A persistent neutrophil-associated immune signature characterizes post-COVID-19 pulmonary sequelae.

Interstitial lung disease and associated fibrosis occur in a proportion of individuals who have recovered from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection through unknown mechanisms. We studied individuals with severe coronavirus disease 2019 (COVID-19) after recovery from acute illness. Individuals with evidence of interstitial lung changes at 3 to 6 months after recovery had an up-regulated neutrophil-associated immune signature including increased chemokines, proteases, and markers of neutrophil extracellular traps that were detectable in the blood. Similar pathways were enriched in the upper airway with a concomitant increase in antiviral type I interferon signaling. Interaction analysis of the peripheral phosphoproteome identified enriched kinases critical for neutrophil inflammatory pathways. Evaluation of these individuals at 12 months after recovery indicated that a subset of the individuals had not yet achieved full normalization of radiological and functional changes. These data provide insight into mechanisms driving development of pulmonary sequelae during and after COVID-19 and provide a rational basis for development of targeted approaches to prevent long-term complications.

NETosis and Nucleosome Biomarkers in Septic Shock and Critical COVID-19 Patients: An Observational Study.

Background: Neutrophil extracellular traps' (NETs') formation is a mechanism of defense that neutrophils deploy as an alternative to phagocytosis, to constrain the spread of microorganisms. Aim: The aim was to evaluate biomarkers of NETs' formation in a patient cohort admitted to intensive care unit (ICU) due to infection. Methods: Forty-six septic shock patients, 22 critical COVID-19 patients and 48 matched control subjects were recruited. Intact nucleosomes containing histone 3.1 (Nu.H3.1), or citrullinated histone H3R8 (Nu.Cit-H3R8), free citrullinated histone (Cit-H3), neutrophil elastase (NE) and myeloperoxidase (MPO) were measured. Results: Significant differences in Nu.H3.1 and NE levels were observed between septic shock and critical COVID-19 subjects as well as with controls (p-values < 0.05). The normalization of nucleosome levels according to the neutrophil count improved the discrimination between septic shock and critical COVID-19 patients. The ratio of Nu.Cit-H3R8 to Nu.H3.1 allowed the determination of nucleosome citrullination degree, presumably by PAD4. Conclusions: H3.1 and Cit-H3R8 nucleosomes appear to be interesting markers of global cell death and neutrophil activation when combined. Nu.H3.1 permits the evaluation of disease severity and differs between septic shock and critical COVID-19 patients, reflecting two distinct potential pathological processes in these conditions.

Circulating Nucleosomes as Potential Markers to Monitor COVID-19 Disease Progression.

The severity of coronavirus disease 2019 (COVID-19) varies significantly with cases spanning from asymptomatic to lethal with a subset of individuals developing Severe Acute Respiratory Syndrome (SARS) and death from respiratory failure. To determine whether global nucleosome and citrullinated nucleosome levels were elevated in COVID-19 patients, we tested two independent cohorts of COVID-19 positive patients with quantitative nucleosome immunoassays and found that nucleosomes were highly elevated in plasma of COVID-19 patients with a severe course of the disease relative to healthy controls and that both histone 3.1 variant and citrullinated nucleosomes increase with disease severity. Elevated citrullination of circulating nucleosomes is indicative of neutrophil extracellular trap formation, neutrophil activation and NETosis in severely affected individuals. Importantly, using hospital setting (outpatient, inpatient or ICU) as a proxy for disease severity, nucleosome levels increased with disease severity and may serve as a guiding biomarker for treatment. Owing to the limited availability of mechanical ventilators and extracorporal membrane oxygenation (ECMO) equipment, there is an urgent need for effective tools to rapidly assess disease severity and guide treatment selection. Based on our studies of two independent cohorts of COVID-19 patients from Belgium and Germany, we suggest further investigation of circulating nucleosomes and citrullination as biomarkers for clinical triage, treatment allocation and clinical drug discovery.