Use of immunoaffinity chromatography for purification of ¹²⁵I-labeled human prolactin

We assessed a simple method for purifying ¹²⁵I-labeled human prolactin, taking advantage of the abundant supplies of monoclonal antibodies available. ¹²⁵I-labeled human prolactin purified by immunoaffinity chromatography is compared with that purified by gel filtration on Sephadex G-100. We used monoclonal antibodies to prolactin to prepare the affinity chromatography columns. Prolactin was radiolabeled by the Chloramine T method, purified by each of the above procedures, and the binding and displacement characteristics were studied in radioimmunoassays in which either monoclonal antibodies or a rabbit anti-prolactin serum was the first antibody. A nonimmune fraction of ¹²⁵I-labeled prolactin that co-eluted with the immunoreactive hormone from Sephadex G-100 was removed by affinity chromatography, which increased the antibody binding of ¹²⁵I-labeled prolactin in the radioimmunoassay in the absence of unlabeled antigen (B/T₀, in percent) twofold or more, increased the assay sensitivity, and increased the slope of antigen displacement measured by the 50% intercept. Several advantages make this the purification method of choice.