Abstract: 　Objective To study the in vitro larvicidal activity of nitric oxide (NO) to the juvenile Schistosoma japoni-cum. Methods Macrophages were induced by LPS or LPS + IFN-γ to produce NO, schistosomula obtained mechanically from cercariae were added to the medium with activated macrophages, the larvicidal activity was observed within 48 h . In order to further confirm the effect of NO, an inhibitor of iNOS,L-NNA (Nω-nitro-L-arginine), was used to inhibit the production of NO, larvicidal activity was measured by the same methods and the difference of dead larvae ratio was compared between the inhibited and uninhibited groups. Results LPS and LPS + IFN-γ can induce macrophages effectively, with the NO production of (109.96±3.70)μmol/L and (113.50±7.38) μmol/L respectively, accordingly the larvicidal effect reached to 91.07% ±2.92% and 96.86%±2.36% respectively. This activity can be inhibited by L-NNA. NO production and dead larvae ratio were reduced significantly in the inhibited group than in the uninhibited one. Conclusion NO produced by activated macrophages can kill schistosomula of Schistosoma japonicum.

Key words: macrophage, Schistosoma japonicum schistcsomula, nitric oxide, cytotoxicity