Background

Immunothrombosis is increased in severe COVID-19 and potentially involved in its pathogenesis but the mechanisms explaining its regulation are unknown. We hypothesized that decreased DNase activity could be associated with increased NETosis and clinical worsening in COVID-19 patients. Our objectives were to compare the balance between NETs biomarkers and DNase activity according to the severity of COVID-19 and to study the mechanisms responsible for the imbalance between NETosis and DNase activity.

Methods

Biological samples were collected from the COLCOV19-BX study for inpatients and the COVERAGE trial (no treatment arm) for outpatients. We studied 93 non-severe, 15 severe and 37 critical COVID-19 patients.

Results

Markers of NETs (MPO-DNA, H3Cit, H3cit-DNA) were higher in the most severe patients. DNase activity was lower and the balance between NET markers and DNase activity was impaired in the most severe patients. We observed a decrease in the amount of circulating DNase1 and DNase1L3 without mutations in the DNase1 and DNase1L3 genes and a quantitative defect of plasmacytoid dendritic cells (pDC), the main cells expressing DNase 1L3, in critical patients. Besides, analysis of public single cell RNAseq data revealed that pDC from COVID-19 patients express less DNase1L3.

Conclusion

Severe and critical COVID-19 were associated with an imbalance between NETs and DNase activity with a defect in the amount of DNase 1 and DNase1L3. DNase1L3 deficiency could be explained by a quantitative defect of pDC. Early identification of patients with NETosis imbalance could allow targeted therapies to prevent clinical worsening, such as DNase administration.