vIRF1 down-regulates constitutive and IFN- and vFLIP-induced MHC-I expression. (A) MHC-I surface expression in LECs expressing vIRF1 and pSIN. Mean and standard deviation were calculated after 3 independent infections (3 days after infection). (B) HLA-A mRNA levels of LECs expressing vIRF1 and pSIN (3 days after infection). Expression is normalized to LECs infected with pSIN. LECs expressing a vIRF1 mutant lacking the p300-binding site (amino acids 1-82) show similar HLA-A mRNA levels to control cells (pSIN). Comparable levels of expression for vIRF1 and vIRF1Δ1-82 were confirmed by RT-PCR, using the same set of primers for both genes. (C) Plot showing the fold increase of MHC-I surface expression due to IFN-α in LECs expressing pSIN, vIRF1, and vMIR1. (D) Percent of CD8⁺/CFSE^low cells among allogeneic PBLs cocultured with LECs infected with pSIN, vIRF1, or vMIR1 for 7 days (see “Materials and methods” for details). (E) vIRF1 and vMIRs reverse the effect of vFLIP on MHC-I. Bar graph shows MHC-I surface expression (geomean fluorescence and standard deviation) of LECs infected with pSIN (pSIN/pSIN), vFLIP and pSIN (vFLIP/pSIN), vFLIP and vIRF1 (vFLIP/vIRF1), and vFLIP, vIRF1, and the vMIRs (vFLIP/vIRF1/vMIR1/vMIR2). Error bars were calculated based on standard deviation.