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Abstract：
Bullous pemphigoid (BP), the most common autoimmune blistering disease, is induced by autoantibodies to type XVII collagen (COL17). Previous studies demonstrated that COL17 harbors several epitopes targeted by autoreactive T and B cells and that the target epitopes change sequentially during the disease course. To elucidate the details of the humoral immune response to COL17, we used an active BP mouse model in which BP is induced by the adoptive transfer of spleen cells from wild-type mice immunized with human COL17-expressing skin grafting to immunodeficient COL17-humanized (Rag-2-/-, mouse Col17-/-, human COL17+) mice. By immunoblot analysis, antibodies to the NC16A domain and other extracellular domains (ECDs) of COL17 were detected earlier than antibodies to intracellular domains (ICDs) in the active BP model. Time course analysis by enzyme-linked immunosorbent assay demonstrated a delayed peak of antibodies to ICD epitopes in active BP model. The blockade of CD40-CD40 ligand interaction soon after the adoptive transfer suppressed the production of antibodies to the non-collagenous 16A (NC16A) domain but not to an ICD epitope, suggesting the sequential activation from T and B cells against the ECD epitopes including the NC16A domain to those against ICD epitopes in vivo. Both wild-type mice immunized with a fragment of the NC16A domain and the recipients of those spleen cells produced IgG antibodies to ICD and ECD epitopes, showing intramolecular epitope spreading from the NC16A domain to other epitopes of COL17. Furthermore, we found that a portion of the active BP model mice show intermolecular epitope spreading from human COL17 to murine BP230. The appearance of antibodies to ICD epitopes of COL17 or of antibodies to murine BP230 did not correlate with the skin changes in the mice, suggesting that those antibodies have low pathogenicity. These results suggest that the immune response to the ECD epitopes of COL17, especially to the NC16A domain, triggers intramolecular, and intermolecular epitope spreading to ICD epitopes of COL17 and to murine BP230. These novel findings provide insight into the mechanism of epitope spreading in organ-specific, antibody-mediated autoimmune disorders.
摘要：
大疱性类天疱疮（BP），最常见的自身免疫性起泡疾病，由针对XVII型胶原(COL17)的自身抗体诱导。先前的研究表明，COL17具有由自身反应性T和B细胞靶向的几种表位，并且在疾病过程中，靶表位依次变化。为了阐明对COL17的体液免疫反应的细节，我们使用了一种活性BP小鼠模型，其中BP是通过将表达人COL17的皮肤移植免疫的野生型小鼠的脾细胞过继转移到免疫缺陷的COL17-人源化（Rag-2-/-，鼠标Col17-/-,人类COL17+)小鼠。通过免疫印迹分析,在活性BP模型中,检测到针对COL17的NC16A结构域和其他胞外域(ECDs)的抗体比针对胞内域(ICDs)的抗体更早.通过酶联免疫吸附测定的时程分析表明，在活性BP模型中，针对ICD表位的抗体峰延迟。过继转移后不久，CD40-CD40配体相互作用的阻断抑制了针对非胶原16A（NC16A）结构域而不是ICD表位的抗体的产生，表明T细胞和B细胞针对包括NC16A结构域在内的ECD表位的顺序激活到针对ICD表位的那些。用NC16A结构域片段免疫的野生型小鼠和这些脾细胞的接受者都产生了针对ICD和ECD表位的IgG抗体，显示分子内表位从NC16A结构域扩散到COL17的其他表位。此外，我们发现一部分活性BP模型小鼠显示分子间表位从人COL17扩散到鼠BP230。针对COL17的ICD表位的抗体或针对鼠BP230的抗体的出现与小鼠的皮肤变化无关。这表明这些抗体具有低致病性。这些结果表明，对COL17的ECD表位，特别是对NC16A结构域的免疫应答，触发分子内，和分子间表位扩展到COL17的ICD表位和鼠BP230。这些新发现提供了对器官特异性表位扩散机制的见解，抗体介导的自身免疫性疾病。
