TSLP联结角膜真菌感染天然免疫与获得性免疫的机制

Fungal keratitis is among the most serious vision-threatening ocular infections. Clarification of the mechanism of corneal fungal infection from the viewpoint of both innate and acquired immunity is the key to treatment and prevention of fungal keratitis. We innovatively demonstrated that TLRs played essential roles in early corneal antifungal innate immunity. At the same time acquired immunity was found to be participated in the process of mid-late corneal immune response to fungal invasion. Innate and acquired immunity cooperate to eliminate fungal pathogens. At present, no research on the intercommunication of innate and acquired immunity in fungal keratitis has been reported. Recent functional studies on acquired-immunity component TSLP have suggested that TSLP was potently induced when human bronchial epithelial cells were exposed to fungi, and TLRs could modulate the expression of TSLP in allergic diseases. Our preliminary studies found that TSLP involved in the process of corneal antifungal immune response, which was closely related to TLRs. In the present project, we intended to further confirm that TSLP could strengthen the early innate immunity mediated by TLRs and participate in the initiation of mid-late acquired immunity in antifungal defensive response, which enhance corneal defense against invading fungi and accelerate inflammation subsiding. A clear understanding of the mechanisms for TSLP bridging the innate and acquired immunity in fungal keratitis is required to more comprehensively investigate the system of corneal immune response to fungal invasion and provide targets for new antifungal pharmaceuticals.

真菌性角膜炎是最严重的致盲性眼病之一，从天然免疫和获得性免疫的双重角度全面揭示角膜抗真菌免疫防御机制是防治角膜真菌感染的关键。我们已经率先证实TLRs是角膜真菌感染早期天然免疫的关键受体，获得性免疫可能参与感染中晚期过程，二者协同清除真菌。目前尚未见有关角膜抗真菌天然免疫与获得性免疫相互联系的研究报道。近年获得性免疫组分TSLP的功能研究揭示真菌刺激人呼吸道上皮细胞高表达TSLP，过敏性疾病中TLRs调控TSLP的表达。我们初步试验发现TSLP参与角膜抗真菌免疫过程并与TLRs密切相关。本课题拟体外实验及动物模型进一步证实TSLP增强角膜真菌感染早期TLRs介导天然免疫、参与启动感染中晚期获得性免疫，提高角膜抗真菌感染的免疫防御能力，促进炎症消退。明确TSLP作为桥梁和纽带联结角膜真菌感染天然免疫与获得性免疫的作用及机制，为更全面的研究角膜抗真菌免疫防御体系及抗真菌感染新药的研发提供靶点。

真菌性角膜炎是一种感染性角膜病变，具有破坏性和致盲性。目前研究认为，在真菌性角膜炎中，机体不同的免疫状态会影响疾病的进程。胸腺基质淋巴细胞生成素是从胸腺基质细胞中发现的，与IL-17类似的短链Ⅰ型细胞因子，它的发现揭示了众多过敏性疾病的发病机制和机理。前期研究我们发现TSLP对角膜中树突细胞等天然免疫细胞的趋化作用和多种细胞因子的促进作用。在我们的研究中，烟曲霉菌刺激人永生化角膜上皮细胞和小鼠后TSLP和TSLP的受体（TSLPR）表达在早期达到高峰,两者结合后，可激活信号转导子以及转录活化子5 (STAT5)，并启动下游基因的表达。同时我们证实真菌感染中TSLPR／STAT5信号通路可能直接由TLR2下游信号分子激活，或间接地由TLR2来源的TSLP激活。Toll样受体（TLRs）是一类富含亮氨酸的跨膜受体家族，在大多数角膜细胞中表达。前期研究已表明在将TLR2、TLR4的配体刺激人角膜上皮细胞时，可以介导TSLP的表达，而在实验动物体内发现的TSLP对Toll样受体同样具有调控作用，或可表明TSLP与Toll样受体之间，存在一个正反馈的循环，两者互相促进。树突细胞作为关键的免疫细胞，在天然免疫应答中可被病原菌、炎症因子及多种免疫成分激活，由未成熟状态活化至成熟状态，可趋化至病原接触、组织破坏或炎症发生位置。研究发现成熟的DC能够表达TSLP，TSLP促进DCs聚集、成熟和迁移。在获得性免疫应答中，TSLP能够促进淋巴细胞増殖，活化，并促进CD4+T细胞向Th2方向分化。我们的研究证明TSLP是角膜抗真菌感染免疫中关键的炎症因子，在感染早期TSLP参与免疫反应，并促进角膜天然免疫应答中重要组分即Toll样受体、趋化因子及抗菌肽的表达。TSLP趋化中性粒细胞，并与树突细胞相互作用，使其激活并趋化到感染部位，完成抗原递呈作用并介导了Th2型获得性免疫反应，联结天然免疫及获得性免疫。