Increased peripheral blood neutrophil activation phenotypes and NETosis in critically ill COVID-19 patients

Abstract

BackgroundIncreased inflammation is a hallmark of COVID-19, with pulmonary and systemic inflammation identified in multiple cohorts of patients. Definitive cellular and molecular pathways driving severe forms of this disease remain uncertain. Neutrophils, the most numerous leukocytes in blood circulation, can contribute to immunopathology in infections, inflammatory diseases and acute respiratory distress syndrome (ARDS), a primary cause of morbidity and mortality in COVID-19. Changes in multiple neutrophil functions and circulating cytokine levels over time during COVID-19 may help define disease severity and guide care and decision making.MethodsBlood was obtained serially from critically ill COVID-19 patients for 11 days. Neutrophil oxidative burst, neutrophil extracellular trap formation (NETosis), phagocytosis and cytokine levels were assessed ex vivo. Lung tissue was obtained immediately post-mortem for immunostaining.ResultsElevations in neutrophil-associated cytokines IL-8 and IL-6, and general inflammatory cytokines IP-10, GM-CSF, IL-1b, IL-10 and TNF, were identified in COVID-19 plasma both at the first measurement and at multiple timepoints across hospitalization (p < 0.0001). Neutrophils had exaggerated oxidative burst (p < 0.0001), NETosis (p < 0.0001) and phagocytosis (p < 0.0001) relative to controls. Increased NETosis correlated with both leukocytosis and neutrophilia. Neutrophils and NETs were identified within airways and alveoli in the lung parenchyma of 40% of SARS-CoV-2 infected lungs. While elevations in IL-8 and ANC correlated to COVID-19 disease severity, plasma IL-8 levels alone correlated with death.ConclusionsCirculating neutrophils in COVID-19 exhibit an activated phenotype with increased oxidative burst, NETosis and phagocytosis. Readily accessible and dynamic, plasma IL-8 and circulating neutrophil function may be potential COVID-19 disease biomarkers.

Altered fibrin clot structure contributes to thrombosis risk in severe COVID-19

“…NETs not only bind FXII but also serve as a potent endogenous inflammation-dependent inducer of FXII autoactivation, eventually propagating thrombosis 21,41 . Enhanced vascular NETosis along with impaired NET clearance were described in COVID-19 patients 35,42 . In line with these findings, several studies found an increase in NET components in COVID-19 plasma including cell-free DNA, myeloperoxidase-DNA complexes, neutrophil elastase-DNA complexes, and citrullinated histone H3 43,44 .…”

Translational suppression of SARS-COV-2 ORF8 protein mRNA as a Viable therapeutic target against COVID-19: Computational studies on potential roles of isolated compounds from Clerodendrum volubile leaves

“…This process is regarded as cytokine storm and has been implicated in the pathology and severity of COVID-19 and its mortality [ 9 , 10 ]. Oxidative bursts in neutrophils have also been implicated in the aggravation of cytokine storm and the pathology of COVID-19 and its complication [ [11] , [12] , [13] ]. Cytokine storm activates the macrophages and neutrophils to produce respiratory bursts which generates superoxides and hydrogen peroxide, thus leading to oxidative stress [ 11 ].…”

Altered neutrophil phenotype and function in non-ICU hospitalised COVID-19 patients correlated with disease severity

“…Our data suggests the energetics of the cells were not overtly compromised, as some “high energy-consuming” functions (such as migration [35]) were elevated. Of note, some of these changes have been described by authors studying COVID-19 before the widespread use of dexamethasone as standard of care [27, 36], suggesting our results are not a treatment effect.…”