PARTIAL ISOLATION OF A MEMBRANE ANTIGEN WHICH INDUCES THE FORMATION OF ANTIBODIES LETHAL TO SCHISTOSOMES CULTURED IN VITRO.

Fractions of adult schistosomes (S. mansoni) were tested for their ability to absorb an IgG antibody activity which appears in the sera of rats and Rhesus monkeys infected with the parasite and is lethal to schistosomula cultured in vitro. The same fractions were tested for their immunogenicity in raising lethal antibody when administered to rats in Freund's adjuvant. The results of these experiments indicated that an antigen which both absorbs and induces the formation of lethal antibody is present almost entirely in the water-insoluble portion of adult schistosome homogenates. The antigen appears to be tightly bound to this membrane fraction since the use of strong anionic detergents is necessary in its extraction. Membranes solubilized in sodium dodecyl sulphate were fractionated by gel filtration on Sephadex columns equilibrated with the detergent. The same specific Sephadex fraction was shown to absorb both rat and Rhesus monkey lethal antibodies as well as induce the antibody when administered to rats. Further purification and analysis suggested that the immunogen was one of four proteins with molecular weights estimated between 21,000 and 33,000 Daltons. Rats vaccinated with partially purified antigen developed levels of lethal antibody similar to those found in animals immune to challenge through previous exposure to the parasite, yet were themselves only marginally resistant to infection. These results indicate that while clearly toxic to schistosomula grown in vitro, lethal antibody operating on its own in vivo is incapable of mediating the rejection of schistosome infections. [ABSTRACT FROM AUTHOR]