Vaccination of mice with gamma-irradiated Schistosoma japonicum cercariae

gamma-irradiated cercarial vaccines induce high levels of protection in mic e against Schistosoma mansoni infection, however, the same has not been wel l established for S. japonicum. Here we describe vaccination studies in mic e with gamma-irradiated S, japonicum cercariae testing the effectiveness of different irradiation doses, number of vaccinations, and mouse strains. In CBA/Ca mice, a single percutaneous exposure to 500 S. japonicum cercariae previously attenuated by 10, 20, 30, 40 or 50 krad gamma-irradiation induce d significant, but comparable levels of protection (34-46%) against challen ge infection. In a repent experiment in C57Bl/6 mice, only groups vaccinate d with 10 or 20 krad gamma-irradiated cercariae showed statistically signif icant, bur lower levels of resistance (20-24%). Multiple vaccination of CBA /Ca mice with 500 20 krad gamma-irradiated cercariae did not improve the re sistance level (40%). Analysis of IgG responses showed no clear correlation between antibody levels and levels of protection, Western blot analysis su ggested that recognition of a 200-kDa antigen might be correlated with prot ection, that antigens of 42 and 50 kDa may be involved in the protection in duced by single vaccination, but that different antigens might be protectiv e in single vs multiple vaccinations. Sera from mice vaccinated with gamma- irradiated cercariae recognized many fewer antigens than more protective se ra from mice vaccinated with UV-attenuated cercariae. These results suggest that the mouse may not be a suitable host for studies involving gamma-irra diated S, japonicum vaccines.