FceRI阳性细胞在日本血吸虫感染所致Th2免疫应答及免疫病理中的作用

Schistosomiasis caused by Schistosoma japonica is still one of the top four infectious diseases prevalent in China. Liver granuloma and liver fibrosis are the major pathological consequences by schistosomiasis, and IL-4-dominant Th2 responses along with the occurrence of type II inflammatory responses are the driving forces for pathological changes seen in schistosomiasis. However, it remains unclear the kind of antigen-resenting cells that direct the development of egg-associated Th2 cells. Previous work by us supported by the completed NCSF grant on the role of basophils in Th2 development in schistosome infection, we uncovered that infiltrated cells positive for high affinity receptor for IgE Fc (FcRI) in spleen following schistosome infection displayed strong Th2-promoting activities which FcRI negative cells barely possessed. FcRI positive cells included not only basophils but also novel subset of dendritic cells positive for FcRI as well as novel FcRI single-positive cells. Both basophils and FcRI positive DC polarize Th2 cells via IL-4-dependent fashion, but depletion of either of them failed to abrogate or reduce Th2 cells and its associated pathologies. On the other hand, FcRI single-positive cells polarize Th2 cells via IL-4-independent fashion. Here we proposed to test that the development of Th2 responses and their associated pathologies in Schistosoma japonica infection depends on the emergence of FcRI-positive cells not dendritic cells. Conditional knockout of FcRI-positive cells using FcRI-DTR transgenic mice proposed to construct in the study together with cell subset adoptive transfer will elucidate relative contribution of different cell subset played by FcRI-positive cells as well as their mechanisms including IL-4-dependence and DC-dependence. Further investigations will also be performed on the origin of FcRI-positive cell subsets and the mechanisms that egg antigens induce the generation and infiltration of these cells in the infected spleen. This study will provide new strategy to treatment of schistosomiasis and other types of type II inflammation associated diseases.

血吸虫感染所致肝肉芽肿及纤维化的产生动因是虫卵抗原诱导的Th2应答及其造成的II型炎症反应，但启动Th2应答的抗原呈递细胞类型和机制仍不明确。我们发现日本血吸虫感染后小鼠脾脏中具有诱导Th2极化能力的抗原呈递细胞集中在大量增加的IgE Fc段高亲和力受体（FceRI）阳性细胞中。其中嗜碱性粒细胞和新发现的三阳性DC以IL-4依赖的方式极化Th2，而FceRI单阳细胞以IL-4非依赖方式诱导Th2极化。据此，我们提出FceRI阳性细胞通过IL-4依赖和非依赖两种方式启动Th2应答的假说。拟通过细胞条件性清除、细胞亚群回输及细胞共培养等手段研究FceRI阳性细胞及其不同亚群在血吸虫感染Th2应答启动、维持和肝脏病理中的主导作用和机制；同时，研究虫卵抗原诱导FceRI阳性细胞产生的机制。揭示FceRI阳性细胞在血吸虫感染虫卵期Th2应答产生及免疫病理中的关键作用，为干预II型炎症应答提供新靶标。

研究背景：.我们发现日本血吸虫感染后小鼠脾脏中体外具有诱导Th2极化能力的抗原呈递细胞集中在大量增加的表达IgE Fc段高亲和力a受体（简称FceRI）阳性细胞中。我们提出假说，病原诱导FceRI阳性细胞在Th2型免疫应答的启动和效应中起着不可或缺的作用。希望在其他组织和细胞基本不表达的FceRIa，成为控制Th2型炎症和疾病（如过敏、哮喘、和纤维化类疾病）的新型靶分子。.研究内容：.首先构建条件性清除FceRI阳性细胞小鼠模型FceRI-DTR，达到给予小鼠白喉毒素DT可清除这些细胞，从而明确FceRI阳性细胞为日本血吸虫感染Th2应答及肝纤维化形成所必需。.骨髓来源的FceRI阳性的嗜碱性粒细胞和树突状细胞（DC）作为抗原呈递细胞，和TCR转基因鼠脾脏初始 CD4 T 细胞共培养，研究嗜碱性粒细胞在促Th2免疫应答的佐剂分子氢氧化铝（Alum）中的作用及机制。最后研究骨髓细胞向FcRI阳性细胞分化的调控，主要是虫卵抗原和IL-3对他们的调控。.重要结果、关键数据及科学意义：.我们完成二株FceRI-DTR基因敲入鼠，一株3’UTR区域插入dtr，而fceRIa编码区完整；另一株是dtr替换掉整个fceRIa，保留UTR区域。二株构建成功但编辑区域基因均未能表达，即FceRI基因及插入的DTR都不表达。初步研究发现， FcεRIα基因表达在3‘UTR区有特殊要求。对该机制的深入研究将对基因敲入编辑的成功与否给出提示。.发现Alum佐剂体外有强直接刺激嗜碱性粒细胞而非DC的促Th2分化的作用，这一作用不依赖于嗜碱性粒细胞的IL-4，与刺激产生细胞因子IL-25和TSLP有关。为FceRI阳性细胞以IL-4非依赖方式促Th2应答提供实例。.发现虫卵抗原在GM-CSF诱导小鼠骨髓细胞生长和分化为DC时，导致FcRI阳性细胞形成，伴随树突状细胞分化减少。该作用依赖于模式受体TLR2。TLR2激动剂Pam3CYS,TLR9的激动剂ODN及过敏原胃蛋白酶也有类似作用。病原相关分子直接刺激骨髓偏分化成不同类型的抗原呈递细胞可能成为他们诱导偏向的免疫应答（I型还是II型）的新机制。