An important function of the gut microbiome is the fermentation of non-digestible dietary fibers into short chain fatty acids (SCFAs). The three primary SCFAs: acetate, propionate, and butyrate, are key mediators of metabolism and immune cell function in the gut mucosa. We previously demonstrated that butyrate at high concentrations decreased human gut lamina propria (LP) CD4 T cell activation in response to enteric bacteria exposure in vitro. However, to date, the mechanism by which butyrate alters human gut LP CD4 T cell activation remains unknown. In this current study, we sought to better understand how exposure to SCFAs across a concentration range impacted human gut LP CD4 T cell function and activation. LP CD4 T cells were directly activated with T cell receptor (TCR) beads in vitro in the presence of a physiologic concentration range of each of the primary SCFAs. Exposure to butyrate potently inhibited CD4 T cell activation, proliferation, and cytokine (IFNγ, IL-17) production in a concentration dependent manner. Butyrate decreased the proliferation and cytokine production of T helper (Th) 1, Th17 and Th22 cells, with differences noted in the sensitivity of LP versus peripheral blood Th cells to butyrate’s effects. Higher concentrations of propionate and acetate relative to butyrate were required to inhibit CD4 T cell activation and proliferation. Butyrate directly increased the acetylation of both unstimulated and TCR-stimulated CD4 T cells, and apicidin, a Class I histone deacetylase inhibitor, phenocopied butyrate’s effects on CD4 T cell proliferation and activation. GPR43 agonism phenocopied butyrate’s effect on CD4 T cell proliferation whereas a GPR109a agonist did not. Our findings indicate that butyrate decreases in vitro human gut LP CD4 T cell activation, proliferation, and inflammatory cytokine production more potently than other SCFAs, likely through butyrate’s ability to increase histone acetylation, and potentially via signaling through GPR43. These findings have relevance in furthering our understanding of how perturbations of the gut microbiome alter local immune responses in the gut mucosa.

肠道微生物组的一个重要功能是将不易消化的膳食纤维发酵成短链脂肪酸 (SCFA)。三种主要的 SCFA：乙酸盐、丙酸盐和丁酸盐，是肠道黏膜中代谢和免疫细胞功能的关键介质。我们之前证明，高浓度丁酸盐会降低人体肠道固有层 (LP) CD4 T 细胞对体外肠道细菌暴露的反应。然而，迄今为止，丁酸盐改变人肠道 LP CD4 T 细胞活化的机制仍然未知。在当前的这项研究中，我们试图更好地了解暴露于不同浓度范围内的 SCFA 如何影响人类肠道 LP CD4 T 细胞的功能和活化。LP CD4 T 细胞在体外被 T 细胞受体 (TCR) 珠直接激活在每种主要 SCFA 的生理浓度范围内。丁酸盐以浓度依赖性方式有效抑制 CD4 T 细胞活化、增殖和细胞因子（IFNγ、IL-17）的产生。丁酸盐降低了 T 辅助细胞 (Th) 1、Th17 和 Th22 细胞的增殖和细胞因子产生，LP 与外周血 Th 细胞对丁酸盐作用的敏感性存在差异。需要相对于丁酸盐更高浓度的丙酸盐和乙酸盐来抑制 CD4 T 细胞活化和增殖。丁酸盐直接增加了未刺激和 TCR 刺激的 CD4 T 细胞的乙酰化，而 Apicidin 是一种 I 类组蛋白去乙酰化酶抑制剂，可表现丁酸盐对 CD4 T 细胞增殖和活化的影响。GPR43 激动剂表现出丁酸盐对 CD4 T 细胞增殖的影响，而 GPR109a 激动剂则没有。我们的研究结果表明丁酸盐减少体外人类肠道 LP CD4 T 细胞活化、增殖和炎性细胞因子产生比其他 SCFA 更有效，可能是通过丁酸盐增加组蛋白乙酰化的能力，也可能是通过 GPR43 信号传导。这些发现有助于进一步了解肠道微生物组的扰动如何改变肠道粘膜的局部免疫反应。