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

Abstract

<h3>Purpose</h3> Clinical infection or colonization of the lung, specifically with <i>Pseudomonas aeruginosa</i> (<i>PsA</i>), is associated with increased incidence of lung allograft injury in lung transplant recipients (LTRs) and with an increase in BAL (bronchoalveolar lavage) pro-inflammatory cytokines. However, the effect of bacterial colonization on sustained innate immune activation and the mechanisms involved are not well understood. We sought to determine the mechanisms underlying persistent pro-inflammatory alveolar macrophage response to <i>PsA</i> stimulation. <h3>Methods</h3> We stimulated THP-1 derived macrophages and BAL-derived alveolar macrophages from LTRs with bacteria representative of infectious pathogens and upper respiratory commensals for up to 96 hours. Using a high dimensional flow cytometry panel, we evaluated macrophage responses including expression of costimulatory molecules (CD80, CD86, CD40); co-inhibitor molecules (B7-H1), pro-inflammatory cytokines (TNF-α, IL-6, IL-8, IL-1β), and anti-inflammatory mediators (IL-10, IL-1RA, and TGF-β). <h3>Results</h3> We observed an upregulation of pro-inflammatory cytokines (TNF-α, IL-6, IL-8, IL-1β) following stimulation by <i>PsA</i> compared to stimulation with other pathogens (<i>Staphylococcus aureus</i>) and oral-commensal bacteria (<i>Prevotella melaninogenica, Streptococcus pneumoniae</i>) in THP-1 macrophages. IL-1 β elevations were sustained for 96 hours after <i>PsA</i> exposure. Alveolar macrophages from LTRs undergoing surveillance bronchoscopy demonstrated elevated levels of IL-6 and showed a similar IL-1β responses to that observed in THP-1 macrophages when exposed to <i>PsA</i>. <h3>Conclusion</h3> <i>PsA</i> induces a sustained increase in IL-1β production in alveolar macrophages from LTRs. Given the prior described role of IL-1β in lung allograft injury and CLAD, further investigations are ongoing to determine clinical correlates of allograft injury with <i>PsA</i> and IL-1β.