Serum anti-PAD4 autoantibodies are present in cystic fibrosis children and increase with age and lung disease severity

Abstract

Cystic fibrosis (CF) lung disease begins early in childhood and is characterized by neutrophilic inflammation of the airways. Neutrophil extracellular traps (NETs) represent one mechanism by which neutrophils contribute to lung damage. The enzyme peptidylarginine deiminase 4 (PAD4) is required for NET formation. Our overall concept is that NET formation delivers PAD4 outside the neutrophil resulting in autoantibody generation, and this autoimmunity may be a novel mechanism contributing to CF lung disease progression. The aim of this study was to investigate clinical predictors of serum anti-PAD4 autoantibody (PAD4 Ab) levels in CF subjects with a wide range of ages from early childhood through middle age. We measured PAD4 Ab levels in sera from 104 CF subjects. PAD4 Abs were detectable among CF children as young as one year of age and elevated compared to paediatric healthy controls. PAD4 Ab levels increased significantly with age (r = 0.584, p <.001) and correlated with lower lung function (r = −0.481, n = 99, p <.001). PAD4 Abs were elevated in subjects with chronic Pseudomonas aeruginosa airways infection (p <.001), but not with other key clinical CF co-variates including sex, CFTR genotype, sweat chloride, pancreatic enzyme use, nutritional status, recent pulmonary exacerbations, Staphylococcus aureus, or CF-related diabetes. PAD4 Ab levels were also correlated with serum anti-double-stranded DNA IgA autoantibodies, which have similarly been shown to be elevated in CF subjects and associated with lung damage. In multivariable analysis, age and lung function remained correlated with PAD4 Ab levels. In summary, we describe novel findings of anti-PAD4 autoantibodies in CF that are present early in childhood, increase over time with age, and correlate with lung disease severity. Autoimmunity to antigens extruded by NETs appears to be an early event in CF lung disease, and airway autoimmunity related to NET formation is a potential mechanism of lung disease progression in CF.

Highlights

• Serum anti-PAD4 autoantibodies are detected in paediatric CF serum and are elevated compared to healthy paediatric controls

• Anti-PAD4 autoantibodies increase with age

• Anti-PAD4 autoantibodies correlate with lower lung function, Pseudomonas aeruginosa airway infection and anti-dsDNA IgA autoantibodies, but not with other key clinical CF co-variates

• Age and lung function remain correlated with anti-PAD4 autoantibodies in multivariable analysis

Keywords:

• Cystic fibrosis
• autoimmunity
• autoantibody
• neutrophils
• neutrophil extracellular traps

Acknowledgements

Human subject samples were provided by the CF Biospecimen Repository at the Children’s Healthcare of Atlanta and Emory University CF Discovery Core. We would like to thank Chris Driggers and Akele Carter for collecting and verifying clinical data for the CF subjects in this study.

Disclosure statement

R.W.L. reports serving on advisory boards for Vertex Pharmaceuticals Incorporated, outside of the submitted work. All other authors report no conflicts of interest.

Additional information

Funding

This work was supported by grants provided by the Cystic Fibrosis Foundation [grant ID: 438903, to B.R. and RDP Centre McCart15R0 to A.S.], the National Institutes of Health [R21 AI130504-01 and 5R01HL136707 to B.R.]. This project was also supported by the National Centre for Advancing Translational Sciences of the National Institutes of Health under Award Number UL1TR002378 to B.R. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.