TNFα from classically activated macrophages accentuates epithelial to mesenchymal transition in obliterative bronchiolitis

Chronic Lung Allograft Dysfunction: Clinical Manifestations and Immunologic Mechanisms

The term "chronic lung allograft dysfunction" has emerged to describe the clinical syndrome of progressive, largely irreversible dysfunction of pulmonary allografts. This umbrella term comprises 2 major clinical phenotypes: bronchiolitis obliterans syndrome and restrictive allograft syndrome. Here, we discuss the clinical manifestations, diagnostic challenges, and potential therapeutic avenues to address this major barrier to improved long-term outcomes. In addition, we review the immunologic mechanisms thought to propagate each phenotype of chronic lung allograft dysfunction, discuss the various models used to study this process, describe potential therapeutic targets, and identify key unknowns that must be evaluated by future research strategies.

Immune dysregulation as a driver of bronchiolitis obliterans

Bronchiolitis obliterans (BO) is a disease characterized by airway obstruction and fibrosis that can occur in all age groups. Bronchiolitis obliterans syndrome (BOS) is a clinical manifestation of BO in patients who have undergone lung transplantation or hematopoietic stem cell transplantation. Persistent inflammation and fibrosis of small airways make the disease irreversible, eventually leading to lung failure. The pathogenesis of BO is not entirely clear, but immune disorders are commonly involved, with various immune cells playing complex roles in different BO subtypes. Accordingly, the US Food and Drug Administration (FDA) has recently approved several new drugs that can alleviate chronic graft-versus-host disease (cGVHD) by regulating the function of immune cells, some of which have efficacy specifically with cGVHD-BOS. In this review, we will discuss the roles of different immune cells in BO/BOS, and introduce the latest drugs targeting various immune cells as the main target. This study emphasizes that immune dysfunction is an important driving factor in its pathophysiology. A better understanding of the role of the immune system in BO will enable the development of targeted immunotherapies to effectively delay or even reverse this condition.

Innovations in Childhood Interstitial and Diffuse Lung Disease

Children's interstitial and diffuse lung diseases (chILDs) are a heterogenous and diverse group of lung disorders presenting during childhood. Infants and children with chILD disorders present with respiratory signs and symptoms as well as diffuse lung imaging abnormalities. ChILD disorders are associated with significant health care resource utilization and high morbidity and mortality. The care of patients with chILD has been improved through multidisciplinary care, multicenter collaboration, and the establishment of patient research networks in the United Stated and abroad. This review details past and current innovations in the diagnosis and clinical care of children with chILD.

Relationship between immune cells and the development of chronic lung allograft dysfunction

A major cause of death for lung transplant recipients (LTRs) is the advent of chronic lung allograft dysfunction (CLAD), which has long plagued the long-term post-transplant prognosis and quality of survival of transplant patients. The intricacy of its pathophysiology and the irreversibility of its illness process present major obstacles to the clinical availability of medications. Immunotherapeutic medications are available, but they only aim to slow down the course of CLAD rather than having any therapeutic impact on the disease's development. For this reason, understanding the pathophysiology of CLAD is essential for both disease prevention and proven treatment. The immunological response in particular, in relation to chronic lung allograft dysfunction, has received a great deal of interest recently. Innate immune cells like natural killer cells, eosinophils, neutrophils, and mononuclear macrophages, as well as adaptive immunity cells like T and B cells, play crucial roles in this process through the release of chemokines and cytokines. The present review delves into changes and processes within the immune microenvironment, with a particular focus on the quantity, subtype, and characteristics of effector immune cells in the peripheral and transplanted lungs after lung transplantation. We incorporate and solidify the documented role of immune cells in the occurrence and development of CLAD with the advancements in recent years.

Lymphocyte Depleting and Modulating Therapies for Chronic Lung Allograft Dysfunction

Chronic lung rejection, also called chronic lung allograft dysfunction (CLAD), remains the major hurdle limiting long-term survival after lung transplantation, and limited therapeutic options are available to slow the progressive decline in lung function. Most interventions are only temporarily effective in stabilizing the loss of or modestly improving lung function, with disease progression resuming over time in the majority of patients. Therefore, identification of effective treatments that prevent the onset or halt progression of CLAD is urgently needed. As a key effector cell in its pathophysiology, lymphocytes have been considered a therapeutic target in CLAD. The aim of this review is to evaluate the use and efficacy of lymphocyte depleting and immunomodulating therapies in progressive CLAD beyond usual maintenance immunosuppressive strategies. Modalities used include anti-thymocyte globulin, alemtuzumab, methotrexate, cyclophosphamide, total lymphoid irradiation, and extracorporeal photopheresis, and to explore possible future strategies. When considering both efficacy and risk of side effects, extracorporeal photopheresis, anti-thymocyte globulin and total lymphoid irradiation appear to offer the best treatment options currently available for progressive CLAD patients. SIGNIFICANCE STATEMENT: Effective treatments to prevent the onset and progression of chronic lung rejection after lung transplantation are still a major shortcoming. Based on existing data to date, considering both efficacy and risk of side effects, extracorporeal photopheresis, anti-thymocyte globulin, and total lymphoid irradiation are currently the most viable second-line treatment options. However, it is important to note that interpretation of most results is hampered by the lack of randomized controlled trials.

