Effect of αGalCer administration on anti-blood group A responses in CD1d^−/− mice. Balb/c CD1d^−/− mice and Balb/c WT (CD1d^+/+) mice were immunized using blood group A-RBCs together with intraperitoneal injection of either αGalCer (4 μg/mouse) or PBS (control) 2 times per week. (A-B) The serum anti-A–specific IgM and IgG levels were determined using ELISA at 2 and 10 weeks after the last immunization, respectively. αGalCer significantly increased the blood group A-specific Ab levels in CD1d^+/+ mice, but the Ab levels did not increase in CD1d^−/− mice. The average values ± SEM for the individual groups are shown. *P < .05 compared with the data from CD1d^+/+ mice without αGalCer. (C-D) The kinetics of the serum IgM and IgG titers against blood group A determinants in Balb/c CD1d^+/+ mice and Balb/c CD1d^−/− mice (25× diluted serum was used). Anti-A Ab production was elicited by intraperitoneal immunization of mice with A-RBC 2 times per week. The average values ± SEM for the individual groups are shown. Balb/c CD1d^−/− mice, n = 4; WT Balb/c mice, n = 5. *P < .05 compared with the respective CD1d^+/+ mice.