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

The microbiome: an integral player in immune homeostasis and inflammation in the respiratory tract

The last decade of microbiome research has highlighted its fundamental role in systemic immune and metabolic homeostasis. The microbiome plays a prominent role during gestation and into early life, when maternal lifestyle factors shape immune development of the newborn. Breast milk further shapes gut colonization, supporting the development of tolerance to commensal bacteria and harmless antigens while preventing outgrowth of pathogens. Environmental microbial and lifestyle factors that disrupt this process can dysregulate immune homeostasis, predisposing infants to atopic disease and childhood asthma. In health, the low-biomass lung microbiome, together with inhaled environmental microbial constituents, establishes the immunological set point that is necessary to maintain pulmonary immune defense. However, in disease perturbations to immunological and physiological processes allow the upper respiratory tract to act as a reservoir of pathogenic bacteria, which can colonize the diseased lung and cause severe inflammation. Studying these host-microbe interactions in respiratory diseases holds great promise to stratify patients for suitable treatment regimens and biomarker discovery to predict disease progression. Preclinical studies show that commensal gut microbes are in a constant flux of cell division and death, releasing microbial constituents, metabolic by-products, and vesicles that shape the immune system and can protect against respiratory diseases. The next major advances may come from testing and utilizing these microbial factors for clinical benefit and exploiting the predictive power of the microbiome by employing multiomics analysis approaches.

Genomic and metabolic versatility of Pseudomonas aeruginosa contributes to its inter-kingdom transmission and survival

Pseudomonas aeruginosa is one of the most versatile bacteria with renowned pathogenicity and extensive drug resistance. The diverse habitats of this bacterium include fresh, saline and drainage waters, soil, moist surfaces, taps, showerheads, pipelines, medical implants, nematodes, insects, plants, animals, birds and humans. The arsenal of virulence factors produced by P. aeruginosa includes pyocyanin, rhamnolipids, siderophores, lytic enzymes, toxins and polysaccharides. All these virulent elements coupled with intrinsic, adaptive and acquired antibiotic resistance facilitate persistent colonization and lethal infections in different hosts. To date, treating pulmonary diseases remains complicated due to the chronic secondary infections triggered by hospital-acquired P. aeruginosa. On the contrary, this bacterium can improve plant growth by suppressing phytopathogens and insects. Notably, P. aeruginosa is one of the very few bacteria capable of trans-kingdom transmission and infection. Transfer of P. aeruginosa strains from plant materials to hospital wards, animals to humans, and humans to their pets occurs relatively often. Recently, we have identified that plant-associated P. aeruginosa strains could be pathologically similar to clinical isolates. In this review, we have highlighted the genomic and metabolic factors that facilitate the dominance of P. aeruginosa across different biological kingdoms and the varying roles of this bacterium in plant and human health.

Prognostic Value of Chest CT Findings at BOS Diagnosis in Lung Transplant Recipients

BACKGROUND

Bronchiolitis obliterans syndrome (BOS) after lung transplantation is characterized by fibrotic small airway remodeling, recognizable on high-resolution computed tomography (HRCT). We studied the prognostic value of key HRCT features at BOS diagnosis after lung transplantation.

METHODS

The presence and severity of bronchiectasis, mucous plugging, peribronchial thickening, parenchymal anomalies, and air trapping, summarized in a total severity score, were assessed using a simplified Brody II scoring system on HRCT at BOS diagnosis, in a cohort of 106 bilateral lung transplant recipients transplanted between January 2004 and January 2016. Obtained scores were subsequently evaluated regarding post-BOS graft survival, spirometric parameters, and preceding airway infections.

RESULTS

A high total Brody II severity score at BOS diagnosis (P = 0.046) and high subscores for mucous plugging (P = 0.0018), peribronchial thickening (P = 0.0004), or parenchymal involvement (P = 0.0121) are related to worse graft survival. A high total Brody II score was associated with a shorter time to BOS onset (P = 0.0058), lower forced expiratory volume in 1 s (P = 0.0006) forced vital capacity (0.0418), more preceding airway infections (P = 0.004), specifically with Pseudomonas aeruginosa (P = 0.002), and increased airway inflammation (P = 0.032).

CONCLUSIONS

HRCT findings at BOS diagnosis after lung transplantation provide additional information regarding its underlying pathophysiology and for future prognosis of graft survival.

The dynamic lung microbiome in health and disease

New methods and technologies within the field of lung biology are beginning to shed new light into the microbial world of the respiratory tract. Long considered to be a sterile environment, it is now clear that the human lungs are frequently exposed to live microbes and their by-products. The nature of the lung microbiome is quite distinct from other microbial communities inhabiting our bodies such as those in the gut. Notably, the microbiome of the lung exhibits a low biomass and is dominated by dynamic fluxes of microbial immigration and clearance, resulting in a bacterial burden and microbiome composition that is fluid in nature rather than fixed. As our understanding of the microbial ecology of the lung improves, it is becoming increasingly apparent that certain disease states can disrupt the microbial-host interface and ultimately affect disease pathogenesis. In this Review, we provide an overview of lower airway microbial dynamics in health and disease and discuss future work that is required to uncover novel therapeutic targets to improve lung health.

Risk of Bronchial Complications After Lung Transplantation With Respiratory Corynebacteria. Results From a Monocenter Retrospective Cohort Study

Corynebacterium spp. are associated with respiratory infections in immunocompromised hosts. A link with bronchial complications after lung transplantation (LTx) has been suggested. We aimed to assess the link between respiratory sampling of Corynebacterium spp. and significant bronchial complication (SBC) after LTx. We performed a single center retrospective study. Inclusion of LTx recipients with at least one respiratory Corynebacterium spp. sample (July 2014 to December 2018). Subjects were matched to unexposed LTx recipients. Primary outcome was SBC occurrence after Corynebacterium spp. isolation. Secondary outcomes were Corynebacterium spp. persistent sampling, chronic lung allograft dysfunction (CLAD) onset and all-cause mortality. Fifty-nine patients with Corynebacterium spp. sampling with 59 without isolation were included. Corynebacterium spp. identification was not associated with SBC occurrence (32.4% vs. 21.6%, p = 0.342). Previous SBC was associated with further isolation of Corynebacterium spp. (OR 3.94, 95% CI [1.72-9.05]). Previous SBC and corticosteroids pulses in the last 3 months were the only factors associated with increased risk of Corynebacterium spp. isolation in multivariate analysis. Corynebacterium spp. sampling was significantly associated with CLAD onset (27.1% vs. 6.9%, p = 0.021). Corynebacterium spp. isolation was not associated with SBC but with higher risk of CLAD. Whether CLAD evolution is affected by Corynebacterium spp. eradication remains to be investigated.

