Reduced degranulation and cytokine production/secretion in FcϵRI-stimulated 4-1BBL^-/- mast cells. (A) Wt (□) and 4-1BB^-/- (▪) BMMCs that had been sensitized overnight with IgE were stimulated for 45 minutes with different concentrations of antigen. Histamine released into culture media was measured. (B) Wt and 4-1BB^-/- BMMCs that had been sensitized overnight with IgE were stimulated for 8 hours with different concentrations of antigen. IL-6 and TNF secreted into culture media was measured. ^*P < .05 (versus wt control, Student t test). (C) Measurement of [Ca²⁺]_i was performed on anti-DNP IgE-sensitized wt and 4-1BBL^-/- mast cells, as described in Figure 5. Results (mean ± SD) shown are representative of at least 2 experiments.