CD55 upregulation in T cells of COVID-19 patients suppresses type-I interferon responses [bulkRNA-seq]

Complement overactivation, has been verified in COVID-19 patients. Complement regulatory proteins, including CD55, control complement overactivation thus eliminating complement deposition and cell lysis. We investigated complement regulatory protein expression in COVID-19 for potential deregulated expression patterns driving disease pathogenesis. Single-cell RNA-seq revealed increased PBMCs CD55 expression in severely and critically ill patients. This increase was also detected upon integrated subclustering analysis of monocyte, T cell and B cell populations. FACS analysis confirmed the significant upregulation of CD55 expression in CD4+ and CD8+ T cell and monocyte populations of severely and critically ill COVID-19 patients. This upregulation was associated with decreased expression of type-I IFN-stimulated genes (ISGs) in patients with severe and critical COVID-19, indicating a suppressor effect of CD55. Silencing of CD55 in T cells from COVID-19 severely ill patients in-vitro and sensitization with SARS-CoV-2 peptides resulted in significantly augmented expression of ISGs and a reversal of their expression to levels similar to control or higher. The present study uncovers, to the best of our knowledge, a novel regulatory effect of CD55 on type-I IFN responses of severely ill COVID-19 patients, thus indicating its contribution to COVID-19 pathogenesis, and identifies a novel mechanistic pathway in the COVID-19 immune response. Overall design: RNA sequencing of PBMCs from COVID-19 patients and healthy controls used for validation of gene expression data uncovered from scRNA-seq analysis.

补体过度激活已在新型冠状病毒肺炎（COVID-19）患者中得到验证。补体调节蛋白（包括CD55）可通过调控补体过度激活，进而消除补体沉积与细胞裂解效应。本研究针对新冠患者体内的补体调节蛋白表达情况展开探究，旨在挖掘驱动疾病发病机制的表达失调模式。
单细胞RNA测序（single-cell RNA-seq）结果显示，重症及危重症新冠患者的外周血单个核细胞（peripheral blood mononuclear cells, PBMCs）中CD55表达水平显著升高。通过对单核细胞、T细胞及B细胞群开展整合亚聚类分析，同样检测到了该表达上调现象。
流式细胞术（Fluorescence-Activated Cell Sorting, FACS）分析证实，重症与危重症新冠患者的CD4+ T细胞、CD8+ T细胞以及单核细胞群体中，CD55的表达均出现显著上调。
该表达上调现象与重症、危重症新冠患者体内I型干扰素刺激基因（type-I IFN-stimulated genes, ISGs）的表达降低存在关联，提示CD55具有免疫抑制效应。
体外实验中，我们对重症新冠患者的T细胞进行CD55基因沉默，并联合SARS-CoV-2肽段致敏，结果显示ISGs的表达水平显著增强，且其表达量逆转至与健康对照组相近甚至更高的水平。
据我们所知，本研究首次揭示了CD55对重症新冠患者I型干扰素应答的新型调控作用，明确了其在新冠发病机制中的贡献，并鉴定出新冠免疫应答中的一条全新分子机制通路。
整体实验设计：对新冠患者与健康对照者的外周血单个核细胞进行RNA测序，用于验证单细胞RNA测序分析所得到的基因表达数据。