NK cell killing of hiECs in the presence and absence of CD47. (A–E) WT, B2M^−/−CIITA^−/−, and B2M^−/−CIITA^−/− CD47 tg hiECs were challenged with primary NK cells (A) or NK cells from a cell line (B–E) using in vitro impedance assays. Graphs show mean ± SD and three independent replicates per group and time point; three different E:T ratios are shown. wt, wild-type.