Proteolytic activity of cysteine protease in excretory-secretory product of Paragonimus westermani newly excysted metacercariae pivotally regulates IL-8 production of human eosinophils

This study investigated the effect of the excretory-secretory product (ESP) of Paragonimus westermani newly excysted metacercariae (PwNEM) on IL-8 production of human mature eosinophils. Treatment of eosinophils with lower concentrations (0.3 and 1 μg/ml) of the ESP significantly (P<0.01) induced IL-8 production, whereas treament of cells with higher concentrations (3 and 10 μg/ml) did not. This effect of the ESP was concentration-dependent. Interestingly, the amount of IL-8 production released into the culture supernatants was inversely correlated with the rate of eosinophil survival. When eosinophils were cultured with the same concentrations of the ESP for 24 h, the ESP resulted in eosinophil death in a dose-dependent manner. To investigate whether high proteolytic activity of proteases in the ESP could cause little production of IL-8, 10 μg/ml of ESP was pretreated with heat at 100°C for 10 min or 56°C for 30 min to reduce its proteolytic activity. IL-8 production of eosinophils incubated with heat-treated ESP was markedly increased comparable to that of cells treated with the lowest concentration used in this study. These findings suggest that the protease in the ESP of PwNEM pivotally regulates IL-8 production by controlling of eosinophil survival, depending on the amount of ESP released in vivo. Thus, the cysteine protease in the ESP of PwNEM could provide a novel role to control recruitment of inflammatory cells in larval-infected lesions in human paragonimiasis.