Isolation of Schistosoma japonicum Egg Glycoprotein Antigens which Sensitize Mice to Lung Granuloma Formation and Elicit an Immediate Hypersensitivity Response

Abstract

Crude Schistosoma japonicum soluble egg antigen (SEA) could be resolved into at least 25–30 Coomassie blue-reactive polypeptides when subjected to polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. Two of these polypeptides also gave a strong reaction for carbohydrate with the periodic acid-Schiff (PAS) reagent. Although only four antigens could be demonstrated by double immunodiffusion in agar against the sera of mice with a 9-week S. japonicum infection, double antibody precipitation of 125I-labeled SEA, followed by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate, revealed the presence of at least 20–22 antigenic species. Crude SEA was fractionated by Concanavalin A-Sepharose 4B chromatography. The resulting fractions, together with crude SEA, were tested for their ability to subcutaneously sensitize mice to lung granuloma formation around S. japonicum eggs subsequently injected intravenously. Strikingly, only the egg glycoprotein antigen fraction, which bound to the lectin column and was eluted with α-methyl-D-mannoside, possessed demonstrable sensitizing activity. Likewise, only this glycoprotein fraction elicited a significant immediate (15-min) footpad response, when injected into the footpads of S. japonicum-infected mice. The biologically active glycoproteins were further purified by repetitive gel filtration chromatography. Two of the isolated glycoproteins (designated gp-1 and gp-2) were shown to be ≥90% pure and to be PAS-reactive; whereas the third (gp-3) was found to be still heterogenous. When the individual purified glycoproteins were tested in the lung granuloma model, all three displayed significant sensitizing activity; however, gp-2 appeared to be the most active. Simiarly, the same glycoprotein antigen elicited a significantly greater immediate footpad reaction in infected mice than did the others.