Extracellular Branched-chain Amino Acids, Especially Valine, Regulate Maturation and Function of Monocyte-derived Dendritic Cells

肝硬化患者的树突状细胞（dc）功能受损。众所周知，肝硬化患者血浆支链氨基酸（BCAA）水平降低。尽管氨基酸在许多器官中与维持细胞结构和功能有关，但关于包括支链氨基酸在内的氨基酸在免疫系统中的作用的数据有限。我们的目的是研究BCAA在人单核细胞源性dc （MoDC）功能中的作用。从健康志愿者和HCV肝硬化患者的PBMC中分离cd14阳性单核细胞（cd14(+)）。在缺乏BCAA或缬氨酸的培养基中，单核细胞能够分化为未成熟的dc，但不能分化为成熟的dc，并表现出CD83的弱表达。剥夺亮氨酸或异亮氨酸对这一过程没有影响。在缺乏BCAA或缬氨酸的培养基中，MoDC同种刺激能力显著降低。Annexin V-FITC/PI染色结果显示，各组细胞死亡和凋亡数量无显著差异。免疫印迹显示缬氨酸或亮氨酸的缺失降低了P-S6激酶的表达。缬氨酸增加了健康志愿者和丙型肝炎肝硬化患者MoDC的同种异体刺激能力和IL-12的产生，并呈剂量依赖性。升高的细胞外缬氨酸浓度可以改善HCV肝硬化患者的树突状细胞功能。这些数据为营养疗法可能对肝硬化患者有益提供了理论依据。

The functions of dendritic cells (DCs) are impaired in patients with liver cirrhosis. It is well known that cirrhotic patients show decreased levels of plasma branched-chain amino acids (BCAA). Although amino acids are associated with maintaining the cell structure and function in many organs, limited data are available regarding the role of amino acids including BCAA in the immune system. We aimed to investigate the roles of BCAA in the function of human monocyte-derived DCs (MoDC). CD14-positive monocytes (CD 14 (+)) were isolated from PBMC from healthy volunteers and HCV cirrhotic patients. In medium deprived of BCAA or valine, monocytes were able to differentiate into immature DCs, but not into mature DCs, and showed their weak expression of CD83. The deprivation of leucine or isoleucine did not affect this process. The MoDC allo-stimulatory capacity was significantly decreased in medium deprived of BCAA or valine. Annexin V-FITC/PI staining showed the numbers of dead and apoptotic cells were not significantly different under any medium. Immunoblotting demonstrated that depletion of valine or leucine decreased P-S6 kinase expression. Valine increased dose-dependently the allo-stimulatory capacity and IL-12 production of MoDC from both healthy volunteers and HCV cirrhotic patients. An elevated extracellular concentration of valine could improve dendritic cell function in HCV cirrhotic patients. These data provide a rationale for nutrition therapy that could be beneficial to patients with cirrhosis.