Development of a [beta]-adrenoceptor vaccine

Aim of the project is to demonstrate that antibodies could be used to activate the [Beta]-adrenoceptor ([Beta]-AR). Identifying a candidate vaccine suitable for administration to cattle which would evoke the production of such antibodies in also investigated.. The efficiency of cattle growth can be enhanced by the use of ß2-adrenoceptor agonist drugs. How-ever, synthetic drugs are not acceptable for use in animal production, and an alternative, immuno-logical manipulation, has been proposed. Thus, one aim of this project was to demonstrate that antibodies could be used to activate the ß2-adrenoceptor (ß2-AR). A second aim was to identify a candidate vaccine suitable for administration to cattle, which would evoke the production of such antibodies. Two vaccine approaches were investigated. Transgenic Escherichia coli which express the human ß2-AR provided one potential source of antigen. However, attempts to affinity purify 2-AR from digitonin solubilised E. coli were unsuccessful. Synthetic peptides were utilised as the second source of antigen. Two of these peptides corresponded to all (24 amino acids) or the N-terminal part (13 amino acids) of the second outer loop of the human ß2-AR. These were designated H24T and H 13C respectively. The third peptide was the bovine homologue of H24T, and was designated bov-H24T accordingly. H24T was highly immunogenic, causing maximum titres assayed by ELISA of 160000 in mice, and 10000 in rabbits and cattle. H13C, was used to immunise mice and rabbits, but evoked antibodies in rabbits only, the maximal titre being about 10000. These results allowed a mouse B epitope on H24T to be partially mapped to positions 185-187 (-Y-A-N-) on the human ß2-AR. Cattle were also immunised with bov-H24T. This peptide was also highly immunogenic, titres rising to a maximum of 12000. Rabbit and bovine antibodies were affinity purified and screened in a number of assays in vitro to determine their interaction with ß₂-AR. Anti-H24T antibodies from three rabbits recognised human ß2-AR, showing some cross-reaction with human ß1- and ß3-AR as determined in immunoblots. Antibodies from one rabbit were investigated further. They were found to increase the affinity of the radioligand [¹²⁵l]- iodocyanopindolol for bovine skeletal muscle ß2-AR. Both rabbit and bovine antibodies induced c-AMP production in rat skeletal muscle at concentrations as low as 1 pM, and increased the potency of isoprenaline in bovine tracheal smooth muscle. This is the first time that anti-ß2-AR antibodies have been shown to evoke a functional response. Thus, it has been shown that antibodies which activate ß2-AR can be raised in cattle in response to a synthetic peptide antigen. Further work will be needed to establish whether this vaccine will mimic the effects of a ß2-agonist drug by increasing the carcase muscle to fat ratio in treated cattle, and whether it is a technology likely to be adopted by the Australian beef industry.