The Role of Infection in Acute Exacerbation of Idiopathic Pulmonary Fibrosis

Infectious respiratory pathogens among patients with acute exacerbation of idiopathic pulmonary fibrosis during the coronavirus disease 2019 pandemic in Japan

BACKGROUND

Few studies have investigated the prevalence of pathogens in patients with acute exacerbation of idiopathic pulmonary fibrosis (AE-IPF), specifically, the interactions between respiratory pathogens and AE-IPF during the coronavirus disease 2019 (COVID-19) pandemic.

OBJECTIVES

We aimed to analyze pathogens in patients with AE-IPF between September 2020 and December 2022.

METHODS

This retrospective observational study was conducted at our hospital between September 2020 and December 2022. In patients with AE-IPF, pre-hospitalization polymerase chain reaction (PCR) tests for respiratory pathogens, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), were performed using multiplex PCR or Smart Gene assay with nasopharyngeal swab specimens. Microbiological assays, including Gram staining, sputum cultures, blood cultures, and urinary antigen tests for Streptococcus pneumoniae and Legionella pneumophila, were also performed.

RESULTS

Forty-nine patients with AE-IPF were included. The median age was 75 years old and 42 (86 %) were male. Only one of the 49 patients (2 %) was positive for SARS-CoV-2. Two of 28 patients (7 %) were positive for human rhinovirus/enterovirus. No bacteria were detected in sputum culture, blood culture, or urinary antigen tests.

CONCLUSIONS

The detection frequency of SARS-CoV-2 infection in patients with AE-IPF was lower than that of human rhinovirus/enterovirus. Continuous analysis for the presence of pathogens is necessary for appropriate infection control because respiratory viruses may increase as the coronavirus pandemic subsides.

CSF3 aggravates acute exacerbation of pulmonary fibrosis by disrupting alveolar epithelial barrier integrity

Idiopathic pulmonary fibrosis (IPF) is a chronic and progressive respiratory disorder characterized by poor prognosis, often presenting with acute exacerbation. The primary cause of death associated with IPF is acute exacerbation of IPF (AE-IPF). However, the pathophysiology of acute exacerbation has not been clearly elucidated yet. This study aims to investigate the underlying pathophysiological molecular mechanism in a mouse AE-PF model. C57BL/6J mice were intratracheally administered bleomycin (BLM, 5 mg/kg) to induce pulmonary fibrosis. After 14 days, lipopolysaccharide (LPS, 2 mg/kg) was injected via the trachea route. Histological assessments, including H&E and Masson staining, as well as inflammatory indicators, were included to evaluate the induction of AE-PF by BLM and LPS in mice. Transcriptomic profiling of pulmonary tissues identified CSF3 as one of the top 10 upregulated DEGs in AE-PF mice. Indeed, administration of exogenous CSF3 protein exacerbated AE-PF in mice. Mechanistically, CSF3 disrupted alveolar epithelial barrier integrity and permeability by regulating specialized cell adhesion complexes such as tight junctions (TJs) and adherens junctions (AJs) via PI3K/p-Akt/Snail pathway, contributing to the aggravation of AE-PF in mice. Moreover, the discovery of elevated sera CSF3 indicated a notable increase in IPF patients during the exacerbation of the disease. Pearson correlation analysis in IPF patients revealed significant positive associations between CSF3 levels and KL-6 levels, LDH levels, CRP levels, respectively. These results provide mechanistic insights into the role of CSF3 in exacerbating of lung fibrotic disease and indicate monitoring CSF3 levels may aid in early clinical decisions for alternative therapy in the management of rapidly progressing IPF.

