Defective degranulation and passive systemic anaphylactic responses in VAMP-8–deficient BMMCs and mice. VAMP-8–deficient and WT BMMCs sensitized overnight with anti-DNP IgE were stimulated for 30 minutes with the indicated concentrations of DNP-HSA (A) or for indicated time points using 10 ng/mL (B), and release of β-hexosaminidase was determined. (C) VAMP-8–deficient and WT BMMCs were sensitized with IgE before stimulation with 10 ng/mL DNP-HSA and release of histamine was determined. Data (percentage release ± SEM) are from 3 individual experiments and are representative of 4, 5, and 2 in panels A, B, and C, respectively. All differences were significant (P < .01) and were determined by one-way ANOVA. (D) In vivo passive systemic anaphylactic challenge of VAMP-8–deficient and WT mice. Mice (n = 7) were passively sensitized intravenously with 30 μg purified IgE-anti-DNP and were challenged 24 hours later with 100 μg DNP-HSA. After 2 minutes, blood plasma was collected and plasma histamine concentrations were determined by ELISA. Horizontal bars represent the means.