Cytokines in Lung Transplantation

Lung transplantation has developed significantly in recent years, but post-transplant care and patients' survival still need to be improved. Moreover, organ shortage urges novel modalities to improve the quality of unsuitable lungs. Cytokines, the chemical mediators of the immune system, might be used for diagnostic and therapeutic purposes in lung transplantation. Cytokine monitoring pre- and post-transplant could be applied to the prevention and early diagnosis of injurious inflammatory events including primary graft dysfunction, acute cellular rejection, bronchiolitis obliterans syndrome, restrictive allograft syndrome, and infections. In addition, preoperative cytokine removal, specific inhibition of proinflammatory cytokines, and enhancement of anti-inflammatory cytokines gene expression could be considered therapeutic options to improve lung allograft survival. Therefore, it is essential to describe the cytokines alteration during inflammatory events to gain a better insight into their role in developing the abovementioned complications. Herein, cytokine fluctuations in lung tissue, bronchoalveolar fluid, peripheral blood, and exhaled breath condensate in different phases of lung transplantation have been reviewed; besides, cytokine gene polymorphisms with clinical significance have been summarized.

Immune processes in the pathogenesis of chronic lung allograft dysfunction: identifying the missing pieces of the puzzle

Lung transplantation is the optimal treatment for selected patients with end-stage chronic lung diseases. However, chronic lung allograft dysfunction remains the leading obstacle to improved long-term outcomes. Traditionally, lung allograft rejection has been considered primarily as a manifestation of cellular immune responses. However, in reality, an array of complex, interacting and multifactorial mechanisms contribute to its emergence. Alloimmune-dependent mechanisms, including T-cell-mediated rejection and antibody-mediated rejection, as well as non-alloimmune injuries, have been implicated. Moreover, a role has emerged for autoimmune responses to lung self-antigens in the development of chronic graft injury. The aim of this review is to summarise the immune processes involved in the pathogenesis of chronic lung allograft dysfunction, with advanced insights into the role of innate immune pathways and crosstalk between innate and adaptive immunity, and to identify gaps in current knowledge.

Pharmacotherapy of chronic lung allograft dysfunction post lung transplantation

Chronic lung allograft dysfunction (CLAD) remains the primary cause of death in lung transplant recipients (LTRs) in spite of improvements in immunosuppression management. Despite advances in knowledge regarding the pathogenesis of CLAD, treatments that are currently available are usually ineffective and delay progression of disease at best. There are currently no evidence-based guidelines for the optimal treatment of CLAD, and management varies widely across transplant centers. Additionally, there are minimal publications available to summarize data for currently available therapies and outcomes in LTRs. We identified the major domains of the medical management of CLAD and conducted a comprehensive search of PubMed and Embase databases to identify articles published from inception to December 2021 related to CLAD in LTRs. Studies published in English pertaining to the pharmacologic prevention and treatment of CLAD were included; highest priority was given to prospective, randomized, controlled trials if available. Prospective observational and retrospective controlled trials were prioritized next, followed by retrospective uncontrolled studies, case series, and finally case reports if the information was deemed to be pertinent. Reference lists of qualified publications were also reviewed to find any other publications of interest that were not found on initial search. In the absence of literature published in the aforementioned databases, additional articles were identified by reviewing abstracts presented at the International Society for Heart and Lung Transplantation and American Transplant Congress annual meetings between 2010-2021. This document serves to provide a comprehensive review of the literature and considerations for the prevention and medical management of CLAD. This article is protected by copyright. All rights reserved.

Effector immune cells in Chronic Lung Allograft Dysfunction: a Systematic Review

Chronic lung allograft dysfunction (CLAD) remains the major barrier to long‐term survival after lung transplantation and improved insight into its underlying immunological mechanisms is critical to better understand the disease and to identify treatment targets. We systematically searched the electronic databases of PubMed and EMBASE for original research publications, published between January 2000 and April 2021, to comprehensively assess current evidence on effector immune cells in lung tissue and bronchoalveolar lavage fluid from lung transplant recipients with CLAD. Literature search revealed 1351 articles, 76 of which met the criteria for inclusion in our analysis. Our results illustrate significant complexity in both innate and adaptive immune cell responses in CLAD, along with presence of numerous immune cell products, including cytokines, chemokines and proteases associated with tissue remodelling. A clear link between neutrophils and eosinophils and CLAD incidence has been seen, in which eosinophils more specifically predisposed to restrictive allograft syndrome. The presence of cytotoxic and T‐helper cells in CLAD pathogenesis is well‐documented, although it is challenging to draw conclusions about their role in tissue processes from predominantly bronchoalveolar lavage data. In restrictive allograft syndrome, a more prominent humoral immune involvement with increased B cells, immunoglobulins and complement deposition is seen. Our evaluation of published studies over the last 20 years summarizes the complex multifactorial immunopathology of CLAD onset and progression. It highlights the phenotype of several key effector immune cells involved in CLAD pathogenesis, as well as the paucity of single cell resolution spatial studies in lung tissue from patients with CLAD.

