CD4⁺T cells reactive to HOD do not boost an antibody response to KEL. Indicated B6 recipients were adoptively transferred with OTII splenocytes that were enriched in CD4⁺ T cells specific for the HOD antigen. 24 hours following adoptive transfer, all recipients were transfused with HOD RBCs, KEL RBCs, (HOD × KEL) RBCs, or a mixture of HOD RBCs and KEL RBCs (HOD + KEL). (A-B) Anti-KEL IgM (A), anti-KEL IgG (A), and anti-HOD IgG (B) antibody formation is shown for transfused recipients 5 days (D5 for IgM) and 14 days (D14 for IgG) after transfusion. Serological analysis for anti-KEL or anti-HOD alloantibodies was done by indirect immunofluorescence staining using HOD, KEL, and B6 RBCs. The MFI depicted was generated by normalizing the MFI of serum samples incubated with KEL (A) or HOD (B) RBCs to the MFI of serum samples incubated with background control B6 RBCs. Error bars represent mean ± SEM. The mean of each group is depicted as a horizontal line. Statistics were generated using a 1-way ANOVA with a Tukey’s post-test. All panels show combinatorial data from experiments reproduced 2 or 3 times, with 5 mice per group. ****P < .0001.