Three assays for the characterization and quantitation of human serum amyloid A

Two different radioimmunoassays (RIA) and an enzyme-linked immunosorbent assay (ELISA) were developed for the quantitation and antigenic characterization of amyloid A (AA) and serum amyloid A (SAA) proteins, and the three assays were evaluated and compared with each other. Sensitivity, reproducibility, effect of denaturation and storage of serum and range of determination were considered. All three assays were found useful, but for different purposes. The most suitable method for the determination of SAA in whole serum was a second antibody precipitation RIA with purified SAA as labelled tracer and standard, and polyclonal rabbit anti-SAA as first antibody. This assay provided SAA concentrations in absolute amounts (mg/l) and acceptable reproducibility without need for prior denaturation of serum. Both advantages and disadvantages of ELISA using monoclonal antibodies to SAA and a solid-phase RIA using AA, SAA, anti-AA and anti-SAA were observed. The three assays were found suitable for antigenic studies of AA and SAA.