Passive immunization with anti-HOD mAb promotes memory lymphocyte formation. (A) General experimental design to test whether passive immunization can lead to RBC-specific lymphocyte memory formation. (B) One week posttransfusion sera from B6.IgH^a recipients were collected assayed for IgG1^b alloantibodies by flow crossmatch against HOD and control B6 RBCs. The percent of IgG1^b+ HOD RBCs for a representative experiment is shown (C) and the number of mice with detectable memory responses across all experiments is provided (D). In parallel, splenocytes were harvested and stained with antibodies against CD19, I-A^b, GL7, and PNA to identify germinal center B cells. Representative flow plots (E) and percentage of germinal center B cells (F) are shown. Flow plots are gated on CD19⁺I-A^b+Thy1.1⁻Thy1.2⁻ leukocytes. Each experiment was performed 3 times with 3 to 5 mice per group. Data were analyzed with a 1-way ANOVA with Dunnett multiple comparisons test to the control PBS group. *P ≤ .05; ****P ≤ .0001.