Differentiation of Acute and Chronic Schistosomiasis by Antibody Responses to Specific Schistosome Antigens

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Abstract
Phenol sulfuric test active peak (PSAP), a schistosome-specific antigen was radiolabeled with Bolton-Hunter reagent, purified, and used in two radioimmunoassays which measured total and IgG-specific antibodies in acutely, early, and chronically Schistosoma mansoni-infected patients. Molecular sieving and lectin chromatography were used to purify PSAP. In Sepharose 4B chromatography PSAP was the only antigenic substance and was one of four distinct peaks. PSAP adhered to concanavalin A and was purified after elution with α-methylmannoside. Total antibody to purified radiolabeled PSAP was measured using polyethylene glycol to precipitate complexes formed after the addition of label to varying dilutions of sera, while Staph A was used to precipitate IgG containing complexes. Most non-IgG-specific antibody was IgM. Since antibody responses were dependent on intensity of infection, ratios of the percent Staph A precipitation to the percent polyethylene glycol precipitation were determined in patients with known duration of infection. Patients with acute schistosomiasis showed depressed ratios indicative of high IgM antibody and low IgG levels, while chronically infected patients had elevated ratios. Thirty-nine sera from acutely or chronically infected patients were evaluated blindly. Twenty-four of 27 patients with clinically diagnosed acute schistosomiasis had detectable antibodies to PSAP and these were correctly classified as acutely infected. Five of six chronically infected patients had anti-PSAP responses and all were correctly identified. Levels of antibodies to a gut-associated proteoglycan, another specific schistosome antigen, enabled correct classification of all but one of the remaining patients. Serologic responses to specific parasite antigens can differentiate acutely infected patients from those chronically infected.