21 - Arginine and immune function

Abstract

L-Arginine (Arg) was traditionally classified as a nutritionally non-essential amino acid for infant and adult humans; however, it is now known that besides serving as a building block for protein, it plays an essential role in the functions of the immune system. Arg is a physiological substrate for the synthesis of nitric oxide (NO), which is a key mediator of immune responses. Additionally, emerging evidence shows that Arg exerts a regulatory role in signal transduction pathways involving mammalian (or mechanistic) targets of rapamycin and specific mitogen-activated protein kinases in immunocytes, thereby affecting immunity. Because of high requirements for Arg in multiple metabolic pathways, dietary Arg supplementation may be a necessary strategy to maintain Arg homeostasis for good health and body functions under many physiological and pathological conditions. Much experimental and clinical data support the notion that Arg is an essential nutrient for both innate and adaptive immune systems in humans and other animals. An important outcome of this research is the availability of Arg- supplemented foods for humans and feed-grade Arg for livestock species. Future studies are needed to address the safety issue of chronic Arg supplementation to mammals so as to fully realize the health benefits of Arg as a functional amino acid.