Modulation of blood fluke development in the liver by hepatic CD4(+) lymphocytes

We have identified an alternate developmental pathway in the life cycle of the trematode pathogen Schistosoma mansoni. This pathway is used in immunod eficient hosts in which the parasite fails to receive appropriate signals f rom the host immune system. Helminth development is altered at an early sta ge during infection, resulting in the appearance of attenuated forms that p rolong survival of host and parasite. Hepatic CD4(+) T lymphocyte populatio ns are an integral component of the immune signal recognized by the parasit e.