Effect of IL-2 on the inhibition of CD94/NKG2A expression by CD28 costimulation. (A-D) A total of 0.5 to 1 × 10⁵ naive IL2^+/+ and IL2^−/− 2C CD8⁺ T cells purified from WT and IL2^−/− 2C TCR Tg mice were stimulated either with (A-B) plate-bound anti-CD3 monoclonal antibody (2.5 μg/mL) with or without anti-CD28 monoclonal antibody (10 μg/mL) in the presence or absence of 50 ng/mL IL-2 or 10 μg/mL anti–IL-2 monoclonal antibody, (C) 1 × 10⁵ flyL^d.B7.ICAM (added once at day 0) or 2 × 10⁵ irradiated T-depleted B10.D2 sAPCs pulsed with 10μM QL9 peptide with or without 50 ng/mL IL-2, or (D) 1 × 10⁵ flyL^d.B7.ICAM (added daily at days 0-2) pulsed with 10μM p2Ca or QL9 peptide. (E-H) A total of 0.5 × 10⁵ naive IL2^−/− 2C CD8⁺ T cells were stimulated either with (E-G) plate-bound anti-CD3 monoclonal antibody (E-F, 2.5 μg/mL; G, 2 and 20 μg/mL) plus 10 μg/mL anti-CD28 monoclonal antibody or (H) 1 × 10⁵ flyL^d.B7.ICAM (added once at day 0) pulsed with the indicated doses of QL9 peptide (10⁻⁴ to 10μM). (E-H) Cultures were supplemented with or without either (E) the indicated amounts of IL-2 (0-100 ng/mL), (F) the various common γ-chain (γ_c) family cytokines (all 50 ng/mL), or (G-H) the indicated concentrations of IL-2 (G, 0-50 ng/mL; H, 0-100 ng/mL). On day 3 after culture, cells were analyzed for CD94 expression by flow cytometry. The percentages of cells in the respective regions (A,D,G) are indicated. (A-H) Data are representative of 3 or 4 independent experiments (B-C,E-F,H; mean ± SD); the inhibition of CD94 expression induced by IL-2 (H) was calculated by the formula: % inhibition = 100 − (100 × % CD94-positive cells treated with IL-2/% CD94-positive cells untreated).