Human, bovine, and equine growth hormone antibodies in patients treated with human growth hormone.

The immunological behavior of sera from hypopituitary patients treated with human GH (hGH) has been studied by homologous and heterologous RIAs using 125I-labeled hormones. Along with antibodies against hGH, antibodies exhibiting antibovine and antiequine GH (anti-bGH and anti-eGH, respectively) activities were also found. Displacement experiments showed that hGH was an effective competitor of 125 I-labeled hGH, whereas bGH and eGH were quite inefficient. Conversely, when the tracer was 125I-labeled bGH, both bGH and eGH were good displacers, while the human hormone was poor. The values of the affinity constants of the various antibodies found in human sera were similar to each other and to those found after immunization of rabbits. These results suggest that the antibodies against bGH and eGH belong to a population separate from those directed against the human hormone. The mechanism by which hGH can express determinants of other animal growth hormones is obscure, although the high degree of conservation of structure in these molecules during evolution must be involved.