Transient airway colonization is associated with airway inflammation after lung transplantation

Unique Changes in the Lung Microbiome following the Development of Chronic Lung Allograft Dysfunction

The importance of lung microbiome changes in developing chronic lung allograft dysfunction (CLAD) after lung transplantation is poorly understood. The lung microbiome-immune interaction may be critical in developing CLAD. In this context, examining alterations in the microbiome and immune cells of the lungs following CLAD, in comparison to the lung condition immediately after transplantation, can offer valuable insights. Four adult patients who underwent lung retransplantation between January 2019 and June 2020 were included in this study. Lung tissues were collected from the same four individuals at two different time points: at the time of the first transplant and at the time of the explantation of CLAD lungs at retransplantation due to CLAD. We analyzed whole-genome sequencing using the Kraken2 algorithm and quantified the cell fractionation from the bulk tissue gene expression profile for each lung tissue. Finally, we compared the differences in lung microbiome and immune cells between the lung tissues of these two time points. The median age of the recipients was 57 years, and most (75%) had undergone lung transplants for idiopathic pulmonary fibrosis. All patients were administered basiliximab for induction therapy and were maintained on three immunosuppressants. The median CLAD-free survival term was 693.5 days, and the median time to redo the lung transplant was 843.5 days. Bacterial diversity was significantly lower in the CLAD lungs than at transplantation. Bacterial diversity tended to decrease according to the severity of the CLAD. Aerococcus, Caldiericum, Croceibacter, Leptolyngbya, and Pulveribacter genera were uniquely identified in CLAD, whereas no taxa were identified in lungs at transplantation. In particular, six taxa, including Croceibacter atlanticus, Caldiserium exile, Dolichospermum compactum, Stappia sp. ES.058, Kinetoplastibacterium sorsogonicusi, and Pulveribacter suum were uniquely detected in CLAD. Among immune cells, CD8+ T cells were significantly increased, while neutrophils were decreased in the CLAD lung. In conclusion, unique changes in lung microbiome and immune cell composition were confirmed in lung tissue after CLAD compared to at transplantation.

Successful Pseudomonas aeruginosa eradication improves outcomes after lung transplantation: a retrospective cohort analysis

Long-term survival after lung transplantation (LTx) is hampered by development of chronic lung allograft dysfunction (CLAD). Pseudomonas aeruginosa is an established risk factor for CLAD. Therefore, we investigated the effect of P. aeruginosa eradication on CLAD-free and graft survival.

Patients who underwent first LTx between July, 1991, and February, 2016, and were free from CLAD, were retrospectively classified according to P. aeruginosa presence in respiratory samples between September, 2011, and September, 2016. P. aeruginosa-positive patients were subsequently stratified according to success of P. aeruginosa eradication following targeted antibiotic treatment. CLAD-free and graft survival were compared between P. aeruginosa-positive and P. aeruginosa-negative patients; and between patients with or without successful P. aeruginosa eradication. In addition, pulmonary function was assessed during the first year following P. aeruginosa isolation in both groups.

CLAD-free survival of P. aeruginosa-negative patients (n=443) was longer compared with P. aeruginosa-positive patients (n=95) (p=0.045). Graft survival of P. aeruginosa-negative patients (n=443, 82%) was better compared with P. aeruginosa-positive patients (n=95, 18%) (p<0.0001). Similarly, P. aeruginosa-eradicated patients demonstrated longer CLAD-free and graft survival compared with patients with persistent P. aeruginosa. Pulmonary function was higher in successfully P. aeruginosa-eradicated patients compared with unsuccessfully eradicated patients (p=0.035).

P. aeruginosa eradication after LTx improves CLAD-free and graft survival and maintains pulmonary function. Therefore, early P. aeruginosa detection and eradication should be pursued.

