第17型輔助性T細胞在人類早期正常與無胚胎懷孕子宮內膜組織中的分佈情形

Abstract

懷孕時哺乳類動物母親面對帶有一半來自父親基因的胎兒之環境下，能夠不予以排斥並且讓胎兒順利著床、發育，顯然地母體子宮環境中的免疫系統必受到適當的調整控制。許多免疫調節機制參與各種調控，才能維持正常懷孕。其中，白血球細胞群是相當重要的。懷孕子宮內膜中 T 細胞佔白血球 10-12％，而 CD4 與 CD8 T 細胞組成的比例跟血液循環中不同，懷孕時期是一比二的比例存在於子宮內膜中。針對 CD4 T 細胞的分群如第一型 (TH1)、第二型 (TH2) 輔助性及調節性 T 細胞與懷孕子宮免疫環境的相關性的已有許多相關探討，然而過去對研究介白素-17 和第17型輔助性 T 細胞 (TH17 cells) 在懷孕子宮內膜是否存在以及其生理意義所知甚少。 T細胞分化為第 17 型輔助性 T 細胞需要一些因子參與，最主要為 TGF-β 與促發炎因子如 IL-6 等。文獻中已報告包括 IL-6、TGF-β及其他如 IL-1β、IFN-γ、TGF 及 TNF-α 等在懷孕初期時期大量表現，而上述懷孕時期表現的細胞激素或許可形成一特殊環境促使第17型輔助性T細胞的發育。我們之前的研究結果指出懷孕早期在子宮內膜中有免疫細胞聚集的現象，代表懷孕時的確發生免疫辨識及活化。在目前了解第 17 型輔助性 T 細胞多為扮演促發炎角色的細胞群，並參考前人與合併我們實驗室的研究，我們認為著床後，第 17 型輔助性 T 細胞存在於子宮內膜中。利用組織染色法，以 CD4 與 IL-17 作為偵測第17型輔助性 T 細胞的標誌，我們試圖找出其位於懷孕子宮內的分佈比例與分佈位置。結果顯示第 17 型輔助性 T 細胞是以聚集的方式在基質上分佈而非零星單獨地散佈。此外，與早期流產病人的組織相比， 正常懷孕的狀況下有較高比例的第 17 型輔助性 T 細胞存在。觀察 IL-6 與TGF-β 兩個促進第 17 型輔助性 T 細胞分化的細胞激素分佈發現 TGF-β 主要集中表現在腺體表皮細胞上，而 IL-6 相較之下較為散佈地表現於基質。細胞激素表現位置可解釋為何第 17 型輔助性 T 細胞的分佈位置較靠近腺體。正常懷孕與早期懷孕中 TGF-β 表現情形並沒有差異，然而 IL-6 在10個來自早期流產的檢體中，皆無法被偵測到。細胞激素的染色結果顯示環境中細胞激素表現的變化可能是造成第 17 型輔助性 T 細胞在正常懷孕與早期流產所佔有比例有顯著差異的原因之一。

Because half of the fetal genome derives from the father, the fetus is considered to be a foreigner by the maternal immune system. However concept is accepted without any rejection. This implies maintenance of normal pregnancy must be modified by several appropriate tolerogenic regulations in mammals. Leukocytes populations are an important component in human endometrium, and the populations increase at the first trimester of pregnancy compared with menstrual cycle. T cells in the human decidua are about 10% to 12% of total immune cells during pregnancy. CD4+ T helper cells are important players to modulate accurate immune responses. Recently a third subset of TH cells known as TH17 cells have been identified. Research in functions and regulatory roles of IL-17 and TH17 cells in human pregnancy is largely undetermined. As previous studies showed that many cytokines expressed in the maternal-fetal interface and exhibited regulatory roles in immunological tolerance, including IL-4, IL-1β, TNF-α, IFN-γ, TGF-β, IL-11, GM-CSF and IL-6. These cytokine milieu may support the differentiation of TH17 cells. IL-17 has been found in the maternal-fetal interface. Our previous results also showed CD8+ T cell-rich lymphoid aggregates are formed in decidua during early pregnancy. It suggests inflammation occurred in local environments and it’s known TH17 cells are one of the main mediator in inducing inflammation. Therefore, we propose that TH17 cells exist in human decidua after implantation. To investigate the TH17 population in decidua, we used immunostaining method to detect CD4+IL-17+ TH17 cells. Data indicated the phenotype of IL-17 producing cells are CD3+CD8- and CD3+CD4+ T cells. The percentage of CD4+IL-17+ TH17 cells in CD4+ T population are 41.5% in decidual tissues obtained from 11 cases of normal pregnancies and 19.5% in the decidua of anembryonic from 10 cases at 7-11 weeks of gestation. The TH17 cells are significantly higher in the decidua of normal pregnancies than that of anembryonic pregnancies. TGF-β is expressed exclusively on glandular epithelium, compared with IL-6 expression that is realatively scattered on stroma in decidua. TH17 cells appear as aggregates on stroma and the localization may be regulated by the existence of TGF-β and IL-6 in the decidua. The cytokine expression between normal and anembryonic pregnancy may be one of the reason causing the significant difference of TH17 population. TGF-β is comparably expressed between normal and anembryonic decidual tissues, however IL-6 positive staining seen to be more in the normal decidual tissues.The data showed TH17 cells proportion are higher in normal pregnancy and this could be the result of cytokine expresion diversity. Furthermore, this might indicate TH17 cells in decidua of human early pregnancy may have a unique role in mediating placenta development through the coordinated action of their effector cytokines.