Effects of the circulating environment of COVID-19 on platelet and neutrophil behavior

Thromboinflammatory complications are well described sequalae of Coronavirus Disease 2019 (COVID-19), and there is evidence of both hyperreactive platelet and inflammatory neutrophil biology that contributes to the thromoinflammatory milieu. It has been demonstrated in other thromboinflammatory diseases that the circulating environment may affect cellular behavior, but what role this environment exerts on platelets and neutrophils in COVID-19 remains unknown. We tested the hypotheses that 1) plasma from COVID-19 patients can induce a prothrombotic platelet functional phenotype, and 2) contents released from platelets (platelet releasate) from COVID-19 patients can induce a proinflammatory neutrophil phenotype. We treated platelets with COVID-19 patient and disease control plasma and found that COVID-19 patient plasma promoted auto-aggregation, thereby reducing response to further stimulation ex-vivo. Neither disease condition increased the number of platelets adhered to a collagen and thromboplastin coated parallel plate flow chamber, but both markedly reduced platelet size. We treated healthy neutrophils with COVID-19 patient and disease control platelet releasate and found that COVID-19 patient platelet releasate increased myeloperoxidase-deoxyribonucleic acid complexes and induced changes to neutrophil gene expression. Together these results suggest aspects of the soluble environment of COVID-19 stimulate circulating platelets, and that the contents released from those platelets can elicit inflammatory neutrophil behavior independent of direct cellular contact. 5 control (COVID negative) patients and 5 COVID positive patients

血栓炎症并发症是2019冠状病毒病（COVID-19）已被充分报道的后遗症。现有研究证实，过度反应的血小板与促炎中性粒细胞的生物学特性共同参与了血栓炎症微环境的形成。已有研究在其他血栓炎症性疾病中发现，循环微环境可调控细胞行为，但该微环境对COVID-19患者体内血小板与中性粒细胞的具体作用仍未明确。本研究针对两项假说展开验证：其一，COVID-19患者血浆可诱导血小板产生促血栓形成的功能表型；其二，COVID-19患者血小板释放的内容物（platelet releasate）可诱导中性粒细胞产生促炎表型。我们分别用COVID-19患者血浆与疾病对照血浆处理血小板，结果显示COVID-19患者血浆可促进血小板自发聚集，进而降低其对外源性离体刺激的应答反应。两组血浆均未使黏附于胶原与凝血活酶包被平行板流动腔（parallel plate flow chamber）的血小板数量增加，但均显著缩小了血小板粒径。我们分别用COVID-19患者与疾病对照者的血小板释放物处理健康中性粒细胞，结果发现COVID-19患者的血小板释放物可增加髓过氧化物酶-脱氧核糖核酸复合物（myeloperoxidase-deoxyribonucleic acid complexes）的生成，并诱导中性粒细胞的基因表达发生改变。综合上述结果，本研究提示COVID-19患者体内可溶性微环境的相关组分可激活循环血小板，且此类血小板释放的内容物无需与中性粒细胞直接接触即可诱导其产生炎性行为。本研究共纳入5名COVID-19阴性对照受试者与5名COVID-19阳性患者。