Challenges in the Diagnosis and Management of Bacterial Lung Infections in Solid Organ Recipients: A Narrative Review

Respiratory infections pose a significant threat to the success of solid organ transplantation, and the diagnosis and management of these infections are challenging. The current narrative review addressed some of these challenges, based on evidence from the literature published in the last 20 years. Specifically, we focused our attention on (i) the obstacles to an etiologic diagnosis of respiratory infections among solid organ transplant recipients, (ii) the management of bacterial respiratory infections in an era characterized by increased antimicrobial resistance, and (iii) the development of antimicrobial stewardship programs dedicated to solid organ transplant recipients.

Multidrug-resistant Gram-negative bacterial infections in solid organ transplant recipients-Guidelines from the American Society of Transplantation Infectious Diseases Community of Practice

These updated guidelines from the Infectious Diseases Community of Practice of the American Society of Transplantation review the diagnosis, prevention, and management of infections due to multidrug-resistant (MDR) Gram-negative bacilli in the pre- and post-transplant period. MDR Gram-negative bacilli, including carbapenem-resistant Enterobacteriaceae, MDR Pseudomonas aeruginosa, and carbapenem-resistant Acinetobacter baumannii, remain a threat to successful organ transplantation. Clinicians now have access to at least five novel agents with activity against some of these organisms, with others in the advanced stages of clinical development. No agent, however, provides universal and predictable activity against any of these pathogens, and very little is available to treat infections with MDR nonfermenting Gram-negative bacilli including A baumannii. Despite advances, empiric antibiotics should be tailored to local microbiology and targeted regimens should be tailored to susceptibilities. Source control remains an important part of the therapeutic armamentarium. Morbidity and mortality associated with infections due to MDR Gram-negative organisms remain unacceptably high. Heightened infection control and antimicrobial stewardship initiatives are needed to prevent these infections, curtail their transmission, and limit the evolution of MDR Gram-negative pathogens, especially in the setting of organ transplantation.

Immunomodulatory Cell Therapy to Target Cystic Fibrosis Inflammation

Cystic fibrosis (CF) is associated with exaggerated and prolonged inflammation in the lungs, which contributes to lung injury, airway mucus obstruction, bronchiectasis, and loss of lung function. This hyperinflammatory phenotype appears to be caused by an imbalance between the pro- and antiinflammatory regulatory pathways, with heightened proinflammatory stimuli, a decreased counter-regulatory response, and reduced effectiveness of immune cell function and inflammatory resolution. Thus, therapies that can target this inflammatory environment would have a major impact on preventing the progression of lung disease. Because of the complex phenotype of CF inflammation, current antiinflammatory regimens have proven to be inadequate for the targeting of these multiple dysregulated pathways and effects. Several approaches using cell therapies have shown potential therapeutic benefit for the treatment of CF inflammation. This review provides an overview of the immune dysfunctions in CF and current therapeutic regimens; explores the field of cell therapy as a treatment for CF inflammation; and focuses on the various cell types used, their immunomodulatory functions, and the current approaches to mitigate the inflammatory response and reduce the long-term damage for patients with CF.

Long-term outcomes and management of lung transplant recipients

Lung transplantation is an established treatment for patients with end-stage lung disease. Improvements in immunosuppression and therapeutic management of infections have resulted in improved long-term survival and a decline in allograft rejection. Allograft rejection continues to be a serious complication following lung transplantation, thereby leading to acute graft failure and, subsequently, chronic lung allograft dysfunction (CLAD). Bronchiolitis obliterans syndrome (BOS), the most common phenotype of CLAD, is the leading cause of late mortality and morbidity in lung recipients, with 50% having developed BOS within 5 years of lung transplantation. Infections in lung transplant recipients are also a significant complication and represent the most common cause of death within the first year. The success of lung transplantation depends on careful management of immunosuppressive regimens to reduce the rate of rejection, while monitoring recipients for infections and complications to help identify problems early. The long-term outcomes and management of lung transplant recipients are critically based on modulating natural immune response of the recipient to prevent acute and chronic rejection. Understanding the immune mechanisms and temporal correlation of acute and chronic rejection is thus critical in the long-term management of lung recipients.

