IgG免疫复合物交联Fc gamma受体介导肥大细胞凋亡在过敏原特异性免疫疗法机制中的作用

Allergy is an adverse inflammatory reaction where the body has an exaggerated immune response to a usually harmless substance or allergen. Mast cells are implicated as one of the most important types of effector cells in allergy. The only curative treatment for allergic diseases is allergen-specific immunotherapy (ASIT) which involves increasing doses of an allergen to achieve desensitization. The mechanisms for ASIT are currently not well understood. However, it is observed that ASIT results in increased allergen-specific IgG and decreased numbers of immune effector cells including mast cells. As our recent work demonstrates that mast cell apoptosis can be induced by crosslinking of Fc gamma receptors by IgG immune-complexes, we propose that this death mechanism may potentially be involved in ASTI. Interestingly, mast cells with a balanced expression of both Fc gamma RIIB and Fc gamma RIIIA are able to resist apoptosis. We believe that this finding can be exploited to further improve the efficacy of ASIT. To confirm whether Fc gamma receptor-mediated apoptosis may account for at least part of the mechanisms of ASIT, in vitro and in vivo studies using both human and mouse models will be performed. The project can be divided into 5 interrelated parts which will examine 1) human mast cell apoptosis in response to crosslinking of Fc gamma receptors; 2) the in vivo evidence of Fc gamma receptor crosslinking-induced mast cell apoptosis in mice; 3)the mechanisms underlying IgG immune complex-induced apoptosis; 4) the relevance of Fc gamma receptor-mediated mast cell apoptosis in a mouse ASIT model; 5) the possibility of blocking Fc gamma RIIIA on connective tissue mast cells to increase the efficiency of Fc gamma receptor-mediated mast cell apoptosis; and 6) use the polymorphisms of Fc gamma receptors as biomarkers for screening responding ASIT patients for developing individualized medicine. The successful completion of this project will lead to novel therapies for the improvement of allergy intervention and patient care.

过敏原特异性免疫疗法（ASIT），是治疗过敏性疾病的根本性治疗手段, 机理仍不完全清楚，且疗效有很大的个体性差异，有发现治疗后过敏原特异性IgG增高而效应细胞如肥大细胞数量减少，但机制不明。申请者前期研究发现：IgG免疫复合物可诱导肥大细胞凋亡，这一促凋亡作用是通过交联细胞表面IgG的受体（Fcgamma受体）完成，且受不同类型受体表达模式调控。我们推测ASIT 治疗中产生的大量IgG和过敏原形成的免疫复合物能交联IgG受体，导致肥大细胞凋亡，从而减轻过敏；而疗效个体性差异，可能是由于IgG受体多态性及表达差异所致。基于此假设，本课题拟深入探索IgG受体交联导致细胞凋亡的机理；建立过敏动物模型，进行ASIT以及联合IgG受体干扰治疗；寻找ASIT治疗病人IgG受体单核苷酸多态性与疗效的相关性。预期将从细胞凋亡角度阐明ASIT的作用机理，提供从IgG受体干扰来优化ASIT治疗方案的研究基础。

项目通过IgG免疫复合作用于原代培养的骨髓源肥大细胞及体内肥大细胞深入地研究了FcgRIIIA和FcgRIIB对肥大细胞凋亡的调节作用，并在过敏性哮喘模型中系统性研究了Fc gamma RIIIA和Fc gamma RIIB 对于过敏性疾病发展的机理。研究结果显示经IgG免疫复合物处理后，FcgRIIA及FcgRIIB基因缺失肥大细胞凋亡均表现为增高，而在WT肥大细胞中，凋亡并没有变化，提示小鼠肥大细胞在其表面如果只表达两类Fcg受体中的一类，即仅表达FcgRIIB，或仅表达FcgRIIIA，则此受体被IgG免疫复合物交联后能引起细胞凋亡。然而， 如果肥大细胞同时表达这两种受体，则能抵抗IgG免疫复合物交联后引起的细胞凋亡，体内实验亦支持这个结果。其次，FcgRIIA及FcgRIIB基因的缺失促进肥大细胞凋亡涉及线粒体依赖途径，但不涉及Caspase家族白蛋活化。进一步发现，抑制性受体FcgRIIB能够抑制过敏性哮喘气道炎症和过敏发应，影响疾病的发展, 而活化性受体FcgRIIIA虽然整体上对过敏性哮喘并未发现明显的的影响，但对体液免疫中过敏原特异性IgE、IgG等水平，及肺局部有一定的抑制作用，故而不能排除活化性受体FcgRIIIA对过敏性哮喘疾病的抑制作用。对过敏性哮喘病人研究中发现，FcgRIIB基因具有高表达者，其外周血中IgE水平明显降低。而在相应的活化性受体FcgRIIA，则未发现这一相关性。