Interleukin-1α Induced Interleukin-8 Production in Human Airway Epithelial Cells Pretreated With Azithromycin: A Possible Mechanism for Neutrophilic BOS?

Long term survival after lung transplantation is hampered by chronic lung allograft dysfunction (CLAD). Patients with high broncho-alveolar lavage (BAL)-neutrophilia may improve with azithromycin therapy. However, BAL neutrophilia can re-develop despite azithromycin, mostly leading to progressive decline in FEV1 and hence Bronchiolitis Obliterans Syndrome (BOS). Neutrophilic BOS is a possible phenotype of CLAD of which the mechanism behind the inflammation is unknown, but previous evidence showed that it is IL-17 independent. Recently Suwara et al. (2014) demonstrated an upregulation of IL 1α and IL-8 in BAL of neutrophilic BOS patients compared to controls.The aim was to investigate the involvement of IL-1α as inducer of the neutrophil chemo-attractant IL-8 to explain neutrophilic BOS, despite azithromycin treatment. Lung bronchial epithelial cells (16HBE) cultured in DMEM-F12 medium were stimulated for 24 hours with 10ng/mL IL-1α. Azithromycin or dexamethasone were added 30 min prior to IL-1α stimulation in different concentrations. After 24 hours, cell supernatant was collected and tested for IL-8 with sandwich ELISA. These experiments were repeated 3 times with each time 6 replicates. IL-1α stimulated 16HBE to produce IL-8. This IL-8 production could only be partially inhibited by azithromycin (Figure 1 A). Dexamethasone on the other hand, was able to completely inhibit the IL-8 production (Figure 1 B). While steroids are able to fully inhibit the IL-8 production by lung epithelial cells after IL-1α stimulation, azithromycin does not. This correlates with the clinical situation in which patients benefit from treatment with dexamethasone and not with azithromycin. IL-1α induced IL-8 production could be a possible working mechanism for neutrophilic BOS. Therefore inhibiting this pathway seems a plausible new therapeutic strategy.