Immunochemical Relatedness of Porcine, Bovine, Ovine and Primate Pituitary Growth Hormones 1

Abstract

Quantitative micro-complement fixation with rabbit antisera to chromatographically purified human growth hormone has been used to measure immunologically the relatedness of 12 nonhuman primate pituitary growth hormones to human growth hormone. Using complement-fixation curves obtained with antihuman growth hormone, the degree of relatedness of nonhuman primate growth hormone to human growth hormone was estimated from the ratio, at antigen-antibody equivalence, of the complement fixed with the cross-reacting (nonhuman) antigen to the complement fixed with the homologous (human) antigen. The reproducibility of this method of estimating the extent of immunological cross-reactions was indicated by a standard error of the mean value for 3 replicated assays of [plus or minus]5%. Significant differences in immunological activity between growth hormones within the order of primates were found. The degree of relatedness, measured im-munochemically, of nonhuman primate growth hormones to human growth hormone appeared to be related to primate phylogenybasedonnonmolecular evidence. Significant immunological similarity between 3 nonprimate growth hormones and human growth hormone was detected by direct complement fixation with porcine, bovine and ovine growth hormones and antihuman growth hormone. Higher concentrations of antihuman growth hormone were required to measure directly the cross-reactions than were used for measuring the homologous, human antigen. However, the complement fixation obtained with human growth hormone and its own antiserum at homologous antibody concentrations was inhibited by the nonprimate growth hormones. Porcine growth hormone fixed more complement with antihuman growth hormone than bovine or ovine growth hormones. The direct fixation of complement with antihuman growth hormone and bovine growth hormone was significantly improved by reduction of 2 of the 4 disulfide bonds in the bovine hormone. We conclude that some of the antigenic determinants of human growth hormone and of porcine, bovine and ovine growth hormones are similar if not identical.