Free DNA in Cystic Fibrosis Airway Fluids Correlates with Airflow Obstruction

Abstract

Chronic obstructive lung disease determines morbidity and mortality of patients with cystic fibrosis (CF). CF airways are characterized by a nonresolving neutrophilic inflammation. After pathogen contact or prolonged activation, neutrophils release DNA fibres decorated with antimicrobial proteins, forming neutrophil extracellular traps (NETs). NETs have been described to act in a beneficial way for innate host defense by bactericidal, fungicidal, and virucidal actions. On the other hand, excessive NET formation has been linked to the pathogenesis of autoinflammatory and autoimmune disease conditions. We quantified free DNA structures characteristic of NETs in airway fluids of CF patients and a mouse model with CF-like lung disease. Free DNA levels correlated with airflow obstruction, fungal colonization, and CXC chemokine levels in CF patients and CF-like mice. When viewed in combination, our results demonstrate that neutrophilic inflammation in CF airways is associated with abundant free DNA characteristic for NETosis, and suggest that free DNA may be implicated in lung function decline in patients with CF.

Neutrophils in cystic fibrosis

“…Neutrophils in CF airways expressed moderate levels of the LPS receptor TLR4, but remarkably high amounts of TLR5, involved in recognition of bacterial flagellin (Koller et al, 2008(Koller et al, , 2009). Levels of free DNA in the CF airway microenvironment were found to correlate with lung function (Marcos et al, 2015). However, besides NETosis-derived DNA other sources of extracellular DNA (such as neutrophil necrosis) probably also contribute to this finding.…”

“…Also, several studies have now provided evidence for NETosis or NETosis-like structures in inflammatory lung diseases (Cheng and Palaniyar, 2013). Regarding CF, separate investigations were performed to further corroborate the concept of NET formation in CF airway fluids (Papayannopoulos et al, 2011;Manzenreiter et al, 2012;Dwyer et al, 2014;Rahman and Gadjeva, 2014;Marcos et al, 2015). Young and coworkers demonstrated that peripheral blood neutrophils derived from CF patients did not show an altered NETosis compared to healthy control neutrophils (Young et al, 2011).…”

The role for neutrophil extracellular traps in cystic fibrosis autoimmunity

“…Given the abundance of nucleic acids in NETs, the induction of autoantibodies by NETosis is likely to be facilitated by TLR 7/9-mediated B cell activation (27). While formation of NETs in the CF lung has been appreciated as both an antibacterial defense mechanism and a contributor to proteaseinduced lung damage (10,(28)(29)(30), the role of NETosis in CF autoimmunity has not been studied.…”

NETs in pneumonia: is just enough the right amount?

“…An additional consideration is how NETs may interact with other parts of the immune system and how this may have a bearing on disease processes. This is further underlined by the finding that levels of NETs are inversely correlated to lung function in cystic fibrosis (CF) [11], and disease severity in chronic obstructive pulmonary disease [12]. A major caveat to all of these studies is that they don't differentiate increased NET production from decreased NET clearance, which may be a crucial missing piece in the puzzle.…”