甲状腺自身抗体糖基化修饰的调控机制及糖基化修饰对不同补体活化途径的影响

Autoimmune thyroid diseases is the major cause of thyroid dysfunction. Thyroglobulin antibodies (TgAb) and thyroid peroxidase antibodies (TPOAb) are the diagnosis markers of AITD. In our previous study, it has been shown that TgAb glycosylation is different in different thyroid diseases, including Graves' disease, Hashimoto's thyroiditis and thyroid papillary cancer. Furthurmore, the different glycosylation profiles of TgAb in serum from Hashimoto' s patients and health controls indicated that glycosylation of TgAb is involved in in the breaking of self-tolerance against thyroglobulin. However, it is only an observational study and the regulation mechanism of IgG glycosylaiton is still unclear. Since the enzyme involved in the production of suger chain is specific, we assume that cytokines imbalance in AITD may induce the change of microenviroment in B cells, which further results in the elevated expression of some specific glycosyltransferase and glycosidase, and then changes the IgG glycosylation correspondently. Complement system is important for autoimmune diseases. It has been reported that different glycosylation of IgG may activate different complement activation pathways in literature. We intend to confirm the three different complement activation pathwas in thyroid tissue in AITD. And based on these results, the glycosylation profile of thyroid autoantibodies will be changed by glycobiology technology. The interact between different glycosylation profiles of thyroid IgG autoantibodies and different complement components will be further studied. These results may provide more evidence about the role of glycosylation on thyroid autoantibodies in the pathgenesis of AITD.

自身免疫甲状腺疾病（AITD）是导致甲状腺功能异常的主要病因，甲状腺自身抗体是AITD的诊断标志。我们在前期工作中虽已发现，甲状腺自身抗体的糖基化修饰在不同甲状腺疾病中存在差异，且抗体的糖基化修饰参与了机体打破对甲状腺自身抗原免疫耐受的过程，但上述研究并未阐明抗体糖基化修饰的调控机制。我们拟利用蛋白质组学、质谱及凝集素芯片等技术在体外实验中证实：AITD中存在的细胞因子的失衡通过改变B细胞的微环境，影响部分糖基转移酶或糖苷酶的表达，进而参与了IgG型抗体糖基化修饰的调控；进一步在验证甲状腺组织中存在补体不同活化途径的基础上，利用糖生物学方法获得不同糖型的IgG型甲状腺自身抗体，进而探讨IgG的不同糖型对补体不同活化途径的影响。上述研究将从IgG糖基化修饰的调控及补体系统活化途径的崭新角度进一步诠释甲状腺自身抗体的糖基化修饰在AITD发病机制中的作用，该系列工作有助于完善AITD的发病机制。

自身免疫甲状腺疾病（AITD）是导致甲状腺功能异常最主要的病因，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，且主要为IgG型。在前期工作中，我们发现IgG型TgAb糖基化修饰在不同甲状腺疾病中存在差异，且抗体的糖基化修饰参与了机体免疫稳态的打破。本课题在前期工作基础上，利用凝集素芯片观察到血清IgG1型而非IgG4型TgAb的糖基化修饰在不同甲状腺疾病中发生显著改变，将IgG糖基化修饰的工作深入到抗体亚型层面；进一步课题组建立了B细胞体外诱导分化体系，利用基质辅助激光解吸电离-飞行时间质谱（MALDI-TOF-MS）及凝集素芯片等技术在体外实验中证实，AITD中存在的细胞因子失衡通过改变B细胞的免疫微环境，影响唾液酸、半乳糖和甘露糖相关的糖基转移酶或糖苷酶表达，进而参与了IgG型抗体糖基化修饰的调控，并且多种细胞因子与不同糖型形成复杂的调控网络；为了探究抗体糖基化修饰对生物学效应（即与补体活化）的影响，课题组利用免疫组化验证了甲状腺组织中存在补体异常活化，且与既往报道不同，补体活化途径以凝集素途径和旁路途径为主，证实补体活化参与了AITD中桥本甲状腺炎（HT）的发病机制。上述研究对IgG糖基化修饰的胞内调控机制进行了重要补充，并揭示了免疫微环境通过调控IgG型抗体的糖基化修饰，影响抗体介导的生物学作用，从而改变其致病性，促进疾病的发生发展，而补体系统活化途径的深入研究，完善了桥本甲状腺炎（HT）的发病机制，并为预防、延缓HT进程提供新的靶点。