Sensitive enzyme-linked immunosorbent assay for human serum amyloid A (SAA) and application to clearance study

Serum amyloid A (SAA), an apolipoprotein of high density lipoprotein (HDL), is a sensitive acute phase reactant. We established a sandwich type enzyme-linked immunosorbent assay for human SAA utilizing a monoclonal antibody and polyclonal antibodies. This assay was sensitive enough to detect SAA at 40 pg/ml. The use of nonionic detergent, Tween-20, in reaction buffer was essential to enhance specific binding of SAA to antibodies and reduce nonspecific binding to plastic. The values by this assay showed a good agreement with those by previously established latex agglutination immunoassay. Plasma clearance of human SAA was studied in mice by injection with SAA-rich human HDL and serial SAA measurement by the present assay. Half-life of injected SAA was 55 minutes, similar to mean of the reported value of murine SAA isotypes.