Pseudomonas-Macrophage IL-1β Interactions in Lung Transplant Recipients

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The objectives of this NRSA individual fellowship are to 1) facilitate the development of research skills necessary for the applicant to become an effective and independent scientist and 2) investigate the mechanisms behind Pseudomonas aeruginosa-induced interleukin-1 beta (IL-1β) production in lung transplantation. Lung transplantation is a life-extending treatment for individuals with end-stage lung diseases; however, long-term outcomes are limited by allograft injury and chronic lung allograft dysfunction (CLAD). While CLAD is defined as a clinical diagnosis with median onset several years after transplantation, the antecedent risk factors may occur months or years prior to diagnosis, supporting a hypothesis that early inflammatory mechanisms could represent important triggers for lung inflammation and injury. Increased bacterial burden, decreased bacterial diversity, and prominence of P. aeruginosa are associated with worsening lung function, graft failure, and CLAD through pathogen-driven inflammatory triggers and impaired innate responses impacting bacterial clearance. The applicant has preliminary data demonstrating that P. aeruginosa upregulates sustained IL-1β production in lung transplant recipient-derived alveolar macrophages compared to other common upper respiratory tract bacteria. Elevated IL-1β has been associated with a decline in lung function and lung inflammation, and chronic lung injury, but few studies have examined the role of pathogen-driven inflammatory triggers on human activation of alveolar macrophage innate immune responses in lung transplantation. This proposal focuses on the mechanisms underlying the interaction between the lung microbiota and its innate sensing by macrophages to address this knowledge gap. We hypothesized that the lung microbiome, particularly those dominated by P. aeruginosa, following transplantation mediates sustained alveolar macrophage proinflammatory responses. To assess the effects of the lung microbiome on macrophages, we used a novel method to isolate lung microbiota from lung transplant recipients for stimulation of macrophages. This proposal uses two approaches to evaluate the impact of P. aeruginosa and Pseudomonas-dominant lung microbiota on immune activation and inflammation: 1) focusing on IL-1β production through activation of the inflammasome using specific canonical sensor proteins and 2) focusing on macrophage immunophenotype. Rigorous immunophenotyping and advanced bioinformatic analysis will be used to elucidate the relationship between P. aeruginosa and inflammasome-activated macrophage IL-1β production in lung transplant recipients. This proposal will add a novel understanding of cellular mechanisms linking microbial lung populations to aberrant innate immune activation, which is critical to developing future therapeutic targets and preventing immune-mediated lung injury. This proposal will provide a rich opportunity for the applicant to establish the laboratory and critical thinking skills necessary for a successful research career.