Bioinspired carbon monoxide delivery using artificial blood attenuates the progression of obliterative bronchiolitis via suppression of macrophage activation by IL-17A

Carbon monoxide (CO) is expected to attenuate the progression of obliterative bronchiolitis (OB), which is a serious complication after lung transplantation. However, issues in terms of feasible exogenous CO supply, such as continuousness and safety, remain unsolved. Here, we applied nano red blood cells, namely hemoglobin vesicles (Hb-V), as a CO cargo based on the biomimetic concept and investigated the therapeutic potential of CO-loaded Hb-V on OB in orthotopic tracheal transplant model mice. The CO-loaded Hb-V was comprised of negatively charged liposomes encapsulating carbonylhemoglobin with a size of ca. 220 nm. The results of histological evaluation showed that allograft luminal occlusion and fibrosis were significantly ameliorated by treatment with CO-loaded Hb-V compared to treatment with saline, cyclosporine, and Hb-V. The therapeutic effects of CO-loaded Hb-V on OB were due to the suppression of M1 macrophage activation in tracheal allografts, resulting from decreased IL-17A production. Furthermore, the expression of TNF-α and TGF-β in tracheal allografts was decreased by CO-loaded Hb-V treatment but not saline and Hb-V treatment, indicating that CO liberated from CO-loaded Hb-V inhibits epithelial-mesenchymal transition. These findings suggest that CO-loaded Hb-V exerts strong therapeutic efficacy against OB via the regulation of macrophage activation by IL-17A and TGF-β-driven epithelial-mesenchymal transition.

Cathepsin B promotes collagen biosynthesis, which drives bronchiolitis obliterans syndrome

Bronchiolitis obliterans syndrome (BOS) is a major complication after lung transplantation (LTx). BOS is characterised by massive peribronchial fibrosis, leading to air trapping-induced pulmonary dysfunction. Cathepsin B, a lysosomal cysteine protease, has been shown to enforce fibrotic pathways in several diseases. However, the relevance of cathepsin B in BOS progression has not yet been addressed. The aim of the study was to elucidate the function of cathepsin B in BOS pathogenesis.We determined cathepsin B levels in bronchoalveolar lavage fluid (BALF) and lung tissue from healthy donors (HD) and BOS LTx patients. Cathepsin B activity was assessed via a fluorescence resonance energy transfer-based assay and protein expression was determined using Western blotting, ELISA and immunostaining. To investigate the impact of cathepsin B in the pathophysiology of BOS, we used an in vivo orthotopic left LTx mouse model. Mechanistic studies were performed in vitro using macrophage and fibroblast cell lines.We found a significant increase of cathepsin B activity in BALF and lung tissue from BOS patients, as well as in our murine model of lymphocytic bronchiolitis. Moreover, cathepsin B activity was associated with increased biosynthesis of collagen and had a negative effect on lung function. We observed that cathepsin B was mainly expressed in macrophages that infiltrated areas characterised by a massive accumulation of collagen deposition. Mechanistically, macrophage-derived cathepsin B contributed to transforming growth factor-β1-dependent activation of fibroblasts, and its inhibition reversed the phenotype.Infiltrating macrophages release active cathepsin B, thereby promoting fibroblast activation and subsequent collagen deposition, which drive BOS. Cathepsin B represents a promising therapeutic target to prevent the progression of BOS.

Restrictive allograft syndrome after lung transplantation

Despite recent advances over the past decade in lung transplantation including improved surgical technique and immunotherapy, the diagnosis and treatment of chronic lung allograft dysfunction remains a significant barrier to recipient survival. Aside from bronchiolitis obliterans syndrome, a restrictive phenotype called restrictive allograft syndrome has recently been recognized and affects up to 35% of all patients with CLAD. The main characteristics of RAS include a persistent and unexplained decline in lung function compared to baseline and persistent parenchymal infiltrates on imaging. The median survival after diagnosis of RAS is 6 to 18 months, significantly shorter than other forms of CLAD. Treatment options are limited, as therapies used for BOS are typically ineffective at halting disease progression. Specific medications such as fibrinolytics are lacking large, multicenter prospective studies. In this manuscript, we discuss the definition, mechanism, and characteristics of RAS while highlighting the similarities and differences between other forms of CLAD. We also review the diagnoses along with current and potential treatment options that are available for patients. Finally, we discuss the existing knowledge gaps and areas for future research to improve patient outcomes and understanding of RAS.

Bronchiolitis obliterans syndrome is associated with increased senescent lymphocytes in the small airways

BACKGROUND

Immunosuppression therapy is ineffective at preventing bronchiolitis obliterans syndrome (BOS), primarily a disease of the small airways (SAs). Our previous reports show increased senescent CD28null T and natural killer T (NKT)-like cells in the peripheral blood of patients with BOS and increased cytotoxic, proinflammatory lymphocytes in the SAs. We hypothesized that the cytotoxic, proinflammatory lymphocytes in the SAs would be steroid-resistant senescent CD28null lymphocytes.

