Immune-mediated pulmonary diseases are a significant public health concern. Analysis of leukocyte behavior in the lung is essential for understanding cellular mechanisms that contribute to normal and diseased states. Here, we used two-photon imaging to study neutrophil extravasation from pulmonary vessels and subsequent interstitial migration. We found that the lungs contained a significant pool of tissue-resident neutrophils in the steady state. In response to inflammation produced by bacterial challenge or transplant-mediated, ischemia-reperfusion injury, neutrophils were rapidly recruited from the circulation and patrolled the interstitium and airspaces of the lung. Motile neutrophils often aggregated in dynamic clusters that formed and dispersed over tens of minutes. These clusters were associated with CD115 + F4/80 + Ly6C + cells that had recently entered the lung. The depletion of blood monocytes with clodronate liposomes reduced neutrophil clustering in the lung, but acted by inhibiting neutrophil transendothelial migration upstream of interstitial migration. Our results suggest that a subset of monocytes serve as key regulators of neutrophil extravasation in the lung and may be an attractive target for the treatment of inflammatory pulmonary diseases.lung | two-photon microscopy | transendothelial migration | ischemia | transplant
Outcomes after lung transplantation are markedly inferior to those after other solid organ transplants. A better understanding of cellular and molecular mechanisms contributing to lung graft injury will be critical to improve outcomes. Advances in this field have been hampered by the lack of a mouse model of lung transplantation. Here, we report a mouse model of vascularized aerated single lung transplantation utilizing cuff techniques. We show that syngeneic grafts have normal histological appearance with minimal infiltration of T lymphocytes. Allogeneic grafts show acute cellular rejection with infiltration of T lymphocytes and recipient-type antigen presenting cells. Our data show that we have developed a physiological model of lung transplantation in the mouse, which provides ample opportunity for the study of nonimmune and immune mechanisms that contribute to lung allograft injury.
It is the prevailing view that adaptive immune responses are initiated in secondary lymphoid organs. Studies using alymphoplastic mice have shown that secondary lymphoid organs are essential to initiate allograft rejection of skin, heart, and small bowel. The high immunogenicity of lungs is well recognized and allograft rejection remains a major contributing factor to poor outcomes after lung transplantation. We show in this study that alloreactive T cells are initially primed within lung allografts and not in secondary lymphoid organs following transplantation. In contrast to other organs, lungs are acutely rejected in the absence of secondary lymphoid organs. Two-photon microscopy revealed that recipient T cells cluster predominantly around lung-resident, donor-derived CD11c+ cells early after engraftment. These findings demonstrate for the first time that alloimmune responses following lung transplantation are initiated in the graft itself and therefore identify a novel, potentially clinically relevant mechanism of lung allograft rejection.
Graft rejection remains a formidable problem contributing to poor outcomes after lung transplantation. Blocking chemokine pathways have yielded promising results in some organ transplant systems. Previous clinical studies have demonstrated upregulation of CCR2 ligands following lung transplantation. Moreover, lung injury is attenuated in CCR2-deficient mice in several inflammatory models. In this study, we examined the role of CCR2 in monocyte recruitment and alloimmune responses in a mouse model of vascularized orthotopic lung transplantation. The CCR2 ligand MCP-1 is upregulated in serum and allografts following lung transplantation. CCR2 is critical for the mobilization of monocytes from the bone marrow into the bloodstream and for the accumulation of CD11c+ cells within lung allografts. A portion of graft-infiltrating recipient CD11c+ cells expresses both recipient and donor MHC molecules. Two-photon imaging demonstrates that recipient CD11c+ cells are associated with recipient T cells within the graft. While recipient CCR2 deficiency does not prevent acute lung rejection and is associated with increased graft infiltration by T cells, it significantly reduces CD4+ Th1 indirect and direct allorecognition. Thus, CCR2 may be a potential target to attenuate alloimmune responses after lung transplantation.
