Origin of Fibroblasts in Rejected Airway: Experiment with Orthotopic Tracheal Allotransplantation Model Using Transgenic GFP Mice

Abstract

Purpose Obliterative bronchiolitis (OB) is a limiting factor that affects long-term survival following lung transplantation. Fibroblasts and myofibroblasts are considered to be the key players in fibrosis in OB. The source of these fibroblasts is still in question. Two major possible sources of the fibroblasts are recipient bone marrow cells and transitioned epithelial cells through epithelial to mesenchymal transition. The aim of this study was to clarify whether the fibroblasts originate from donor or from recipient. Methods and Materials We performed orthotopic tracheal transplantation with the combination of transgenic C57BL/6 mice ubiquitously expressing green fluorescent protein (GFP) (B6-Tg) and BALB/c mice, where syngeneic with BALB/c to BALB/c combination. After transplantation, ten allogeneic recipients (five each in BALB/c to B6-Tg; and B6-Tg to BALB/c groups) and three syngeneic recipients were sacrificed on day 28. Histologic evaluation was done by using hematoxylin-eosin (H&E) staining and immunofluorescence staining of the myofibroblast marker (α-SMA) and GFP. Results Subepithelial fibrosis was observed in rejected airway on H&E ( Figure A, B, every scale bar means 100 μm). In grafts from BALB/c to B6-Tg ( Figure A, C), α-SMA (red) positive subepithelial fibrotic areas were also GFP (green) positive. Conversely in grafts from B6-Tg to BALB/c ( Figure B, D), α-SMA positive fibrotic areas were GFP negative. Conclusions The results showed that the fibroblasts in rejected airway originated from recipient, but the issue of exact source of fibroblasts (central stem cells vs local transitioned epithelial cells through epithelial to mesenchymal transition) still remained unclear.