LAD2 cells were stably transduced with control shRNA or shRNA lentivirus targeted against GRK2 or GRK3. (A, B) Quantitative PCR was performed to assess the GRK2 and GRK3 knockdown and results are expressed as a ratio of GRK2 or GRK3 to GAPDH mRNA levels. (C, D) Cells were stimulated with different concentrations of C3a (0.1, 1, 10, and 100 nM) and percent degranulation (β-hexosaminidase release) was determined. (E): Control and GRK2 KD cells were exposed to different concentrations of compound 48/80 and percent degranulation was determined. C3a (1 nM) was used as control. Data represent the mean ± SEM from three independent experiments. Statistical significance was determined by unpaired two-tailed t test. *, p<0.05; **, p<0.01; and ***, p<0.001.