Increased Peripheral Blood Neutrophil Activation Phenotypes and Neutrophil Extracellular Trap Formation in Critically Ill Coronavirus Disease 2019 (COVID-19) Patients: A Case Series and Review of the Literature

Abstract

Background Increased inflammation has been well defined in COVID-19, while definitive pathways driving severe forms of this disease remain uncertain. Neutrophils are known to 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 neutrophil function in COVID-19 may give insight into disease pathogenesis and identify therapeutic targets. Methods Blood was obtained serially from critically ill COVID-19 patients for eleven days. Neutrophil extracellular trap formation (NETosis), oxidative burst, phagocytosis and cytokine levels were assessed. Lung tissue was obtained immediately post-mortem for immunostaining. Pubmed searches for neutrophils, lung and COVID-19 yielded ten peer-reviewed research articles in English. Results Elevations 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 both at first measurement and across hospitalization (p<0.0001). COVID neutrophils had exaggerated oxidative burst (p<0.0001), NETosis (p<0.0001) and phagocytosis (p<0.0001) relative to controls. Increased NETosis correlated with leukocytosis and neutrophilia, and neutrophils and NETs were identified within airways and alveoli in lung parenchyma of 40% of SARS-CoV-2 infected lungs available for examination (2 out of 5). While elevations in IL-8 and ANC correlated with disease severity, plasma IL-8 levels alone correlated with death. Conclusions Literature to date demonstrates compelling evidence of increased neutrophils in the circulation and lungs of COVID-19 patients. importantly, neutrophil quantity and activation correlates with severity of disease. Similarly, our data shows that circulating neutrophils in COVID-19 exhibit an activated phenotype with enhanced NETosis and oxidative burst.

Longitudinal characterization of circulating neutrophils uncovers distinct phenotypes associated with disease severity in hospitalized COVID-19 patients

“…While IgA-induced NETosis would have a beneficial component in mucosal linings by preventing viral entry, it would be ineffective or even harmful in other locations, as neutrophils in the bloodstream perform their most protective phagocytic functions in response to IgG antibodies. Many studies have shown that NETosis is a defining feature of severe disease 49,72,73 , and here, we demonstrate that NETosis can be strongly induced by IgA antibodies, which may be the dominant effector function occurring in patients with high ratios of IgA1-to-IgG1 antibodies in plasma. Several potential therapeutics have been suggested for use in autoimmune disease contexts aimed at inhibiting NETosis such as PAD4 inhibition or administration of recombinant human thrombomodulin 74 , and similar strategies could be applied to NETosis in the context of severe COVID-19.…”

Neutrophil Extracellular Trap Formation Potential Correlates with Lung Disease Severity in COVID-19 Patients

“…COVID-19 patients are reported to have increased serum IL-8 levels that correlate with disease severity, but the cellular source(s) have not been definitively identified [ 20 , 38 , 39 ]. Neutrophils are a source of IL-8 production, and neutrophil IL-8 production and release may result in amplification of systemic inflammation.…”

“…Several studies have demonstrated the presence of NET fragments or cell-free DNA in the plasma of COVID-19 patients [14][15][16][17], and post-mortem analysis reveals the presence of NETs in lung tissue of COVID-19 patients [17][18][19]. An elevation in cytokines, including IL-8, has also been observed in the plasma of COVID-19 patients [20], but the cellular source is not clear. Neutrophil elastase has been implicated in the pathogenesis of lung disease, and elastase inhibitors have been used in clinical trials with mixed results [9,[21][22][23][24].…”

Dexmedetomidine does not directly inhibit neutrophil extracellular trap production

“…Our research group has a longstanding interest in the biology and pathobiology of NETs in animal models of infectious diseases such as necrotizing fasciitis 10 and bacterial pneumonia 11 , and recently we studied NET phenotypes in critically ill patients with COVID-19 12 . In parallel, we have examined how NETosis is modulated by common medications including statins 13 , tamoxifen 14 , desferoxamine 15 , and propofol 16 .…”