Infectious Triggers of Chronic Lung Allograft Dysfunction

Survival after lung transplantation is limited in large part due to the high incidence of chronic rejection, known as chronic lung allograft dysfunction (CLAD). Pulmonary infections are a frequent complication in lung transplant recipients, due both to immunosuppressive medications and constant exposure of the lung allograft to the external environment via the airways. Infection is a recognized risk factor for the development of CLAD, and both acute infection and chronic lung allograft colonization with microorganisms increase the risk for CLAD. Acute infection by community acquired respiratory viruses, and the bacteria Pseudomonas aeruginosa and Staphylococcus aureus are increasingly recognized as important risk factors for CLAD. Colonization by the fungus Aspergillus may also augment the risk of CLAD. Fostering this transition from healthy lung to CLAD in each of these infectious episodes is the persistence of an inflammatory lung allograft environment.

Staphylococcus via an interaction with the ELR+ CXC chemokine ENA-78 is associated with BOS

Staphylococcus aureus is the most commonly isolated gram-positive bacterium after lung transplantation (LT) and has been associated with poor posttransplant outcomes, but its effect on bronchiolitis obliterans syndrome (BOS) and death in the context of the allograft inflammatory environment has not been studied. A three-state Cox semi-Markovian model was used to determine the influence of allograft S. aureus and the ELR+ CXC chemokines on the survival rates and cause-specific hazards for movement from lung transplant (State 1) to BOS (State 2), from transplant (State 1) to death (State 3), and from BOS (State 2) to death (State 3). Acute rejection, pseudomonas pneumonia, bronchoalveolar lavage fluid (BALF) CXCL5 and its interaction with S. aureus all increased the likelihood of transition from transplant to BOS. Transition to death from transplant was facilitated by pseudomonas infection and single lung transplant. Movement from BOS to death was affected by the interaction between aspergillus, pseudomonas and CXCL5, but not S. aureus. S. aureus isolation had state specific effects after LT and only in concert with elevated BALF CXCL5 concentrations did it augment the risk of BOS. Pseudomonas and elevated BALF concentrations of CXCL5 continued as significant risk factors for BOS and death after BOS in lung transplantation.

Differential cytokine, chemokine and growth factor expression in phenotypes of chronic lung allograft dysfunction

BACKGROUND

Chronic lung allograft dysfunction is a heterogeneous entity limiting long-term survival after lung transplantation. Different clinical phenotypes (bronchiolitis obliterans syndrome [BOS]-neutrophilic BOS-restrictive allograft syndrome [RAS]) have been identified but the mechanisms remain elusive.

METHODS

In this study, we measured 34 different cytokines, chemokines, and growth factors in bronchoalveolar lavage fluid of 20 stable patients, 20 patients suffering from non-neutrophilic BOS, 17 from neutrophilic BOS, and 20 from RAS using classic enzyme-linked immunosorbent assay and multiplex technology.

RESULTS

Total cell count and % neutrophils were elevated in neutrophilic BOS and RAS compared to stable and non-neutrophilic BOS patients, whereas also the % eosinophils was elevated at diagnosis of RAS. Levels of interleukin (IL)-1β (P<0.01), IL-1Rα (P<0.001), IL-6 (P<0.001), IL-8/CXCL8 (P<0.001), IP-10/CXCL10 (P<0.05), MCP-1/CCL2 (P<0.05), macrophage inflammatory protein (MIP)-1α/CCL3 (P<0.001), MIP-1β/CCL4, and vascular endothelial growth factor (VEGF; P<0.05) were differentially regulated in RAS compared to stable, whereas in neutrophilic BOS IL-1β (P<0.001), IL-1Rα (P<0.01), IL-7 (P<0.05), IL-8/CXCL8 (P<0.001), MCP-3/CXCCL7 (P<0.05) and MIP-1α/CCL-3 (P<0.05) were significantly upregulated compared to stable patients. We could not detect any differences between non-neutrophilic BOS and stable patients. Interestingly, bronchoalveolar lavage IL-6, interferon gamma-induced protein (IP)-10/CXCL10 and interferon-inducible T-cell alpha chemoattractant/chemokine (C-X-C motif) ligand 11 (ITAC/CXCL10) were associated with survival after diagnosis in RAS patients.

