Functional expression of a novel Kunitz type protease inhibitor from the human blood fluke Schistosoma mansoni.

Schistosomes are able to survive for prolonged periods in the blood system， despite continuous contact with coagulatory factors and mediators of the host immune system. Protease inhibitors likely play a critical role in host immune modulation thereby promoting parasite survival in this extremely hostile environment. Even though Kunitz type serine protease inhibitors have been shown to play important physiological functions in a range of organisms these proteins are less well characterised in parasitic helminths.