Excessive activation of CD4⁺ T cells increases cytokine production substantially and induces immune-mediated diseases. Procyanidins are polyphenols with anti-inflammatory properties. Procyanidin B2 (PCB2) gallate [specifically, PCB2 3,3′′-di-O-gallate (PCB2DG)] inhibits cytokine production through the suppression of glycolysis via mammalian target of rapamycin (mTOR) in T cells. Several amino acids play critical roles in T cell activation, especially glutamine, which is important in mTOR signaling and interferon-γ (IFN-γ) production in CD4⁺ T cells. However, the mechanisms underlying the effects of PCB2DG, including its interaction partners, have yet to be clarified. In the present study, the mechanisms underlying the inhibitory effect of PCB2DG on IFN-γ through glutamine metabolism regulation were investigated. We found that PCB2DG treatment reduced intracellular glutamine levels in CD4⁺ T cells, whereas the addition of glutamine abrogated the inhibitory effects of PCB2DG on IFN-γ production. The PCB2DG-induced reduction in intracellular glutamine accumulation led to the upregulated expression of activating transcription factor 4, which was induced by the cytoprotective signaling pathway in the amino acid response. In addition, the mRNA and protein expression levels of alanine serine cysteine transporter 2 (ASCT2), a major glutamine transporter in CD4⁺ T cells, were not altered by PCB2DG treatment. Further analysis using a target identification strategy revealed that PCB2DG binds to ASCT2, suggesting that PCB2DG interacts directly with this major glutamine transporter to inhibit glutamine influx. Overall, this study indicates that ASCT2 is a novel target protein of a dietary polyphenol and provides new insights into the mechanism underlying the immunomodulatory effects of polyphenols.

^{CD4 +} T 细胞的过度激活显着增加细胞因子的产生并诱发免疫介导的疾病。原花青素是具有抗炎特性的多酚。原花青素 B2 (PCB2) 没食子酸酯 [特别是 PCB2 3,3''-二-O-没食子酸酯 (PCB2DG)] 通过 T 细胞中雷帕霉素哺乳动物靶标 (mTOR) 抑制糖酵解来抑制细胞因子的产生。几种氨基酸在 T 细胞活化中起着关键作用，尤其是谷氨酰胺，它在 CD4 ^{+中的 mTOR 信号传导和干扰素-γ (IFN-γ) 产生中很重要}T 细胞。然而，PCB2DG 影响的潜在机制，包括其相互作用伙伴，尚待阐明。在本研究中，研究了 PCB2DG 通过谷氨酰胺代谢调节对 IFN-γ 产生抑制作用的潜在机制。我们发现 PCB2DG 处理降低了 CD4 ^{+中的细胞内谷氨酰胺水平}T 细胞，而添加谷氨酰胺消除了 PCB2DG 对 IFN-γ 产生的抑制作用。PCB2DG 诱导的细胞内谷氨酰胺积累减少导致激活转录因子 4 的表达上调，这是由氨基酸反应中的细胞保护信号通路诱导的。此外，丙氨酸丝氨酸半胱氨酸转运蛋白 2 (ASCT2) 的 mRNA 和蛋白表达水平，它是 CD4 ^{+中的主要谷氨酰胺转运蛋白}T 细胞未因 PCB2DG 处理而改变。使用目标识别策略的进一步分析表明 PCB2DG 与 ASCT2 结合，表明 PCB2DG 直接与这种主要谷氨酰胺转运体相互作用以抑制谷氨酰胺流入。总的来说，这项研究表明 ASCT2 是膳食多酚的一种新型靶蛋白，并为多酚免疫调节作用的潜在机制提供了新的见解。