DAP10 is required for optimal expansion of alloantigen-specific NK cells. (A) 150,000 CD45.1⁺ WT Ly49D⁺ NK cells and CD45.2⁺ DAP10-deficient Ly49D⁺ NK cells were cotransferred into DAP10+12 KO mice that had been depleted of CD8⁺ T cells followed by infection with 5 × 10⁴ pfu Δm157 MCMV on day 0. 4,000,000–5,000,000 T cell– and NK cell–depleted BALB/c splenocytes were injected on days 0.5, 1.5, and 3 pi. Alloantigen-primed NK cells were isolated from spleens of recipient mice 28 d after primary alloantigen stimulation, transferred into naive DAP10+12 KO mice, and then challenged with Ly49D alloantigen stimulation. (B) The absolute number of Ly49D⁺ NK cells in the blood after the primary Ly49D alloantigen stimulation is shown. (C) The absolute number of alloantigen-primed Ly49D⁺ NK cells in the spleen on day 28 pi. Data are representative of 2 experiments (n = 4 mice per experiment). (D) Secondary expansion of alloantigen-primed Ly49D⁺ NK cells in the spleen on day 7 after alloantigen stimulation was represented as the fold-expansion relative to the number of alloantigen-primed NK cells detected in the spleen of mice adoptively transferred without rechallenge by alloantigen stimulation. Data are pooled from 3 experiments (n = 9 mice). *, P < 0.05; **, P < 0.005 versus Hcst^−/−. Error bars show SEM.