SYK inhibition abrogates PLCG2^R665W induced downstream activation. (A) Calcium influx induced by 3 μg/ml α-IgM stimulation was measured in PLCγ2^−/− DT40 stably expressed with either WT human PLCG2 or R665W mutant. The data represents AUC by 6 replicates. In the treatment settings, 1.0 μM ibrutinib was pretreated for 1 hour followed by washout; and 0.5 μM GS-9973 or 2.5 μM R406 was treated continuously. *P < .05; ***P < .001; NS = P > .05. (B) Downstream signaling was examined in PLCγ2^−/− DT40 expressing either WT PLCG2 or R665W mutant. Cells were treated with 0.5 μg/ml α-IgM for 15 minutes; 1.0 μM ibrutinib was pretreated for 1 hour followed by washout; and 0.5 μM GS-9973 or 2.5 μM R406 was treated.