ATF3 deficiency inhibits MC granule mediator release. (A) WT or ATF3-null MCs were cultured in IL-3/SCF for 5 weeks, starved of growth factor for 6 hours, washed, and then sensitized with anti-DNP IgE and stimulated with various concentrations of DNP–bovine serum albumin (BSA) for 30 minutes. Degranulation was measured as β-hexosaminidase (β-Hex) release. (B) Cysteinyl leukotrienes from culture medium was determined by specific enzyme-linked immunoabsorbent assay. Results are expressed as mean ± SEM for 3 independent experiments. *P < .05 by comparison to WT. (C) Passive cutaneous anaphylaxis. Anti-DNP IgE (20 ng) was injected intradermally in the left ear, whereas the right ear received saline as a control. After 24 hours, mice received 100 μg of DNP-BSA containing Evan blue dye (0.5% wt/vol) by tail vein injection. Tissue from both ears was collected 45 minutes later and was used for extraction of the Evan blue dye. The optical density was measured at 620 nm. Data are means ± SEM (n = 4 mice in each group). *P < .05 compared with the IgE group of the WT mice.