CONCLUSION

There were major differences in cytokine and chemokine expression in our different study groups. Especially IL-6, but also IP-10/CXCL10, and VEGF may be interesting mediators in RAS.

An international ISHLT/ATS/ERS clinical practice guideline: diagnosis and management of bronchiolitis obliterans syndrome

Bronchiolitis obliterans syndrome (BOS) is a major complication of lung transplantation that is associated with poor survival. The International Society for Heart and Lung Transplantation, American Thoracic Society, and European Respiratory Society convened a committee of international experts to describe and/or provide recommendations for 1) the definition of BOS, 2) the risk factors for developing BOS, 3) the diagnosis of BOS, and 4) the management and prevention of BOS. A pragmatic evidence synthesis was performed to identify all unique citations related to BOS published from 1980 through to March, 2013. The expert committee discussed the available research evidence upon which the updated definition of BOS, identified risk factors and recommendations are based. The committee followed the GRADE (Grading of Recommendation, Assessment, Development and Evaluation) approach to develop specific clinical recommendations. The term BOS should be used to describe a delayed allograft dysfunction with persistent decline in forced expiratory volume in 1 s that is not caused by other known and potentially reversible causes of post-transplant loss of lung function. The committee formulated specific recommendations about the use of systemic corticosteroids, cyclosporine, tacrolimus, azithromycin and about re-transplantation in patients with suspected and confirmed BOS. The diagnosis of BOS requires the careful exclusion of other post-transplant complications that can cause delayed lung allograft dysfunction, and several risk factors have been identified that have a significant association with the onset of BOS. Currently available therapies have not been proven to result in significant benefit in the prevention or treatment of BOS. Adequately designed and executed randomised controlled trials that properly measure and report all patient-important outcomes are needed to identify optimal therapies for established BOS and effective strategies for its prevention.

The need for a new animal model for chronic rejection after lung transplantation

The single most important cause of late mortality after lung transplantation is obliterative bronchiolitis (OB), clinically characterized by a decrease in lung function and morphologically by characteristic changes. Recently, new insights into its pathogenesis have been acquired: risk factors have been identified and the use of azithromycin showed a dichotomy with at least 2 different phenotypes of bronchiolitis obliterans syndrome (BOS). It is clear that a good animal model is indispensable to further dissect and unravel the pathogenesis of BOS. Many animal models have been developed to study BOS but, so far, none of these models truly mimics the human situation. Looking at the definition of BOS, a good animal model implies histological OB lesions, possibility to measure lung function, and airway inflammation. This review sought to discuss, including pros and cons, all potential animal models that have been developed to study OB/BOS. It has become clear that a new animal model is needed; recent developments using an orthotopic mouse lung transplantation model may offer the answer because it mimics the human situation. The genetic variants among this species may open new perspectives for research into the pathogenesis of OB/BOS.

Aspirated bile: a major host trigger modulating respiratory pathogen colonisation in cystic fibrosis patients

Chronic respiratory infections are a leading global cause of morbidity and mortality. However, the molecular triggers that cause respiratory pathogens to adopt persistent and often untreatable lifestyles during infection remain largely uncharacterised. Recently, bile aspiration caused by gastro-oesophageal reflux (GOR) has emerged as a significant complication associated with respiratory disease, and cystic fibrosis (CF) in particular. Based on our previous finding that the physiological concentrations of bile influence respiratory pathogens towards a chronic lifestyle in vitro, we investigated the impact of bile aspiration on the lung microbiome of respiratory patients. Sputum samples (n = 25) obtained from a cohort of paediatric CF patients were profiled for the presence of bile acids using high-resolution liquid chromatography-mass spectrometry (LC-MS). Pyrosequencing was performed on a set of ten DNA samples that were isolated from bile aspirating (n = 5) and non-bile aspirating (n = 5) patients. Both denaturing gradient gel electrophoresis (DGGE) and pyrosequencing revealed significantly reduced biodiversity and richness in the sputum samples from bile aspirating patients when compared with non-aspirating patients. Families and genera associated with the pervasive CF microbiome dominated aspirating patients, while bacteria associated with the healthy lung were most abundant in non-aspirating patients. Bile aspiration linked to GOR is emerging as a major host trigger of chronic bacterial infections. The markedly reduced biodiversity and increased colonisation by dominant proteobacterial CF-associated pathogens observed in the sputum of bile aspirating patients suggest that bile may play a major role in disease progression in CF and other respiratory diseases.

