新生儿Fc受体在自身免疫甲状腺疾病中的表达及作用

Hashimoto's thyroiditis (HT) and Graves’ disease (GD) are two main kinds of autoimmune thyroid diseases (AITD).Thyroglobulin antibody (TgAb) and thyroid peroxidase antibody (TPOAb) are diagnostic hallmarks of HT, which also participate in the pathogenesis of AITD. But the concrete pathogenic mechanism was still indistinct till now. Neonatal Fc receptor (FcRn) is a kind of speific immunoglobulin G (IgG) receptor, which is presented in multiple organs. It has been reported that FcRn is participatd in some physiological and immune processes, such as transferring IgG, acquired immunity and antigen presenting.Recently years, it has been shown that FcRn expresses in thyrocytes. However the functions and pathogenicity of FcRn were unclear so far. Considering the transporting capacity of IgG by FcRn, we will study the relationship between FcRn and IgG of thyroid autoantibodies to explore whether FcRn is involved in the pathogenesis of AITD. Thyroid tissues from thyroidectomy patients were collected and divided into three groups: normal thyroid, HT and GD thyroid (four cases for each group). Expressions of FcRn will be determined by RT-PCR and Western blot, capabilities of transporting IgG by FcRn will be evaluated by Confocal laser technology and Transwell assay, the influencing factors (thyroxine and cytokines) of FcRn expression will be compared in different groups. The location of FcRn in thyrocyte will also be determined by Immunoelectron microscopy colloidal gold method. Our study will provide more evidence about whether FcRn is involved in the pathogenesis of AITD.

自身免疫甲状腺疾病（AITD）包括桥本甲状腺炎（HT）和Graves病（GD）等。甲状腺球蛋白抗体（TgAb）和甲状腺过氧化物酶抗体（TPOAb）是AITD的标志性抗体，也参与其发病机制，但具体致病机制不明确。近年发现一种免疫球蛋白G（IgG）的特异受体新生儿Fc受体（FcRn），其可在甲状腺细胞表达。FcRn主要参与IgG的转运。我们推测FcRn可转运甲状腺自身抗体进入甲状腺细胞发挥细胞毒作用参与AITD的发病机制。拟收集病理为正常甲状腺、HT和GD的甲状腺组织行细胞培养：应用RT-PCR和Western Blot法测定FcRn表达；激光共聚焦技术、transwell法观察FcRn对TPOAb和TgAb的转运能力；免疫电镜胶体金法定位其表达位置；研究影响其表达的因素；阻断FcRn表达后再次评价其对甲状腺自身抗体的转运能力。以阐明FcRn是否介导甲状腺自身抗体的转运而参与AITD发病机制。

背景：甲状腺球蛋白抗体（ TgAb）和甲状腺过氧化物酶抗体（ TPOAb）是桥本甲状腺炎（HT）的标志性抗体，二者均以免疫球蛋白G（ IgG）型为主。体外研究已证实，IgG型TgAb和TPOAb可通过抗体依赖的细胞介导的细胞毒作用损伤甲状腺滤泡细胞。甲状腺球蛋白（Tg）储存于滤泡腔内，甲状腺过氧化物酶（TPO）亦表达于甲状腺细胞顶面。因此甲状腺滤泡的组织结构决定了Tg和TPO难以与循环中相应的抗体结合而发生免疫反应。新生儿Fc受体（FcRn）是IgG Fc受体的一种，可转运IgG。因此我们推测FcRn可能通过介导IgG型TgAb和TPOAb的转运而参与HT的发病机制。本研究 拟探讨在正常和HT甲状腺细胞中FcRn的表达、位置以及影响其表达的因素。.方法：分别收集手术切除的病理为正常和HT的甲状腺组织各4例，进行体外细胞培养。采用逆转录聚合酶链反应（RT-PCR）和蛋白免疫印迹（Western Blot, WB）法测定正常和HT细胞FcRn的表达。应用免疫电镜胶体金法定位FcRn在甲状腺细胞内的位置，采用免疫荧光法检测甲状腺细胞内吞的IgG型TgAb（TgAb IgG）及FcRn的表达位置。应用不同浓度的Th1和Th2细胞因子（IFN-γ、TNF-α和IL-10、IL-4）分别刺激甲状腺细胞以观察细胞因子对FcRn表达的调节。在Transwell小室中培养具有极性的原代甲状腺细胞进行IgG型TgAb、总IgG的直接转运的研究。.结果：甲状腺组织表达FcRn。FcRn主要分布于甲状腺细胞的细胞质、细胞膜、线粒体和囊泡内。人总IgG和IgG型TgAb均可以pH依赖的方式被内吞入甲状腺细胞，并与甲状腺细胞内FcRn存在共定位。FcRn在HT甲状腺组织中的表达水平低于正常甲状腺细胞。Th1和Th2细胞因子呈剂量依赖性下调正常甲状腺细胞和HT甲状腺细胞FcRn的表达。Transwell小室中验证TgAb IgG和总IgG可由基底测向顶端侧转运，该种转运为pH依赖性、且为单向转运。.结论：FcRn可介导甲状腺细胞内IgG型TgAb的转运和代谢，并且FcRn的转运功能和IgG种类无关。FcRn可能通过介导IgG的转运参与了HT的发病机制。