Depletion of CI/NKG2⁺ NK cells prevents rejection of bone marrow grafts from class I–deficient mice. Recipient mice (β2m^-/- or B6) were treated with mAbs to deplete the indicated NK-cell subset, followed by lethal irradiation. At day 0, a mixture of CFSE-labeled bone marrow cells from β2m^-/- Ly5.1⁺ and B6 (Ly5.2) mice was injected intravenously. After 3 days, splenocytes were stained with PE-conjugated anti-Ly5.1 Ab. The results are represented as graft acceptance, calculated as the ratio of β2m^-/- (Ly5.1⁺) bone marrow cells to B6 (Ly5.1^-) bone marrow cells among gated CFSE-positive cells. The B6 cells serve as a nonrejected internal reference population. (A) Representative histograms depicting results in which the test graft was rejected (in untreated B6 mice, left) or accepted (B6 mice from which NK1.1⁺ cells were depleted, middle). The effect of depleting Ly49C/I⁺ and NKG2⁺ NK cells is shown in the right panel. The percentage of positive cells (marked by a bar) are indicated in each panel. Note that many of the nonstaining cells in all the panels are in the lowest fluorescence channel along the left axis due to the compensation settings of the flow cytometer. (B) Acceptance of β2m^-/- bone marrow grafts by control mice or B6 mice depleted of NKG2A⁺ NK cells, Ly49C/I⁺ NK cells, or both subsets. Data represent the mean ± SEM (n = 3 mice). Results were reproduced in a replicate experiment. (C) Acceptance of β2m^-/- bone marrow grafts by B6 mice treated with mAbs to deplete the indicated cell populations, or by control β2m^-/- mice. Data represent the mean ± SEM (n = 2 mice). Results were reproduced in 2 replicate experiments. The Ly49C/I- and NKG2A-depleted group differed significantly from the Ly49A/G2-depleted group (P ≤ .04) but not from the NK1.1-depleted group (P = .5).