Egr-1 is required for the full responsiveness of TNF and IL-13 production by mast cells in response to FcϵRI aggregation. Mouse BMMCs from wild-type mice or Egr-1–deficient mice were sensitized with anti-TNP IgE and stimulated with TNP-BSA (10 ng/mL). (A-B) Cell pellets were used for RNA isolation. Real-time quantitative PCR was performed to determine TNF and IL-13 expression. TNF and IL-13 expression was normalized to endogenous control GAPDH. The data are expressed as relative mRNA level compared with the average expression level in wild-type BMMCs treated with TNP-BSA for 1 hour (= 1) because at this time point TNF and IL-13 showed the highest expression level. (C-D) Cell-free supernatants were used for examining TNF and IL-13 production by ELISA. Error bars represent standard error (A-B, n = 3; C-D, n = 5).