Immunological studies with rat pituitary growth hormone: I. Basic studies with immunodiffusion and antihormone tests

Abstract

Four rhesus monkeys, four rabbits, and three guinea pigs were immunized with rat pituitary growth hormone (RGH) in Freund's adjuvant. Antisera from all monkeys produced good precipitin reactions with RGH in the double-diffusion procedure in agar, while antisera from none of the rabbits showed any precipitin reaction, even after continued immunization. All guinea pigs yielded antisera that would precipitate RGH, but the reactions were much less intense than those obtained with any of the monkey antisera. These results demonstrated a significant quantitative difference in precipitin antibody response on the part of three different host species that were immunized with the same antigen, RGH. Monkey antiserum to RGH, tested by double diffusion in agar or by immunoelectrophoresis, gave a single, strong precipitin line with highly purified RGH or with a crude saline extract of the rat pituitary. Monkey antiserum to RGH was capable of demonstrating a reaction of identity between RGH and growth hormone from a wide variety of species, including the sheep, the ox, the pig, the rabbit, the guinea pig, and the humpback whale, suggesting the existence of a common antigenic relationship in the structure of growth hormone from these species. Only the monkey or human growth hormone did not show a cross-reaction with this antiserum, a phenomenon which was also observed with guinea pig antiserum to RGH. In vivo experiments utilizing the tibia assay in hypophysectomized rats showed that the monkey antiserum was capable of neutralizing the growth-promoting activity of purified RGH, a crude saline extract of rat pituitary, or purified growth hormones from other species, when these preparations were injected subcutaneously at a different site from that of antiserum injection. However, human growth hormone could not be neutralized even when three times the amount of antiserum was employed. The findings of this investigation, based on precipitin reactions in agar and neutralization of hormone activity in vivo, have clearly demonstrated the antigenicity of RGH, the detectability of RGH in crude pituitary extracts, the similarity in antigenic structure of growth hormones from a wide variety of animal species, and the apparent difference of this common antigenic structure from that of primate growth hormone.