Endothelial Cell Injury and Activation in a Murine Model of Left Lung Transplantation

Abstract

<h3>Purpose</h3> Endothelial cells are the first non-self-barrier encountered by the recipient's immune system after allograft transplantation and thus are involved early during alloimmune response. Our goal was to study processes of endothelial cell injury/activation in a mouse model of lung transplantation. <h3>Methods</h3> Mouse orthotopic left lung transplantation was performed in isografts (C57BL/6 to C57BL/6) and allografts (Balbc to C57BL/6), both received daily immunosuppression (10 mg/kg cyclosporin A and 1.6 mg/kg methylprednisolone) and were serially sacrificed at day 1, 7 and 35 post-transplant (n=6/timepoint/group). Left transplanted lungs were made into single cell suspension and absolute cell numbers were quantified by flow cytometry for CD31+ endothelial cells, CD45+ leukocytes and MHCI/II, VCAM-1 and ICAM-1 for cell activation. One additional allograft and isograft were scanned with high resolution (HR) <i>ex vivo</i> microCT (µCT) to visualize airways and blood vessels at day 70 post transplantation. <h3>Results</h3> Endothelial cell numbers decreased from day 1 until day 7 (p=0.03) in allografts and recovered slightly at day 35. While in isografts, endothelial cells seemed to increase non-significantly over time. In contrast, leukocytes significantly increased at day 7 in allografts versus day 1 (p=0.036) and isografts at day 7 (p=0.003). Leukocytes remained stable in isografts over time (p=0.3). Mean fluorescence intensity (MFI) was increased for MHC I/II and VCAM-1 (p=0.003; p<0.0001; p=0.04) on endothelial cells, the MFI of MHC I/II and ICAM-1 on leukocytes was increased in allografts versus isografts (p=0.0002; p=0.006; p=0.002). HR µCT showed normal airway morphology while lumen of arteries and veins was narrowed in allograft compared to isograft. Arterioles and venules were occluded in allograft. <h3>Conclusion</h3> Destruction of endothelial cells may represent the very first onset of alloimmune response post lung transplantation and warrant further investigations towards diagnostic and therapeutic approaches.