FIG. 7.

SLO-induced activation of p38 MAP kinase is critical for the production of TNF-α but not for the degranulation of mast cells. (Top) Mast cells were activated with SLO (1 μg/ml), and cell lysates were prepared at the indicated times. Activation of the stress-activated MAP kinases p38 and JNK was assessed by Western blotting using antibodies specific for the phosphorylated kinases. After stripping of the blot, reprobing with an antibody against total p38 MAP kinase served as an equal-loading control. The experiment shown is representative of two experiments with comparable results. (Middle and bottom) Mast cells were stimulated with SLO (1 μg/ml) for 1 h in the presence of the indicated concentrations of the p38 MAP kinase inhibitor SB203580. Thereafter, biologically active TNF-α was determined in the supernatants (secreted) and in the cell lysates (intracellular) obtained by freezing and thawing. Degranulation was measured as the release of β-hexosaminidase after 30 min. Shown are the means of three experiments. The error bars represent standard deviations.