Immunization against Schistosoma japonicum in Rhesus Monkeys produced by Irradiated Cercariæ

Abstract

IN schistosome infection, it has been generally accepted that the antigens for stimulating the production of immune antibodies are the results of the production of eggs in the hosts^1,2. Recently, we³ demonstrated that inoculations of rhesus monkeys with the cercariæ of the non-human (zoophilic) strain of S. japonicum gave marked protection against a subsequent challenge with its human (pathogenic) strain. Since the non-human strain of S. japonicum is usually unable to develop into mature worms in rhesus monkeys, it indicates that the presence of schistosome eggs in the tissues is not necessary for the development of acquired resistance and that the antigens for stimulating the production of potent immune bodies may originate from schistosomulæ. This point of view was confirmed by Sadun et al.⁴. The question still remains whether this type of acquired resistance can be produced by the schistosomulæ of the human strain. This can be answered by inoculation of rhesus monkeys with irradiated cercariæ of the human strain before they are challenged with non-irradiated cercariæ.