Immunological approaches for manipulation of animal growth, body composition and fecundity.
The ability to manipulate certain physiological processes by using the immune system, so as to regulate endocrine secretions and/or actions is clearly possible. The dramatic effects of immunocastration and the ability to increase ovulation rates in sheep are probably the best examples. Other approaches along similar lines have produced equivocal results, the effects of immunization against somatostatin being the most notable case. Although anti-idiotypic antibody approaches to producing hormone mimics have also been shown to be attainable and, indeed, possibly involved in certain auto-immune dysfunctions of the endocrine system, to date no successful applications of this approach have been demonstrated in commercial livestock. The ability to enhance hormone action using antibodies is an extremely promising area. Its prospects probably hinge on the ability to synthesize suitable short peptides which will mimic epitopes on the hormone and so permit the development of active immunization techniques to produce polyclonal antibodies of restricted and enhancing specificity. It seems less likely that administration of hormones pre-complexed to monoclonal antibodies has any potential as a practical approach to manipulating animal productivity. All of these approaches involving active immunization suffer the same limitations: the highly variable response of individual animals and the general inability to regulate the duration of the response; a need to find suitable adjuvants to replace the almost universally used and commercially unacceptable Freund's adjuvant; and the problem of trying to generate what, in most cases, is an auto-immune response. A second group of approaches consists of attempts to use antibodies in their classical role, that is by targeting antigens or cells for destruction by the immune system. These include, for example, antibodies directed against adipose tissue or cytotoxic antibodies to specific hormones aimed at destruction of the hormone-secreting cells. Since these are passive immunization techniques, the antibodies can be assessed carefully in vitro and administered in appropriate doses. However, success in these applications is largely dependent on the inability of damaged tissues to regenerate, since retreatment is generally precluded because of the anti-immunoglobulin response induced in treated animals. Toleragenic forms of such antibodies or the use of appropriate immunosuppressants may ultimately remove this limitation. Perhaps the greatest current limitation to the use of all of these techniques in animal production systems, however, is public resistance to the use of such techniques.(ABSTRACT TRUNCATED AT 400 WORDS)