Alveolar epithelial cells of lung fibrosis patients are susceptible to severe virus-induced injury

Patients with pulmonary fibrosis (PF) often experience exacerbations of their disease, characterised by a rapid, severe deterioration in lung function that is associated with high mortality. Whilst the pathobiology of such exacerbations is poorly understood, virus infection is a trigger. The present study investigated virus-induced injury responses of alveolar and bronchial epithelial cells (AECs and BECs, respectively) from patients with PF and age-matched controls (Ctrls). Air-liquid interface (ALI) cultures of AECs, comprising type I and II pneumocytes or BECs were inoculated with influenza A virus (H1N1) at 0.1 multiplicity of infection (MOI). Levels of interleukin-6 (IL-6), IL-36γ and IL-1β were elevated in cultures of AECs from PF patients (PF-AECs, n = 8-11), being markedly higher than Ctrl-AECs (n = 5-6), 48 h post inoculation (pi) (P<0.05); despite no difference in H1N1 RNA copy numbers 24 h pi. Furthermore, the virus-induced inflammatory responses of PF-AECs were greater than BECs (from either PF patients or controls), even though viral loads in the BECs were overall 2- to 3-fold higher than AECs. Baseline levels of the senescence and DNA damage markers, nuclear p21, p16 and H2AXγ were also significantly higher in PF-AECs than Ctrl-AECs and further elevated post-infection. Senescence induction using etoposide augmented virus-induced injuries in AECs (but not viral load), whereas selected senotherapeutics (rapamycin and mitoTEMPO) were protective. The present study provides evidence that senescence increases the susceptibility of AECs from PF patients to severe virus-induced injury and suggests targeting senescence may provide an alternative option to prevent or treat the exacerbations that worsen the underlying disease.

Rate of severe and fatal infections in a cohort of patients with interstitial lung disease associated with rheumatoid arthritis: a multicenter prospective study

Objective

To describe severe infection, foci of infection, microorganisms, associated factors, and impact on mortality in patients with rheumatoid arthritis-associated interstitial lung disease (RA-ILD).

Patients and methods

The study was based on a multicenter prospective cohort of patients with RA-ILD followed up from 2015 to 2023. The main outcome measures were incident severe infection and fatal infection. We evaluated infectious foci, etiologic agents, vaccination status, variables associated with lung function, and clinical-therapeutic variables in RA. The incidence rate (IR) for infection and mortality was calculated per 100 person-years, and 3 multivariate models were constructed to explore factors associated with infection.

Results

We followed up 148 patients with RA-ILD for a median 56.7 months (699.3 person-years). During this period, 142 patients (96%) had at least 1 infection. A total of 368 infectious episodes were recorded, with an IR of 52.6 per 100 person-years. Of the 48 patients who died, 65% did so from infection. Respiratory infections were the most common first infection (74%), infection overall (74%), and fatal infection (80%) and were caused mostly by SARS CoV-2, Streptococcus pneumoniae, Pseudomonas aeruginosa, and influenza A virus. The factors associated with an increased risk of infection and death in patients with RA-ILD were age, inflammatory activity, and therapy with corticosteroids and immunosuppressants.

Conclusion

Patients with RA-ILD have a high risk of serious infection, especially respiratory infection. Infection develops early, is recurrent, and is frequently fatal. The presence of associated factors such as advanced age, joint inflammation, and treatment highlight the importance of integrated and preventive medical care.

The Role of Lung Microbiome in Fibrotic Interstitial Lung Disease-A Systematic Review

Interstitial Lung Disease (ILD) involves lung disorders marked by chronic inflammation and fibrosis. ILDs include pathologies like idiopathic pulmonary fibrosis (IPF), connective tissue disease-associated ILD (CTD-ILD), hypersensitivity pneumonitis (HP) or sarcoidosis. Existing data covers pathogenesis, diagnosis (especially using high-resolution computed tomography), and treatments like antifibrotic agents. Despite progress, ILD diagnosis and management remains challenging with significant morbidity and mortality. Recent focus is on Progressive Fibrosing ILD (PF-ILD), characterized by worsening symptoms and fibrosis on HRCT. Prevalence is around 30%, excluding IPF, with a poor prognosis. Early diagnosis is crucial for optimizing outcomes in PF-ILD individuals. The lung microbiome comprises all the microorganisms that are in the respiratory tract. Relatively recent research try to evaluate its role in respiratory disease. Healthy lungs have a diverse microbial community. An imbalance in bacterial composition, changes in bacterial metabolic activities, or changes in bacterial distribution within the lung termed dysbiosis is linked to conditions like COPD, asthma and ILDs. We conducted a systematic review of three important scientific data base using a focused search strategy to see how the lung microbiome is involved in the progression of ILDs. Results showed that some differences in the composition and quality of the lung microbiome exist in ILDs that show progressive fibrosing phenotype. The results seem to suggest that the lung microbiota could be involved in ILD progression, but more studies showing its exact pathophysiological mechanisms are needed.

