Immunogenetic analysis of the pathogenesis of the seronegative autoimmune disease

重症肌无力（MG）是一种以神经肌肉连接处乙酰胆碱受体（AChR）的自身免疫反应为特征的疾病。由于儿童期发病的MG患者血清AChR抗体呈阴性或低滴度，分析儿童期发病的重症肌无力的病因有助于阐明血清阴性自身免疫性疾病的发病机制。我们用PCR/SSO方法检测了儿童发病的一般(G)型MG患者的HLA-DRB、DQA和DQB等位基因的频率，用RT-PCR检测了来自自体AChR致敏T细胞系的TCR Vα/β库。G型儿童期发病MG患者与DRB1^*1302 / DQA1^*0102 / DQB1^*0604等位基因单倍型强相关（pc<10^<-20 bb0, rr =53.4）。在这些患者的临床过程中，细胞免疫应答对复发或加重起着重要作用。DQB1^*0604在DQB1链的第57位有一个疏水残基（缬氨酸，V），被发现与儿童期发病的G型MG密切相关。DQB链的这种氨基酸多态性可能与胰岛素依赖性糖尿病有关，其发病机制被认为是T细胞介导的免疫。这些数据表明，T细胞介导的免疫可能与儿童期发病的G型MG的发展有关。因此，HLA-DQB链中的多态性残基可能与临床独特的潜在一般（LG）型或G型MG的易感性有关。此外，AChR致敏的G型MG患者CD4+ T细胞株强烈表达TCRVα1、2或3克隆和TCRVβ 6.1或8克隆。这些T细胞系通过产生IL-2和IFN-γ激活了th1样表型。综上所述，LG+G型儿童期发病MG患者的发病机制可能与其他类型的成人发病MG患者不同，其中自身抗体被认为是致病的。

Myasthenia gravis (MG) is a disease characterized by an autoimmune reaction against the acetylcholine receptor (AChR) at the neuromuscular junction. As the childhood-onset MG patients had negative or low titer of the serum AChR antibody, it was useful for the elucidation in the pathogenesis of the seronegative autoimmune diseases to analysis the cause of the childhood-onset myasthenia gravis. We have examined the frequencies of HLA-DRB, DQA and DQB alleles by PCR/SSO method and TCR Vα/β repertories from autologous AChR sensitized T cell line using RT-PCR in the childhood-onset MG patients with the general (G) type. The childhood-onset MG patients with G type were strongly associated with DRB1^*1302 / DQA1^*0102 / DQB1^*0604 allelic haplotype (pc<10^<-20>, R.R.=53.4). In the clinical course of these patients, the cellular immune responses have played the important role for the recurrence or the exacerbation. DQB1^*0604, which was found to be strongly associated with G type MG with childhood-onset, has a hydrophobic residue (valine, V) at position 57 of the DQB1 chain. This amino acid polymorphism of the DQB chain may be associated with insulin dependent diabetes mellitus, which is thought T cell-mediated immunity as the pathogenesis of the development. This data suggest that T cell-mediated immunity may be associated with development of G type MG with the childhood-onset. Therefore, the polymorphic residues in the HLA-DQB chain may contribute to susceptibility to clinically unique latent general (LG) type or G type MG.Furthermore, AChR sensitized CD4+ T cell line from G type MG patient expressed strongly TCRVα1, 2 or 3, and TCRVβ 6.1 or 8 clone. These T cell lines had activated TH1-like phenotype by IL-2 and IFN-γ production. In conclusion, childhood-onset MG patients with LG+G type may differ in the pathogenic mechanisms from those with other types of MG with adult-onset in which the autoantibodies are thought to be pathogenic.