Amino acids can affect the development, maintenance, and response of the immune system and both the absolute amounts and the balance of the nutrients as a whole are important.
Severe deficiencies of these nutrients impair the immune system and increase susceptibility to infectious diseases. However, amino acid deficiencies that are severe enough to noticeably affect bird performance are very rare when birds are fed with scientifically formulated commercial diets.
The immune system is essential for life and appears to have a very high priority for many amino acids in relation to muscle accretion and is surprisingly resistant to marginal deficiencies of commonly limiting amino acids such as methionine and lysine. However, some amino acids, both essential and nonessential, modify the immune response by modulating key regulatory actions of the immune system (known as immunomodulation).
Modulation of the immune system by diet can decrease the incidence of some types of infectious diseases and minimize the adverse effects of the immune response on growth, egg production and the incidence of metabolic diseases.
Arginine and tryptophan are the main immunomodulatory amino acids.
Mechanisms of interaction between nutrients and immunity
Amino acids are crucial substrates for proteins that mediate all immune functions, including cell and defense proteins. Leukocytes have an excellent ability to compete with other tissues for low levels of some, but not all, of the amino acids. In addition, an immune response is accompanied by the mobilization of nutrients from muscle and other tissues, which supply adequate amounts of some amino acids to the leukocytes, but not all of those needed. In general, developing T lymphocytes appear to be the leukocyte population most susceptible to nutrient deficiencies.With decreased lymphocyte-mediated immunity, exaggerated innate immune system responses often occur during infection and result in robust inflammatory responses and largely explain the accompanying immunopathology.
There are a variety of amino acids that modulate the immune system. For example, some of them, as arginine and tryptophan, formulated at dietary inclusion levels that are clearly above the nutritional requirement regulate the type of response to a pathogen. Unlike increasing nutrients from deficient to sufficient levels, where many indices of immunocompetence are elevated, supplementation of immunomodulatory nutrients causes some components of immunity to be elevated and others to be decreased; in other words, the types and intensities of responses are changed.
Conclusions
The metabolic benefits and costs of the immunoregulatory effects of these nutrients depend on the types of pathogens in the bird's environment.
The resulting changes may be favorable for some pathogens and facilitate their damage to the host.
However, they may increase susceptibility to those pathogens controlled by responses that are diminished by their deficiency.
