Studies on the adsorption of host antigens by Schistosoma mansoni

Abstract

The trematode parasite Schistosoma mansoni adsorbs a variety of antigens from it's mammalian host. These adsorbed components may play a role in the parasite's ability to escape the host's immune response to the parasite. Some of these host proteins are eluted into culture medium when the parasites are cultivated in vitro up to 4 hours. The resulting "eluate" was examined by 1-D and 2-D gel electrophoresis, as well as immunoblotting utilizing various antisera to mouse blood proteins. The parasite elutes all classes and subclasses of hose immunoglobulin into culture medium, except IgD and IgE. Albumin and α-2-macroglobulin determinants are also present in the eluate. Other host proteins known to be adsorbed by the parasite are not present in eluate, these include erythrocyte antigens, the complement component C3, MHC class I antigens, and fibronectin. Several other proteins in the eluate share migration and staining patterns in 2-D electrophoretic gels with normal mouse serum, but these remain unidentified. The parasite also elutes, secretes and excretes a variety of proteins of parasite origin into the culture medium. Various parasite life cycle stages present in the mammalian host were examined for the presence of mouse IgG on the parasite's tegumental surface using a fluorescenated immunoprobe. The data indicates that male juvenile parasites present in the liver at day 28 post infection and on acquire the ability to absorb host IgG following pairing with female worms. Unpaired male worms of the same age do not have mouse IgG present on their tegumental surface, nor do any other life cycle stage, except adult male worms. To quantify the adsorption of host IgG by adult male worms, parasites were denuded of host proteins by short term cultivation, the incubated in various concentration of 125I-mouse IgG to determine how much radiolabeled IgG saturated the parasite's tegumental IgG binding sites; or were incubated in a constant amount of 125I-mouse IgG for various times to determine how long it took to saturate the parasite's tegumental IgG binding sites. Eluted adult male worms can adsorb as much as approximately 80 pg of IgG per worm...