Idiopathic pulmonary fibrosis (IPF) is a chronic degenerative disease with poor survival and no effective treatments. Its pathophysiology involves the accumulation of extracellular matrix components within the interstitial alveolar walls, significantly impairing gas exchange. Presently, there is no comprehensive understanding of pathogenesis mechanisms, and animal models do not allow the study of the localised fibrotic responses that initiate the disease. We hypothesised that injury-induced site-specific disruption of the alveolar epithelium would impair cross-talk with resident immune cells, promoting fibrosis. We therefore developed a novel technique for intrabronchial delivery of bleomycin into one lung lobe to induce localised fibrosis in C57BL/6 mice.
We validated this technique with specific delivery of Al594 fluorescent dye and Al647-CD3+ lymphocytes in euthanised and anaesthetised mice. Subsequent experiments with bleomycin confirmed the successful establishment of a segmental lobe administration model, with fibrosis limited to the challenged lobe. To identify peaks of inflammation and fibrosis, we performed segmental broncho-alveolar lavage (sBAL) and confirmed the potential relevance of this model.
Dense fibrotic areas revealed cell aggregates resembling tertiary lymphoid structures (TLS). Previously observed in IPF patients, TLS have been poorly characterised, but are believed to be involved in modulating fibrotic responses. Consistent with this result, we detected a selective expansion of CD4+ T and B cells in sBAL and in the challenged lung tissue at the peak of fibrosis. These results provided further evidence for the role of the adaptive immune system during fibrotic processes.
This project establishes a novel segmental intrabronchial delivery technique in mice for the study of localised fibrotic responses in vivo, thereby opening new avenues for the study of the pathogenesis mechanisms underlying IPF.