It is well known that the
cysteine proteases in excretory-secretory product (ESP) of Paragonimus westermani newly excysted metacercariae (PwNEM) are capable of degrading
IgG in vitro. Recent evidence suggests that the
IgG-coated surface, such as found on parasites, is one of the most effective physiologic stimuli for granulocyte activation. Therefore, this study was designed to investigate the effect of excretory-secretory product (ESP) of PwNEM on
superoxide production of granulocytes stimulated with
IgG. The 96-well plates were coated with human
IgG (0, 10, 30, 100 micrograms/ml) in the absence or presence of ESP. When granulocytes were incubated in the wells coated with human
IgG in the presence of ESP, the level of
superoxide production of granulocytes was reduced to about 90% when compared to the cells incubated in the wells coated with
IgG alone. This inhibitory effect of the ESP on
IgG-induced
superoxide production of granulocytes was concentration-dependent. These results suggest that ESP secreted by PwNEM may be important in the control of effector functions of granulocytes stimulated with
IgG in human
paragonimiasis.