Dabie bandavirus (severe fever with thrombocytopenia syndrome virus [SFTSV]) induces an immunopathogenic disease with a high fatality rate; however, the mechanisms underlying its clinical manifestations are largely unknown. In this study, we applied targeted proteomics and single-cell transcriptomics to examine the differential immune landscape in SFTS patient blood. Serum immunoprofiling identified low-risk and high-risk clusters of SFTS patients based on inflammatory cytokine levels, which corresponded to disease severity. Single-cell transcriptomic analysis of SFTS patient peripheral blood mononuclear cells (PBMCs) at different infection stages showed pronounced expansion of B cells with alterations in B-cell subsets in fatal cases. Furthermore, plasma cells in which the interferon (IFN) pathway is downregulated were identified as the primary reservoir of SFTSV replication. This study identified not only the molecular signatures of serum inflammatory cytokines and B-cell lineage populations in SFTSV-induced fatalities but also plasma cells as the viral reservoir. Thus, this suggests that altered B-cell function is linked to lethality in SFTSV infections.IMPORTANCE SFTSV is an emerging virus discovered in China in 2009; it has since spread to other countries in East Asia. Although the fatality rates of SFTSV infection range from 5.3% to as high as 27%, the mechanisms underlying clinical manifestations are largely unknown. In this study, we demonstrated that SFTSV infection in fatal cases caused an excessive inflammatory response through high induction of proinflammatory cytokines and chemokines and the aberrant inactivation of adaptive immune responses. Furthermore, single-cell transcriptome sequencing (RNA-seq) analysis of SFTS patient PBMCs revealed that SFTSV targets the B-cell lineage population, especially plasma cells, as the potential viral reservoir in patients for whom the infection is fatal. Thus, SFTSV infection may inhibit high-affinity antibody maturation and secretion of plasma B cells, suppressing neutralizing antibody production and thereby allowing significant virus replication and subsequent fatality.

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乐备实是国内专注于提供高质量蛋白检测以及组学分析服务的实验服务专家，自2018年成立以来，乐备实不断寻求突破，公司的服务技术平台已扩展到单细胞测序、空间多组学、流式检测、超敏电化学发光、Luminex多因子检测、抗体芯片、PCR Array、ELISA、Elispot、PLA蛋白互作、多色免疫组化、DSP空间多组学等30多个，建立起了一套涵盖基因、蛋白、细胞以及组织水平实验的完整检测体系。

 
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