Animal models of acute exacerbation of pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive scarring interstitial lung disease with an unknown cause. Some patients may experience acute exacerbations (AE), which result in severe lung damage visible on imaging or through examination of tissue samples, often leading to high mortality rates. However, the etiology and pathogenesis of AE-IPF remain unclear. AE-IPF patients exhibit diffuse lung damage, apoptosis of type II alveolar epithelial cells, and an excessive inflammatory response. Establishing a reliable animal model of AE is critical for investigating the pathogenesis. Recent studies have reported a variety of animal models for AE-IPF, each with its own advantages and disadvantages. These models are usually established in mice with bleomycin-induced pulmonary fibrosis, using viruses, bacteria, small peptides, or specific drugs. In this review, we present an overview of different AE models, hoping to provide a useful resource for exploring the mechanisms and targeted therapies for AE-IPF.

Differential Transcriptomic Signatures of Small Airway Cell Cultures Derived from IPF and COVID-19-Induced Exacerbation of Interstitial Lung Disease

Idiopathic pulmonary fibrosis (IPF) is a pathological condition wherein lung injury precipitates the deposition of scar tissue, ultimately leading to a decline in pulmonary function. Existing research indicates a notable exacerbation in the clinical prognosis of IPF patients following infection with COVID-19. This investigation employed bulk RNA-sequencing methodologies to describe the transcriptomic profiles of small airway cell cultures derived from IPF and post-COVID fibrosis patients. Differential gene expression analysis unveiled heightened activation of pathways associated with microtubule assembly and interferon signaling in IPF cell cultures. Conversely, post-COVID fibrosis cell cultures exhibited distinctive characteristics, including the upregulation of pathways linked to extracellular matrix remodeling, immune system response, and TGF-β1 signaling. Notably, BMP signaling levels were elevated in cell cultures derived from IPF patients compared to non-IPF control and post-COVID fibrosis samples. These findings underscore the molecular distinctions between IPF and post-COVID fibrosis, particularly in the context of signaling pathways associated with each condition. A better understanding of the underlying molecular mechanisms holds the promise of identifying potential therapeutic targets for future interventions in these diseases.

Acute Exacerbations of Interstitial Lung Diseases: Focus on Biomarkers

Interstitial lung diseases (ILDs) are a large group of pulmonary disorders characterized histologically by the cardinal involvement of the pulmonary interstitium. The prototype of ILDs is idiopathic pulmonary fibrosis (IPF), an incurable disease characterized by progressive distortion and loss of normal lung architecture through unchecked collagen deposition. Acute exacerbations are dramatic events during the clinical course of ILDs, associated with high morbidity and mortality. Infections, microaspiration, and advanced lung disease might be involved in the pathogenesis of acute exacerbations. Despite clinical scores, the prediction of the onset and outcome of acute exacerbations is still inaccurate. Biomarkers are necessary to characterize acute exacerbations better. We review the evidence for alveolar epithelial cell, fibropoliferation, and immunity molecules as potential biomarkers for acute exacerbations of interstitial lung disease.

A Systematic Review and Meta-analysis of Clinical, Respiratory, and Biochemical Risk Factors for Acute Exacerbation of idiopathic Pulmonary Fibrosis

BACKGROUND

A better capacity to identify patients with idiopathic pulmonary fibrosis (IPF) at risk of acute exacerbation (AEIPF) might improve outcomes and reduce healthcare costs.