Aspergillus-Specific IgG Antibodies are Associated With Fungal-Related Complications and Chronic Lung Allograft Dysfunction After Lung Transplantation

Fungal exposure and sensitization negatively affect outcomes in various respiratory diseases, however, the effect of fungal sensitization in lung transplant (LTx) recipients is still unknown. We performed a retrospective cohort study of prospectively collected data on circulating fungal specific IgG/IgE antibodies, and their correlation with fungal isolation, chronic lung allograft dysfunction (CLAD) and overall survival after LTx. 311 patients transplanted between 2014 and 2019 were included. Patients with elevated Aspergillus fumigatus or Aspergillus flavus IgG (10%) had more mold and Aspergillus species isolation (p = 0.0068 and p = 0.0047). Aspergillus fumigatus IgG was specifically associated with Aspergillus fumigatus isolation in the previous or consecutive year (AUC 0.60, p = 0.004 and AUC 0.63, p = 0.022, respectively). Elevated Aspergillus fumigatus or Aspergillus flavus IgG was associated with CLAD (p = 0.0355), but not with death. Aspergillus fumigatus, Aspergillus flavus or Aspergillus niger IgE was elevated in 19.3% of patients, but not associated with fungal isolation, CLAD or death. Mold isolation and Aspergillus species isolation from respiratory cultures were associated with CLAD occurrence (p = 0.0011 and p = 0.0005, respectively), and Aspergillus species isolation was also associated with impaired survival (p = 0.0424). Fungus-specific IgG could be useful in long-term follow-up post-LTx, as a non-invasive marker for fungal exposure, and thus a diagnostic tool for identifying patients at risk for fungal-related complications and CLAD.

Markers of Bronchiolitis Obliterans Syndrome after Lung Transplant: Between Old Knowledge and Future Perspective

Bronchiolitis obliterans syndrome (BOS) is the most common form of CLAD and is characterized by airflow limitation and an obstructive spirometric pattern without high-resolution computed tomography (HRCT) evidence of parenchymal opacities. Computed tomography and microCT analysis show abundant small airway obstruction, starting from the fifth generation of airway branching and affecting up to 40-70% of airways. The pathogenesis of BOS remains unclear. It is a multifactorial syndrome that leads to pathological tissue changes and clinical manifestations. Because BOS is associated with the worst long-term survival in LTx patients, many studies are focused on the early identification of BOS. Markers may be useful for diagnosis and for understanding the molecular and immunological mechanisms involved in the onset of BOS. Diagnostic and predictive markers of BOS have also been investigated in various biological materials, such as blood, BAL, lung tissue and extracellular vesicles. The aim of this review was to evaluate the scientific literature on markers of BOS after lung transplant. We performed a systematic review to find all available data on potential prognostic and diagnostic markers of BOS.

PGF2α facilitates pathological retinal angiogenesis by modulating endothelial FOS-driven ELR+ CXC chemokine expression

The pathological retinal angiogenesis often causes blindness. Current anti-angiogenic therapy for proliferative retinopathy targets the vascular endothelial growth factor (VEGF), but many patients do not radically benefit from this therapy. Herein, we report that circulating prostaglandin (PG) F_2α metabolites were increased in type 2 diabetic patients with proliferative retinopathy, and the PGF_2α receptor (Ptgfr) was upregulated in retinal endothelial cells (ECs) from a mouse model of oxygen-induced retinopathy (OIR). Further, disruption of the PTGFR receptor in ECs attenuated OIR in mice. PGF_2α promoted the proliferation and tube formation of human retinal microvascular endothelial cells (HRMECs) via the release of ELR⁺ CXC chemokines, such as CXCL8 and CXCL2. Mechanistically, the PGF_2α /PTGFR axis potentiated ELR⁺ CXC chemokine expression in HRMECs through the G_q /CAMK2G/p38/ELK-1/FOS pathway. Upregulated FOS-mediated ELR⁺ CXC chemokine expression was observed in retinal ECs from PDR patients. Moreover, treatment with PTGFR inhibitor lessened the development of OIR in mice in a CXCR2-dependent manner. Therefore, inhibition of PTGFR may represent a new avenue for the treatment of retinal neovascularization, particularly in PDR.

Prognostic implications of and clinical risk factors for acute lung injury and organizing pneumonia after lung transplantation: Data from a multicenter prospective cohort study

We determined prognostic implications of acute lung injury (ALI) and organizing pneumonia (OP), including timing relative to transplantation, in a multicenter lung recipient cohort. We sought to understand clinical risks that contribute to development of ALI/OP. We analyzed prospective, histologic diagnoses of ALI and OP in 4786 lung biopsies from 803 adult lung recipients. Univariable Cox regression was used to evaluate the impact of early (≤90 days) or late (>90 days) posttransplant ALI or OP on risk for chronic lung allograft dysfunction (CLAD) or death/retransplantation. These analyses demonstrated late ALI/OP conferred a two- to threefold increase in the hazards of CLAD or death/retransplantation; there was no association between early ALI/OP and these outcomes. To determine risk factors for late ALI/OP, we used univariable Cox models considering donor/recipient characteristics and posttransplant events as candidate risks. Grade 3 primary graft dysfunction, higher degree of donor/recipient human leukocyte antigen mismatch, bacterial or viral respiratory infection, and an early ALI/OP event were significantly associated with increased late ALI/OP risk. These data from a contemporary, multicenter cohort underscore the prognostic implications of ALI/OP on lung recipient outcomes, clarify the importance of the timing of these events, and identify clinical risks to target for ALI/OP prevention.

Comprehensive analysis for clarifying transcriptomics landscapes of spread through air spaces in lung adenocarcinoma

Patients with spread through air spaces (STAS) have worse postoperative survival and a higher recurrence rate in lung adenocarcinoma, even in the earliest phases of the disease. At present, the molecular pathogenesis of STAS is not well understood. Therefore, to illustrate the underlying pathogenic mechanism of STAS, we accomplished a comprehensive analysis of a microarray dataset of STAS. Differential expression analysis revealed 841 differentially expressed genes (DEGs) between STAS_positive and STAS_negative groups. Additionally, we acquired two hub genes associated with survival. Gene set variation analysis (GSVA) confirmed that the main differential signaling pathways between the two groups were hypoxia VHL targets, PKC, and pyrimidine metabolism pathways. Analysis of immune activity showed that the increased expression of MHC-class-Ⅰ was observed in the STAS_positive group. These findings provided novel insights for a better knowledge of pathogenic mechanisms and potential therapeutic markers for STAS treatment.

Multidrug-resistant infections in solid organ transplant recipients: a focus on risk factors, prevention and treatment strategies

Solid organ transplantation is the best therapeutic option for patients with end-stage organ disease and, according to the data from international registries, there has been a steady increase in numbers and results. However, post-transplant infections remain a fearsome complication with, in the last decade, an increasing incidence of episodes due to antibiotic-resistant bacteria and opportunistic agents. In this paper, we summarize the most relevant and updated knowledge concerning infections from multidrug-resistant germs in solid organ transplant recipients, focusing on risk factors, treatment and prevention strategies, and antimicrobial pharmacokinetics relevant to this particular population of patients.

