The role of recipient derived interleukin-17A in a murine orthotopic lung transplant model of restrictive chronic lung allograft dysfunction

•Bronchiolitis Obliterans Syndrome and Restrictive Allograft Syndrome are the main phenotypes of chronic rejection•A murine major HLA mismatched orthotopic lung transplant model with immune suppressive regime mimics the clinical situation•The murine histopathology rather presents as RAS•IL 17A K.O. mice demonstrated an involvement of IL17A in is bronchovascular inflammation but does not seem to drive fibrogenesis

The single most important cause of late mortality after lung transplantation is chronic lung allograft dysfunction (CLAD). However, the pathological development of CLAD was not as simple as previously presumed and subclassification phenotypes, bronchiolitis obliterans syndrome (BOS) and restrictive CLAD (rCLAD), have been introduced. We want to re-investigate how CLAD manifests in the murine orthotopic lung transplant model and investigate the role of interleukin 17A (IL-17A) within this model.Orthotopic LTx was performed in CB57BL/6, IL-17 WT and IL-17 KO mice. In a first experiment, CB57BL/6 mice receiving an isograft (CB57BL/6) or allograft (BALB/C) were compared. In a second experiment IL-17 WT and IL-17 KO mice (both CB57BL/6 background) received an allograft (BALB/C). Mice received daily immunosuppression with steroids and cyclosporine and were sacrificed 10 weeks after transplantation for histopathological analysis by an experienced lung pathologist.After murine orthotopic lung transplantation, the allograft histopathologically presented features of human rCLAD (i.e. overt inflammation, pleural/parenchymal fibrosis and obliterative bronchiolitis). In the IL-17A KO group, less inflammation in the bronchovascular axis (p = 0.03) was observed and a non-significant trend towards less bronchovascular fibrosis, pleural/septal inflammation and fibrosis, and parenchymal inflammation and fibrosis when compared to WT mice.The major mismatch orthotopic lung transplant model resembles features of human rCLAD. IL-17A mediated immunity is involved in the inflammatory component, but had little influence on the degree of fibrosis. Further mechanistic and therapeutic studies in this mouse model are needed to fully understand the mechanisms in rCLAD.