Fractionation of Schistosoma japonicum soluble egg antigen glycoproteins by hydrophobic interaction chromatography

We are currently studying the soluble egg antigens of Schistosoma japonicum in an attempt to determine which antigens are potent immunogens. Previously, we demonstrated by Ouchterlony immunodiffusion and inhibition of the circumoval precipitin test that the glycoprotein fraction of soluble egg antigens contains the antigens which are most immunogenic in natural infections. The soluble egg antigen glycoproteins have now been further fractionated via hydrophobic interaction chromatography on phenyl Sepharose. We found that there were at least two antigens involved in the circumoval precipitin reaction. Both the hydrophilic antigen which we call japonicum antigen glycoprotein II (JAG II) and a mixture of hydrophobic antigens (JAG III and the JAG IV complex) were capable of causing a 50% inhibition of the COP reaction around S. japonicum eggs. JAG II was not a major serological antigen of S. japonicum since it gave only a weak precipitin line upon Ouchterlony immunodiffusion analysis with pooled sera from Filipino patients with chronic S. japonicum infections. Hydrophobic interaction chromatography yielded preparations which were sufficiently pure for use in radioimmunoassays. By radioimmunoassay, the best antigens among the glycoproteins were moderately hydrophobic JAG III and the JAG IV complex. They had large amounts of antibody directed toward them in patients with schistosomiasis japonica and exhibited little reactivity with S. mansoni. The hydrophilic glycoproteins JAG I and II were poor immunogens and extensively cross-reacted with S. mansoni. This cross-reactivity means that diagnostic tests with crude soluble egg antigens would run the risk of potential false-negative results in patients with other trematode infections.