SCHISTOSOMA-MANSONI SOLUBLE EGG ANTIGENS .1. IDENTIFICATION AND PURIFICATION OF 3 MAJOR ANTIGENS, AND EMPLOYMENT OF RADIOIMMUNOASSAY FOR THEIR FURTHER CHARACTERIZATION
A cell-mediated immunologic granulomatous response to S. mansoni eggs is now generally accepted as being responsible for the hepatosplenic disease of chronic schistosomiasis. Previous investigations demonstrated that a soluble extract of S. mansoni eggs (SEA) induces and elicits granulomatous hypersensitivity and other forms of cell-mediated immunologic reactivity. Mice with chronic light S. mansoni 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 3 major serologic antigens which were designated MSA1, MSA2 and MSA3. Initial studies with Sephadex G-200 gel filtration and polyacrylamide gel electrophoresis (PAGE) indicated that the 3 antigens were markedly different in molecular weight, and at least 2 of the 3 were glycoproteins. The antigens were then extracted from crude SEA by absorption to a concanavalin A Sepharose affinity column. The eluted antigens were separated from each other by ion exchange chromatography on DEAE cellulose. On 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 molecular weight. These studies showed that MSA1 and MSA2 are glycoproteins of MW 137,000 and 465,000 daltons, respectively; the MW of MSA3 is in the range of 50,000-70,000 daltons. PAGE of the purified antigens revealed the following Rf: MSA1 = 0.34, MSA2 = 0.20 and MSA3 = 0.48. MSA1 and MSA2 were employed in radioimmunoassays using the Farr (NH4)2SO4 method. 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.