The effect of tumor expression of MHC class I and B7-1 on the proportion of Ly49D⁺ NK cells in the spleen on days 15 and 20 after tumor cell challenge. (A) Representative FACS profiles of NK1.1⁺ and Ly49D⁺ cells among total spleen cells isolated on day 20 after tumor cell inoculation. (B) Summary of NK cell subsets on days 15 and 20 after tumor cell inoculation. Data in left panels are means and SD of an experiment involving 4 (MHC⁺B7^-) or 5 mice (MHC⁺B7⁺, MHC^-B7⁺) per group. Data in the right panel are means and SE of 2 independent experiments. The number of mice are MHC⁺B7^-(5), MHC⁺B7⁺ (8), MHC^-B7⁺ (3), and PBS (4). ^*indicates P < .05; ^**, P < .01.