Most, if not all, peripheral immune cells in humans and animals express tyrosine hydroxylase (TH), the rate limiting enzyme in catecholamine synthesis. Since TH is typically studied in the context of brain catecholamine signaling, little is known about changes in TH production and function in peripheral immune cells. This knowledge gap is due, in part, to the lack of an adequately sensitive assay to measure TH in immune cells expressing lower TH levels compared to other TH expressing cells. Here, we report the development of a highly sensitive and reproducible Bio-ELISA to quantify picogram levels of TH in multiple model systems. We have applied this assay to monocytes isolated from blood of persons with Parkinson’s disease (PD) and to age-matched, healthy controls. Our study unexpectedly revealed that PD patients’ monocytes express significantly higher levels of TH protein in peripheral monocytes relative to healthy controls. Tumor necrosis factor (TNFα), a pro-inflammatory cytokine, has also been shown to be increased in the brains and peripheral circulation in human PD, as well as in animal models of PD. Therefore, we investigated a possible connection between higher levels of TH protein and the known increase in circulating TNFα in PD. Monocytes isolated from healthy donors were treated with TNFα or with TNFα in the presence of an inhibitor. Tissue plasminogen activator (TPA) was used as a positive control. We observed that TNFα stimulation increased both the number of TH+ monocytes and the quantity of TH per monocyte, without increasing the total numbers of monocytes. These results revealed that TNFα could potentially modify monocytic TH production and serve a regulatory role in peripheral immune function. The development and application of a highly sensitive assay to quantify TH in both human and animal cells will provide a novel tool for further investigating possible PD immune regulatory pathways between brain and periphery.

大多数（如果不是全部）人类和动物的外周免疫细胞表达酪氨酸羟化酶 (TH)，这是儿茶酚胺合成中的限速酶。由于 TH 通常是在脑儿茶酚胺信号传导的背景下研究的，因此人们对 TH 产生和外周免疫细胞功能的变化知之甚少。这种知识差距部分是由于缺乏足够灵敏的测定来测量与其他 TH 表达细胞相比表达较低 TH 水平的免疫细胞中的 TH。在这里，我们报告了一种高度敏感和可重复的生物 ELISA 的开发，以量化多个模型系统中 TH 的皮克水平。我们已将此测定应用于从帕金森病 (PD) 患者血液中分离的单核细胞，以及年龄匹配的健康对照。我们的研究出乎意料地表明，与健康对照相比，PD 患者的单核细胞在外周单核细胞中表达的 TH 蛋白水平明显更高。肿瘤坏死因子 (TNFα) 是一种促炎细胞因子，在人类 PD 的大脑和外周循环以及 PD 动物模型中也显示出增加。因此，我们研究了较高水平的 TH 蛋白与已知的 PD 循环 TNFα 增加之间的可能联系。从健康供体分离的单核细胞用 TNFα 或在抑制剂存在下用 TNFα 处理。组织纤溶酶原激活剂 (TPA) 用作阳性对照。我们观察到 TNFα 刺激增加了 TH+ 单核细胞的数量和每个单核细胞的 TH 数量，而不增加单核细胞的总数。这些结果表明，TNFα 可能会改变单核细胞 TH 的产生，并在外周免疫功能中发挥调节作用。开发和应用高灵敏度测定法来量化人类和动物细胞中的 TH，将为进一步研究大脑和外周之间可能的 PD 免疫调节通路提供一种新工具。