FIGURE 3.

Anti-A Abs could not be intentionally induced in CD4⁺ T cell–deficient mice. A, Injection (3 weekly injections beginning at the age of 7 wk) of Hu-A BCM in WT mice induced abundant anti-A Ab production. B–D, In contrast to WT mice, in T cell–deficient strains of both sexes, anti-A Ab production was not further augmented by a similar Hu-A BCM injection. E and F, CD4⁺ T cells were isolated from WT B6 spleen and adoptively transferred into 4-wk-old sex-matched CD4KO mice (8–12 × 10⁶ cells) in a similar procedure to Figure 2A–C. The presence of CD4⁺ T cells rendered CD4KO mice responsive to stimulation by Hu-A BCM. Anti-A Abs were measured by hemagglutination using reagent RBCs from A-transgenic mice. Two-way ANOVA analyses were used to compare groups for anti-A Abs. ns, nonsignificant (P ≥ 0.05); **P ≤ 0.01; ***P ≤ 0.001; ****P ≤ 0.0001. A-Ag, A-antigen; Ab, antibody; ANOVA, analysis of variance; CD4KO, CD4 knockout; Hu-A BCM, human ABO-A blood cell membrane; MHC, major histocompatibility complex; TCR, T-cell receptor; WT, wild type.