Background: High levels of circulating neutrophil extracellular traps (NETs) are associated with a poor prognosis in influenza A infection. It remains unclear whether NETs in the plasma or bronchoalveolar lavage fluid (BALF) can predict clinical outcomes in influenza.
Methods: One hundred eighteen patients who were diagnosed with H1N1 influenza in 2017-2018 were recruited. NETs were assessed in plasma and BALF samples by quantifying cell-free DNA (cfDNA) and protein-DNA complexes. Predictions of severe illness and 60-day mortality were analyzed with receiver operating characteristic curves.
Results: The NET levels were significantly elevated in the BALF and contributed to the pathology of lungs, yet it was not associated with disease severity or mortality in patients severely infected with H1N1. Plasma NET levels were significantly increased in the patients with severe influenza and positively correlated with the oxygen index and sequential organ failure assessment scores. High levels of plasma cfDNA (> 286.6 ng/ml) or histone-bound DNA (> 9.4 ng/ml) discriminated severe influenza from mild, and even higher levels of cfDNA (> 306.3 ng/ml) or histone-bound DNA (> 23.1 ng/ml) predicted fatal outcomes in severely ill patients.
Conclusions: The cfDNA and histone-bound DNA in plasma represent early predictive biomarkers for the prognosis of influenza.