Protease inhibitors inhibit the allergen-induced phosphorylation of p44 MAPK. HDMA (25 μg/ml) and GCA (12.5 μg/ml) were pre-incubated for 30 minutes at 37°C with E64 (20 μM), a cysteine protease inhibitor, or Pepstatin A (20 μM), an aspartate protease inhibitor. Then, A549 cells were exposed to HDMA or GCA for 24 hours. Total cellular protein extract was subjected to western blot analysis. The ratio of relative intensity of phospho-p44 MAPK / p44 MAPK was graphed. The experiments were repeated twice and the result of a set of representative experiments is shown.