Background
Although excessive neutrophil activation plays a pivotal role in hyperinflammatory complications in severe acute COVID-19, the role of neutrophils in the development of post-acute sequelae of SARS-CoV-2 (PASC) remains relatively unknown.
Methods
We utilized cross-sectional blood samples from individuals with pulmonary PASC [PPASC, n=57] and two control groups (those infected with no residual symptoms [RC, n=36] and those with no history of SARS-CoV-2 infection [HC, n=26]). Soluble markers of neutrophil activation, neutrophil extracellular traps (NETs), and inflammation were analyzed in plasma samples. A subset of the study samples was used for bulk RNA sequencing (RNA-seq) of neutrophils to identify differences in gene expression between PPASC and controls. To assess neutrophil activation in the lungs after COVID-19 recovery, we used lung samples from SARS-CoV-2-infected K18-hACE2 mice that survived 30 days post-infection (dpi). Neutrophil infiltration, activation status, and NET formation were evaluated, and bulk RNA-seq was performed on lung tissues.
Results
RNA-seq of neutrophils revealed enrichment in pathways associated with neutrophil activation (neutrophil degranulation and NET signaling pathway) and coagulation/thrombosis (Fig 1). Plasma levels of NET markers, such as dsDNA and CitH3, and inflammatory cytokines, TNF-α, IL-1β, IL-10, and IFN-γ were increased in the PPASC group compared with RC and HC groups. We found that sustained NET formation within the lung tissue was detected in survivor mice. Further, RNA-seq analysis of lung revealed significant enrichment of NET formation and necroptosis pathways in survivor mice compared with uninfected mice.
Conclusions
These findings suggest that persistent neutrophil dysfunction contributes to inflammatory and thrombotic gene signatures in pulmonary PASC, highlighting that targeting neutrophil activation may offer therapeutic benefit for pulmonary sequelae of PASC.
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