Mechanistic analysis of an IRF7-dependent pathway in virus-induced fibrosis in chronic lung allograft dysfunction

Chronic lung allograft dysfunction (CLAD) significantly limits long-term survival of lung transplant recipients, with viral infections acting as critical contributors to its pathogenesis. The mechanisms linking viral infections to CLAD-associated airway fibrosis remain incompletely understood. This study investigates the role of the type I interferon (IFN) master regulator IRF7 in virus-induced airway fibrogenesis.

CLAD (Bronchiolitis obliterans syndrome (BOS)), Stable LTx, and non-transplanted lung tissues were analysed by spatial transcriptomics (GeoMx; n = 5 CLAD (BOS), n = 3 Stable LTx, n = 3 controls), Western blotting, and immunostaining. Primary bronchial epithelial cells in air-liquid-interface (ALI) culture and a human precision-cut lung slice (PCLS) ex vivo model were exposed to Influenza A virus (IAV) with or without IRF7 silencing, IL-33 blockade, or MMP-9 inhibition. Group comparisons used Mann-Whitney tests and one-way ANOVA with Tukey's post hoc test; spatial differential expression used linear models with Benjamini-Hochberg correction (α = 0.05).

Spatial transcriptomics identified enrichment of IFN-stimulated genes including IRF7, STAT1, IFI44L, and GBP1 in the CLAD (BOS) epithelial compartment alongside antiviral effector genes (DDX58, TLR3) and pro-fibrotic programmes (TGFB1, SMAD2/3, ACTA2). Western blotting confirmed significantly increased IRF7 and phosphorylated IRF7 with airway-centric distribution in CLAD (BOS) (p < 0.01; n = 3-4). IAV exposure upregulated IRF7, α-SMA, SMAD2/3, and soluble collagen in ALI cultures (all p < 0.01; n = 3-6); IRF7 silencing attenuated these markers and reduced virus-induced IL-33 at mRNA and protein levels (p < 0.05). IL-33 blockade independently reduced α-SMA (p < 0.05), confirming IL-33 as a downstream IRF7 mediator. IAV increased MMP-9 secretion (p < 0.0001); IRF7 or IL-33 blockade attenuated MMP-9, while MMP-9 inhibition reduced α-SMA (p < 0.0001). All findings were replicated in human PCLS (p < 0.05; n = 5-6).

These findings delineate an IRF7-IL-33-MMP-9 axis linking viral infections to airway fibrogenesis, offering mechanistic insight into CLAD (BOS) pathogenesis. Therapeutic targeting of this pathway may mitigate fibrotic remodelling in lung transplant recipients.

NIH 1R01HL161620 (N.S.S.). Caredx IIT (N.S.S).