“…Resistance to reinfection with Schistosorna mansoni develops in a variety of experimental hosts during the course of a chronic infection, or following vaccination with radiation attenuated cercariae or schistosomula (Smithers & Doenhoff 1982). Whilst the levels of protection developed in the two models are similar, the mechanisms responsible for measurable immunity are thought to differ (Smithers & Miller 1980), and, in vaccine-induced resistance, there is now convincing evidence for the role of specific immunological mechanisms (Dean, Bukowski & Clark 1981a, James, Labine & Sher 1981, Sher et al 1982, James & Sher 1983. In vitro cytotoxicity assays, used as probes of host resistance and parasite susceptibility, have shown that newly transformed schistosomula are susceptible to a variety of humoral and/or cellular effector mechanisms, but that older stages make use of sophisticated evasive stratagems to avoid immune attack (Smithers, McLaren & Ramalho-Pinto 1977, McLaren 1980, 1984, McLaren & Smithers 1982.…”