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Abstract
Introduction Excessive neutrophilic airways inflammation is the central feature of bronchiectasis but little is known about the role of serum neutrophils in bronchiectasis. Lipid mediators derived from arachidonic acid such as Lipoxin (LX)A4 are known to regulate the inflammatory process and generate pro-inflammatory, anti-inflammatory and pro-resolving mediators. In this research work, we propose to describe the function of peripheral neutrophils in bronchiectasis and the effect of LXA4.
Methods Three study groups were included in this study when clinically stable: 6 healthy volunteers; 6 patients with mild bronchiectasis with a Bronchiectasis Severity Index (BSI) score 0–4; 6 with severe bronchiectasis (BSI scores >9). Freshly isolated peripheral neutrophils from the groups were treated with LXA4 or vehicle control and we assessed spontaneous neutrophil apoptosis at 20 hours, neutrophil activation, neutrophil degranulation, phagocytosis of GFP labelled Pseudomonas aeruginosa and expression of LXA4 receptor formyl peptide receptor (FPR)2.
Results In vehicle treated neutrophils, there was increased viability and less apoptosis in bronchiectasis patients compared to healthy volunteers; Figure 1. There was a significant increase in CD11b upregulation; p = 0.01 and CD62L shedding; p = 0.01 in bronchiectasis patients compared to healthy volunteers. There was a significant increase in neutrophil degranulation with myeloperoxidase (MPO) release, in bronchiectasis patients; p = 0.04. There was an increase in neutrophil phagocytosis of GFP labelled Pseudomonas aeruginosa by neutrophils from bronchiectasis patients, p = 0.03, compared to healthy volunteers; Figure1.
In LXA4 treated neutrophils, there was no effect of LXA4 on spontaneous neutrophil apoptosis. There was a significant reduction in n-formyl-methyl-leucyl-phenylalanine (fMLF)-induced CD11b upregulation and CD62L shedding by LXA4 in a dose dependent manner in all three groups. There was a significant reduction in cytochalasin-B and fMLF-induced activation of neutrophils and release of MPO, by LXA4 in all three groups. There was significant improvement in neutrophil phagocytosis of GFP labelled Pseudomonas aeruginosa in a dose dependent manner in all three groups. There was a statistically significant increase in FPR2 receptor expression in healthy volunteers compared to bronchiectasis patients when treated with LXA4 100nM, p = 0.03.
Conclusion Serum neutrophils in bronchiectasis are primed and activated compared to healthy volunteers. The pro-resolving mediator LXA4 stabilised the neutrophil whilst promoting neutrophil phagocytosis.
a. Statistically significant increase in the% of viable neutrophils and a decrease in apoptotic neutrophils in bronchiectasis; *p = 0.02, ***p = 0.0003, ****p < 0.001. b. Cytospin from a bronchiectasis patient after 20 hours apoptosis showing large numbers of viable neutrophils. c. Statistically significant increase in the% of phagocytosis in bronchiectasis patients at baseline and increase with Lipoxin in a dose dependent manner; *p = 0.02, **p = 0.004. d. Confocal image of phagocytosed GFP labelled Pseudomonas by neutrophil.