METHODS

Intracellular cytotoxic mediator granzyme B, interferon (IFN)-γ and tumor necrosis factor (TNF)-α proinflammatory cytokines, and CD28 were measured in the blood, bronchoalveolar lavage, large airway, and SA brushing T and NKT-like cells from 10 patients with BOS, 11 stable lung transplant recipients, and 10 healthy age-matched controls. SA brushings were cultured in the presence of ±1 µmol/liter prednisolone, ±5 mg/liter theophylline, and ±2.5 ng/ml cyclosporine A, and IFN-γ and TNF-α proinflammatory cytokines were assessed using flow cytometry.

RESULTS

Increased SA CD28null T and NKT-like cells were identified in patients with BOS compared with that in the controls and stable transplant recipients. Loss of CD28 was associated with increased T and NKT-like cells expressing granzyme B, IFN-γ, and TNF-α. Loss of CD28 expression by CD8+ T cells was significantly associated with forced expiratory volume in 1 sec (R = 0.655, p = 0.006) and with time after transplantation (R = -0.552, p = 0.041). Treatment with prednisolone + theophylline + cyclosporin A inhibited IFN-γ and TNF-α production by SA CD28null CD8+ T and NKT-like cells additively.

CONCLUSIONS

BOS is associated with the loss of CD28 in SA cytotoxic, proinflammatory senescent T and NKT-like lymphocytes. Treatment options that target the proinflammatory nature of these cells in the SAs may improve graft survival.

Autoantibodies in lung transplantation

Chronic lung allograft dysfunction (CLAD) comprises both bronchiolitis obliterans syndrome and restrictive allograft syndrome as subtypes. After lung transplantation, CLAD remains a major limitation for long-term survival, and lung transplant recipients therefore have poorer outcomes compared with recipients of other solid organ transplants. Although the number of lung transplants continues to increase globally, the field demands detailed understanding of immunoregulatory mechanisms and more effective individualized therapies to combat CLAD. Emerging evidence suggests that CLAD is multifactorial and involves a complex, delicate interplay of multiple factors, including perioperative donor characteristics, inflammation induced immediately following transplant, post-transplant infection and interplay between allo- and autoimmunity directed to donor antigens. Recently, identification of stress-induced exosome release from the transplanted organ has emerged as an underlying mechanism in the development of chronic rejection and promises to prompt novel strategies for future therapeutic interventions. In this review, we will discuss recent studies and ongoing research into the mechanisms for the development of CLAD, with emphasis on immune responses to lung-associated self-antigens-that is, autoimmunity.

Precision medicine: integration of genetics and functional genomics in prediction of bronchiolitis obliterans after lung transplantation

PURPOSE OF REVIEW

Lung transplantation (LTx) can be a life saving treatment in end-stage pulmonary diseases, but survival after transplantation is still limited. Posttransplant development of chronic lung allograft dysfunction with bronchiolits obliterans syndrome (BOS) as the major subphenotype, is the main cause of morbidity and mortality. Early identification of high-risk patients for BOS is a large unmet clinical need. In this review, we discuss gene polymorphisms and gene expression related to the development of BOS.

RECENT FINDINGS

Candidate gene studies showed that donor and recipient gene polymorphisms affect transplant outcome and BOS-free survival after LTx. Both selective and nonselective gene expression studies revealed differentially expressed fibrosis and apoptosis-related genes in BOS compared with non-BOS patients. Significantly, recent microarray expression analysis of blood and broncho-alveolar lavage suggest a role for B-cell and T-cell responses prior to the development of BOS. Furthermore, 6 months prior to the development of BOS differentially expressed genes were identified in peripheral blood cells.

SUMMARY

Genetic polymorphisms and gene expression changes are associated with the development of BOS. Future genome wide studies are needed to identify easily accessible biomarkers for prediction of BOS toward precision medicine.

TLR3 promotes MMP-9 production in primary human airway epithelial cells through Wnt/β-catenin signaling

Background

Airway epithelial cells (AEC) act as the first line of defence in case of lung infections. They constitute a physical barrier against pathogens and they participate in the initiation of the immune response. Yet, the modalities of pathogen recognition by AEC and the consequences on the epithelial barrier remain poorly documented.

Method

We investigated the response of primary human AEC to viral (polyinosinic-polycytidylic acid, poly(I:C)) and bacterial (lipopolysaccharide, LPS) stimulations in combination with the lung remodeling factor Transforming Growth Factor-β (TGF-β).

