(A) Binding of preformed IgE/omalizumab ICs to FcγRs in CHO cells stably transfected with each one of the human FcγRs (16). Upper histograms show binding of an anti-FLAG mAb as a control for FcγR expression. Lower histograms show binding of ICs or IgE FITC alone. Data are representative of 3 independent experiments. (B) Binding of omalizumab to human C1q assessed by ELISA. An irrelevant IgG1 mutated in its Fc portion at position 322 (K₃₂₂A) to preclude binding to C1q was used as a negative control. Results in B show mean ± SD from data pooled from 2 independent experiments (total of n = 4 replicates). Expression of CD66b (C), CD62L (D), and CD32 (E) on purified CD45⁺CD15⁺ human neutrophils after 1 hour of incubation with omalizumab/IgE immobilized ICs, IgE, or medium alone. Results in C–E show values from neutrophils from individual donors normalized against cells stimulated with medium alone; bars indicate mean ± SEM of n = 7 total values per group pooled from 3 independent experiments. (F) CD62L expression on CD11b⁺Ly6G⁺ neutrophils purified form hFcγR^KI or FcγR^null mice after 1 hour of incubation with ICs or medium. Results in F show values from individual mice with bars indicating mean ± SEM pooled from 2 (FcγR^null; total n = 4/group) or 3 (hFcγR^KI; total n = 5/group) independent experiments. *P < 0.05; **P < 0.01; ***P < 0.001 using 1-way ANOVA in B, contrast linear model in C–E, and Welch test in F. For further details on the statistical analysis, please refer to Supplemental Table 1.