Microbiota in heart and lung transplantation: implications for innate-adaptive immune interface

PURPOSE OF REVIEW

Transplantation continues to be the only treatment option for end-stage organ failure when other interventions have failed. Although short-term outcomes have improved due to advances in perioperative care, long-term outcomes continue to be adversely affected by chronic rejection. Little is known about the role microbiota play in modulating alloimmune responses and potentially contributing to graft failure. Initial data have identified a correlation between specific changes of the recipient and/or donor microbiota and transplant outcomes. In this review, we will focus on recent findings concerning the complex interplay between microbiota and the innate immune system after heart and lung transplantation.

RECENT FINDINGS

Gut microbiome derangements in heart failure promote an inflammatory state and have lasting effects on the innate immune system, with an observed association between increased levels of microbiota-dependent metabolites and acute rejection after cardiac transplantation. The lung allograft microbiome interacts with components of the innate immune system, such as toll-like receptor signalling pathways, NKG2C+ natural killer cells and the NLRP3 inflammasome, to alter posttransplant outcomes, which may result in the development of chronic rejection.

SUMMARY

The innate immune system is influenced by alterations in the microbiome before and after heart and lung transplantation, thereby offering potential therapeutic targets for prolonging allograft survival.

Correlation between BAL CXCR3 chemokines and lung allograft histopathologies: A multicenter study

The histopathologic diagnosis of acute allograft injury is prognostically important in lung transplantation with evidence demonstrating a strong and consistent association between acute rejection (AR), acute lung injury (ALI), and the subsequent development of chronic lung allograft dysfunction (CLAD). The pathogenesis of these allograft injuries, however, remains poorly understood. CXCL9 and CXCL10 are CXC chemokines induced by interferon-γ and act as potent chemoattractants of mononuclear cells. We hypothesized that these chemokines are involved in the mononuclear cell recruitment associated with AR and ALI. We further hypothesized that the increased activity of these chemokines could be quantified as increased levels in the bronchoalveolar lavage fluid. In this prospective multicenter study, we evaluate the incidence of histopathologic allograft injury development during the first-year post-transplant and measure bronchoalveolar CXCL9 and CXCL10 levels at the time of the biopsy. In multivariable models, CXCL9 levels were 1.7-fold and 2.1-fold higher during AR and ALI compared with "normal" biopsies without histopathology. Similarly, CXCL10 levels were 1.6-fold and 2.2-fold higher during these histopathologies, respectively. These findings support the association of CXCL9 and CXCL10 with episodes of AR and ALI and provide potential insight into the pathogenesis of these deleterious events.

Inferior outcomes in lung transplant recipients with serum Pseudomonas aeruginosa specific cloaking antibodies

BACKGROUND

Chronic Lung Allograft Dysfunction (CLAD) limits long-term survival following lung transplantation. Colonization of the allograft by Pseudomonas aeruginosa is associated with an increased risk of CLAD and inferior overall survival. Recent experimental data suggests that 'cloaking' antibodies targeting the O-antigen of the P. aeruginosa lipopolysaccharide cell wall (cAbs) attenuate complement-mediated bacteriolysis in suppurative lung disease.

METHODS

In this retrospective cohort analysis of 123 lung transplant recipients, we evaluated the prevalence, risk factors and clinical impact of serum cAbs following transplantation.

RESULTS

cAbs were detected in the sera of 40.7% of lung transplant recipients. Cystic fibrosis and younger age were associated with increased risk of serum cAbs (CF diagnosis, OR 6.62, 95% CI 2.83-15.46, p < .001; age at transplant, OR 0.69, 95% CI 0.59-0.81, p < .001). Serum cAbs and CMV mismatch were both independently associated with increased risk of CLAD (cAb, HR 4.34, 95% CI 1.91-9.83, p < .001; CMV mismatch (D+/R-), HR 5.40, 95% CI 2.36-12.32, p < .001) and all-cause mortality (cAb, HR 2.75, 95% CI 1.27-5.95, p = .010, CMV mismatch, HR 3.53, 95% CI 1.62-7.70, p = .002) in multivariable regression analyses.

CONCLUSIONS

Taken together, these findings suggest a potential role for 'cloaking' antibodies targeting P. aeruginosa LPS O-antigen in the immunopathogenesis of CLAD.

The Impact of Resistant Bacterial Pathogens including Pseudomonas aeruginosa and Burkholderia on Lung Transplant Outcomes

Pseudomonas and Burkholderia are gram-negative organisms that achieve colonization within the lungs of patients with cystic fibrosis, and are associated with accelerated pulmonary function decline. Multidrug resistance is a hallmark of these organisms, which makes eradication efforts difficult. Furthermore, the literature has outlined increased morbidity and mortality for lung transplant (LTx) recipients infected with these bacterial genera. Indeed, many treatment centers have considered Burkholderia cepacia infection an absolute contraindication to LTx. Ongoing research has delineated different species within the B. cepacia complex (BCC), with significantly varied morbidity and survival profiles. This review considers the current evidence for LTx outcomes between the different subspecies encompassed within these genera as well as prophylactic and management options. The availability of meta-genomic tools will make differentiation between species within these groups easier in the future, and will allow more evidence-based decisions to be made regarding suitability of candidates colonized with these resistant bacteria for LTx. This review suggests that based on the current evidence, not all species of BCC should be considered contraindications to LTx, going forward.

The lung microbiome in lung transplantation

Culture-independent study of the lower respiratory tract after lung transplantation has enabled an understanding of the microbiome - that is, the collection of bacteria, fungi, and viruses, and their respective gene complement - in this niche. The lung has unique features as a microbial environment, with balanced entry from the upper respiratory tract, clearance, and local replication. There are many pressures impacting the microbiome after transplantation, including donor allograft factors, recipient host factors such as underlying disease and ongoing exposure to the microbe-rich upper respiratory tract, and transplantation-related immunosuppression, antimicrobials, and postsurgical changes. To date, we understand that the lung microbiome after transplant is dysbiotic; that is, it has higher biomass and altered composition compared to a healthy lung. Emerging data suggest that specific microbiome features may be linked to host responses, both immune and non-immune, and clinical outcomes such as chronic lung allograft dysfunction (CLAD), but many questions remain. The goal of this review is to put into context our burgeoning understanding of the lung microbiome in the postlung transplant patient, the interactions between microbiome and host, the role the microbiome may play in post-transplant complications, and critical outstanding research questions.

