BALB/c recipient mice were 1) not transfused (negative control ●), 2) given a single transfusion with non-leukoreduced untreated B6 PRP (single transfusion control ■), or transfused with non-leukoreduced untreated B6 PRP 2 weeks after initial transfusion with either 3) leukoreduced UV+R treated PRP alone (π), 4) UV+R treated PRP containing UV+R treated WBCs (θ), 5) UV+R treated PRP containing untreated WBCs (◆), 6) UV+R treated PRP containing 5% EtOH-treated WBCs (apoptotic ○), or 7) UV+R treated PRP containing freeze/thaw-treated WBCs (necrotic □), all from allogeneic B6 donors. Two weeks after last transfusion, serum from recipients was screened for antibodies against B6 target cells by flow cytometry. Shown is combined data from three independent experiments (N=13–15 per group). Groups were compared by ANOVA with Dunnet’s post-test to compare each group to the single untreated PRP transfusion control (X). **p<0.01 and ****p<0.0001.