Prothrombotic antibody origin in COVID-19

Despite vaccine development, COVID-19 continues to cause significant morbidity and mortality, with thrombotic complications contributing to severe disease. We previously showed that a subset of hospitalized patients developed prothrombotic platelet-activating antibodies. Here, we used single-cell RNA sequencing of B and T cells, single B-cell V(D)J sequencing, and plasma cytokine and chemokine analysis to define immune signatures distinguishing patients who did (PEA+) or did not (PEA-) form these antibodies. While overall B-cell populations were comparable between groups, PEA+ patients showed robust clonal expansion within extrafollicular (EF) B-cell clusters, enriched for clones bearing structural signatures characteristic of prothrombotic platelet-activating antibodies. The expanded clones in PEA+patients exhibited upregulated IFNgamma signaling and inflammatory gene programs, reduced class switching, and inefficient somatic hypermutation, all supporting an EF B-cell response. In parallel, PEA+ patients exhibited substantial Th1-cell expansion with enrichment of IL-12 and other inflammatory pathways mirroring those observed in the patients' B cells. Plasma cytokine and chemokine analysis confirmed elevation of Th1-associated mediators, including IL-12, in PEA+patients. Together, these convergent findings provide compelling evidence for an immunologic axis whereby IFNgamma produced by IL-12-induced Th1 cells promotes an extrafollicular B-cell response that gives rise to prothrombotic platelet-activating antibodies in COVID-19.

尽管疫苗研发已取得进展，新型冠状病毒肺炎（COVID-19）仍持续造成大量发病与死亡，血栓性并发症（thrombotic complications）是重症病例的重要致病因素。我们此前的研究发现，部分住院患者体内会产生促血栓形成的血小板活化抗体（prothrombotic platelet-activating antibodies）。本研究通过对B细胞与T细胞开展单细胞RNA测序（single-cell RNA sequencing）、单细胞B细胞V(D)J测序（single B-cell V(D)J sequencing），并结合血浆细胞因子（cytokine）与趋化因子（chemokine）分析，明确了区分产生（PEA+）与不产生（PEA-）此类抗体的患者的免疫特征（immune signatures）。尽管两组患者的总体B细胞群体比例相近，但PEA+患者的滤泡外（extrafollicular, EF）B细胞簇内出现了显著的克隆扩增（clonal expansion），且扩增克隆富集有与促血栓形成血小板活化抗体结构特征相符的序列。PEA+患者体内的扩增克隆表现出干扰素-γ（IFNγ）信号通路与炎症基因程序的上调、类别转换（class switching）能力降低以及体细胞高频突变（somatic hypermutation）效率低下，上述特征均支持滤泡外B细胞应答的发生。与此同时，PEA+患者体内出现大量Th1细胞（Th1 cell）扩增，且富集有白细胞介素-12（IL-12）及其他与患者B细胞中观察到的通路特征一致的炎症通路。血浆细胞因子与趋化因子分析证实，PEA+患者体内与Th1细胞相关的介质（包括IL-12）水平升高。综上，这些协同一致的研究结果为一条免疫轴提供了有力证据：由IL-12诱导的Th1细胞产生的干扰素-γ可促进滤泡外B细胞应答，进而在COVID-19患者体内产生促血栓形成的血小板活化抗体。