Immobilization of immunoglobulins onto surface-treated and untreated polystyrene beads for radioimmunoassays

The immunoreactivity of anti-triiodothyronine (anti-T3) IgG, pretreated at acidic pH and adsorbed onto polystyrene beads, was significantly greater than that determined for native anti-T3 IgG immobilized at optimum pH 3.5. Acidic-pH-pretreated IgG, adsorbed at pH 7.0 onto ethanol-treated beads, had less immunoreactivity than that on untreated beads and gave values similar to those of native IgG adsorbed onto activated beads at pH 9.6. The rate of immobilization onto treated beads was significantly greater than onto untreated ones, and the binding was reproducible (intra- and inter-batch coating CV, 3.7-4.6% and 7.2%, respectively) and very resistant to successive washings. A post-washing incubation in 10 mg/L bovine serum albumin solution was required to eliminate the decreased immobilized immunoreactivity caused by some washing reagents. For solid-phase radioimmunoassays of T3, 40% less antibody was needed when acidic-pH-pretreated IgG was adsorbed onto untreated beads or when native IgG was adsorbed onto ethanol-treated beads, in comparison with native IgG adsorbed onto untreated beads. Results and assay characteristics with such beads were comparable with results for solid-phase and liquid-phase polyethylene glycol assay of T3.