Anti-HOD mAb IgG2c leads to enhanced T-cell proliferation and increases RBC consumption by DCs. To evaluate RBC consumption, B6 mice were passively immunized followed by a DiO⁺ HOD RBC transfusion. Spleens were harvested 18 to 24 hours posttransfusion and leukocytes were stained to delineate cell subsets. The percent erythrophagocytosis of total Thy1.2⁻TER119⁻ leukocytes was determined (A) and the DiO MFI of individual APC subsets was calculated (B). To assess whether passive immunization modulated T-cell responses, B6 mice were adoptively transferred with 1 × 10⁵ purified CD4⁺ OTII T cells labeled with CellTrace-far-red (FR). The next day, recipient mice were passively immunized with PBS, nonspecific anti-K mAb IgG2c, or anti-HOD mAb IgG2c followed by a HOD RBC transfusion. CellTrace-FR dilution (C) and absolute number (D) was determined for CD4⁺Va2⁺Vb5⁺Thy1.1⁺ OTII T cells 3 days posttransfusion. Each experiment was performed 3 times with 3 to 5 mice per group. Representative data are shown. Data were analyzed with a 1-way ANOVA with Dunnett’s multiple comparisons test to the control PBS group. *P ≤ .05, **P ≤ .01, ****P ≤ .0001.