The Profiles of Long Non-coding RNA and mRNA Transcriptome Reveals the Genes and Pathway Potentially Involved in Pasteurella multocida Infection of New Zealand Rabbits

Infection with Pasteurella multocida (P. multocida) causes severe epidemic diseases in rabbits and is responsible for the pronounced economic losses in the livestock industry. Long non-coding RNAs (lncRNAs) have been proven to exert vital functions in regulating the host immune responses to bacterial attacks. However, little is known about how lncRNAs participate in the rabbit's immune response against P. multocida infection in the lungs. LncRNA and mRNA expression profiles were analyzed by transcriptomics and bioinformatics during P. multocida infection. A total of 336 lncRNAs and 7,014 mRNAs were differentially regulated at 1 day and 3 days post infection (dpi). Nearly 80% of the differentially expressed lncRNAs exhibited an increased expression at 3 dpi suggesting that the P. multocida genes are responsible for regulation. Moreover, GO and KEGG enriched analysis indicated that the immune-related pathways including pattern recognition receptors (PRRs), cytokines, and chemokines were significantly enriched at 3 dpi. These results indicate that the dysregulated immune-related genes may play crucial roles in defending against P. multocida attacks. Overall, these results advance our cognition of the role of lncRNAs and mRNAs in modulating the rabbit's innate immune response against P. multocida attacks, which will offer a valuable clue for further studies into exploring P. multocida-related diseases in human.

A prevalent and culturable microbiota links ecological balance to clinical stability of the human lung after transplantation

There is accumulating evidence that the lower airway microbiota impacts lung health. However, the link between microbial community composition and lung homeostasis remains elusive. We combine amplicon sequencing and bacterial culturing to characterize the viable bacterial community in 234 longitudinal bronchoalveolar lavage samples from 64 lung transplant recipients and establish links to viral loads, host gene expression, lung function, and transplant health. We find that the lung microbiota post-transplant can be categorized into four distinct compositional states, 'pneumotypes'. The predominant 'balanced' pneumotype is characterized by a diverse bacterial community with moderate viral loads, and host gene expression profiles suggesting immune tolerance. The other three pneumotypes are characterized by being either microbiota-depleted, or dominated by potential pathogens, and are linked to increased immune activity, lower respiratory function, and increased risks of infection and rejection. Collectively, our findings establish a link between the lung microbial ecosystem, human lung function, and clinical stability post-transplant.

Overview and Challenges of Bronchiolar Disorders

Bronchiolar abnormalities are common and can occur in conditions that affect either the large airways or the more distal parenchyma. In this review, we focus on the diagnosis and management of primary bronchiolar disorders, or conditions in which bronchiolitis is the predominant pathologic process, including constrictive bronchiolitis, follicular bronchiolitis, acute bronchiolitis, respiratory bronchiolitis, and diffuse panbronchiolitis. Due to the nature of abnormalities in the small airway, clinical and physiological changes in bronchiolitis can be subtle, making diagnosis challenging. Primary bronchiolar disorders frequently present with progressive dyspnea and cough that can be out of proportion to imaging and physiologic studies. Pulmonary function tests may be normal, impaired in an obstructive, restrictive, or mixed pattern, or have an isolated decrease in diffusion capacity. High-resolution computed tomography scan is an important diagnostic tool that may demonstrate one or more of the following three patterns: 1) solid centrilobular nodules, often with linear branching opacities (i.e., "tree-in-bud" pattern); 2) ill-defined ground glass centrilobular nodules; and 3) mosaic attenuation on inspiratory images that is accentuated on expiratory images, consistent with geographic air trapping. Bronchiolitis is often missed on standard transbronchial lung biopsies, as the areas of small airway involvement can be patchy. Fortunately, many patients can be diagnosed with a combination of clinical suspicion, inspiratory and expiratory high-resolution computed tomography scans, and pulmonary function testing. Joint consultation of clinicians with both radiologists and pathologists (in cases where histopathology is pursued) is critical to appropriately assess the clinical-radiographic-pathologic context in each individual patient.

Lung microbiota predict chronic rejection in healthy lung transplant recipients: a prospective cohort study

BACKGROUND

Alterations in the respiratory microbiome are common in chronic lung diseases, correlate with decreased lung function, and have been associated with disease progression. The clinical significance of changes in the respiratory microbiome after lung transplant, specifically those related to development of chronic lung allograft dysfunction (CLAD), are unknown. The aim of this study was to evaluate the effect of lung microbiome characteristics in healthy lung transplant recipients on subsequent CLAD-free survival.

METHODS

We prospectively studied a cohort of lung transplant recipients at the University of Michigan (Ann Arbor, MI, USA). We analysed characteristics of the respiratory microbiome in acellular bronchoalveolar lavage fluid (BALF) collected from asymptomatic patients during per-protocol surveillance bronchoscopy 1 year after lung transplantation. For our primary endpoint, we evaluated a composite of development of CLAD or death at 500 days after the 1-year surveillance bronchoscopy. Our primary microbiome predictor variables were bacterial DNA burden (total 16S rRNA gene copies per mL of BALF, quantified via droplet digital PCR) and bacterial community composition (determined by bacterial 16S rRNA gene sequencing). Patients' lung function was followed serially at least every 3 months by spirometry, and CLAD was diagnosed according to International Society of Heart and Lung Transplant 2019 guidelines.

FINDINGS

We analysed BALF from 134 patients, collected during 1-year post-transplant surveillance bronchoscopy between Oct 21, 2005, and Aug 25, 2017. Within 500 days of follow-up from the time of BALF sampling, 24 (18%) patients developed CLAD, five (4%) died before confirmed development of CLAD, and 105 (78%) patients remained CLAD-free with complete follow-up. Lung bacterial burden was predictive of CLAD development or death within 500 days of the surveillance bronchoscopy, after controlling for demographic and clinical factors, including immunosuppression and bacterial culture results, in a multivariable survival model. This relationship was evident when burden was analysed as a continuous variable (per log₁₀ increase in burden, HR 2·49 [95% CI 1·38-4·48], p=0·0024) or by tertiles (middle vs lowest bacterial burden tertile, HR 4·94 [1·25-19·42], p=0·022; and highest vs lowest, HR 10·56 [2·53-44·08], p=0·0012). In patients who developed CLAD or died, composition of the lung bacterial community significantly differed to that in patients who survived and remained CLAD-free (on permutational multivariate analysis of variance, p=0·047 at the taxonomic level of family), although differences in community composition were associated with bacterial burden. No individual bacterial taxa were definitively associated with CLAD development or death.

INTERPRETATION

Among asymptomatic lung transplant recipients at 1-year post-transplant, increased lung bacterial burden is predictive of chronic rejection and death. The lung microbiome represents an understudied and potentially modifiable risk factor for lung allograft dysfunction.

FUNDING

US National Institutes of Health, Cystic Fibrosis Foundation, Brian and Mary Campbell and Elizabeth Campbell Carr research gift fund.