Interaction between Pseudomonas and CXC chemokines increases risk of bronchiolitis obliterans syndrome and death in lung transplantation

RATIONALE

Pseudomonas aeruginosa is the most commonly isolated gram-negative bacterium after lung transplantation and has been shown to up-regulate glutamic acid-leucine-arginine-positive (ELR(+)) CXC chemokines associated with bronchiolitis obliterans syndrome (BOS), but the effect of pseudomonas on BOS and death has not been well defined.

OBJECTIVES

To determine if the influence of pseudomonas isolation and ELR(+) CXC chemokines on the subsequent development of BOS and the occurrence of death is time dependent.

METHODS

A three-state model was developed to assess the likelihood of transitioning from lung transplant (state 1) to BOS (state 2), from transplant (state 1) to death (state 3), and from BOS (state 2) to death (state 3). This Cox semi-Markovian approach determines state survival rates and cause-specific hazards for movement from one state to another.

MEASUREMENTS AND MAIN RESULTS

The likelihood of transition from transplant to BOS was increased by acute rejection, CXCL5, and the interaction between pseudomonas and CXCL1. The pseudomonas effect in this transition was due to infection rather than colonization. Movement from transplant to death was facilitated by pseudomonas infection and single lung transplant. Transition from BOS to death was affected by the length of time in state 1 and by the interactions between any pseudomonas isolation and CXCL5 and aspergillus, either independently or in combination.

CONCLUSIONS

Our model demonstrates that common post-transplantation events drive movement from one post-transplantation state to another and influence outcomes differently depending upon when after transplantation they occur. Pseudomonas and the ELR(+) CXC chemokines may interact to negatively influence lung transplant outcomes.

Anti-inflammatory and immunomodulatory properties of azithromycin involved in treatment and prevention of chronic lung allograft rejection

Chronic lung allograft rejection is the single most important cause of death in lung transplant recipients after the first postoperative year, resulting in a 5-year survival rate of approximately 50%, which is far behind that of other solid organ transplantations. Spirometry is routinely used as a clinical marker for assessing pulmonary allograft function and diagnosing chronic lung allograft rejection after lung transplantation (LTx). As such, a progressive obstructive decline in pulmonary allograft function (forced expiratory volume in 1 sec [FEV1]) in absence of all other causes (currently defined as bronchiolitis obliterans syndrome [BOS]) is considered to reflect the evolution of chronic lung allograft rejection. BOS has a 5-year prevalence of approximately 45% and is thought to be the final common endpoint of various alloimmunologic and nonalloimmunologic injuries to the pulmonary allograft, triggering different innate and adaptive immune responses. Most preventive and therapeutic strategies for this complex process have thus far been largely unsuccessful. However, the introduction of the neomacrolide antibiotic azithromycin (AZI) in the field of LTx as of 2003 made it clear that some patients with established BOS might in fact benefit from such therapy due to its various antiinflammatory and immunomodulatory properties, as summarized in this review. Particularly in patients with an increased bronchoalveolar lavage neutrophilia (i.e., 15%-20% or more), AZI treatment could result in an increase in FEV1 of at least 10%. More recently, it has become clear that prophylactic therapy with AZI actually may prevent BOS and improve FEV1 after LTx, most likely through its interactions with the innate immune system. However, one should always be aware of possible adverse effects related to AZI when implementing this drug as prophylactic or long-term treatment. Even so, AZI therapy after LTx can generally be considered as safe.

