Multiple Antibody Response in Schistosoma Mansoni Infections: Antigenic Constituents in Eggs, Cercariae, and Adults (Excretions and Secretions) Determined by Flocculation Reactions, Cross Absorption and Double Diffusion Studies
Elvio H. Sadun
Elvio H. SadunDepartment of Medical Zoology, Walter Reed Army Institute of Research, World Health Organization, Washington, D. C., Switzerland
Studies were conducted to determine whether extracts from egg and adult stages of schistosomes could be coated onto cholesterol-lecithin crystals and thus be used effectively for the serological diagnosis of schistosomiasis. The reactions obtained in the slide flocculation test with antigens from eggs, cercariae, and adult excretions and secretions (ES) were compared in artificially immunized and experimentally infected animals, as well as in naturally infected humans, to determine whether they stimulated or detected distinct humoral factors or whether they differed only in the relative proportions of common antigens. Furthermore, attempts were made to isolate and define some of the soluble antigenic fractions present in egg, cercaria and adult Schistosoma mansoni extracts to ascertain which are common to various stages; to characterize the antigenic fractions which are adsorbed onto cholesterol-lecithin crystals; and to compare results obtained with the slide flocculation test and immunoelectrophoresis before and after homologous and heterologous serum absorption.
Although flocculation tests with all three antigens gave consistently satisfactory results, the ES antigen seemed to confer to the test the greatest sensitivity and specificity. Homologous and heterologous absorptions revealed the presence of stage-specific reacting fractions which stimulate distinct humoral factors.
Each of the three antigenic extracts formed bands by immunoelectrophoresis when reacted against antisera from either artificially immunized or infected animals. Although cercaria and egg antigens were quite reactive with these antisera, forming 12 and 13 consistently demonstrable bands, respectively, the adult ES antigen was less reactive, forming only 8 bands. With the exception of the adult ES antigen, the largest number of bands was noted when antigens were tested with homologous antisera from artificially immunized animals. Sera from infected rabbits and monkeys produced 5 to 7 consistently demonstrable bands with the three antigens. The sera from infected animals produced some bands against the three antigens which were not observed in tests using sera from artificially immunized animals.
Homologous and heterologous absorptions of sera against cercaria and egg extracts uniformly reduced their reactivity in the immunoelectrophoresis tests. However, after only a single absorption reactivity was not completely eliminated, and these sera frequently retained immunoelectrophoretic activity against individual antigenic components. On the other hand, single absorptions uniformly eliminated all homologous serum activity in the slide flocculation test. Cercaria and egg antigens had more in common with each other than either had in common with the adult ES antigen.
The comparison between the results obtained by the slide flocculation test and by immunoelectrophoresis before and after serum absorptions revealed many similarities and supported the conclusion that the adult ES antigen confers to the test the greatest degree of sensitivity.
Present address: Laboratoire de Biochimie, Faculté de Médicine, Dakar, Senegal (Afrique Occidentale).