In vivo aggregation of FcγRIIA induces passive systemic anaphylaxis. (A,C-D) Indicated FcγRIIA-transgenic mice were injected with 50 μg (gray symbols) or 150 μg (black symbols) of mAb IV.3, and central temperatures were monitored (n = 3). Nontransgenic littermates injected with 150 μg mAb IV.3 were used as controls (open symbols, n = 3). (A) FcRγ^−/−, (C) 3KO, (D) 5KO backgrounds. (B) Schematic representation of Fc receptors expressed in the different mouse models used in this study. (E-F) Mice were injected with indicated preformed mouse IC and central temperatures were monitored. Gray symbols indicate mice injected with 50 μg of mAb IV.3 24 hours before challenge (n = 4). Top panel (E) n = 5, (F) n = 4. Bottom panel (E) 3KO or 3KOIIA n = 3, (F) 3KO n = 3, 3KOIIA+iso n = 4. (A,C-F) Data are represented as mean ± SEM and are representative of at least 2 independent experiments (**P < .01; ***P < .001).