Fractionation and Quantitation of Egg Antigens from Schistosoma japonicum by the Single-Tube Kinetic-Dependent Enzyme-Linked Immunosorbent Assay (K-ELISA): Higher Antigenic Activity in Urea-Soluble than in Aqueous-Soluble Fractions

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Abstract
To identify sources of high potency antigens for use in serodiagnosis, aqueous-soluble egg antigens from S. japonicum were extracted with Dulbecco''s phosphate-buffered saline. Residual particulates were solubilized with Tris-[tris(hydroxymethyl)aminomethane]-buffered 8 M urea, yielding a urea-soluble egg antigen fraction. The urea-soluble fraction was further fractionated with Bio Gel A50m and QAE-Sephadex. All fractions were quantitatively assayed for their specific antigenic activities against serum specimens from infected rabbits by the single-tube enzyme-linked immunosorbent assay (k-ELISA). In antigen rate-limiting conditions, the urea-soluble particulate fractions were more antigenically active than the aqueous-soluble fraction. In antigen-excess and antibody-limiting assay conditions, the ideal conditions for serologic assays, the urea-derived antigens also showed superior activities against sera from infected humans. Analysis of SDS[sodium dodecyl sulfate]-polyacrylamide gel electrophoresis (SDS-PAGE) on gradient gels revealed numerous low molecular weight protein bands in the aqueous-soluble fraction, whereas the urea-soluble fractions appeared to be much simpler with the majority of their proteins concentrated in 1 or 2 high MW bands (.gtoreq. 200 kdaltons). Electro-transfer blots of the SDS-PAGE onto nitrocellulose papers and subsequent visualization of antigens by enzyme-linked immunoabsorbence confirmed these findings. Apparently, the urea-soluble fraction of S. japonicum eggs is antigenically active and has potential use in the development of a diagnostic reagent.