Lung Transplant Pathology: An Overview on Current Entities and Procedures

Alloimmune reactions are, besides various infections, the major cause for impaired lung allograft function following transplant. Acute cellular rejection is not only a major trigger of acute allograft failure but also contributes to development of chronic lung allograft dysfunction. Analogous to other solid organ transplants, acute antibody-mediated rejection has become a recognized entity in lung transplant pathology. Adequate sensitivity and specificity in the diagnosis of alloimmune reactions in the lung can only be achieved by synoptic analysis of histopathologic, clinical, and radiological findings together with serologic and microbiologic findings.

Pseudomonas aeruginosa and acute rejection independently increase the risk of donor-specific antibodies after lung transplantation

Factors contributing to donor-specific HLA antibody (DSA) development after lung transplantation have not been systematically evaluated. We hypothesized that the isolation of Pseudomonas aeruginosa in respiratory specimens would increase the risk of DSA development. Our objective was to determine the risk of DSA development associated with the isolation of Pseudomonas aeruginosa after lung transplantation. We conducted a single-center retrospective cohort study of primary lung transplant recipients and examined risk factors for DSA development using Cox regression models. Of 460 recipients, 205 (45%) developed DSA; the majority developed Class II DSA (n = 175, 85%), and 145 of 205 (71%) developed DSA to HLA-DQ alleles. Univariate time-dependent analyses revealed that isolation of Pseudomonas from respiratory specimens, acute cellular rejection, and lymphocytic bronchiolitis are associated with an increased risk of DSA development. In multivariable analyses, Pseudomonas isolation, acute cellular rejection, and lymphocytic bronchiolitis remained independent risk factors for DSA development. Additionally, there was a direct association between the number of positive Pseudomonas cultures and the risk of DSA development. Our findings suggest that pro-inflammatory events including acute cellular rejection, lymphocytic bronchiolitis, and Pseudomonas isolation after transplantation are associated with an increased risk of DSA development.

Bronchiolitis obliterans syndrome and restrictive allograft syndrome after lung transplantation: why are there two distinct forms of chronic lung allograft dysfunction?

Bronchiolitis obliterans syndrome (BOS) had been considered to be the representative form of chronic rejection or chronic lung allograft dysfunction (CLAD) after lung transplantation. In BOS, small airways are affected by chronic inflammation and obliterative fibrosis, whereas peripheral lung tissue remains relatively intact. However, recognition of another form of CLAD involving multiple tissue compartments in the lung, termed restrictive allograft syndrome (RAS), raised a fundamental question: why there are two phenotypes of CLAD? Increasing clinical and experimental data suggest that RAS may be a prototype of chronic rejection after lung transplantation involving both cellular and antibody-mediated alloimmune responses. Some cases of RAS are also induced by fulminant general inflammation in lung allografts. However, BOS involves alloimmune responses and the airway-centered disease process can be explained by multiple mechanisms such as external alloimmune-independent stimuli (such as infection, aspiration and air pollution), exposure of airway-specific autoantigens and airway ischemia. Localization of immune responses in different anatomical compartments in different phenotypes of CLAD might be associated with lymphoid neogenesis or the de novo formation of lymphoid tissue in lung allografts. Better understanding of distinct mechanisms of BOS and RAS will facilitate the development of effective preventive and therapeutic strategies of CLAD.

The role of innate immunity in the long-term outcome of lung transplantation

Long-term survival after lung transplantation remains suboptimal due to chronic lung allograft dysfunction (CLAD), a progressive scarring process affecting the graft. Although anti-donor alloimmunity is central to the pathogenesis of CLAD, its underlying mechanisms are not fully elucidated and it is neither preventable nor treatable using currently available immunosuppression. Recent evidence has shown that innate immune stimuli are fundamental to the development of CLAD. Here, we examine long-standing assumptions and new concepts linking innate immune activation to late lung allograft fibrosis.

Influence of azithromycin and allograft rejection on the post-lung transplant microbiota

BACKGROUND

Alterations in the lung microbiota may drive disease development and progression in patients with chronic respiratory diseases. Following lung transplantation (LTx), azithromycin is used to both treat and prevent chronic lung allograft dysfunction (CLAD). The objective of this study was to determine the association between azithromycin use, CLAD, acute rejection, airway inflammation, and bacterial microbiota composition and structure after LTx.

METHODS

Bronchoalveolar lavage samples (n = 219) from 69 LTx recipients (azithromycin, n = 32; placebo, n = 37) from a previously conducted randomized placebo-controlled trial with azithromycin were analyzed. Samples were collected at discharge, 1, and 2 years following randomization and at CLAD diagnosis. Bacterial microbial community composition and structure was determined using 16S ribosomal RNA gene sequencing and associated with clinically important variables.

RESULTS

At discharge and following 1 and 2 years of azithromycin therapy, no clear differences in microbial community composition or overall diversity were observed. Moreover, no changes in microbiota composition were observed in CLAD phenotypes. However, acute rejection was associated with a reduction in community diversity (p = 0.0009). Significant correlations were observed between microbiota composition, overall diversity, and levels of inflammatory cytokines in bronchoalveolar lavage, particularly CXCL8.

CONCLUSIONS

Chronic azithromycin usage did not disturb the bacterial microbiota. However, acute rejection episodes were associated with bacterial dysbiosis.

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.

Variations in Oral Microbiota Composition Are Associated With a Risk of Throat Cancer

In this study, a next-generation sequencing strategy on 16S ribosomal RNA (16S rRNA) gene was employed to analyze 70 oral samples from 32 patients with throat cancer, nine patients with vocal cord polyp, and 29 healthy individuals (normal controls). Using this strategy, we demonstrated, for the first time, that the salivary microbiota of cancer patients were significantly different from those of patients with a polyp and healthy individuals. We observed that the beta diversity of the cancer group was divergent from both the normal and polyp groups, while alpha-diversity indices such as the Chao1 estimator (P = 8.1e-05), Simpson (P = 0.0045), and Shannon (P = 0.0071) were significantly reduced in cancer patients compared with patients containing a polyp and normal healthy individuals. Linear discriminant analysis (LDA) and Kruskal–Wallis test analyses and real-time quantitative polymerase chain reaction (qPCR) verification test revealed that the genera Aggregatibacter, Pseudomonas, Bacteroides, and Ruminiclostridium were significantly enriched in the throat cancer group compared with the vocal cord polyp and normal control groups (score value >2). Finally, diagnostic models based on putatively important constituent bacteria were constructed with 87.5% accuracy [area under the curve (AUC) = 0.875, 95% confidence interval (CI): 0.695–1]. In summary, in this study we characterized, for the first time, the oral microbiota of throat cancer patients without smoking history. We speculate that these results will help in the pathogenic mechanism and early diagnosis of throat cancer.

