Pregnancy Zone Protein is Associated with Airway Infection, Neutrophil Extracellular Trap Formation and Disease Severity in Bronchiectasis.

BACKGROUND: Pregnancy zone protein (PZP) is a broad-spectrum immunosuppressive protein believed to suppress T-cell function during pregnancy to prevent fetal rejection. It has not previously been reported in the airway.

OBJECTIVES: To characterise PZP in the bronchiectasis airway including its relationship with disease severity.

METHODS: Label free liquid chromatography/mass spectrometry was performed for sputum protein profiling between HRCT confirmed bronchiectasis patients with and without P. aeruginosa infection. Sputum and serum PZP was measured by validated ELISA. Airway infection status was established by culture and 16S rRNA sequencing. Immunofluorescence, ELISA and electron microscopy was used to identify the cellular source of PZP in neutrophils treated with multiple stimuli.

RESULTS: Elevated PZP was identified by LC/MS as being associated with P. aeruginosa infection. In a validation study of 124 patients, sputum, but not serum levels of PZP were significantly associated with the bronchiectasis severity index, the frequency of exacerbations and symptoms. Airway infection with Proteobacteria such as P. aeruginosa was associated with higher levels of PZP. PZP in sputum was directly related to airway bacterial load. Neutrophils induced to form neutrophil extracellular traps (NETs) with phorbol myristate acetate (PMA) released high concentrations of PZP in-vitro, and fluorescence microscopy confirmed the presence of PZP in NETs, while fluorescence and electron microscopy localised PZP to the cytoplasm and nuclei of neutrophils. Effective antibiotic therapy reduced sputum PZP.

CONCLUSION: PZP is released into NETs. We report a novel link between airway infection, NET formation and disease severity in bronchiectasis during chronic airway inflammation.