SAA induces rapid secretion of IL-8 from neutrophils.

(A) Freshly prepared neutrophils were stimulated with 2 μM SAA at 37°C for 4 hours in serum-free medium. The secreted (from supernatant; closed bars) and cell-associated (from cell lysate; open bars) cytokines were detected by ELISA. The percentage of cell-associated cytokines in SAA-stimulated samples are 22% (IL-1β), 20% (IL-6), 3% (TNF-α), and 36% (IL-8). In unstimulated neutrophils, 77% of IL-8 is present in cell-associated form. (B) Neutrophils were similarly stimulated with LPS from E coli0111:B4 (LPS1) and S minnesota Re595 (LPS2), SAA, and TNF-α for 4 hours, at the indicated concentrations. Cell-associated IL-8 (open bars) and secreted IL-8 (closed bars) were determined by ELISA. All data are presented as mean ± SEM of 3 independent experiments, each performed in duplicate.