Schistosoma mansoni: Vaccination of mice with highly X-irradiated cercariae

Abstract

Vaccination against schistosomiasis with highly X-irradiated Schistosoma mansoni cercariae was studied in mice. The optimum dose of X radiation for the attenuation of cercariae was in the range of 24–48 krad. In selecting the optimum dose, lesions caused by migrating schistosomula in the lungs of the immunized host were considered. Cercariae exposed to 48 krad caused fewer lesions than those exposed to 24 krad but still effected a comparable worm reduction. The percentages of worm reduction in mice immunized with 48-krad X-irradiated cercariae increased with the number of immunizations up to the fifth immunization and then fluctuated in the sixth, seventh, and eighth days without increase. The optimum dose of immunizing cercariae was 500, and the optimum time interval for successive immunizations was 4 weeks. There was no significant difference in susceptibility to infection in the adult mice 161 to 694 days of age. The duration of acquired immunity in immunized mice is long, still evident 545 days from the last immunization. The present studies clearly showed that with the bioengineering method, the worm reduction in the immunized mice reached 91.1%, the effect of immunization was stronger in mice immunized with the highly X-irradiated cercariae than with the low X-irradiated cercariae, and X-irradiated cercariae were demonstrated to be a strong inducing agent for immunity in mice.