Promotion of animal growth with a monoclonal antibody specific to growth hormone receptor.

A monoclonal antibody (mAb), designated 2C3, was raised against the growth hormone receptor (GHR) of rats. In a radioimmunoassay, 2C3 was found to compete with iodinated porcine GH (pGH) tracer for the binding to GHR, suggesting that GHR binding sites for pGH and 2C3 were identical or closely adjacent. The competition curve generated by 2C3 was identical to that generated by cold pGH, suggesting that the binding affinities of 2C3 and pGH to GHR were very similar. Administration of hypophysectomized rats with 2C3 resulted in the growth of these GH-deficient animals for a long period of time, mimicking the somatogenic effect of GH. However, this effect was abolished when 2C3 was injected into animals in the presence of exogenous GHR. A control mAb recognizing a GHR epitope distal from its binding site for GH failed to produce the growth in rats. Taken together, findings from the present study indicate that 2C3 is fully capable of engaging with GHR and subsequently triggering the growth response in rats. This mAb may also prove useful as a biologically active agonist for better understanding the initiation of the physiological process of GHR.