Effect of LPS prestimulation on expression of TLR4 and on TNFα production. The MC/9 mast cell line was prestimulated with LPS (10 and 100 ng/ml) and the expression of TLR4 (A) and the production of TNFα after a second challenge with LPS (1 μg/ml) (B) were determined by immunoblotting and ELISA, respectively. The production of TNFα was significantly reduced in a dose-dependent manner after prestimulation with LPS 100 ng/ml (* p < 0.01). However, this reduction was not mediated by a reduction in TLR4 expression, as shown. Values are mean and SEM from 3 independent experiments.