IFN-γ–induced Qa-1b inhibits reactivation of α-GalCer–primed iNKT cells by α-GalCer. (A) Qa-1^b expression on splenic MNCs isolated from WT and IFN-γ^–/– mice was analyzed 2.5 days after intraperitoneal administration of α-GalCer or OCH. Thin lines indicate the staining of MNCs from vehicle-treated mice with anti–Qa-1^b mAb; bold lines, the staining of MNCs from α-GalCer– or OCH-treated mice with anti–Qa-1^b mAb; and dotted lines, the staining with isotype-matched control Ig. Similar results were obtained from 3 independent experiments. (B) Kinetics of serum IL-4 induction after α-GalCer injection into vehicle-primed wild-type mice (▿), vehicle-primed IFN-γ^–/– mice (▵), α-GalCer–primed IFN-γ^–/– mice (□), or OCH-primed IFN-γ^–/– mice (○). Priming was performed 2.5 days before. Serum IL-4 was not detectable in the vehicle-injected mice (data not shown). Data are represented as the mean ± SD of 5 mice in each group. Similar results were obtained from 3 independent experiments.