Ferret Lung Transplantation Models Differential Lymphoid Aggregate Morphology Between Restrictive and Obstructive Forms of Chronic Lung Allograft Dysfunction

Background. Long-term survival after lung transplantation remains limited by chronic lung allograft dysfunction (CLAD). CLAD has 2 histologic phenotypes, namely obliterative bronchiolitis (OB) and restrictive alveolar fibroelastosis (AFE), which have distinct clinical presentations, pathologies, and outcomes. Understanding of OB versus AFE pathogenesis would improve with better animal models. Methods. We utilized a ferret orthotopic single-lung transplantation model to characterize allograft fibrosis as a histologic measure of CLAD. Native lobes and No CLAD allografts lacking aberrant histology were used as controls. We used morphometric analysis to evaluate the size and abundance of B-cell aggregates and tertiary lymphoid organs (TLOs) and their cell composition. Quantitative RNA expression of 47 target genes was performed simultaneously using a custom QuantiGene Plex Assay. Results. Ferret lung allografts develop the full spectrum of human CLAD histology including OB and AFE subtypes. While both OB and AFE allografts developed TLOs, TLO size and number were greater with AFE histology. More activated germinal center cells marked by B-cell lymphoma 6 Transcription Repressor, (B-cell lymphoma 6) expression and fewer cells expressing forkhead box P3 correlated with AFE, congruent with greater diffuse immunoglobulin, plasma cell abundance, and complement 4d staining. Furthermore, forkhead box P3 RNA induction was significant in OB allografts specifically. RNA expression changes were seen in native lobes of animals with AFE but not OB when compared with No CLAD native lobes. Conclusions. The orthotopic ferret single-lung transplant model provides unique opportunities to better understand factors that dispose allografts to OB versus AFE. This will help develop potential immunomodulatory therapies and antifibrotic approaches for lung transplant patients.

Automated summary

This study utilized a ferret transplantation model to investigate the characteristics and pathogenesis of obliterative bronchiolitis (OB) and restrictive alveolar fibroelastosis (AFE) in chronic lung allograft dysfunction (CLAD). The results showed that both OB and AFE allografts developed tertiary lymphoid organs (TLOs), but AFE had larger and more abundant TLOs. The expression of B-cell lymphoma 6 Transcription Repressor (BCL-6) and forkhead box P3 were associated with AFE, along with higher levels of immunoglobulins, plasma cells, and complement 4d. This study provides valuable insights into the factors contributing to OB and AFE, and may guide the development of immunomodulatory and antifibrotic therapies for lung transplant patients.