Cross-linking of Schistosoma mansoni antigens and their covalent binding on the surface of polystyrene microtitration trays for use in the ELISA.

The usefulness of the enzyme-linked immunosorbent assay (ELISA) for serodiagnosis is limited by the incomplete and unequal binding of individual antigens present in a complex antigen preparation. We therefore investigated 2 modifications of the commonly used antigen coating procedure in the ELISA. Schistosoma mansoni antigens cross-linked by N-ethyl-N'-(3-dimethylaminopropyl)-carbodiimide (EDC), and then adsorbed on polystyrene microtitration trays, tested with sera from patients, and from immunized rabbits, showed an increase in the ELISA results, with respect to both absorbance values and titers. Measurement of specific antibodies against low molecular weight schistosomal antigens, which is not possible in the standard ELISA, was made possible by adsorption of a cross-linked antigen preparation. Covalent binding of cross-linked antigens to modified microtitration trays, gave a further increase in ELISA readings when the antibody response of S. mansoni infected mice to lower molecular weight antigens was assayed. In assays of patients' sera, a further increase in sensitivity of the ELISA was occasionally obtained by binding cross-linked antigens covalently. With some sera the use of physically adsorbed cross-linked antigens gave optimal results.