Characterization of the Glycoprotein Antigens Which Mediate the Schistosoma japonicum Circumoval Precipitin Reaction

Abstract

The circumoval precipitin test is a serological test used for diagnosis of schistosomiasis japonica. Soluble egg antigens of Schistosoma japonicum block the formation of the circumoval precipitin by serum from infected humans. Consequently, circumoval precipitin inhibition was used to monitor purification of the soluble egg antigens of S. japonicum. Crude egg antigens were separated into protein and glycoprotein fractions by lectin chromatography on concanavalin A Sepharose. The glycoprotein fraction produced two intense precipitin lines upon immunodiffusion analysis with human chronic infection sera. The protein fraction produced two faint precipitin lines which did not cross-react with those of the glycoprotein fraction. The glycoprotein fraction contained 90% of the circumoval precipitin inhibitory activity. Isoelectric focusing of (125)I-labeled concanavalin A Sepharose fractions revealed at least four groups of potential S. japonicum antigens, termed JAG I, II, and III, and a JAG IV complex. These had isoelectric points ranging from 3.2 to 6.7. In these respects, the S. japonicum egg antigen glycoproteins are similar to those of Schistosoma mansoni. The glycoproteins were further separated by diethylaminoethyl ion-exchange chromatography. On immunodiffusion analysis it was found that one of the strong Ouchterlony precipitin lines was associated with glycoproteins that did not adsorb to diethyl-aminoethyl columns, whereas the second Ouchterlony precipitin was heterodisperse, being present in the first, second, and third of the four peaks eluted from the diethylaminoethyl column. Immunoelectrophoresis of the diethylaminoethyl fractions demonstrated that the antigen present in highest concentration in soluble egg antigen glycoproteins, JAG II, was extremely heterodisperse in its behavior on diethylaminoethyl columns. This is unlike the S. mansoni antigens which can be easily separated by diethylaminoethyl ion-exchange chromatography.