致病性抗IFN-γ自身抗體通過阻礙受體組裝和介導的Fc反應起作用

摘 要：

抗干擾素（IFN）-γ自身抗體（AIGAs）是晚發性免疫缺陷伴彌漫性分枝桿菌和其他機會性感染的致病因素。AIGAs會阻斷IFN-γ的功能，但它們對IFN-γ信號傳導的影響尚不清楚。使用單細胞捕獲方法，我們從具有AIGAs的患者中分離出19種對IFN-γ有反應的單克隆抗體（mAbs）。所有抗體均顯示出對IFN-γ的高親和力（KD < 10^-9 M），但僅有八種中和了IFN-γ-STAT1信號傳導和HLA-DR表達。信號阻斷和結合親和力相關，並歸因於體細胞超突變。交叉競爭試驗鑑定出AIGAs在IFN-γ上的三個不重疊的結合位點（I-III）。 我們發現，位點I的mAb通過阻止IFN-γ與IFN-γR1的結合來中和IFN-γ。位點II和III的mAbs在細胞表面結合受體結合的IFN-γ，破壞IFN-γR1-IFN-γR2異二聚體化，從而阻止下游信號傳導。位點III的mAbs通過抗體-IFN-γ複合物在細胞上介導抗體依賴的細胞毒性。致病性AIGAs通過雙重阻斷IFN-γ信號傳導和消除對IFN-γ有反應的細胞，導致分枝桿菌感染。

Anti-interferon (IFN)–γ autoantibodies (AIGAs) are a pathogenic factor in late-onset immunodeficiency with disseminated mycobacterial and other opportunistic infections. AIGAs block IFN-γ function, but their effects on IFN-γ signaling are unknown. Using a single-cell capture method, we isolated 19 IFN-γ–reactive monoclonal antibodies (mAbs) from patients with AIGAs. All displayed high-affinity (KD < 10−9 M) binding to IFN-γ, but only eight neutralized IFN-γ–STAT1 signaling and HLA-DR expression. Signal blockade and binding affinity were correlated and attributed to somatic hypermutations. Cross-competition assays identified three nonoverlapping binding sites (I–III) for AIGAs on IFN-γ. We found that site I mAb neutralized IFN-γ by blocking its binding to IFN-γR1. Site II and III mAbs bound the receptor-bound IFN-γ on the cell surface, abolishing IFN-γR1–IFN-γR2 heterodimerization and preventing downstream signaling. Site III mAbs mediated antibody-dependent cellular cytotoxicity, probably through antibody–IFN-γ complexes on cells. Pathogenic AIGAs underlie mycobacterial infections by the dual blockade of IFN-γ signaling and by eliminating IFN-γ–responsive cells.