FIG 2.

EBNA1 inhibits ULBP1 expression, which protects newly infected cells from NK cell-mediated killing. (A) Primary B cells infected with either wt-EBV or ΔEBNA1-EBV at equal infection rates as determined by EBER in situ hybridization (red), GFP expression (green), and blast formation. The mean percentages of cells positive for each marker 4 days postinfection are provided ± standard deviations. At least 50 cells were counted for each condition. (B) Levels of ULBP1 mRNA quantified by qRT-PCR and normalized to TBP expression at different time points following B-cell infection with wt-EBV or ΔEBNA1-EBV. The levels of ULBP1 mRNA were set to 100% for wt-EBV-infected cells (n = 3; error bars show standard error). (C) Expression of ULBP1 mRNA in H1299 cells and H1299 cells expressing EBNA1 quantified by qRT-PCR and normalized to GAPDH expression. The levels of ULBP1 mRNA were set to 100% in cells not expressing EBNA1 (n = 2; error bars show standard error). (D) NK cell cytotoxicity with B cells 4 days after infection with wt-EBV or ΔEBNA1-EBV (target cells) cocultured at a 1:10 ratio with interleukin-2 (IL-2)-stimulated NK cells (effector cells) in the presence or absence of blocking anti-NKG2D antibody. Data are presented after normalization against uninfected cells and given as the percentage of degranulating cells where response to K562 cells is 100% degranulation (n = 5; error bars show standard error). *, P < 0.05.