Unlike other solid organs, vascularized mouse lung transplantation has only recently been developed. In this publication we describe the detailed method for performing a vascularized and aerated mouse orthotopic lung transplant, which to date represents the most physiologic mouse model of lung transplantation. The procedure is divided into two separate portions consisting of donor harvest followed by implantation using the cuff technique for bronchovascular anastomoses. After a several month training period the procedure can be successfully mastered and in experienced hands requires approximately 90 minutes to perform. After an initial learning curve perioperative survival is close to 100%. As over time the donor hematopoietic cells in the transplanted lung are replaced by those of the host, thereby creating a “chimeric lung”, this model represents a novel research tool for the study of transplantation biology as well as other disease processes such as malignancies.
Acute rejection continues to present a major obstacle to successful lung transplantation. Although CD4+ T lymphocytes are critical for the rejection of some solid organ grafts, the role of CD4+ T cells in the rejection of lung allografts is largely unknown. In this study, we demonstrate in a novel model of orthotopic vascularized mouse lung transplantation that acute rejection of lung allografts is independent of CD4+ T cell-mediated allorecognition pathways. CD4+ T cell-independent rejection occurs in the absence of donor-derived graft-resident hematopoietic APCs. Furthermore, blockade of the CD28/B7 costimulatory pathways attenuates acute lung allograft rejection in the absence of CD4+ T cells, but does not delay acute rejection when CD4+ T cells are present. Our results provide new mechanistic insight into the acute rejection of lung allografts and highlight the importance of identifying differences in pathways that regulate the rejection of various organs.
Lung transplantation remains the only therapeutic option for many patients suffering from end-stage pulmonary disease. Long-term success after lung transplantation is severely limited by the development of bronchiolitis obliterans. The murine heterotopic tracheal transplantation model has been widely used for studies investigating pathogenesis of obliterative airway disease and immunosuppressive strategies to prevent its development. Despite its utility, this model employs proximal airway that lacks airflow and is not vascularized. We have developed a novel model of orthotopic vascularized lung transplantation in the mouse, which leads to severe vascular rejection in allogeneic strain combinations. Here we characterize differences in the fate of airway epithelial cells in nonimmunosuppressed heterotopic tracheal and vascularized lung allograft models over 28 days. Up-regulation of growth factors that are thought to be critical for the development of airway fibrosis and interstitial collagen deposition were similar in both models. However, while loss of airway epithelial cells occurred in the tracheal model, airway epithelium remained intact and fully differentiated in lung allografts, despite profound vascular rejection. Moreover, we demonstrate expression of the anti-apoptotic protein Bcl-2 in airway epithelial cells of acutely rejected lung allografts. These findings suggest that in addition to alloimmune responses, other stimuli may be required for the destruction of airway epithelial cells. Thus, the model of vascularized mouse lung transplantation may provide a new and more physiologic experimental tool to study the interaction between immune and nonimmune mechanisms affecting airway pathology in lung allografts.
Since the onset of the COVID-19 pandemic, researchers around the world have made efforts to assess its impact on youth mental health; however, the breadth of this topic has impeded a clear assessment of pandemic outcomes. This study aimed to address this gap by reviewing changes in youth (age ≤ 25) mental health, psychological wellbeing, substance use, and the use or delivery of relevant services during the pandemic. PubMed and Embase were searched in May 2021 to conduct a rapid review of the literature. The results encompass 156 primary publications and are reported using a narrative synthesis. Studies of mental health (n = 122) and psychological wellbeing (n = 28) generally indicated poor outcomes in many settings. Publications regarding substance use (n = 41) noted overall declines or unchanged patterns. Studies of service delivery (n = 12) indicated a generally positive reception for helplines and telehealth, although some youth experienced difficulties accessing services. The findings indicate negative impacts of the pandemic on youth mental health, with mixed results for substance use. Services must support marginalized youth who lack access to telehealth. Supplementary Information The online version contains supplementary material available at 10.1007/s40894-022-00185-6.
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