A sensitive homologous radioimmunoassay for human relaxin-2 (H-RLX-2) based on antibodies characterized by epitope mapping studies

We present a sensitive homologous radioimmunoassay (RIA) for the quantitati ve determination of human relaxin (hRLX) in human serum, plasma, seminal pl asma, and urine. This assay is based on a rabbit antiserum which was genera ted using recombinant hRLX-2 as immunogen. Using I-125-hRLX-2 as tracer and a total incubation time of 20 - 24 hours t he radio immuno assay showed linearity in a range of 60 - 4000 ng/l, a lowe r detection limit of 38 ng/l and a mean recovery rate of 98.5 %. Intraassay variation was 4.0 % (mean = 526 ng/l) and 11.9 % (mean = 2368 ng/l), and i nterassay variation 10.7 % (mean = 256 ng/l) and 13.1 % (mean = 2368 ng/l). Using hRLX-2 hexapeptides on polystyrene pins, epitopes recognized by the h RLX-2 specific rabbit antiserum were determined experimentally, and compare d to predicted epitopes. Both methods led to comparable, results. The antis erum, recognizing different epitopes, showed no cross-reactivity with human insulin, hZn-insulin, hIGF-I, hIGF-II, human inhibin alpha -subunit, two d ifferent forms of seminal plasma inhibin like peptide, spermolaxin, ubiquit in, prolactin, LH, FSH and hCG.