More extensive Ly49 receptor down-regulation and improved functional responses of NK cells expressing single inhibitory receptors in the presence of multiple MHC class I alleles. (A) Surface expression of inhibitory Ly49 receptors (GeoMFI) relative to MHC^−/− NK cells (dotted line). Summary of 6 to 15 experiments with n = 11 D^b, n = 9 K^bD^b and n = 8 K^bD^bD^d mice. *P < .05; **P < .01; ***P < .001. (B) Identification of viable NK cells expressing only single inhibitory receptors. Gates are indicated with gray lines. FSC-A indicates forward light scatter area and SSC, side light scatter. (C) Degranulation of naive NK cells from MHC^−/−, D^b, K^bD^b, and K^bD^bD^d mice expressing only 1 inhibitory receptor (indicated in the matrix). Presented as mean percentage of CD107a⁺ NK cells with SEM, and PBS control background subtracted, within the specified single Ly49 subset after anti-NKG2D stimulation.