Taheri, Mojtaba

Technological innovations have improved many barriers in lung transplantation, but high rates of acute and chronic rejection still limit lung allograft survival. This may be explained by the unique environment of the lung. As a mucosal barrier organ, the lung is constantly exposed to the external environment, leading to unique immunological features that are not seen in other transplantable solid organ allografts such as hearts, kidneys, and livers. Thus, the higher rates of rejection and poor long-term survival of lung transplant recipients may stem from the global immunosuppression strategies that are indiscriminately used for all solid organ grafts. Data from our laboratory, and others, have demonstrated that the unique immunoregulatory pathways of the lung may require different strategies for long-term graft survival. For example, depletion of CD8 + T cells typically contributes to the acceptance of transplanted organs. However, these cells facilitate lung allograft acceptance through interferon gamma mediated nitric oxide production. Interestingly CD8 + T cells modify and polarize eosinophils to produce nitric oxide as a means of tolerance induction. Such eosinophils also function to maintain long-term lung allograft acceptance by interfering with humoral alloimmunity. For most other organs eosinophils are suspected to contribute to graft rejection. In this review, we aim to describe the cytokine pathways involved in lung allograft rejection or tolerance, contrast such pathways to those evident in other solid organs, and discuss the need for further studies that can be used to design rational methods for altering the cytokine environment to improve lung allograft survival.

Respiratory failure occurs more frequently after thoracic surgery than abdominal surgery. Although the etiology for this complication is frequently attributed to underlying lung disease present in patients undergoing thoracic surgery, this notion is often unfounded because many patients with normal preoperative pulmonary function often require prolonged oxygen supplementation even after minimal resection of lung tissue. Using a murine model of pulmonary resection and peripheral blood samples from patients undergoing resection of the lung or abdominal organs, we demonstrated that lung surgery initiates a proinflammatory loop that results in damage to the remaining lung tissue, noncardiogenic pulmonary edema, hypoxia, and even death. Specifically, we demonstrated that resection of murine lung tissue increased concentrations of the homeostatic cytokine interleukin-7, which led to local and systemic activation of type 2 innate lymphoid cells. This process activated lung-resident eosinophils and facilitated stress-induced eosinophil maturation in the bone marrow in a granulocyte-macrophage colony-stimulating factor–dependent manner, resulting in systemic eosinophilia in both mice and humans. Up-regulation of inducible nitric oxide synthase in lung-resident eosinophils led to tissue nitrosylation, pulmonary edema, hypoxia, and, at times, death. Disrupting this activation cascade at any stage ameliorated deleterious outcomes and improved survival after lung resection in the mouse model. Our data suggest that repurposing US Food and Drug Administration–approved eosinophil-targeting strategies may potentially offer a therapeutic intervention to improve outcomes for patients who require lung resection for benign or malignant etiology.