Schistosoma mansoni soluble egg antigens. I. Identification and purification of three major antigens, and the employment of radioimmunoassay for their further characterization.

A cell-mediated immunologic granulomatous response to Schistosoma mansoni eggs is now generally accepted as being responsible for the hepatosplenic disease of chronic schistosomiasis. Previous investigations have demonstrated that a soluble extract of S. mansoni eggs (SEA) both induces and elicits granulomatous hypersensitivity and other forms of cell-mediated immunologic reactivity. Mice with chronic light S. amnsoni infections show spontaneous suppression of granulomatous hypersensitivity in the presence of high levels of anti-SEA antibodies. Immunodiffusion analysis using antiserum obtained from these mice and SEA resulted in the identification of three major serologic antigens which have been designated MSA1, MSA2, and MSA2. Initial studies with Sephadex G-200 gel filtration and polyacrylamide gel electrophoresis indicated that the three antigens were markedly different in m.w. and at least two of the three were glycoproteins. The antigens were then extracted from crude SEA by adsorption to a concanavalin A Sepharose affininity column. The eluted antigens were separated from each other by ion exchange chromatography on DEAE cellulose. On polyacrylamide gel electrophoresis (PAGE) MSA1 and MSA2 were homogenous; MSA3 was estimated to be 70% pure. The purified antigens were radiolabeled and were passed through Sephadex G-200 or Bio-Gel A 1.5 columns to determine their m.w. These studies have shown that MSA1 and MSA2 are glycoproteins of m.w. 137,000 and 465,000 daltons, respectively; the m.w. of MSA3 is in the range of 50,000 to 70,000 daltons. PAGE of the purified antigens revealed the following R.F.s: MSA1=0.34, MSA2=0.20, and MSA3=0.48. MSA1 and MSA2 were employed in radioimmunoassays using the ammonium sulfate method of Farr. On the basis of immunodiffusion analysis and radioimmunoassay, MSA1 exhibits a degree of stage and species specificity consistent with the granulomatous response to S. mansoni eggs. The potential specificity of the MSA1 radioimmunoassay and its great sensitivity suggest a role in the immunodiagnosis of schistosomiasis.