An ultrasensitive, nonisotopic immunoassay for hyaluronan using the streptavidin-biotin system

A time-resolved fluoroimmunoassay for measuring hyaluronan concentrations in plasma and several biological fluids is described. The solid-phase immunoassay is based on the competition between aggregation of hyaluronan with the cartilage proteoglycan monomer, followed by binding of a monoclonal antibody to keratan sulfate of the proteoglycan and a biotinylated anti-mouse IgG. Fluorescence can be measured by a time-resolved fluorometer after binding of Eu(3+)-labelled streptavidin to the biotinylated IgG. The assay is precise and correlates well (r = 0.986) with the only established radioimmunoassay known. The results show that it is essential to perform a blank run without addition of proteoglycan, as endogenous proteoglycan disturbs the measurement and causes underestimation of plasma hyaluronan. The distinguishing feature of this assay is its extreme sensitivity (< 0.24 microgram/l of plasma). The mean analytical recovery after serial dilutions and addition was 100.3 and 101.3%, the within-assay and between-assay coefficients of variation were 3.67% and 7.02%, respectively.