Pseudomonas aeruginosa Induced Airway Epithelial Injury Drives Fibroblast Activation: A Mechanism in Chronic Lung Allograft Dysfunction.

Bacterial infections after lung transplantation cause airway epithelial injury and are associated with an increased risk of developing bronchiolitis obliterans syndrome. The damaged epithelium is a source of alarmins that activate the innate immune system, yet their ability to activate fibroblasts in the development of bronchiolitis obliterans syndrome has not been evaluated. Two epithelial alarmins were measured longitudinally in bronchoalveolar lavages from lung transplant recipients who developed bronchiolitis obliterans syndrome and were compared to stable controls. In addition, conditioned media from human airway epithelial cells infected with Pseudomonas aeruginosa was applied to lung fibroblasts and inflammatory responses were determined. Interleukin-1 alpha (IL-1α) was increased in bronchoalveolar lavage of lung transplant recipients growing P. aeruginosa (11.5 [5.4-21.8] vs. 2.8 [0.9-9.4] pg/mL, p < 0.01) and was significantly elevated within 3 months of developing bronchiolitis obliterans syndrome (8.3 [1.4-25.1] vs. 3.6 [0.6-17.1] pg/mL, p < 0.01), whereas high mobility group protein B1 remained unchanged. IL-1α positively correlated with elevated bronchoalveolar lavage IL-8 levels (r(2)  = 0.6095, p < 0.0001) and neutrophil percentage (r(2)  = 0.25, p = 0.01). Conditioned media from P. aeruginosa infected epithelial cells induced a potent pro-inflammatory phenotype in fibroblasts via an IL-1α/IL-1R-dependent signaling pathway. In conclusion, we propose that IL-1α may be a novel therapeutic target to limit Pseudomonas associated allograft injury after lung transplantation.

IL-1α released from damaged epithelial cells is sufficient and essential to trigger inflammatory responses in human lung fibroblasts.

Activation of the innate immune system plays a key role in exacerbations of chronic lung disease, yet the potential role of lung fibroblasts in innate immunity and the identity of epithelial danger signals (alarmins) that may contribute to this process are unclear. The objective of the study was to identify lung epithelial-derived alarmins released during endoplasmic reticulum stress (ER stress) and oxidative stress and evaluate their potential to induce innate immune responses in lung fibroblasts. We found that treatment of primary human lung fibroblasts (PHLFs) with conditioned media from damaged lung epithelial cells significantly upregulated interleukin IL-6, IL-8, monocyte chemotactic protein-1, and granulocyte macrophage colony-stimulating factor expression (P<0.05). This effect was reduced with anti-IL-1α or IL-1Ra but not anti-IL-1ß antibody. Costimulation with a Toll-like receptor 3 ligand, polyinosinic-polycytidylic acid (poly I:C), significantly accentuated the IL-1α-induced inflammatory phenotype in PHLFs, and this effect was blocked with inhibitor of nuclear factor kappa-B kinase subunit beta and TGFß-activated kinase-1 inhibitors. Finally, Il1r1-/- and Il1a-/- mice exhibit reduced bronchoalveolar lavage (BAL) neutrophilia and collagen deposition in response to bleomycin treatment. We conclude that IL-1α plays a pivotal role in triggering proinflammatory responses in fibroblasts and this process is accentuated in the presence of double-stranded RNA. This mechanism may be important in the repeated cycles of injury and exacerbation in chronic lung disease.