Respiratory pathogens adopt a chronic lifestyle in response to bile

Chronic respiratory infections are a major cause of morbidity and mortality, most particularly in Cystic Fibrosis (CF) patients. The recent finding that gastro-esophageal reflux (GER) frequently occurs in CF patients led us to investigate the impact of bile on the behaviour of Pseudomonas aeruginosa and other CF-associated respiratory pathogens. Bile increased biofilm formation, Type Six Secretion, and quorum sensing in P. aeruginosa, all of which are associated with the switch from acute to persistent infection. Furthermore, bile negatively influenced Type Three Secretion and swarming motility in P. aeruginosa, phenotypes associated with acute infection. Bile also modulated biofilm formation in a range of other CF-associated respiratory pathogens, including Burkholderia cepacia and Staphylococcus aureus. Therefore, our results suggest that GER-derived bile may be a host determinant contributing to chronic respiratory infection.

Diagnostic value of antibodies against Pseudomonas aeruginosa in bronchoalveolar lavage fluid after lung transplantation

BACKGROUND

Pseudomonal airway colonization is a risk factor for chronic allograft dysfunction after lung transplantation (LTx). Pseudomonas aeruginosa exoproteases are involved in initiating colonization, and immune complexes directed against these proteases may activate innate immune responses.

OBJECTIVE

To investigate whether specific antibodies against pseudomonal proteases could be measured in bronchoalveolar lavage (BAL) fluid, whether they are associated with innate immune responses, and whether they could identify patients with chronic P. aeruginosa colonization after LTx.

MATERIALS AND METHODS

BAL fluid from 40 noncolonized and 25 chronically colonized LTx recipients was retrospectively assayed for IgG antibodies against P. aeruginosa alkaline protease (AP), elastase (Ela), and exotoxin (Exo), and for BAL total and differential cell counts and IL-8 protein concentration.

RESULTS

BAL anti-Ela and anti-Exo antibody titers were significantly increased in colonized compared with noncolonized patients (P = .009 and P = .02, respectively), whereas anti-AP titers were comparable (P = .79). Antibody titers strongly correlated with each other, and anti-Ela and anti-Exo titers, but not anti-AP titers, also correlated with BAL total cellularity, neutrophilia, and IL-8 protein concentration. Anti-Ela antibodies demonstrated the greatest diagnostic value in receiver operating characteristic analysis to detect chronic airway colonization (P = .009), followed by anti-Exo (P = .02) and anti-AP (P = .79). A combination of all 3 antibodies resulted in overall sensitivity of 45% (95% confidence interval [CI], 29.3-61.5), specificity of 88% (95% CI, 68.8-97.5), and positive predictive value of 55% (95% CI, 38.5-70.7).

CONCLUSION

P. aeruginosa proteases in BAL may be associated with local innate immune responses, and could have the potential to enable detection of chronic colonization after LTx.

Relevance of GERD in lung transplant patients

Lung transplantation has become a valuable treatment for end-stage pulmonary disorders in an attempt to improve quality of life and extend survival. Development of chronic rejection, also known as bronchiolitis obliterans syndrome (BOS), is responsible for the vast majority of deaths after lung transplantation. Up to 50% of lung transplant patients develop BOS within the first 5 years after transplantation. A high prevalence of gastroesophageal reflux and aspiration of gastric components has been described after lung transplantation. Reflux and aspiration have been implicated in the development of BOS and antireflux surgery has been proposed; however, the causal relationship with BOS and the impact of reflux in lung transplantation survival needs to be further elucidated.

Exhaled carbon monoxide as a noninvasive marker of airway neutrophilia after lung transplantation

BACKGROUND

Neutrophilic airway inflammation and associated oxidative stress contribute to airway injury and the development of bronchiolitis obliterans syndrome after lung transplantation (LTx). Exhaled carbon monoxide (eCO) reflects heme oxygenase-1 activity in response to oxidative stress. We investigated whether airway neutrophilia and eCO levels are associated in stable LTx recipients.

METHODS

In this cross-sectional pilot study, 45 stable LTx recipients were included. During routine follow-up at the outpatient clinic, pulmonary function testings together with eCO measurements before broncho-alveolar lavage (BAL) were performed. BAL cell differentials and interleukin (IL)-8 protein levels were assessed and correlated with eCO.

