Immune-cell activation and functional plasticity are closely linked to metabolic reprogramming that is required to supply the energy and substrates for such dynamic transformations. During such processes, immune cells metabolize many kinds of molecules including nucleic acids, sugars and lipids, which is called immunometabolism. This review will mainly focus on amino acids and their derivatives among such metabolites and describe the functions of these molecules in the immune system. Although amino acids are essential for, and well known as, substrates for protein synthesis, they are also metabolized as energy sources and as substrates for functional catabolites. For example, glutamine is metabolized to produce energy through glutaminolysis and tryptophan is consumed to supply nicotinamide adenine dinucleotide, whereas arginine is metabolized to produce nitric acid and polyamine by nitric oxide synthase and arginase, respectively. In addition, serine is catabolized to produce nucleotides and to induce methylation reactions. Furthermore, in addition to their intracellular functions, amino acids and their derivatives are secreted and have extracellular functions as immunotransmitters. Many amino acids and their derivatives have been classified as neurotransmitters and their functions are clear as transmitters between nerve cells, or between nerve cells and immune cells, functioning as immunotransmitters. Thus, this review will describe the intracellular and external functions of amino acid from the perspective of immunometabolism and immunotransmission.

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氨基酸：免疫代谢物和免疫递质的关键来源。

免疫细胞的激活和功能可塑性与代谢重编程紧密相关，而代谢重编程是为这种动态转化提供能量和底物所必需的。在这样的过程中，免疫细胞代谢包括核酸，糖和脂质在内的许多种类的分子，这被称为免疫代谢。这篇综述将主要关注氨基酸及其在这类代谢产物中的衍生物，并描述这些分子在免疫系统中的功能。尽管氨基酸对于蛋白质合成的底物是必不可少的，但众所周知，它们也被代谢为能源和功能性分解代谢物的底物。例如，谷氨酰胺通过谷氨酰胺分解代谢产生能量，色氨酸被消耗以提供烟酰胺腺嘌呤二核苷酸，而精氨酸则被一氧化氮合酶和精氨酸酶代谢产生硝酸和多胺。另外，丝氨酸被分解代谢以产生核苷酸并诱导甲基化反应。此外，除了其细胞内功能外，氨基酸及其衍生物也被分泌并具有细胞外功能作为免疫递质。许多氨基酸及其衍生物已被分类为神经递质，其功能清楚地作为神经细胞之间或神经细胞与免疫细胞之间的递质，起免疫递质的作用。因此，本综述将从免疫代谢和免疫传递的角度描述氨基酸的细胞内和外部功能。丝氨酸被分解代谢产生核苷酸并诱导甲基化反应。此外，除了其细胞内功能外，氨基酸及其衍生物也被分泌并具有细胞外功能作为免疫递质。许多氨基酸及其衍生物已被分类为神经递质，其功能清楚地作为神经细胞之间或神经细胞与免疫细胞之间的递质，起免疫递质的作用。因此，本综述将从免疫代谢和免疫传递的角度描述氨基酸的细胞内和外部功能。丝氨酸被分解代谢产生核苷酸并诱导甲基化反应。此外，除了其细胞内功能外，氨基酸及其衍生物也被分泌并具有细胞外功能作为免疫递质。许多氨基酸及其衍生物已被分类为神经递质，其功能清楚地作为神经细胞之间或神经细胞与免疫细胞之间的递质，起免疫递质的作用。因此，本综述将从免疫代谢和免疫传递的角度描述氨基酸的细胞内和外部功能。许多氨基酸及其衍生物已被分类为神经递质，其功能清楚地作为神经细胞之间或神经细胞与免疫细胞之间的递质，起免疫递质的作用。因此，本综述将从免疫代谢和免疫传递的角度描述氨基酸的细胞内和外部功能。许多氨基酸及其衍生物已被分类为神经递质，其功能清楚地作为神经细胞之间或神经细胞与免疫细胞之间的递质，起免疫递质的作用。因此，本综述将从免疫代谢和免疫传递的角度描述氨基酸的细胞内和外部功能。