Results

We showed a strong production of pro-inflammatory cytokines (Interleukin (IL)-6, Tumor Necrosis Factor α, TNFα) or chemokines (CCL2, CCL3, CCL4, CXCL10, CXCL11) by AEC stimulated with poly(I:C). Cytokine and chemokine production, except CXCL10, was Toll Like Receptor (TLR)-3 dependent and although they express TLR4, we found no cytokine production after LPS stimulation. Poly(I:C), but not LPS, synergised with TGF-β for the production of matrix metalloproteinase-9 (MMP-9) and fibronectin. Mechanistic analyses suggest the secretion of Wnt ligands by AEC along with a degradation of the cellular junctions after poly(I:C) exposure, leading to the release of β-catenin from the cell membrane and stimulation of the Wnt/β-catenin pathway.

Conclusion

Our results highlight the cross talk between TGF-β and TLR signaling in bronchial epithelium and its impact on the remodeling process.

Electronic supplementary material

The online version of this article (10.1186/s12931-017-0690-y) contains supplementary material, which is available to authorized users.

Plasma and bronchoalveolar lavage samples in acute lung allograft rejection: the potential role of cytokines as diagnostic markers

The role of differential cytology patterns in peripheral blood and bronchoalveolar lavage samples is increasingly investigated as a potential adjunct to diagnose acute and chronic allograft dysfunction after lung transplantation. While these profiles might facilitate the diagnosis of acute cellular rejection, low sensitivity and specificity of these patterns limit direct translation in a clinical setting. In this context, the identification of other biomarkers is needed. This review article gives an overview of cytokine profiles of plasma and bronchoalveolar lavage samples during acute cellular rejection. The value of these cytokines in supporting the diagnosis of acute cellular rejection is discussed. Current findings on the topic are highlighted and experimental settings for future research projects are identified.

T Cells Promote Bronchial Epithelial Cell Secretion of Matrix Metalloproteinase-9 via a C-C Chemokine Receptor Type 2 Pathway: Implications for Chronic Lung Allograft Dysfunction

Chronic lung allograft dysfunction (CLAD) is the major limitation of long-term survival after lung transplantation. CLAD manifests as bronchiolitis obliterans syndrome (BOS) or restrictive allograft syndrome (RAS). Alloimmune reactions and epithelial-to-mesenchymal transition have been suggested in BOS. However, little is known regarding the role of allogenicity in epithelial cell differentiation. Primary human bronchial epithelial cells (BECs) were treated with activated T cells in the presence or absence of transforming growth factor (TGF)-β. The expression of epithelial and mesenchymal markers was investigated. The secretion of inflammatory cytokines and matrix metalloproteinase (MMP)-9 was measured in culture supernatants and in plasma from lung transplant recipients (LTRs): 49 stable, 29 with BOS, and 16 with RAS. We demonstrated that C-C motif chemokine 2 secreted by T cells supports TGF-β-induced MMP-9 production by BECs after binding to C-C chemokine receptor type 2. Longitudinal investigation in LTRs revealed a rise in plasma MMP-9 before CLAD onset. Multivariate analysis showed that plasma MMP-9 was independently associated with BOS (odds ratio [OR] = 6.19, p = 0.002) or RAS (OR = 3.9, p = 0.024) and predicted the occurrence of CLAD 12 months before the functional diagnosis. Thus, immune cells support airway remodeling through the production of MMP-9. Plasma MMP-9 is a potential predictive biomarker of CLAD.

Mesenchymal Stromal Cell Therapy for Chronic Lung Allograft Dysfunction: Results of a First-in-Man Study

Chronic lung transplant rejection (termed chronic lung allograft dysfunction [CLAD]) is the main impediment to long‐term survival after lung transplantation. Bone marrow‐derived mesenchymal stromal cells (MSCs) represent an attractive cell therapy in inflammatory diseases, including organ rejection, given their relative immune privilege and immunosuppressive and tolerogenic properties. Preclinical studies in models of obliterative bronchiolitis and human trials in graft versus host disease and renal transplantation suggest potential efficacy in CLAD. The purpose of this phase 1, single‐arm study was to explore the feasibility and safety of intravenous delivery of allogeneic MSCs to patients with advanced CLAD. MSCs from unrelated donors were isolated from bone marrow, expanded and cryopreserved in a GMP‐compliant facility. Patients had deteriorating CLAD and were bronchiolitis obliterans (BOS) grade ≥ 2 or grade 1 with risk factors for rapid progression. MSCs (2 x 10⁶ cells per kilogram patient weight) were infused via a peripheral vein twice weekly for 2 weeks, with 52 weeks follow‐up. Ten Patients (5 male, 8 bilateral, median [interquartile range] age 40 [30–59] years, 3 BOS2, 7 BOS3) participated. MSC treatment was well tolerated with all patients receiving the full dosing schedule without any procedure‐related serious adverse events. The rate of decline in forced expiratory volume in one second slowed after the MSC infusions (120 ml/month preinfusion vs. 30 ml/month postinfusion, p = .08). Two patients died at 152 and 270 days post‐MSC treatment, both from progressive CLAD. In conclusion, infusion of allogeneic bone marrow‐derived MSCs is feasible and safe even in patients with advanced CLAD. Stem Cells Translational Medicine2017;6:1152–1157

