Absence of activating FcγR expression in cells driven by CD11c or Zbtb promoters abrogates RBC alloimmunization. (A) FcRγ^fl/fl mice were bred with cre-expressing transgenic mice and spleens were harvested and stained with antibodies to delineate cell subsets and FcγR expression and relative MFIs of individual FcγRs are displayed as a heat map. To assess the functional consequence of modulating expression of activating FcγRs, recipients were passively immunized with anti-HOD mAb IgG2c, nonspecific anti-K mAb IgG2c, or control PBS followed by an RBC transfusion (as described in Figure 1). Survival of HOD RBCs was calculated at 24 hours posttransfusion (B) and over a 21-day time course (C). IgM (D) and total Igs (E) anti-HOD alloantibodies were determined for days 7, 14, and 21 by flow crossmatch. 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 multiple comparisons test to control B6 mice. *P ≤ .05, **P ≤ .01, ***P ≤ .001, ****P ≤ .0001.