Transmembrane arginine prevents down-regulation of cell-surface expression of KIR2DL1 after interaction with its ligand. YT-Indy cells expressing KIR2DL1 alleles *00401 and *010 were coincubated with target 721.221-Cw6 cells for the indicated times. Cell-surface expression of KIR2DL1 was detected using KIR2DL1 mAb. Left panel shows cell-surface expression of KIR2DL1*00401, and right panel shows KIR2DL1*010. Data shown are representative of 3 independent experiments.