REGIONAL INFECTION AND INFLAMMATION IN CYSTIC FIBROSIS: A PILOT STUDY WITH LUNG EXPLANTS AND A NOVEL HISTOPATHOLOGY GRADING SYSTEM

Abstract

SESSION TITLE: Genetic and Developmental Disorders Posters SESSION TYPE: Original Investigation Posters PRESENTED ON: October 18-21, 2020 PURPOSE: The objective of this study was to use lung explants to determine the influence of nonmucoid and mucoid Pseudomonas aeruginosa (P.a.) variants on lobar inflammation and tissue damage in cystic fibrosis (CF). METHODS: We obtained three lung explants from adult CF patients undergoing lung transplantation. 1cm^3 superficial (parenchymal) and deep (airway) biopsies were obtained from all lung lobes in each explant (n=35 biopsies). Each biopsy was split into two fractions. One was homogenized to be plated on P.a.-isolation media (for growth of nonmucoid/mucoid P.a.) and also applied to a multiplex cytokine array. The other tissue fraction was formalin-fixed and prepared for hematoxylin and eosin (H&E) staining. A pathologist blindly assessed H&E slides for five indicators of tissue damage via a novel histopathology scoring scheme for CF lung tissue. RESULTS: All biopsies were categorized as infected with no P.a., nonmucoid P.a. only, mucoid P.a. only, or mixed mucoid and nonmucoid P.a. Mucoid and nonmucoid variants were distributed throughout the CF lung explants, without preference for specific lobes. Independent of infection, there were no statistically significant differences in inflammatory cytokines or histopathology among all lung lobes. However, mucoid P.a. infection, in single- or mixed-variant populations, was associated with greater concentrations of IL-1β, TNF-α, and IFN-γ compared to nonmucoid P.a. infection (p<0.01). Additionally, as mucoid P.a. percentage increased within a mixed-variant infection, the concentrations of all pro-inflammatory cytokines tested also increased: IL-1β, TNF-α, IL-6, IL-8, and IFN-γ (p<0.05). Despite the association between mucoid P.a. infection and cytokine concentrations, there was no correlation between P.a. variants and histopathology in this cohort. CONCLUSIONS: In CF lung explants, there were no differences in inflammation or tissue damage among lung lobes. Independent of lobe, mucoid P.a. infection was associated with greater regional inflammation. There were no significant differences in histopathology of the lung tissue when comparing mucoid or nonmucoid P.a. infection. CLINICAL IMPLICATIONS: In this pilot study, we demonstrated that mucoid P.a. infection was associated with acute-on-chronic inflammation in lung explants. As such, current/novel antimicrobials should target mucoid P.a. isolates throughout CF patients’ lifetimes. Furthermore, correlations between P.a. infection and inflammation within this cohort suggest that cytokines merit further study as long-term biomarkers in CF. Finally, although P.a. infection was not associated with tissue damage, we applied a detailed histopathology scoring system to CF patient lung tissue for the first time. This method can be utilized in future large-cohort studies investigating host-bacterial relationships in situ. DISCLOSURES: No relevant relationships by Don Hayes, source=Web Response No relevant relationships by Sankalp Malhotra, source=Web Response No relevant relationships by Daniel Wozniak, source=Web Response No relevant relationships by Ching Yang, source=Web Response