Lack of association of Aspergillus colonization with the development of bronchiolitis obliterans syndrome in lung transplant recipients: An international cohort study

BACKGROUND

Bronchiolitis obliterans syndrome (BOS) is a major limitation in the long-term survival of lung transplant recipients (LTRs). However, the risk factors in the development of BOS remain undetermined. We conducted an international cohort study of LTRs to assess whether Aspergillus colonization with large or small conidia is a risk factor for the development of BOS.

METHODS

Consecutive LTRs from January 2005 to December 2008 were evaluated. Rates of BOS and associated risk factors were recorded at 4 years. International Society of Heart and Lung Transplantation criteria were used to define fungal and other infections. A Cox proportional-hazards-model was constructed to assess the association between Aspergillus colonization and the development of BOS controlling for confounders.

RESULTS

A total of 747 LTRs were included. The cumulative incidence of BOS at 4 years after transplant was 33% (250 of 747). Additionally, 22% of LTRs experienced Aspergillus colonization after transplantation. Aspergillus colonization with either large (hazard ratio [HR] = 0.6, 95% confidence interval [CI] = 0.3-1.2, p = 0.12) or small conidia (HR = 0.9, 95% CI = 0.6-1.4, p = 0.74) was not associated with the development of BOS. Factors associated with increased risk of development of BOS were the male gender (HR = 1.4, 95% CI = 1.1-1.8, p = 0.02) and episodes of acute rejection (1-2 episodes, HR = 1.5, 95% CI = 1.1-2.1, p = 0.014; 3-4 episodes, HR = 1.6, 95% CI = 1.0-2.6, p = 0.036; >4 episodes, HR = 2.2, 95% CI = 1.1-4.3, p = 0.02), whereas tacrolimus use was associated with reduced risk of BOS (HR = 0.6, 95% CI = 0.5-0.9, p = 0.007).

CONCLUSIONS

We conclude from this large multicenter cohort of lung transplant patients, that Aspergillus colonization with large or small conidia did not show an association with the development of BOS.

Gene Expression Profiling of Bronchoalveolar Lavage Cells During Aspergillus Colonization of the Lung Allograft

BACKGROUND

Aspergillus colonization after lung transplant is associated with an increased risk of chronic lung allograft dysfunction (CLAD). We hypothesized that gene expression during Aspergillus colonization could provide clues to CLAD pathogenesis.

METHODS

We examined transcriptional profiles in 3- or 6-month surveillance bronchoalveolar lavage fluid cell pellets from recipients with Aspergillus fumigatus colonization (n = 12) and without colonization (n = 10). Among the Aspergillus colonized, we also explored profiles in those who developed CLAD (n = 6) or remained CLAD-free (n = 6). Transcription profiles were assayed with the HG-U133 Plus 2.0 microarray (Affymetrix). Differential gene expression was based on an absolute fold difference of 2.0 or greater and unadjusted P value less than 0.05. We used NIH Database for Annotation, Visualization and Integrated Discovery for functional analyses, with false discovery rates less than 5% considered significant.

RESULTS

Aspergillus colonization was associated with differential expression of 489 probe sets, representing 404 unique genes. "Defense response" genes and genes in the "cytokine-cytokine receptor" Kyoto Encyclopedia of Genes and Genomes pathway were notably enriched in this list. Among Aspergillus colonized patients, CLAD development was associated with differential expression of 69 probe sets, representing 64 unique genes. This list was enriched for genes involved in "immune response" and "response to wounding", among others. Notably, both chitinase 3-like-1 and chitotriosidase were associated with progression to CLAD.

CONCLUSIONS

Aspergillus colonization is associated with gene expression profiles related to defense responses including cytokine signaling. Epithelial wounding, as well as the innate immune response to chitin that is present in the fungal cell wall, may be key in the link between Aspergillus colonization and CLAD.

Association between chronic bacterial airway infection and prognosis of bronchiolitis obliterans syndrome after hematopoietic cell transplantation

Bronchiolitis obliterans syndrome (BOS) is a rare pulmonary complication of hematopoietic stem cell transplantation (HSCT) with high mortality. Chronic bacterial airway infection (CAI) causes exacerbation and progression of several airway diseases, and bacterial airway colonization was shown to be associated with BOS after lung transplantation.We assessed the association between CAI and clinical course in patients with BOS after HSCT. This retrospective study included 910 patients undergoing allogeneic HSCT between 2005 and 2013 at our institution. BOS diagnosis was reevaluated according to the 2014 US National Institutes of Health criteria. Sputum and bronchial lavage culture results, pulmonary function, and survival were compared between patients with and without CAI.Median follow-up was 974.5 (261.5-2748.5) days. BOS was diagnosed in 27 (3.0%) patients, including 18 males. Median age at BOS diagnosis was 45 (40.5-58) years. Nine patients had ≥2 positive sputum cultures for bacteria or one positive bronchial lavage culture for nontuberculous mycobacteria (CAI+), whereas 9 patients had negative sputum/bronchial lavage culture or only one positive sputum culture (CAI-). Median change in forced expiratory volume in 1 s within 6 months after BOS diagnosis and overall survival were significantly worse in CAI+ patients than in CAI- patients (-250 vs +260 mL, P = .002, and 1340 days vs not reached, P = .04, respectively). No other factors including patient demographics or transplant protocol affected prognosis. There were no differences in clinical characteristics of patients with and without CAI, except for the time from transplantation to BOS diagnosis (214 vs 768 days for CAI+ and CAI-, respectively; P = .02).CAI was associated with worse outcomes in patients with BOS after HSCT. Further prospective studies should assess the association between the airway microbiome and changes in pulmonary function after HSCT to improve prognosis.

The Impact of Allograft CXCL9 during Respiratory Infection on the Risk of Chronic Lung Allograft Dysfunction

Background

The long term clinical significance of respiratory infections after lung transplantation remains uncertain.

Methods

In this retrospective single-center cohort study of 441 lung transplant recipients, we formally evaluate the association between respiratory infection and chronic lung allograft dysfunction (CLAD). We furthermore hypothesized that bronchoalveolar lavage fluid (BALF) CXCL9 concentrations are augmented during respiratory infections, and that episodes of infection with elevated BALF CXCL9 are associated with greater CLAD risk.

Results

In univariable and multivariable models adjusted for other histopathologic injury patterns, respiratory infection, regardless of the causative organism, was a strong predictor of CLAD development (adjusted HR 1.8 95% CI 1.3-2.6). Elevated BALF CXCL9 concentrations during respiratory infections markedly increased CLAD risk in a dose-response manner. An episode of respiratory infection with CXCL9 concentrations greater than the 25^th, 50^th, and 75^th percentile had adjusted HRs for CLAD of 1.8 (95% CI 1.1-2.8), 2.4 (95% CI 1.4-4.0) and 4.4 (95% CI 2.4-8.0), respectively.

