Treg cells preferentially inhibit the apoptosis of CD27⁺CD45RA⁻ M CD8⁺ T cells. (A) Total CD8⁺ T cells were stimulated for 48 hours with anti-CD3 antibodies in the presence of CD4⁺CD25⁻ T cells (open symbols) or Treg cells (filled symbols). Percentages of annexin V⁺ cells on total and gated M, E, and TE CD8⁺ T cells are shown (n = 8). (B) Sorted M and E CD8⁺ T cells were stimulated in the presence of CD4⁺CD25⁻ T cells or Treg cells. In each condition, percentages of annexin V⁺ cells were estimated at 48 hours. Histograms represent the ratio of annexin V⁺ M and E cells observed in CD4⁺CD25⁻ (□) and Treg cell cocultures (■). P values were calculated using a paired Student t test.