Abstract. Schistosoma circulating antigens were used for the detection of active infection. Anti-S. mansoni IgG2a monoclonal antibody (MAb) designated C5C4 was generated. The target epitope of this MAb was detected in adult worms, eggs, and cercariae antigenic extracts of S. mansoni and S. haematobium, had a molecular size of 63 kD, and was not detected in Fasciola hepatica and Ascaris. In addition, a 50-kD degradation product was identified only in the urine of infected individuals. Analysis by high-performance liquid chromatography of the purified antigen demonstrated only one peak. The 63-kD antigen was characterized as a protein containing 40.4% hydrophobic, 7.5% acidic, and 8.8% basic amino acids. The C5C4 MAb was used in a Fast Dot-ELISA for rapid and simple diagnosis of human schistosomiasis. The 63-kD circulating antigen was detected in 92% of urine samples from 330 S. mansoniinfected individuals, with 16% false-positive results among 130 noninfected individuals.The identification and characterization of schistosome antigens in different developmental stages and the assessment of their role in host-parasite interactions are needed as a step toward the diagnosis of human schistosomiasis. 1 Several investigators have isolated and characterized many of the schistosomiasis antigens in different developmental stages of the parasite that have a potential application in immunodiagnosis. [2][3][4] In the present study, we have identified and characterized a schistosome antigen using a specific anti-Schistosoma mansoni mouse monoclonal antibody (MAb) and evaluated the suitability of this MAb in the immunodiagnosis of S. mansoni infection. MATERIALS AND METHODSMonoclonal antibody subtype and isotype determination. A hybridoma cell line designated C5C4 was produced from mice infected with S. mansoni as described by Attallah and others. 5 An ELISA was used to characterize the anti-S. mansoni MAb (C5C4). A microliter plate (Costar, Cambridge, MA) was coated with 50 g/ml of this MAb in 0.05 M carbonate/bicarbonate buffer, pH 9.6. After blocking with 200 l/well of 0.3% nonfat milk, a 1:500 dilution of mouse IgG1, IgG2a, IgG2b, and IgG3 MAbs produced in sheep (The Binding Site, Birmingham, United Kingdom) were added and incubated at 37ЊC for 2 hr. Sheep anti-mouse IgGalkaline phosphatase conjugate (Sigma, St. Louis, MO) was added at a dilution of 1:1,000 for 1 hr at 37ЊC. Fifty microliters per well (1 mg/ml) of p-nitrophenyl phosphate in 0.1 M glycine buffer, pH 10.4, were added and the plate was incubated for 20 min at 37ЊC. The reaction was stopped with 3 N NaOH and the optical density was read at 405 nm using an EL 311 microplate autoreader (Bio-Tek Instruments, Winooski, VT).Preparation of antigenic extracts. The S. mansoni and S. haematobium antigenic extracts of worms (SWAP), cercariae (CAP), and eggs (SEA) were prepared according to the method of Da Silva and Ferri. 6 The same method was used for the preparation of Fasciola hepatica and Ascaris lumbricoides antigenic extracts. The protein content was determined u...

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