RESULTS

In the studied cohort, eCO levels were increased in patients with elevated (>3%) BAL neutrophilia compared with those with normal BAL neutrophilia (P=0.025). Furthermore, eCO levels significantly correlated with BAL neutrophilia and IL-8 levels in the cohort as a whole (r=0.50; P=0.0005 for total cells, r=0.43; P=0.003 for %cells and r=0.30; P=0.045 for IL-8). This was even more obvious in the LTx recipients with increased (>3%) BAL neutrophilia (r=0.70; P=0.0007 for total cells and r=0.80; P<0.0001 for %cells). For a cutoff of 4 ppm, sensitivity, specificity, positive and negative predictive value of eCO for detecting elevated BAL neutrophilia were 84.0%, 45.0%, 65.6%, and 69.2%, respectively (P=0.049).

CONCLUSIONS

Elevated eCO levels in stable LTx recipients may reflect an increased BAL neutrophilia and could, therefore, be used as a noninvasive marker for airway inflammation after LTx.

The role of intrapulmonary de novo lymphoid tissue in obliterative bronchiolitis after lung transplantation

Chronic rejection after lung transplantation is manifested as obliterative bronchiolitis (OB). The development of de novo lymphoid tissue (lymphoid neogenesis) may contribute to local immune responses in small airways. Compared with normal lungs, the lung tissue of 13 lung transplant recipients who developed OB demonstrated a significantly larger number of small, airway-associated, peripheral node addressin-positive (PNAd(+)) high endothelial venules (HEVs) unique to lymphoid tissue (p < 0.001). HEVs were most abundant in lesions of lymphocytic bronchiolitis and "active" OB infiltrated by lymphocytes compared with those of "inactive" OB. T cells in lymphocytic bronchiolitis and active OB were predominantly of the CD45RO(+)CCR7(-) effector memory phenotype. Similar lymphoid tissue was also observed in the rat lung after intrapulmonary transplantation of allograft trachea (Brown Norway (BN) to Lewis), but not after isograft transplantation. Subsequent orthotopic transplantation of the recipient Lewis lung containing a BN trachea into an F(1) (Lewis x BN) rat demonstrated stable homing of Lewis-derived T cells in the lung and their Ag-specific effector function against the secondary intrapulmonary BN trachea. In conclusion, we found de novo lymphoid tissue in the lung composed of effector memory T cells and HEVs but lacking delineated T cell and B cell zones. This de novo lymphoid tissue may play a critical role in chronic local immune responses after lung transplantation.

Targeting allograft injury and inflammation in the management of post-lung transplant bronchiolitis obliterans syndrome

Chronic allograft dysfunction, manifesting as bronchiolitis obliterans syndrome (BOS), is the major cause of morbidity and mortality in human lung transplant recipients. While alloimmunity has a definite role, there is increasing interest in overall allograft injury and subsequent inflammation and remodeling. This review deals with nonalloimmune factors that may potentiate alloimmune injury. We discuss infection and reflux/aspiration as examples of allograft injury, which may lead to chronic loss of graft function and BOS. Surgical and nonsurgical treatments aimed at preventing these insults and improving survival are considered. The need for further evidence, including randomized-controlled trials, to evaluate the role of medical and surgical therapies is emphasized by the current literature.

Bronchiolitis obliterans syndrome: alloimmune-dependent and -independent injury with aberrant tissue remodeling

Long-term success in lung transplantation continues to be challenged by chronic graft dysfunction, which is manifest as bronchiolitis obliterans syndrome (BOS). The mechanisms of BOS involve both immune-mediated pathways (rejection, autoimmune-like mechanisms), and alloimmune-independent pathways (infection, aspiration, ischemia, primary graft failure), which lead to a fibroproliferative responses. BOS correlates histologically with obliterative bronchiolitis in terminal bronchioles and evidence of aberrant remodeling in the airway epithelium, vasculature, stroma, and lymphoid system. A potentially important mechanism that supports the progressive and therapy-resistant nature of BOS is a continuous cycle of ongoing injury and aberrant remodeling. Namely, anatomical and functional abnormalities induce and exacerbate immune-mediated and alloimmune-independent pathways through various mechanisms (e.g., epithelial remodeling decreases mucociliary clearance that exacerbates aspiration-related injury). From this viewpoint, we review current therapeutic strategies and revisit the role of transplant surgeons in attenuating the initial transplant-related injuries to prevent the lung grafts from entering the remodeling-injury cycle.

