MZB cell-mediated platelet alloimmune response relies on CD4⁺ T cells. (A) BALB/C mice were treated 4 and 2 days before each transfusion with an immunodepleting antibody against CD4⁺ T cells or their respective isotype-matched controls. Anti-H2^b IgG antibody production was evaluated 7 days after each transfusion by flow cytometry in CD4⁺ T cell immunodepleted (blue bars) BALB/C mice and in control mice that received an isotype control (red bars). Results are presented as the mean fluorescence intensity of Alexa-488 GaM IgG antibodies bound to H2^b platelets (MFI ± SEM, n = 8). (B) Alloimmunized BALB/C mice were injected with 2.10⁸ Oregon green CFDA-SE-labeled platelets from C57BL/6J mice. The kinetics of elimination of transfused platelets were determined from the percentage of Oregon green-positive platelets among 10 000 RAM.1⁺ platelets in CD4⁺ T cell depleted (blue line) and mice that received isotype control (red line) at each time point (± SEM; ∗∗P < .01; ∗∗∗P < .001; 2-way ANOVA; n = 7). ANOVA, analysis of variance; SEM, standard error of the mean.