Impact of IL-5 on anti-A Ab production after stimulation with blood group A-RBCs. (A) Balb/c CD1d^−/− mice and WT CD1d^+/+ mice (n = 5 in each group) were immunized with human blood group A-RBCs (5 × 10⁸/mouse). The levels of cytokines in serum were analyzed at the indicated time points using cytometric bead array flex sets (CBA). Blood group A determinants significantly increased the level of IL-5 in CD1d^+/+ mice, but this cytokine level did not increase in CD1d^−/− mice. In contrast, blood group A determinants did not increase the levels of IL-4, IL-9, IL-17, IL-21, and IFN-γ in either CD1d^−/− or CD1d^+/+ mice. (B) Balb/c WT mice received intraperitoneal injection of anti-mouse CD1d mAb (n = 5). Mice that received injections of isotype-matched Ab served as controls (n = 5). The mice were immunized with human blood group A-RBCs (5 × 10⁸/mouse) on day 1 after mAb administration. The level of IL-5 in serum was analyzed at the indicated time points using CBA. Treatment with anti-CD1d mAb significantly inhibited IL-5 production against blood group A epitopes in the mice. (C-E) Balb/c WT mice received intraperitoneal injection of anti-mouse IL-5 mAb (n = 5) 30 minutes prior to immunization with human blood group A-RBCs (5 × 10⁸/mouse). Mice that received injections of isotype-matched Ab served as controls (n = 5). The mice were immunized with human blood group A-RBCs 2 times at 1-week interval after mAb administration. (C) Anti-A IgM concentrations were measured using ELISA before immunization. (D) Anti-A IgM concentrations were measured at 2 weeks after the first immunization. (E) Anti-A IgM concentrations were measured at 3 weeks after the first immunization. Treatment with anti-IL-5 mAb significantly inhibited Ab production against blood group A epitopes in the mice. The average values ± SEM for the individual groups are shown. *P < .05 compared with the data from CD1d^−/− mice and data from WT mice treated with isotype-matched Ab.