Resistance againstSchistosoma mansoniinduced by highly irradiated infections: studies on species specificity of immunization and attempts to transfer resistance

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Abstract
Significant levels of resistance against Schistosoma mansoai challenge were developed by mice exposed to highly irradiated (20 krad.) cercariae of the homologous species (53–67%), whereas vaccination with S. bovis, S. haematobiurn or S.japonicuni failed to confer significant levels of resistance (–5–12%), thus confirming the specificity ofthe immunizing procedure. Attempts to transfer resistance to naive recipients by injection of serum and of spleen or lymph node cells from donor mice vaccinated with highly irradiated cercariae were largely unsuccessful. However, significant levels of resistance could be transferred to mice by injection of serum from rabbits exposed to irradiated cercariae. Comparable levels of resistance were conferred by injection of serum at the time of challenge (34–69%) or 5–6 days later (31–56%). Tn contrast, sera from rabbits injected with solubleegg antigen or homogenized cercariae failed to confer protection upon recipient mice. Sera from vaccinated mice, vaccinated rabbits and antigen-injected rabbits all caused cell adherence to skin-transformed schistosomula hut neither the level of adherence nor the serum titre correlated with the ability to confer protection to mice.