Abstract
RationaleThe chemokine interleukin-8 is implicated in the development of bronchopulmonary dysplasia in preterm infants. The 77-amino acid isoform of interleukin-8 (interleukin-877) is a less potent chemoattractant than other shorter isoforms. Although interleukin-877 is abundant in the preterm circulation, its regulation in the preterm lung is unknown.ObjectivesTo study expression and processing of pulmonary interleukin-877 in preterm infants who did and did not develop bronchopulmonary dysplasia.MethodsTotal interleukin-8 and interleukin-877 were measured in bronchoalveolar lavage fluid from preterm infants by immunoassay. Neutrophil serine proteases were used to assess processing. Neutrophil chemotaxis assays and degranulation of neutrophil matrix metalloproteinase-9 were used to assess interleukin-8 function.Main ResultsPeak total interleukin-8 and interleukin-877 concentrations were increased in infants who developed bronchopulmonary dysplasia compared to those who did not. Shorter forms of interleukin-8 predominated in the preterm lung (96.3% No-bronchopulmonary dysplasia vs 97.1% bronchopulmonary dysplasia, p>0.05). Preterm bronchoalveolar lavage fluid significantly converted exogenously added interleukin-877 to shorter isoforms (p<0.001). Conversion was greater in bronchopulmonary dysplasia infants (p<0.05). This conversion was inhibited by α-1 antitrypsin and antithrombin III (p<0.01). Purified neutrophil serine proteases efficiently converted interleukin-877 to shorter isoforms in a time- and dose-dependent fashion; shorter interleukin-8 isoforms were primarily responsible for neutrophil chemotaxis (p<0.001). Conversion by proteinase-3 resulted in significantly increased interleukin-8 activity in vitro (p<0.01).ConclusionsShorter, potent, isoforms interleukin-8 predominate in the preterm lung, and are increased in infants developing bronchopulmonary dysplasia, due to conversion of interleukin-877 by neutrophil serine proteases and thrombin. Processing of interleukin-8 provides an attractive therapeutic target to prevent development of bronchopulmonary dysplasia.
Highlights
Persistent lung inflammation, in the form of a poorly resolved neutrophilia, is implicated in the pathogenesis of bronchopulmonary dysplasia (BPD) [1], which is a common disease of preterm infants [2, 3]
Peak total IL-8 concentration and corresponding IL-877 (No-BPD 144.3 pg/ml, 83.6–552.6 pg/ml vs BPD 2753 pg/ml, 140.1–5668 pg/ml; p50.03, Figure 1b) concentration in bronchoalveolar lavage fluid (BALF) were significantly higher in the BPD infants compared to No-BPD infants
IL-877 was a minor proportion of the total IL-8 in all of the samples, and there was no significant difference between the two groups (IL-877 in No-BPD median 2.9%, 1.3–5.3% vs BPD 2.3%, 1.5–3.0%; p50.39, Figure 1c); significant correlation was observed between total IL-8 expression and corresponding IL-877 concentration in preterm BALF (n522, Spearman r50.94, p,0.0001; Figure S3 in File S1)
Summary
Persistent lung inflammation, in the form of a poorly resolved neutrophilia, is implicated in the pathogenesis of bronchopulmonary dysplasia (BPD) [1], which is a common disease of preterm infants [2, 3]. IL-8 (CXCL-8) is an early response chemokine, which is a key chemoattractant for PMNs to sites of inflammation It is synthesised by a variety of cells including alveolar macrophages, endothelial cells, epithelial cells, fibroblasts etc. In-vitro, IL-8 seems to be the dominant CXC chemokine [5] produced by alveolar macrophages and accounts for most of the chemotactic activity on PMNs [6]. It has consistently been detected in increased concentration from epithelial lining fluid in lungs of ventilated preterm infants who later develop BPD [4, 7], and has been observed to increase before the peak of inflammatory cell influx [8]. Results from observational studies on IL-8 in the lungs of preterm infants suggests a key role in persistent neutrophil-driven inflammation, and consequent lung injury, observed in infants developing BPD [10]
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