Conclusions

Thus, we demonstrate that respiratory infections, regardless of the causative organism, are strong predictors of CLAD development. We furthermore demonstrate for the first time, the prognostic importance of BALF CXCL9 concentrations during respiratory infections on the risk of subsequent CLAD development.

CXCL4 contributes to host defense against acute Pseudomonas aeruginosa lung infection

Platelets have been implicated in pulmonary inflammation following exposure to bacterial stimuli. The mechanisms involved in the platelet-mediated host response to respiratory bacterial infection remain incompletely understood. In this study, we demonstrate that platelet-derived chemokine (C-X-C motif) ligand 4 (CXCL4) plays critical roles in a mouse model of acute bacterial pneumonia using Pseudomonas aeruginosa. Platelets are activated during P. aeruginosa infection, and mice depleted of platelets display markedly increased mortality and impaired bacterial clearance. CXCL4 deficiency impairs bacterial clearance and lung epithelial permeability, which correlate with decreased neutrophil recruitment to BALF. Interestingly, CXCL4 deficiency selectively regulates chemokine production, suggesting that CXCL4 has an impact on other chemokine expression. In addition, CXCL4 deficiency reduces platelet-neutrophil interactions in blood following P. aeruginosa infection. Further studies revealed that platelet-derived CXCL4 contributes to the P. aeruginosa-killing of neutrophils. Altogether, these findings demonstrate that CXCL4 is a vital chemokine that plays critical roles in bacterial clearance during P. aeruginosa infection through recruiting neutrophils to the lungs and intracellular bacterial killing.

Double lung transplantation in an HIV-positive patient with Mycobacterium kansasii infection

Good outcomes with kidney and liver transplantation in HIV-positive patients have led clinicians to recommend lung transplantation in HIV-positive patients based on extrapolated data. Pre-transplant mycobacterial infection is associated with an increased risk of developing new infection or aggravating existing infection, though it does not contraindicate transplantation in non-HIV-infected patients. However, no data exists regarding the outcome of HIV-positive patients with pre-transplant mycobacterial infection. We report a case of double lung transplantation in a 50-year-old HIV-positive patient with alpha-1 antitrypsin deficiency. Prior to transplantation, Mycobacterium kansasii was isolated in one sputum culture and the patient was considered merely colonized as no clinical evidence of pulmonary or disseminated disease was present. The patient successfully underwent a double lung transplantation. Nontuberculous mycobacterial infection was diagnosed histologically on examination of native lungs. Surveillance and watchful waiting were chosen over treatment of the infection. HIV remained under control post-transplantation with no AIDS-defining illnesses throughout the follow-up. A minimal acute rejection that responded to increased corticosteroids was reported. At 12 months post-transplant, a bronchiolitis obliterans syndrome was diagnosed after a drop in FEV1. No evidence of isolation nor recurrence of nontuberculous mycobacteria was reported post-transplantation. At 15 months post-transplant, the patient remained stable with an FEV1 of 30%. The presence of pre-transplant nontuberculous mycobacterial infection did not translate into recurrence of nontuberculous mycobacterial infection post-transplant. Whether it contributed to bronchiolitis obliterans syndrome remains unknown.

Risks associated with lung transplantation in cystic fibrosis patients

INTRODUCTION

Survival after lung transplantation lags behind outcomes of other solid organ transplants, and complications from lung transplant are the second most common cause of death in cystic fibrosis. Evolving surgical techniques, therapeutics, and perioperative management have improved short-term survival after lung transplantation, yet have not translated into significant improvement in long-term mortality. Areas covered: We review risk factors for poor long-term outcomes among patients with cystic fibrosis undergoing lung transplantation to highlight areas for improvement. This includes reasons for organ dysfunction, complications of immunosuppression, further exacerbation of extrapulmonary complications of cystic fibrosis, and quality of life. A literature search was performed using PubMed-indexed journals. Expert commentary: There are multiple medical and socioeconomic barriers that threaten long-term survival following lung transplant for patients with cystic fibrosis. An understanding of the causes of each could elucidate treatment options. There is a lack of prospective, multicenter, randomized control trials due to cost, complexity, and feasibility. Ongoing prospective studies should be reserved for the most promising interventions identified in retrospective studies in order to improve long-term outcomes.

Impact of gram negative bacteria airway recolonization on the occurrence of chronic lung allograft dysfunction after lung transplantation in a population of cystic fibrosis patients

Background

Chronic Lung Allograft Dysfunction (CLAD) is the main cause of morbidity and mortality after the first year following lung transplantation (LTx). Risk factors of CLAD have been extensively studied, but the association between gram-negative bacteria (GNB) bronchial colonization and the development of CLAD is controversial. The purpose of our study was to investigate the association between post-transplant recolonization with the same species or de-novo colonization with a new GNB species and CLAD. The same analysis was performed on a sub-group of patients at the strain level using Matrix Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry technique.

Results

Forty adult cystic fibrosis (CF) patients who underwent a first bilateral LTx in the University Hospital of Marseille, between January 2010 and December 2014, were included in the study. Patients with GNB de-novo colonization had a higher risk of developing CLAD (OR = 6.72, p = 0.04) and a lower rate of CLAD-free survival (p = 0.005) compared to patients with GNB recolonization. No conclusion could be drawn from the subgroup MALDI-TOF MS analysis at the strain level.

Conclusion

Post-LTx GNB airway recolonization seems to be a protective factor against CLAD, whereas de-novo colonization with a new species of GNB seems to be a risk factor for CLAD.

Electronic supplementary material

The online version of this article (10.1186/s12866-018-1231-7) contains supplementary material, which is available to authorized users.

Host-Pathogen Interactions and Chronic Lung Allograft Dysfunction

Lung transplantation is now considered to be a therapeutic option for patients with advanced-stage lung diseases. Unfortunately, due to post-transplant complications, both infectious and noninfectious, it is only a treatment and not a cure. Infections (e.g., bacterial, viral, and fungal) in the immunosuppressed lung transplant recipient are a common cause of mortality post transplant. Infections have more recently been explored as factors contributing to the risk of chronic lung allograft dysfunction (CLAD). Each major class of infection-(1) bacterial (Staphylococcus aureus and Pseudomonas aeruginosa); (2) viral (cytomegalovirus and community-acquired respiratory viruses); and (3) fungal (Aspergillus)-has been associated with the development of CLAD. Mechanistically, the microbe seems to be interacting with the allograft cells, stimulating the induction of chemokines, which recruit recipient leukocytes to the graft. The recipient leukocyte interactions with the microbe further up-regulate chemokines, amplifying the influx of allograft-infiltrating mononuclear cells. These events can promote recipient leukocytes to interact with the allograft, triggering an alloresponse and graft dysfunction. Overall, interactions between the microbe-allograft-host immune system alters chemokine production, which, in part, plays a role in the pathobiology of CLAD and mortality due to CLAD.

