Overexpression of catalytically inactive PLD1 enhances FcϵRI-induced histamine release. Two cell lines of each type transfected with PLD1 (A) or PLD2 (B) were stimulated for 45 minutes with the indicated concentrations of antigen. Histamine release into the supernatants is expressed as the percentage of the total content of the cells. Data represent the mean ± SD from 4 independent experiments. The paired t test for the percentage of release curves was statistically significant compared with the 2 controls as indicated: ^*P < .05, ^**P < .005, ^***P < .0005.