A Systematic Review of the Role of Dysfunctional Wound Healing in the Pathogenesis and Treatment of Idiopathic Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive interstitial lung disorder showcasing an interaction between genetic predisposition and environmental risks. This usually involves the coaction of a mixture of cell types associated with abnormal wound healing, leading to structural distortion and loss of gas exchange function. IPF bears fatal prognosis due to respiratory failure, revealing a median survival of approximately 2 to 3 years. This review showcases the ongoing progress in understanding the complex pathophysiology of IPF and it highlights the latest potential clinical treatments. In IPF, various components of the immune system, particularly clotting cascade and shortened telomeres, are highly involved in disease pathobiology and progression. This review also illustrates two US Food and Drug Administration (FDA)-approved drugs, nintedanib (OFEV, Boehringer Ingelheim, Ingelheim am Rhein, Germany) and pirfenidone (Esbriet, Roche, Basel, Switzerland), that slow IPF progression, but unfortunately neither drug can reverse the course of the disease. Although the mechanisms underlying IPF remain poorly understood, this review unveils the past and current advances that encourage the detection of new IPF pathogenic pathways and the development of effective treatment methods for the near future.

Active compounds extracted from extra virgin olive oil counteract mesothelial-to-mesenchymal transition of peritoneal mesothelium cells exposed to conventional peritoneal dialysate: in vitro and in vivo evidences

During peritoneal dialysis (PD), peritoneal mesothelial cells undergo a transition from an epithelial phenotype to a mesenchymal phenotype that, together with the inflammatory process, promotes tissue fibrosis and a failure of peritoneal membrane function. To date, there is no definitive treatment for the progressive thickening and angiogenesis of the peritoneal membrane associated with PD. In this study we tested, in vitro and in vivo, the ability of active compounds extracted from extra virgin olive oil (AC-EVOO) to counteract the mesothelial-to-mesenchymal transition process (MMT) observed in mesothelial cells chronically exposed to the conventional peritoneal dialysate (DL). In particular, we used a cultivar from southern Italy known to have a high polyphenol content. Our results showed that, in mesothelial cells exposed to DL, the combined treatment with AC-EVOO prevented the genic and protein upregulation of key mesenchymal and inflammatory markers, as well as the MCs' migratory capacity. Concomitantly, we tested the antifibrotic efficacy of AC-EVOO in mesothelial cells obtained from effluents of patients undergoing PD, whose "fibroblast-like" phenotype was defined by flow-cytometry assay. We observed that in these cells AC-EVOO significantly mitigated, but did not reverse, the MMT process. In conclusion, our preliminary results suggest that AC-EVOO can interfere with critical factors in the process of differentiation, preventing myofibroblast formation, but once fibrosis has already progressed it is unable to promote the redifferentiation to the epithelial phenotype. Further studies are needed to establish whether AC-EVOO could represent a new therapeutic target to prevent peritoneal fibrosis.

Airway remodelling in the transplanted lung

Following lung transplantation, fibrotic remodelling of the small airways has been recognized for almost 5 decades as the main correlate of chronic graft failure and a major obstacle to long-term survival. Mainly due to airway fibrosis, pulmonary allografts currently show the highest attrition rate of all solid organ transplants, with a 5-year survival rate of 58 % on a worldwide scale. The observation that these morphological changes are not just the hallmark of chronic rejection but rather represent a manifestation of a multitude of alloimmune-dependent and -independent injuries was made more recently, as was the discovery that chronic lung allograft dysfunction manifests in different clinical phenotypes of respiratory impairment and corresponding morphological subentities. Although recent years have seen considerable advances in identifying and categorizing these subgroups on the basis of clinical, functional and histomorphological changes, as well as susceptibility to medicinal treatment, this process is far from over. Since the actual pathophysiological mechanisms governing airway remodelling are still only poorly understood, diagnosis and therapy of chronic lung allograft dysfunction presents a major challenge to clinicians, radiologists and pathologists alike. Here, we review and discuss the current state of the literature on chronic lung allograft dysfunction and shed light on classification systems, corresponding clinical and morphological changes, key cellular players and underlying molecular pathways, as well as on emerging diagnostic and therapeutic approaches.

The IL-1 cytokine family and its role in inflammation and fibrosis in the lung

The IL-1 cytokine family comprises 11 members (7 ligands with agonist activity, 3 receptor antagonists and 1 anti-inflammatory cytokine) and is recognised as a key mediator of inflammation and fibrosis in multiple tissues including the lung. IL-1 targeted therapies have been successfully employed to treat a range of inflammatory conditions such as rheumatoid arthritis and gouty arthritis. This review will introduce the members of the IL-1 cytokine family, briefly discuss the cellular origins and cellular targets and provide an overview of the role of these molecules in inflammation and fibrosis in the lung.

