Amoebic cysteine protease activity is required for IL-8 production in HMC-1 cells induced by E. histolytica-derived secretory products (SPs). (A) IL-8 production in HMC-1 cells stimulated with SPs from native or modified wild-type SPs either heat-treated (100 °C, 10 min) or treated with 25 μM protease inhibitor (E64c). (n = 4) (B) CP activity from native or modified wild-type SPs with heat- (100 °C, 10 min) or 25 μM protease inhibitor (E64c or PMSF) treatment were measured using z-Arg-Arg-pNA·2 HCl as a substrate. The level of activity is shown as a percentage relative to the control. (n = 3). All reactions were performed in triplicate measurements of each experiment. Data are presented as the mean ± SEM of at least three independent experiments. The asterisks indicate the results of comparisons with the controls (*p < 0.05. **p < 0.01).