FIG. 6.
BZLF1 inhibits LMP1-mediated upregulation of MHC class I expression. (A) Flow cytometric analysis of surface MHC class I expression in LMP1-transfected EBV-negative DG75 cells. Each transfection included 1 μg of the GFP expression vector pEGFP-N1, cotransfected with either 4 μg of pSG5 empty vector DNA, 4 μg of an LMP1 expression plasmid, 4 μg each of an LMP1 expression plasmid and a BZLF1 expression plasmid, or 4 μg each of an LMP1 expression plasmid and an IκBαΔN expression plasmid. The total amount of DNA per transfection was kept constant by addition of an appropriate amount of pSG5 empty vector DNA. MHC class I expression was detected 48 h following transfection by staining cells with MAb Tü149 followed by RPE-conjugated anti-IgG antibodies and analyzing by flow cytometry. The MFI of RPE staining (cell surface MHC class I molecules) on the GFP-positive (transfected) viable cell population was quantified. Results shown are means and standard errors from triplicate experiments. (B) Effect of BZLF1 and IκBαΔN on constitutive surface MHC class I expression in EBV-negative cells. DG75 cells were cotransfected with 1 μg of a marker plasmid (the GFP expression vector pEGFP-N1) together with 4 μg of either pSG5 empty vector DNA, a BZLF1 expression plasmid, or an IκBαΔN expression plasmid. At 48 h following transfection, the cells were stained for MHC class I expression exactly as for Fig. 6A, and the MFI of RPE staining (cell surface MHC class I molecules) on the GFP-positive (transfected) viable cell population was quantified. Results shown are means and standard errors from triplicate experiments.