MACS-separated CD8+ T cells were cultured in triplicate on an immobilized anti-CD3 mAb (0.005 μg/ml [upper panel] or 0.01 μg/ml [lower panel]) in combination with recombinant MICA-129Met-Fc, MICA-129Val-Fc, and OVA-Fc proteins at various concentrations (1.0, 0.5, 0.1, 0.0 μg/ml). After 72 h, 25% of the supernatant was harvested and IL-2 concentrations were measured by ELISA. The harvested medium was replaced by the same volume containing 1 μCi 3H-labeled thymidine. After 12 h, the plates were completely harvested and the DNA-bound radioactivity was determined. The means and SD of the stimulation index (SI) are displayed (n = 4). Significant differences between MICA-129Met/Val-Fc and OVA-Fc proteins were found when the antigen-specific signal (anti-CD3) was limited (*P < 0.05, t-test; upper left panel: 1.0 μg/ml: MICA-129Met-Fc versus OVA-Fc P = 0.0372 and MICA-129Val-Fc versus OVA-Fc P = 0.0366; upper right panel: 1.0 μg/ml: MICA-129Met-Fc versus OVA-Fc P = 0.0499 and MICA-129Val-Fc versus OVA-Fc P = 0.0192; 0.5 μg/ml: MICA-129Met-Fc versus OVA-Fc P = 0.0164 and MICA-129Val-Fc versus OVA-Fc P = 0.0357; lower left panel: 0.5 μg/ml: MICA-129Met-Fc versus OVA-Fc P = 0.0287 and MICA-129Val-Fc versus OVA-Fc P = 0.0232; lower right panel: 1.0 μg/ml: MICA-129Met-Fc versus OVA-Fc P = 0.0171 and MICA-129Val-Fc versus OVA-Fc P = 0.0484). 