Rapid, low-technology field- and laboratory-applicable enzyme-linked immunosorbent assays for immunodiagnosis of Schistosoma mansoni

Abstract

Simple and rapid polystyrene- and nitrocellulose-based enzyme-linked immunosorbent assays were developed for detecting antibodies against adult Schistosoma mansoni microsomal antigens. The polystyrene test uses the Nunc Immuno Stick System. A single dilution of the antibody source being tested, the conjugate, and the substrate (3,3',5,5'-tetramethylbenzidine) are placed in tubes. Dried, antigen-coated polystyrene sticks are then exposed to the reagents by immersion. Once the sticks are sensitized, an entire assay can be completed in 8 min. Positive reactions result in a rich blue color in the substrate tube and can be distinguished with the naked eye. In the nitrocellulose-based test, a nitrocellulose sheet with antigen drawn in a line by pen is cut to produce identical strips. The ligand-binding steps and washings are performed in the troughs of incubation trays. The exposure times required for a single dilution of the antibody source being tested, the conjugate, and the substrate (3,3'-diaminobenzidine) are 5 min, 5 min, and 7.5 min, respectively. Once sensitized strips are available, an entire assay can be run in 50 min. Both techniques can assay serum or whole blood. The characteristics of polystyrene- and nitrocellulose-based techniques allow them to be used successfully in field studies and in minimally equipped laboratories.