AIMS

We critically appraised the available evidence of the differences in clinical, respiratory, and biochemical parameters between AEIPF and IPF patients with stable disease (SIPF) by conducting a systematic review and meta-analysis.

METHODS

PubMed, Web of Science and Scopus were reviewed up until August 1, 2022, for studies reporting differences in clinical, respiratory, and biochemical parameters (including investigational biomarkers) between AEIPF and SIPF patients. The Joanna Briggs Institute Critical Appraisal Checklist was used to assess the risk of bias.

RESULTS

Twenty-nine cross-sectional studies published between 2010 and 2022 were identified (all with a low risk of bias). Of the 32 meta-analysed parameters, significant differences were observed between groups, assessed through standard mean differences or relative ratios, with age, forced vital capacity, vital capacity, carbon monoxide diffusion capacity, total lung capacity, oxygen partial pressure, alveolar-arterial oxygen gradient, P/F ratio, 6 min walk test distance, C-reactive protein, lactate dehydrogenase, white blood cell count, albumin, Krebs von den Lungen 6, surfactant protein D, high mobility group box 1 protein, and interleukin-1β, 6, and 8.

CONCLUSIONS

We identified significant differences between AEIPF and SIPF patients in age and specific parameters of respiratory function, inflammation, and epithelial lung damage. Prospective studies are warranted to determine the capacity of these parameters to predict AEIPF more accurately (PROSPERO registration number: CRD42022356640).

C-type lectin Mincle initiates IL-17-mediated inflammation in acute exacerbations of idiopathic pulmonary fibrosis

RATIONALE

Acute exacerbation of idiopathic pulmonary fibrosis (AE-IPF) has a poor prognosis and high mortality. However, there is limited information regarding the mechanisms of AE-IPF.

AIMS

We aimed to explore the function of macrophage-inducible C-type lectin (Mincle) in AE-IPF.

METHODS

In the present study, Mincle was detected in the lung tissues of AE-IPF patients. Mincle-deficient (Mincle^-/-) mice and wild-type C57BL/6 mice were administered bleomycin (BLM), followed by HSV1 viral infection to establish the AE-IPF model.

RESULTS

Mincle was increased in the lung tissues of AE-IPF patients compared with those with stable IPF (P = 0.04) and healthy controls (P = 0.009). The survival rate of the Mincle^-/-+BLM+HSV group was higher than that of the WT+BLM+HSV group. The mice in the Mincle^-/-+BLM+HSV group exhibited milder inflammation and lower acute lung injury scores (P = 0.008). Mincle was expressed on inflammatory monocytes and neutrophils (CD11b+Gr1 +F4/80-) and monocyte-derived macrophages (Mo-AMs, CD11b+Gr1 +F4/80 +) in the BALF of AE-IPF mice. Mo-AMs were significantly increased in the WT+BLM+HSV group compared with the WT+BLM+PBS (P < 0.0001) and Mincle^-/-+BLM+HSV (P = 0.0009) groups. Deletion of Mincle decreased the proportion of Th17 cells and Mo-AMs in the Mincle^-/-+BLM+HSV group.

CONCLUSIONS

Mincle contributed to acute inflammation in AE-IPF by promoting Th17 differentiation.

The Role of Serum 1,25-Dihydroxy Vitamin D3 and PCT in Idiopathic Pulmonary Fibrosis

OBJECTIVE

Biomarkers for the acute exacerbation of idiopathic pulmonary fibrosis (AE-IPF) are urgently needed to provide better patient management. We aimed to investigate whether serum 1,25(OH)2D3 (1,25-dihydroxy vitamin D3) levels predict AE-IPF and whether they could be a potential prognostic biomarker for IPF.