Airway colonization and gastric aspiration after lung transplantation: do birds of a feather flock together?

BACKGROUND

Both gastroesophageal reflux and airway colonization with Pseudomonas aeruginosa (P aeruginosa) are common in lung transplantation (LTx) recipients. There is mounting evidence that, due to their interaction with the epithelium, both may be involved in chronic allograft dysfunction/bronchiolitis obliterans syndrome (BOS) after LTx. We investigated whether gastric aspiration and airway colonization with P aeruginosa after LTx are associated.

METHODS

In this retrospective, cross-sectional, case-control study, 24 stable double (SS) LTx recipients were included. Markers of gastroesophageal reflux (pepsin, bile acids) and airway inflammation (neutrophilia and interleukin-8 (IL-8)) were evaluated in bronchoalveolar lavage (BAL) samples of post-operatively colonized (n = 12) and non-colonized matched-control LTx recipients (n = 12).

RESULTS

BAL bile acid levels, but not pepsin levels, as well as neutrophilia and IL-8 protein levels were significantly elevated in colonized compared with non-colonized patients. Furthermore, bile acid levels, but not pepsin levels, correlated positively with BAL neutrophilia and IL-8 protein levels.

CONCLUSIONS

Bile acid aspiration and airway colonization by P aeruginosa after LTx seem to be associated. This relationship between reflux and airway colonization and their role in the development of chronic allograft dysfunction/BOS after LTx should be further elucidated; nevertheless, induction of IL-8-mediated neutrophilic airway inflammation may be a putative mechanism.

The role of the IL23/IL17 axis in bronchiolitis obliterans syndrome after lung transplantation

Bronchiolitis obliterans syndrome (BOS) is the leading cause of death after lung transplantation. Treatment is challenging, as the precise pathophysiology remains unclear. We hypothesize that T(H)17 lineage plays a key role in the pathophysiology of BOS by linking T-cell activation to neutrophil influx and chronic inflammation. In a cross-sectional study, bronchoalveolar lavage (BAL) samples of 132 lung transplant recipients were analyzed. Patients were divided in four groups: stable or suffering from infection (INF), acute rejection (AR) or BOS. The upstream T(H)17 skewing (TGF-beta/IL1beta/IL6/IL23), T(H)17 counteracting (IL2), T(H)17 effector cytokine (IL17) and the principal neutrophil-attracting chemokine (IL8), were quantified at the mRNA or protein level in combination with the cell profiles. The BOS group (n = 36) showed an increase in IL1beta protein (x1.5), IL6 protein (x3), transforming growth factor-beta (TGF-beta) mRNA (x3), IL17 mRNA (x20), IL23 mRNA (x10), IL8 protein (x2), IL8 mRNA (x3) and a decrease in IL2 protein (x0.8). The infection group (n = 11) demonstrated an increase in IL1beta protein (x5), IL6 protein (x20), TGF-beta mRNA (x10), IL17 mRNA (x300), IL23 mRNA (x200) and IL8 protein (x6). The acute rejection group (n = 43) only revealed an increase in IL6 protein (x6) and IL8 protein (x2) and a decrease in IL2 protein (x0.7). Lymphocytes and neutrophils were increased in all groups compared to the stable (n = 42). Our findings demonstrate the IL23/IL17 axis to be involved in the pathophysiology of BOS potentially triggering the IL8-mediated neutrophilia. IL6, IL1beta and IL23 seem to be skewing cytokines and IL2 a counteracting cytokine for T(H)17 alignment. The involvement of TGF-beta could not be confirmed, either as T(H)17 steering or as counteracting cytokine.