Higher frequencies of responding NK cells in the presence of multiple MHC class I alleles. (A) Frequencies of CD107a⁺ NK cells after stimulation with plate-bound antibodies against NK1.1 and NKG2D or in the absence of antibody (PBS) for 5 hours. One representative experiment of 11. (B) Summaries of all 11 experiments performed, expressed as mean percentage of CD107a⁺CD3⁻DX5⁺ NK cells with SEM. *P < .05 and **P < .01.