Glycopeptides in soluble egg antigen of Schistosoma mansoni: Isolation, characterization, and elucidation of their immunochemical and immunopathological relation to the major egg glycoprotein (MEG)

The major egg glycoprotein (MEG) of Schistosoma mansoni was purified by ion-exchange chromatography of glycoprotein fraction obtained from soluble egg antigen (SEA) by lectin affinity chromatography. Small carbohydrate-rich fragments (CRF) contained in the glycoprotein fraction of SEA were isolated by ultrafiltration followed by dialysis (10 to 13 kd). Comparison of MEG and CRF yielded the following results: purified MEG (79 kd) contains about 77% carbohydrate, and CRF contains 92.5% carbohydrate. When radioiodinated and run by SDS-PAGE, each yielded a single band with respective Rf values of around 0.33 and 1.0. CRF is capable of inhibiting, in a Farr-type RIA, the binding of ¹²⁵I-MEG to serum from chronically infected mice. Furthermore, CRF and MEG exhibit a single and continuous line of radioimmunodiffusion. CRF, unlike SEA, SEA glycoproteins, or purified MEG, is incapable of eliciting delayed footpad swelling in egg-sensitized mice or of inducing granulomatous hypersensitivity, when given at amounts equivalent to or higher than MEG by protein or carbohydrate content. Thus, whereas SEA, SEA glycoproteins, or MEG elicited in a representative test net swelling of 0.28 mm, 0.34 mm, and 0.29 mm, respectively, CRF gave net swelling of 0.06 mm, similar to the control value (0.07 mm) in unsensitized mice. Also, mice sensitized to viable eggs, SEA, or purified MEG exhibited, after i.v. challenge with viable eggs, a mean area of granulomas in the lungs of 12,389 μm², 16,412 μm², and 12,354 μm², respectively, as compared with 7940 μm² in CRF-sensitized mice and 8428 μm² in unsensitized control mice. Thus, CRF appears to contain fragments of MEG that are serologically active but immunopathologically inactive at the concentrations used.