ICSBP stimulates GAS reporter activity in JAK/STAT-pathway-deficient cells. 2fTGH, U3A, U4A, and γ1A cells were cotransfected with the WT GAS reporter and expression vector for ICSBP, IRF-1, or STAT1 and then were treated with or without human IFNγ (200 units/ml) for 6 h before harvest. Values represent the average of five determinations ±SD.