IL-21於調控Th2細胞分化與Th2免疫反應之角色

Abstract

過敏性呼吸道疾病是一種慢性發炎疾病，造成的原因為Th2免疫反應失衡。其機制是由於病人呼吸道對特定的外來物質(過敏原)產生過敏反應，導致過敏原專一性Th2細胞的活化、Th2相關的細胞激素IL-4、IL-5和IL-13大量產生、血管擴張、平滑肌收縮、黏液以及抗體IgE的產生，造成呼吸道發炎。先前的文獻指出，在過敏性鼻炎動物模式中，IL-21藉由降低B細胞產生IgE的能力減緩過敏性鼻炎的症狀。但IL-21是否影響Th2細胞則尚未明瞭。在此實驗中，我們藉體內與體外試驗探討IL-21是否調控Th2細胞的分化與Th2免疫反應。 首先，我們探討IL-21是否影響Th2細胞分化。將DO11.10小鼠的CD4 T細胞以Th2條件培養時同時加入不同濃度之rmIL-21後分析培養細胞分泌的Th2相關細胞激素，結果顯示，加入IL-21培養的細胞其分泌Th2相關細胞激素的能力降低，其中以IL-4下降最為明顯，且Th2細胞激素的下降並非IL-21造成細胞死亡所致。再者，利用在小鼠致敏前給予Ad-mIL-21觀察其於Th2-derived過敏性動物模式對Th2細胞分化的影響。與施打Ad-mock的小鼠相比，接受Ad-mIL-21的小鼠支氣管肺泡沖洗液中IL-4、IL-5與IL-13濃度亦顯著下降。 接著，我們探究IL-21是否調控Th2免疫反應。以不同濃度rmIL-21刺激小鼠Th2條件培養後的細胞，發現細胞分泌的Th2相關細胞激素(IL-4、IL-5與IL-13)降低。再者，利用給予已致敏小鼠Ad-mIL-21後，支氣管肺泡沖洗液中IL-4濃度顯著下降。進一步分析發現，IL-4濃度的下降並非IL-21造成CD4 T細胞死亡所致而可能為藉由降低GATA3的表現而抑制細胞分泌IL-4。最後Th2相關細胞激素受到IL-21影響而降低的情形同樣能在以不同濃度rhIL-21刺激過敏性疾病病人分離出之周邊血單核球細胞的實驗中觀察到。 綜合以上實驗，IL-21能抑制Th2細胞的分化，並抑制Th2細胞的功能。其可能的機制為IL-21藉由負向調控GATA3與降低IL-4於肺臟中之表現量抑制過度的Th2免疫反應，並非IL-21造成Th2細胞死亡導致Th2相關細胞激素減少。

Allergic airway disease is a chronic inflammation, which is regarded as Th2 weighted imbalance. After allergens or parasitic helminthes stimulation, the phenomena of eosinophil increase, mast cell activation, immunoglobulin E (IgE) antibody production and cytokines such as interleukin (IL)–4, IL-5, and IL-13 secreted by Th2 cells are contributed to allergic disease. Previous study suggests that IL-21 administration into the nostril alleviates murine allergic rhinitis by means of reducing the production of IgE. However, whether IL-21 affects Th2 cells is still unknown. In this study, we investigated the role of IL-21 in the regulation of Th2 cell differentiation and Th2 immune responses in vitro and in vivo. First, we explored whether IL-21 affects the Th2 cell differentiation. The secretion of IL-4 from DO11.10 CD4 T cells which were cultured with different concentration of IL-21 under Th2 polarizing condition was decreased. In addition, we confirmed that the decreased level of IL-4 was not caused by IL-21-inducing apoptosis of cells. Furthermore, we also observed the significantly decreased level of Th2-associated cytokines in the BALF of OVA/Alumimmunized mice which were received Ad-mIL-21 before OVA immunization. Besides, the administration of Ad-mIL-21 reduced IL-4 production in the BALF of OVA/Alum immunized mice. Furthermore, IL-21 administration decreased the expression of transcription factor GATA3 of T cells. In conclusion, our results demonstrated that IL-21 decreased the Th2 cell differentiation and Th2 immune response. Moreover, the effects of IL-21 in the down regulation of Th2 cells were resulted in the down-regulation of GATA3 but not the apoptosis of Th2-producing cells.