we investigated the expression and phosphorylation of IRF3 with or without overexpression of FOSL1 and found that FOSL1 could inhibit phosphorylation of IRF3 but not the expression of IRF3 at the total protein level after poly(I:C) stimulation in 293T cells (Fig. 4A).