Rapid, sensitive enzyme-linked immunosorbent assays (ELISA) foi serum amyloid A (apoSAA) in human plasma and tissue culture fluids1

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Abstract
Two direct binding enzyme-linked immunosorbent assays (ELISA) for human acute phase serum amyloid A isoforms (apoSAA1 and apoSAA2) are described, a single antibody method for serum and plasma samples and a double antibody method for tissue culture supernatants. Both methods employ polyvalent, monospecific rabbit anti-human apoSAA antiserum that does not react with constitutive apoSAA in plasma or tissue culture samples. In the presence of 3M KBr, pH 9.6, all apoSAA isoforms are passively adsorbed to microtiter plate wells in quantities proportional to their concentrations. The absolute concentrations of total acute phase apoSAA isoforms in samples can be determined from a standard curve constructed from samples of known apoSAA concentration incubated at the same time. For clinical evaluation of serum and plasma specimens, apoSAA is bound to microtiter wells at ambient temperature (∼25°C) after which its concentration is determined directly with horseradish peroxidase (HRP)-conjugated anti-apoSAA immunoglobulins. The sensitivity for detection of acute phase apoSAA isoforms in plasma was found to be 1 μMg/ml. In order to measure apoSAA in tissue culture supernatants, apoSAA is bound to wells at 37°C and detected using anti-rabbit apoSAA antiserum and HRP-conjugated goat anti-rabbit immunoglobulins; the sensitivity for detection of acute phase isoforms was I μg/ml.