Expression of Egr-1 by mast cells after FcϵRI aggregation. (A-B) Mouse bone marrow–derived mast cells (BMMCs) were sensitized with anti-TNP IgE and stimulated with TNP-BSA (10 ng/mL) for 15, 30, 60, or 180 minutes. RNA isolated from these cells was reverse transcribed to cDNA and subjected to real-time quantitative PCR. Egr-1 expression was normalized to endogenous control GAPDH. The data are expressed as relative mRNA levels compared with the average expression level in BMMCs treated with TNP-BSA for 15 minutes (= 1) because at this time point Egr-1 showed the highest expression level. The PCR products were also separated by agarose gel and stained with ethidium bromide. Untreated BMMCs (NT) showed no Egr-1 expression, whereas TNP induced a rapid and transient expression of Egr-1. Error bars represent standard errors from 3 independent experiments.