Relative distribution of various antigenic determinants on the human growth hormone surface

The relative distribution of 12 antigenic determinants on the surface of the human growth hormone (hGH) molecule has been established. The necessary information was obtained by testing the ability of paired monoclonal antibodies (MAb) to bind simultaneously or not, to 125I-hGH which leads to the formation of 1:2 or 1:1, Ag-Ab complexes, respectively. The results obtained indicate that the epitopes occupy a large percentage of the total hGH molecular surface and revealed the existence of; an antigenic region specific for hGH; at least two independent domains of immunological identity between hGH and human placental lactogen (hPL), one of them also shared by heterologous GH; and other independent areas of partial cross reactivity with hPL. MAb competition experiments in a solid-phase RIA showed the unreliability of this technique for mapping purposes. The distribution of the hGH epitopes suggested in this work is in accord with present views on protein antigenicity and also explains data existing in the literature concerning the behavior of some of the MAb tested here.