Integrating the immune system with the regulation of growth and efficiency

¹ Departments of Food Science & Human Nutrition and Animal Science, Iowa State University, Ames IA 50011

^* To whom correspondence should be addressed. E-mail: mspurloc{at}iastate.edu.

	Abstract

Muscle growth in meat animals is a complex process governed by integrated signals emanating from multiple endocrine and immune cells. A generalized phenomenon among meat animal industries is that animals commonly fail to meet their genetic potential for growth in commercial production settings. Recent evidence indicates that adipocytes and myofibers are equipped with functional pattern recognition receptors, and are capable of responding directly to the corresponding pathogens and other receptor ligands. Thus, these cells are active participants in the innate immune response and, as such, produce a number of immune and metabolic regulators, including pro-inflammatory cytokines and adiponectin. Specifically, the transcription factor, nuclear factor kappa B, is activated in adipocytes and muscle cells by bacterial lipopolysaccharide and certain saturated fatty acids, which are potent agonists for the Toll-like receptor-4 pattern recognition receptor. Receptor activation results in the local production of interleukin-6 and tumor necrosis factor-, and creates a local environment by which these cytokines regulate both metabolic and immunological pathways. However, adipocytes are also the predominant source of the anti-inflammatory hormone, adiponectin, which suppresses the activation of nuclear factor kappa B and the production of pro-inflammatory cytokines. The molecular ability to recognize antigens and produce regulatory molecules strategically positions adipocytes and myofibers to regulate growth locally, and to reciprocally regulate metabolism in peripheral tissues.

Key Words: Adipocytes, cytokines, growth, inflammation, myofibers