Pseudomonas aeruginosa Induced Airway Epithelial Injury Drives Fibroblast Activation: A Mechanism in Chronic Lung Allograft Dysfunction

Bacterial infections after lung transplantation cause airway epithelial injury and are associated with an increased risk of developing bronchiolitis obliterans syndrome. The damaged epithelium is a source of alarmins that activate the innate immune system, yet their ability to activate fibroblasts in the development of bronchiolitis obliterans syndrome has not been evaluated. Two epithelial alarmins were measured longitudinally in bronchoalveolar lavages from lung transplant recipients who developed bronchiolitis obliterans syndrome and were compared to stable controls. In addition, conditioned media from human airway epithelial cells infected with Pseudomonas aeruginosa was applied to lung fibroblasts and inflammatory responses were determined. Interleukin-1 alpha (IL-1α) was increased in bronchoalveolar lavage of lung transplant recipients growing P. aeruginosa (11.5 [5.4-21.8] vs. 2.8 [0.9-9.4] pg/mL, p < 0.01) and was significantly elevated within 3 months of developing bronchiolitis obliterans syndrome (8.3 [1.4-25.1] vs. 3.6 [0.6-17.1] pg/mL, p < 0.01), whereas high mobility group protein B1 remained unchanged. IL-1α positively correlated with elevated bronchoalveolar lavage IL-8 levels (r(2)  = 0.6095, p < 0.0001) and neutrophil percentage (r(2)  = 0.25, p = 0.01). Conditioned media from P. aeruginosa infected epithelial cells induced a potent pro-inflammatory phenotype in fibroblasts via an IL-1α/IL-1R-dependent signaling pathway. In conclusion, we propose that IL-1α may be a novel therapeutic target to limit Pseudomonas associated allograft injury after lung transplantation.

Advances in Understanding Bronchiolitis Obliterans After Lung Transplantation

Bronchiolitis obliterans syndrome (BOS) remains a major complication after lung transplantation, causing significant morbidity and mortality in a majority of recipients. BOS is believed to be the clinical correlate of chronic allograft dysfunction, and is defined as an obstructive pulmonary function defect in the absence of other identifiable causes, mostly not amenable to treatment. Recently, it has become clear that BOS is not the only form of chronic allograft dysfunction and that other clinical phenotypes exist; however, we focus exclusively on BOS. Radiologic findings typically demonstrate air trapping, mosaic attenuation, and hyperinflation. Pathologic examination reveals obliterative bronchiolitis lesions and a pure obliteration of the small airways (< 2 mm), with a relatively normal surrounding parenchyma. In this review, we highlight recent advances in diagnosis, pathologic examination, and risk factors, such as microbes, viruses, and antibodies. Although the pathophysiological mechanisms remain largely unknown, we review the role of the airway epithelium and inflammation and the various experimental animal models. We also clarify the clinical and therapeutic implications of these findings. Although significant progress has been made, the exact pathophysiological mechanisms and adequate therapy for posttransplantation BOS remain unknown, highlighting the need for further research to improve long-term posttransplantation BOS-free and overall survival.

The Impact of Infection on Chronic Allograft Dysfunction and Allograft Survival After Solid Organ Transplantation

Infectious diseases after solid organ transplantation (SOT) are a significant cause of morbidity and reduced allograft and patient survival; however, the influence of infection on the development of chronic allograft dysfunction has not been completely delineated. Some viral infections appear to affect allograft function by both inducing direct tissue damage and immunologically related injury, including acute rejection. In particular, this has been observed for cytomegalovirus (CMV) infection in all SOT recipients and for BK virus infection in kidney transplant recipients, for community-acquired respiratory viruses in lung transplant recipients, and for hepatitis C virus in liver transplant recipients. The impact of bacterial and fungal infections is less clear, but bacterial urinary tract infections and respiratory tract colonization by Pseudomonas aeruginosa and Aspergillus spp appear to be correlated with higher rates of chronic allograft dysfunction in kidney and lung transplant recipients, respectively. Evidence supports the beneficial effects of the use of antiviral prophylaxis for CMV in improving allograft function and survival in SOT recipients. Nevertheless, there is still a need for prospective interventional trials assessing the potential effects of preventive and therapeutic strategies against bacterial and fungal infection for reducing or delaying the development of chronic allograft dysfunction.

Epithelial-mesenchymal transition: An emerging target in tissue fibrosis

Epithelial-mesenchymal transition (EMT) is involved in a variety of tissue fibroses. Fibroblasts/myofibroblasts derived from epithelial cells contribute to the excessive accumulation of fibrous connective tissue in damaged tissue, which can lead to permanent scarring or organ malfunction. Therefore, EMT-related fibrosis cannot be neglected. This review highlights the findings that demonstrate the EMT to be a direct contributor to the fibroblast/myofibroblast population in the development of tissue fibrosis and helps to elucidate EMT-related anti-fibrotic strategies, which may enable the development of therapeutic interventions to suppress EMT and potentially reverse organ fibrosis.

Seeding of recipient-originated epithelial cells attenuates epithelial to mesenchymal transition in rat tracheal allotransplantation

OBJECTIVE

The specific role and mechanism of epithelium in the progression of obliterative airway disease (OAD) after tracheal allotransplantation remain poorly understood. In this study, we used rat heterotopic tracheal transplantation to investigate the mechanism of epithelial cell seeding during the process of OAD.

