Figure 4. BCR downstream signaling in Eμ-myc B cells is relatively resistant to ibrutinib.

BCR signaling was measured by intracellular phospho-flow cytometry in splenic B cells incubated with ibrutinib prior to IgM ligation without (A-C) or with (D and E) H₂O₂. A-C) Mean fluorescence intensities (MFI) prior to and at intervals after IgM ligation from one representative experiment (left) and histograms showing one representative mouse per genotype (right) for Btk pY223 (A), Plcγ2 pY759 (B), and Erk1/2 pT203/Y205 (C). D, E) MFI without and intervals after BCR ligation and H₂O₂ addition for Erk1/2 pT203/Y205 (D) and Plcγ2 pY759 (E). Each protein was measured in at least three experiments with 3–4 mice of each genotype per experiment. Error bars are SEM; A, ^*p≤0.025 and ^**p≤0.005; B, ^*p≤0.050 and ^**p≤0.005; C, ^*p≤0.005; D, p^*≤0.001 and ^**p≤0.05; E, p^*≤0.004 and ^**p=0.02. In A-C, p-values compare phospho-protein levels between Eμ-myc and wild-type littermates, and in D and E compare phospho-protein levels in Eμ-myc and wild-type littermate B cell only treated with ibrutinib (p values for other comparisons not denoted).