SYK expression in 15 day culture-derived basophils treated with AS serum ± Ab10523 (anti-FcgRIIb/Cd32b). The various stimuli were added at day 3 of culture and analysis of SYK done by flow cytometry. Panel A; flow cytometry of cells treated with control serum at 1% (serum previously determined to not induce release). Panel B: flow cytometry of cells treated with AS serum at 1% (known to induce release). Panel C: summary results from 2–3 experiments (n=3 for 1% and n=2 for 2% serum), expressed relative to control serum, 22E7 (anti-FceRI Ab) at a concentration previously determined to induce 5% of maximum release. For the AS treated cells, combining results for both 1% and 2% concentrations, FceRI = surface FceRI expression (n=3), Al.Blue = counts of alcian blue positive cells (n=3), Tot.Hist. = total histamine content (n=2).