The development of a fluoroimmunoassay for beta-2-microglobulin in serum

A liquid-phase fluoroimmunoassay has been developed for the measurement of beta-2-microglobulin in undiluted serum or plasma. Protein labelled with fluorescein-isothiocyanate at a molar ratio of 1:2 respectively is employed as a tracer together with an antiserum to beta-2-microglobulin raised in a sheep. Separation is achieved by means of rabbit anti-sheep immunoglobulin G and, following precipitation of the bound fraction by centrifugation, the free fraction together with any potentially interfering factors is removed in the supernatant. Finally the precipitate is dissolved and the fluorescence measured. The assay is simple and rapid in that all reactants, including the second antibody, can be added at the start of the assay and equilibrium is attained within 60 min. The assay is reproducible and sufficiently sensitive to allow measurement of normal serum levels and has a wide range avoiding the need for sample dilution. Results correlated well with those of an established radioimmunoassay.