Effect of growth factors on A23187-stimulated AA release in CD34⁺ cells compared with other cell types. Suspensions of (A) day 1 CD34⁺ cells, (B) TF-1 cells, and (C) neutrophils were incubated for 10 minutes with either growth factor diluent (0.01% vol/vol FCS), GM-CSF (10 ng/mL), IL-3 (10 ng/mL), TNF (500 U/mL), or SCF (100 ng/mL) and then stimulated with 1 μmol/L A23187. Arachidonate release was measured as described in Materials and Methods and expressed as a percentage of growth factor diluent control. The number of replicate experiments performed are indicated in the figure. The statistical significance of the differences between cytokine- and diluent-mediated priming are shown (*.05 > P > .01; **.01 > P > .001; ***.001 > P; Student’s paired t-test). The absolute values of the background release of AA was 4.6% ± 0.4%, 3.1% ± 0.3%, and 2.3% ± 0.2% of total cell radioactivity for CD34⁺ cells, TF-1 cells, and neutrophils, respectively. Similarly, A23187-stimulated AA release was 7.2% ± 0.8%, 5.6% ± 0.6%, and 6.9% ± 1.1% in the FCS-primed samples.