PARTICIPANTS AND METHODS

This prospective study included 72 patients with IPF (31 with stable IPF and 41 with AE-IPF). All participants were recruited during hospitalisation at Tianjin Chest Hospital and were followed up for at least 12 months. Demographics, comorbidities, arterial blood gas, and serum biochemical profile, radiological features, and anti-fibrotic therapy were evaluated. Serum concentrations of 1,25(OH)2D3 and transforming growth factor beta1 (TGFβ1) were detected using enzyme-linked immunosorbent assay (ELISA). Risk factors for AE-IPF were identified using multivariate analysis. Prognostic factors were assessed using Kaplan-Meier and Cox regression analyses.

RESULTS

Baseline values of alveolar-arterial oxygen difference (A-aDO2) (40.85 mmHg vs 29.2 mmHg, p =0.035), white blood cell counts (10.09 ± 4.2×109/L vs 7.46 ± 7.84×109/L, p <0.001), percentage of monocytes (7.36 ± 1.36% vs 6.6 ± 1.2%, p =0.017), C-reactive protein (CRP) (2.1 mg/dL vs 1.12 mg/dL, p =0.015) and procalcitonin (PCT) (36.59% vs 3.23%, p <0.001) were significantly higher in AE-IPF patients than in stable IPF patients. Instead, the mean concentration of serum calcium and 1,25(OH)2D3 at baseline were higher in IPF patients with stable disease than in those with acute exacerbation (2.17 ± 0.13 nmol/L vs 2.09 ± 0.13 nmol/L, p =0.023 and 16.62 pg/mL vs 11.58 pg/mL, p <0.001, respectively). In multivariate analysis, a higher proportion of patients with lower serum 1,25(OH)2D3 levels experienced AE-IPF (OR 0.884, 95% CI 0.791-0.987, p =0.029), and rising serum PCT level (PCT > 0.05 ng/mL) was associated with an increased risk of mortality (HR 3.664, 95% CI 1.010-12.900, p =0.043).

CONCLUSION

Decreased serum 1,25(OH)2D3 is associated with an increased risk of acute exacerbation for patients with IPF. A high serum PCT level is predictive of worse prognosis in IPF patients. 1,25(OH)2D3 may be a potential biomarker for AE-IPF, while PCT could be a prognostic biomarker for IPF.

IL-9 and IL-9 receptor expression in lymphocytes from bronchoalveolar lavage fluid of patients with interstitial lung disease

INTRODUCTION

IL-9, mainly produced by T helper 9 (Th9) cells, promotes allergic airway inflammation and remodeling through the interaction with its receptor (IL-9R). Th9 cells and IL-9 have also been implicated in tissue fibrosis and autoimmunity pathways. However, the role of IL-9/IL-9R in the pathogenesis of interstitial lung disease (ILD) is unknown.

AIM

To evaluate IL-9/IL-9R expression in bronchoalveolar lavage fluid (BALF) lymphocytes of patients with various ILDs.

METHODS

Consecutive patients with ILD, who underwent BAL for diagnostic purposes, were studied. As control group, consecutive patients without evidence of ILD were included. Immunocytochemical staining of BALF lymphocytes for IL-9 and IL-9R was performed and evaluated by two independent readers.

RESULTS

45 patients, of them 8 had idiopathic pulmonary fibrosis (IPF), 12 nonspecific interstitial pneumonia (NSIP), 10 sarcoidosis, 9 hypersensitivity pneumonitis (HP), 6 cryptogenic organizing pneumonia (COP), and 24 controls were studied. In the ILD group, the highest BALF lymphocyte count was seen in HP followed by NSIP, COP, sarcoidosis, and IPF (p < 0.05 for HP vs IPF). The highest percentages of IL-9 and IL-9R positive lymphocytes were seen in COP. Conversely, NSIP showed the lowest rate of IL-9, and sarcoidosis the lowest rate of IL-9R positive lymphocytes. Only in NSIP, a direct correlation between IL and 9 and IL-9R positive lymphocytes was seen (r = 0.639, p = 0.025).

CONCLUSION

BALF lymphocytes IL-9 and IL-9R expression differs between various ILDs and could reflect different pathogenetic mechanisms.

