Modulation of the Effectiveness of Growth Hormone with a Monoclonal Antibody

Abstract

A monoclonal antibody (mAb), designated PS-11.2, was generated by immunizing mice with recombinant porcine growth hormone (pGH). This antibody recognized GHs of porcine, bovine (bGH) and chicken (cGH) origins, but not human GH, ovine prolactin, somatostatin S-14, and GH-releasing factor (1-29-NH₂. Western analysis indicated that PS-11.2 predominantly identified not only the 22.5-kD protein but also its 45-kD dimer. It also recognized the 4.5- and 10-kD fragments of pGH resulting from trypsin digestion. The binding kinetics of PS-11.2 to pGH was determined by the biospeciflc interaction analysis in a real-time mode. The association and dissociation rate constants were estimated as 1.4 x 10⁵M^-1 s^-1 and 2.2 x 10^-4 s^-1, respectively, thus producing an overall affinity of K_d = 1.6 x 10^-9 M. It partially inhibited the interaction of pGH and GH-binding protein in a competitive radioimmunoassay, suggesting that the pGH epitope recognized by PS-11.2 was closely related to the region responsible for engaging with GH receptors. Growth-deficient hypophysectomized rats were used for functional evaluation and shown to grow in response to the treatment of pGH. This effect was further augmented when pGH was administered together with PS-11.2, although antibody itself did not promote the growth of these animals. The antibody-mediated effect continued beyond the 5-day treatment period, indicating its long-lasting effect. Similar enhancement by PS-11.2 was also observed with bGH and cGH in this rat model. Therefore, the present findings clearly suggest that the somatogenesis of GH can be potentiated by PS-11.2 and that this mAb may serve as a useful tool for improving the growth performance of livestock.