Pseudomonas aeruginosa Elicits Sustained IL-1β Upregulation in Alveolar Macrophages from Lung Transplant Recipients

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Abstract
Background: Isolation of Pseudomonas aeruginosa ( PsA ) is associated with increased BAL (bronchoalveolar lavage) inflammation and lung allograft injury in lung transplant recipients (LTR). However, the effect of PsA on macrophage responses in this population is incompletely understood. We examined human alveolar macrophage (AM) responses to PsA and Pseudomonas dominant microbiome in healthy lung transplant recipients (LTR). Methods: We stimulated THP-1 derived macrophages (THP-1M) and human AM from LTR with different bacteria and LTR BAL derived microbiome characterized as Pseudomonas-dominant. Macrophage responses were assessed by high dimensional flow cytometry, including their intracellular production of cytokines (TNF-α, IL-6, IL-8, IL-1β, IL-10, IL-1RA, and TGF-β). Pharmacological inhibitors were utilized to evaluate the role of the inflammasome in PsA -macrophages interaction. Results: We observed upregulation of pro-inflammatory cytokines (TNF-α, IL-6, IL-8, IL-1β) following stimulation by PsA compared to other bacteria ( Staphylococcus aureus, Prevotella melaninogenica, Streptococcus pneumoniae ) in both THP-1 derived and LTR AM, predominated by IL-1β. IL-1β production from THP-1 was sustained after PsA stimulation for up to 96 hours and 48 hours in LTR AM. Treatment with the inflammasome inhibitor BAY11-7082 abrogated macrophage IL-1β and IL-18 production after PsA exposure. BAL Pseudom onas-dominant microbiota elicited an increased IL-1β, similar to PsA , an effect abrogated by the addition of antibiotics. Conclusion: PsA and PsA -dominant lung microbiota induce sustained IL-1β production in LTR AM. Pharmacological targeting of the inflammasome reduces PsA -macrophage-IL1β responses, underscoring their use in lung transplant recipients.

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