NK cells reduce activated and IFN-γ–secreting donor T cells. (A) CD25 expression on CD45.1⁺ Foxp3⁻ and CD4⁺ or CD8⁺ donor T cells reisolated from spleen, pLN, or mLN of Tcon (white histograms) or Tcon + NK mice (gray histograms) on day 4, or a naive control mouse (dotted line). Percentage of T cells from Tcon or Tcon + NK animals expressing CD25 is quantified in the bar graphs. CD25 expression is reduced in Tcon + NK animals in the spleen, mLN, and pLN (*P < .05, **P < .01, ***P < .001). (B) Intracellular cytokine staining demonstrates decreased IFN-γ secretion from Tcon + NK (gray histograms) compared with Tcon (white histograms) animals in the spleen on day 3. Graphic representation of summary statistics with SE appear to the right of histograms (*P < .05, IL-2 was NS). Unstimulated staining controls are depicted in the dotted lines. (C) Quantification of absolute cell numbers reisolated from Tcon and Tcon + NK animals on day 4. Donor CD4⁺ and CD8⁺ numbers are reduced in Tcon + NK mice from pLN and spleen (*P < .05, **P < .01). For all, data are averaged from 3 to 4 mice and are representative of 2 to 3 independent experiments. Error bars represent SE.