Competitive enzyme immunoassay for detection of complement-fixing antibodies in diagnostic virology

A competitive enzyme immunoassay was developed to detect serum complement-fixing antibodies in virus diseases. This assay utilized conglutinin-covered plastic beads as the solid phase to detect specific antibody-antigen complexes that competed for complement with a probe complex comprised of Escherichia coli beta-galactosidase and its specific antibody. Binding to the solid phase is C3bi mediated, and when specific antibody-antigen complexes are not present the probe is bound and an enzymatic reaction ensues. This type of competitive assay was introduced in the field of immunopathology for investigating circulating immune complexes by Manca et al. (Clin. Immunol. Immunopathol. 16:131-141, 1980). The assay gave satisfactory results in terms of specificity, reproducibility, and handling, enabling laboratories to obtain results in 5 h. The sensitivity of the method coincided with that of the complement fixation test. However, this technique offers several advantages over conventional complement fixation because it requires less time, is easier to perform, and gives more reliable quantitative results. The data obtained indicated that this competition assay offers a feasible alternative to conventional complement fixation tests and should be useful in routine diagnostic applications and in seroepidemiological surveys.