Transcriptomic Analysis on Responses of Murine Lungs to Pasteurella multocida Infection

Pasteurella multocida infection in cattle causes serious epidemic diseases and leads to great economic losses in livestock industry; however, little is known about the interaction between host and P. multocida in the lungs. To explore a fully insight into the host responses in the lungs during P. multocida infection, a mouse model of Pasteurella pneumonia was established by intraperitoneal infection, and then transcriptomic analysis of infected lungs was performed. P. multocida localized and grew in murine lungs, and induced inflammation in the lungs, as well as mice death. With transcriptomic analysis, approximately 10⁷ clean reads were acquired. 4236 differently expressed genes (DEGs) were detected during P. multocida infection, of which 1924 DEGs were up-regulated. By gene ontology (GO) and Kyoto encyclopedia of genes and genomes (KEGG) enrichments, 5,303 GO enrichments and 116 KEGG pathways were significantly enriched in the context of P. multocida infection. Interestingly, genes related to immune responses, such as pattern recognition receptors (PRRs), chemokines and inflammatory cytokines, were significantly up-regulated, suggesting the key roles of these genes in P. multocida infection. Transcriptomic data showed that IFN-γ/IL-17-related genes were increased, which were validated by qRT-PCR, ELISA, and immunoblotting. Our study characterized the transcriptomic profile of the lungs in mice upon Pasteurella infection, and our findings could provide valuable information with respect to better understanding the responses in mice during P. multocida infection.

Inflammasomes and IL-1 biology in the pathogenesis of allograft dysfunction

Inflammasomes are high-molecular-weight cytosolic complexes that mediate the activation of caspases. There are many inflammasomes, and each is influenced by a unique pattern-recognition receptor response. Two signals are typically involved in the inflammasome pathways. Signal one involves recognition of pathogen-associated molecular patterns (PAMPs), such as LPS or other colonizing/invading microbes, that interact with TLRs, which induce the downstream production of pro-IL-1β. This is followed by signal two, which involves recognition of PAMPs or damage-associated molecular patterns (DAMPs), such as uric acid or ATP, via NLRP3, which leads to caspase-1-dependent cleavage of pro-IL-1β to active IL-1β and pyroptosis. Ultimately, these two signals cause the release of multiple proinflammatory cytokines. Both PAMPs and DAMPs can be liberated by early insults to the allograft, including ischemia/reperfusion injury, infections, and rejection. The consequence of inflammasome activation and IL-1 expression is the upregulation of adhesion molecules and chemokines, which leads to allograft neutrophil sequestration, mononuclear phagocyte recruitment, and T cell activation, all of which are key steps in the continuum from allograft insult to chronic allograft dysfunction.

Impact of Allograft Injury Time of Onset on the Development of Chronic Lung Allograft Dysfunction After Lung Transplantation

The impact of allograft injury time of onset on the risk of chronic lung allograft dysfunction (CLAD) remains unknown. We hypothesized that episodes of late-onset (≥6 months) allograft injury would produce an augmented CXCR3/ligand immune response, leading to increased CLAD. In a retrospective single-center study, 1894 transbronchial biopsy samples from 441 lung transplant recipients were reviewed for the presence of acute rejection (AR), lymphocytic bronchiolitis (LB), diffuse alveolar damage (DAD), and organizing pneumonia (OP). The association between the time of onset of each injury pattern and CLAD was assessed by using multivariable Cox models with time-dependent covariates. Bronchoalveolar lavage (BAL) CXCR3 ligand concentrations were compared between early- and late-onset injury patterns using linear mixed-effects models. Late-onset DAD and OP were strongly associated with CLAD: adjusted hazard ratio 2.8 (95% confidence interval 1.5-5.3) and 2.0 (1.1-3.4), respectively. The early-onset form of these injury patterns did not increase CLAD risk. Late-onset LB and acute rejection (AR) predicted CLAD in univariable models but lost significance after multivariable adjustment for late DAD and OP. AR was the only early-onset injury pattern associated with CLAD development. Elevated BAL CXCR3 ligand concentrations during late-onset allograft injury parallel the increase in CLAD risk and support our hypothesis that late allograft injuries result in a more profound CXCR3/ligand immune response.

Interleukin-1α induced release of interleukin-8 by human bronchial epithelial cells in vitro: assessing mechanisms and possible treatment options

Survival after lung transplantation is hampered by chronic lung allograft dysfunction (CLAD). Persistently elevated BAL-neutrophilia is observed in some patients despite treatment with azithromycin, which may be induced by IL-1α. Our aim is to establish an in vitro model, assess mechanistic pathways and test different therapeutic strategies of IL-1α-induced release of IL-8 by human bronchial epithelial cells. Bronchial epithelial cells (16HBE) were stimulated with IL-1α with or without azithromycin or dexamethasone. IL-8 protein was analyzed in cell supernatant. Different MAP kinases (p38, JNK, ERK^1/2 , Iκβ) and targets known to be involved in tumor formation (PI3K, Akt) were investigated. Finally, different treatment options were tested for their potential inhibitory effect. IL-1α induced IL-8 in bronchial epithelial cells, which was dose-dependently inhibited by dexamethasone but not by azithromycin. IL-1α induced p38 and Akt phosphorylation, but activation of these MAPK was not inhibited by dexamethasone. JNK, ERK^1/2 , Iκβ and PI3K were not activated. None of the tested drugs reduced the IL-1α induced IL-8 production. We established an in vitro model wherein steroids inhibit the IL-1α-induced IL-8 production, while azithromycin was ineffective. Despite using this simple in vitro model, we could not identify a new treatment option for azithromycin-resistant airway neutrophilia.

A severe Mycoplasma pneumoniae pneumonia inducing an acute antibody-mediated pulmonary graft rejection

A 40-year-old cystic fibrosis woman with a history of double-lung transplantation 2 years previously was admitted for a progressive respiratory distress. Physical examination revealed fever (39°C) and diffuse bilateral lung crackles. Laboratory findings included severe hypoxemia and inflammatory syndrome. Bronchoalveolar lavage and serological test were positive for mycoplasma pneumonia. As the patient did not improve after 3 days of antibiotics and donor-specific HLA antibodies had been detected, an acute antibody-mediated graft rejection was treated with high-dose corticosteroids, plasma exchange, intravenous immunoglobulin, and rituximab. The patient rapidly improved. Unfortunately, 6 months after this episode, she developed a bronchiolitis obliterans syndrome with a dependence to noninvasive ventilator leading to the indication of retransplantation. This case illustrates the possible relationship between infection and humoral rejection. These two diagnoses should be promptly investigated and systematically treated in lung transplant recipients.