STUDY DESIGN

Prospective, basic science.

SETTING

Research laboratory.

SUBJECTS AND METHODS

In total, 120 Sprague Dawley (SD) rats and 90 Wistar rats were used. Tracheas from SD rats were implanted into SD rats (syngeneic, n = 30) or Wistar rats (allogeneic, n = 30), and SD rat tracheas (seeded with Wistar rat-derived epithelial cells 6 days after transplantation) were transplanted into Wistar rats (seeded allogeneic, n = 30). Grafts were harvested at 7, 14, or 30 days after transplantation for histologic, quantitative reverse transcriptional polymerase chain reaction or Western blot analyses.

RESULTS

Syngrafts retained normal histologic structures, while the corresponding allografts demonstrated less ciliated epithelia and more lumenal occlusion. Seeding of epithelial cells ameliorated the histologic changes, reduced the expression of epithelial to mesenchymal transition (EMT)-related transcriptional factors and mesenchymal markers, and dampened the expression of transforming growth factor β1 (TGF-β1) and phosphorylation of smad3.

CONCLUSION

Seeding of recipient epithelial cells inhibits the progression of OAD by attenuating EMT via TGF-β-Smad signaling in rat heterotopic tracheal allografts. Clinically, the injection of recipient-originated epithelial cells might provide new insights into the treatment for OAD after tracheal allotransplantation.

Adaptive and innate immune responses in a rat orthotopic lung transplant model of chronic lung allograft dysfunction

Acute rejection and respiratory infections are major risk factors for chronic lung allograft dysfunction (CLAD) after lung transplantation. To shed light on the enigmatic etiology of CLAD, we test the following hypotheses using a new experimental model: (i) Alloimmune-independent pulmonary inflammation reactivates alloimmunity. (ii) Alloimmunity enhances the susceptibility of the graft toward pathogen-associated molecular patterns. Pulmonary Fischer 344 to Lewis rat allografts were treated with lipopolysaccharide (LPS), which consistently results in lesions typical for CLAD. Grafts, local lymph nodes, and spleens were harvested before (day 28) and after LPS application (days 29, 33, and 40) for real-time RT-PCR and immunohistochemistry. Mixed lymphocyte reactions were performed on day 33. Four weeks after transplantation, lung allografts displayed mononuclear infiltrates compatible with acute rejection and overexpressed most components of the toll-like receptor system. Allografts but not secondary lymphoid organs expressed increased levels of Th1-type transcription factors and cytokines. LPS induced macrophage infiltration as well as mRNA expression of pro-inflammatory cytokines and effector molecules of innate immunity. Unexpectedly, T-cell reactivity was not enhanced by LPS. We conclude that prevention of CLAD might be accomplished by local suppression of Th1 cells in stable grafts and by controlling innate immunity during alloimmune-independent pulmonary inflammation.

Mechanistic differences between phenotypes of chronic lung allograft dysfunction after lung transplantation

Distinct phenotypes of chronic lung allograft dysfunction (CLAD) after lung transplantation are emerging with lymphocytic bronchiolitis (LB)/azithromycin reversible allograft dysfunction (ARAD), classical or fibrotic bronchiolitis obliterans syndrome (BOS), and restrictive allograft syndrome (RAS) proposed as separate entities. We have additionally identified lung transplant recipients with prior LB, demonstrating persistent airway neutrophilia (PAN) despite azithromycin treatment. The aim of this study was to evaluate differences in the airway microenvironment in different phenotypes of CLAD. Bronchoalveolar lavage (BAL) from recipients identified as stable (control), LB/ARAD, PAN, BOS, and RAS were evaluated for differential cell counts and concentrations of IL-1α, IL-1β, IL-6, IL-8, and TNF-α. Primary human bronchial epithelial cells were exposed to BAL supernatants from different phenotypes and their viability measured. BOS and RAS showed increased BAL neutrophilia but no change in cytokine concentrations compared with prediagnosis. In both LB/ARAD and PAN, significant increases in IL-1α, IL-1β, and IL-8 were present. BAL IL-6 and TNF-α concentrations were increased in PAN and only this phenotype demonstrated decreased epithelial cell viability after exposure to BAL fluid. This study demonstrates clear differences in the airway microenvironment between different CLAD phenotypes. Systematic phenotyping of CLAD may help the development of more personalized approaches to treatment.

Innate immune cells in transplantation

PURPOSE OF REVIEW

To examine the recent literature on the role of innate cells in immunity to transplanted tissue. It specifically addresses the impact of monocytes/macrophages, neutrophils, natural killer cells, and platelets.

RECENT FINDINGS

Current research indicates that innate immunity plays a dual role in response to transplanted tissue with the ability to either facilitate rejection or promote tolerance. Intriguingly, some of these cells are even capable of reacting to allogeneic cells, a feature usually only attributed to cells of the adaptive immune system.

SUMMARY

This review highlights the new therapeutic targets in the innate immune system that may be useful in the treatment of transplant recipients. It also emphasizes the need to use caution in exploring these new therapeutics.