人類表現CD40L之調節性T細胞的表型與功能分析

Abstract

調節性T細胞為一特化的細胞群，他們透過抑制其他免疫細胞的功能，以達成調節個體免疫反應之效果。近來有研究指出，調節性T細胞會展現適應性，以因應環境中的刺激。在老鼠的實驗模型中，調節性T細胞因發炎細胞激素的影響，甚至能發展出增進免疫反應之功效。然而，目前對於人類調節性T細胞是否具有相同的促進免疫特性還不甚了解。此篇研究的目的為鑑定出人類表現CD40L的調節性T細胞，並分析其表型特徵與功能特性。 來自健康成人血液中的調節性T細胞，在強烈的CD3/TCR刺激下，得以表現CD40L。我們也從口腔癌患者的細胞中觀察到，相較於來自周邊血的調節性T細胞，腫瘤浸潤型淋巴球內的調節性T細胞面對刺激，有較高的比例會表現CD40L。藉由分析DNA的甲基化程度，發現CD40L+和CD40L-的調節性T細胞在FOXP3啟動子和TSDR的位置，皆展現低程度的甲基修飾，表示這兩群細胞均屬穩定的調節性T細胞。根據調節性T細胞常見的標記表現模式，顯示CD40L+和CD40L-調節性T細胞具有相似的表型特徵。在傳統的調節性T細胞功能分析中，CD40L+調節性T細胞展現較強的免疫抑制活性；而當單核球存在於實驗系統內，兩種調節性T細胞的免疫抑制活性則相當。此外，CD40L+與CD40L-調節性T細胞相比，具有較強的細胞激素生產率。與抑制功能相反的是，CD40L+調節性T細胞能夠促進樹突細胞表現成熟的細胞表徵，CD83。並且，與前述的樹突細胞表型特徵相符，經CD40L+調節性T細胞刺激後的樹突細胞，更能增進異體CD8+ T細胞的增生與活化。綜上所述，本篇研究指出，人類CD40L+調節性T細胞除了免疫抑制功能外，也可能具有促進免疫反應的效力。

Regulatory T cells are first discovered to regulate immune response through suppression to other immune cells. Upon facing environmental stimuli, it has been suggested that Treg cells show adaptive properties, even reported to provide a helper function in a mouse model. However, little is unknown about the helper activity of human Treg cells. The aims of this study are to identify human CD40L-expressing Treg cells along with their phenotypic and functional characteristics. In this study, we isolated human Treg cells from healthy donors and identified CD40L-expressing Treg cells after strong CD3/TCR stimulation. We found Treg cells from tumor-infiltrating lymphocytes (TILs) of oral cancer showed stronger tendency to express CD40L under restimulation. Through DNA methylation analyses, both CD40L+ and CD40L- Treg cells were hypomethylated at FOXP3 promoter and Treg-specific demethylated region (TSDR), suggesting that both subsets are stable Treg cells. According to the expression patterns of Treg-associated markers, CD40L+ Treg cells exhibited similar phenotype to CD40L- counterpart. As for the suppression function, CD40L+ Treg cells showed superior suppressive activity on proliferation and cytokine production of Tconv cells. Nonetheless, the suppressive activities of both Treg subsets were equivalent in suppression assay with monocytes. CD40L+ Treg cells displayed consistently higher cytokine productivity than CD40L- Treg cells in both suppression systems. Furthermore, CD40L+ Treg cells promoted CD83 expression on dendritic cells, a marker for dendritic cell maturation. Consistent with the phenotype, CD40L+ Treg-treated dendritic cells possessed better capacity to promote allogeneic CD8+ T cell activation and proliferation. In summary, these results indicated that human CD40L-expressing Treg cells might have positive effects on immune response apart from their suppressive function.