Neoself-antigens are the primary target for autoreactive T cells in human lupus

Major histocompatibility complex class II (MHC-II) is the most significant genetic risk factor for systemic lupus erythematosus (SLE), but the nature of the self-antigens that trigger autoimmunity remains unclear. Unusual self-antigens, termed neoself-antigens, are presented on MHC-II in the absence of the invariant chain essential for peptide presentation. Here, we demonstrate that neoself-antigens are the primary target for autoreactive T cells clonally expanded in SLE. When neoself-antigen presentation was induced by deleting the invariant chain in adult mice, neoself-reactive T cells were clonally expanded, leading to the development of lupus-like disease. Furthermore, we found that neoself-reactive CD4+ T cells were significantly expanded in SLE patients. A high frequency of Epstein-Barr virus reactivation is a risk factor for SLE. Neoself-reactive lupus T cells were activated by Epstein-Barr-virus-reactivated cells through downregulation of the invariant chain. Together, our findings imply that neoself-antigen presentation by MHC-II plays a crucial role in the pathogenesis of SLE. Overall design: We performed scRNA sequencing to understand the effect of MHC-class II dysfunction on autoimmunity. details of the HTO antibodies HTO: barcode sequence: hashtagged sample (condition/treatment) TotalSeq-C0301 anti-mouse Hashtag 1 Antibody: ACCCACCAGTAAGAC: mouse splenic CD4 T cells isolated by magnetic beads, replicate 1 TotalSeq-C0304 anti-mouse Hashtag 4 Antibody: AAAGCATTCTTCACG: mouse splenic CD4 T cells isolated by magnetic beads, replicate 2 TotalSeq-C0306 anti-mouse Hashtag 6 Antibody: TATGCTGCCACGGTA: mouse splenic CD4 T cells isolated by magnetic beads, replicate 3

主要组织相容性复合体II类（Major histocompatibility complex class II，MHC-II）是系统性红斑狼疮（systemic lupus erythematosus，SLE）最为关键的遗传风险因子，但触发自身免疫的自身抗原本质仍未阐明。一类被称为新自身抗原（neoself-antigens）的特殊自身抗原，可在缺乏肽提呈必需的恒定链（invariant chain）的前提下由MHC-II分子提呈。本研究证实，新自身抗原是SLE患者体内克隆扩增的自身反应性T细胞的主要靶标。在成年小鼠中通过敲除恒定链诱导新自身抗原提呈后，新自身抗原反应性T细胞发生克隆扩增，进而诱发狼疮样疾病。此外，本研究发现SLE患者体内新自身抗原反应性CD4阳性T细胞（CD4+ T cells）显著扩增。EB病毒（Epstein-Barr virus，EBV）再激活的高发生率是SLE的一项风险因子。EB病毒再激活的细胞可通过下调恒定链，激活新自身抗原反应性狼疮T细胞。综上，本研究结果表明，MHC-II介导的新自身抗原提呈在SLE的发病机制中发挥关键作用。

整体实验设计：为探究MHC-II功能异常对自身免疫的影响，我们开展了单细胞RNA测序（single-cell RNA sequencing，scRNA-seq）。
HTO抗体详情：HTO：条形码序列 | 带标签样本（条件/处理方式）
TotalSeq-C0301 抗小鼠标记1抗体：ACCCACCAGTAAGAC | 磁珠分离的小鼠脾脏CD4阳性T细胞，重复实验1
TotalSeq-C0304 抗小鼠标记4抗体：AAAGCATTCTTCACG | 磁珠分离的小鼠脾脏CD4阳性T细胞，重复实验2
TotalSeq-C0306 抗小鼠标记6抗体：TATGCTGCCACGGTA | 磁珠分离的小鼠脾脏CD4阳性T细胞，重复实验3