Essential role of IL-17 in acute exacerbation of pulmonary fibrosis induced by non-typeable Haemophilus influenzae

Background: Acute exacerbation (AE) of idiopathic pulmonary fibrosis (IPF) has a poor prognosis and lacks effective therapy. Animal models that mimic AE-IPF can greatly accelerate investigation of its pathogenesis and development of effective therapy. However, there are few reports of animal models of AE-IPF caused by bacteria. Thus, our study aimed to establish a mouse model of bacterium-induced AE-IPF and explore the potential pathogenic mechanism of AE-IPF. Methods: Mice were instilled intranasally with bleomycin (BLM) followed by non-typeable Haemophilus influenzae (NTHi) strain NT127. Murine survival, bacterial load, body weight and pulmonary histopathological changes were evaluated. We analyzed the T cell and inflammatory cell responses in the lungs. Results: Infection with 10⁷ CFU NT127 triggered AE in mice with PF induced by 30 μg BLM. Compared with BLM-instilled mice, the BLM/NT127-treated mice showed more obvious airway inflammation, lower survival rate, higher inflammatory cell response, and increased proportions and numbers of IL-17⁺CD4⁺, IL-17⁺ γδ T, IL-22⁺CD4⁺ and regulatory T (Treg) cells in lungs. γδ T cells were the predominant source of IL-17. IL-17 gene knockout mice with AE-IPF had quicker body weight recovery, milder pulmonary inflammation and fibrosis, stronger IL-22⁺CD4⁺T, TGF-β⁺ γδ T and Treg cell responses, and weaker neutrophil and eosinophil responses than wild-type mice with AE-IPF. Conclusions: NTHi infection after BLM-induced IPF can cause AE-IPF in a murine model. This novel model can be used to investigate the pathogenesis of AE-IPF and develop new therapies for AE-IPF caused by bacteria. IL-17 is essential for the development of AE-IPF, and it may be a new therapeutic target for bacteria-induced AE-IPF.

Elevated Expression of Growth Differentiation Factor-15 Is Associated With Acute Exacerbation of Idiopathic Pulmonary Fibrosis

Backgrounds

Growth differentiation factor 15 (GDF-15) is a highly divergent member of the TGF-β superfamily and has been implicated in various biological functions. However, the expression of GDF-15 in patients with acute exacerbation of idiopathic pulmonary fibrosis (AE-IPF) is unclear.

Method

The study included 47 AE-IPF patients, 61 stable IPF (S-IPF) subjects, and 31 healthy controls (HCs). Serum GDF-15 levels and their expression in the lung were measured. The correlation between serum GDF-15 and other clinical parameters and the risk factors for AE occurrence and the survival of IPF patients were analyzed.

Results

Serum GDF-15 levels were significantly elevated in AE-IPF patients (1279.22 ± 540.02 pg/ml) as compared with HCs (891.30 ± 479.90 pg/ml) or S-IPF subjects (107.82 ± 14.21 pg/ml) (both p < 0.001). The protein and mRNA expressions of GDF-15 in the lung of AE-IPF patients were significantly increased as compared with S-IPF cases (p = 0.007 and p = 0.026, respectively). The serum GDF-15 level was correlated with the clinical variables of inflammation, metabolism, and disease severity in IPF subjects (all p < 0.05). The GDF-15 serum concentration was significantly higher in decedents than in survivors (p = 0.005). A serum GDF-15 level above 989.3 pg/ml was a risk factor for AE occurrence (p = 0.04), and the level above 1,075.76 pg/ml was an independent predictor for survival in IPF cases (p = 0.007).

Conclusions

The GDF-15 level was significantly elevated in subjects with AE-IPF. GDF-15 could be a promising biomarker for AE occurrence and survival in IPF patients.

Inhibition of lung microbiota-derived proapoptotic peptides ameliorates acute exacerbation of pulmonary fibrosis

Idiopathic pulmonary fibrosis is an incurable disease of unknown etiology. Acute exacerbation of idiopathic pulmonary fibrosis is associated with high mortality. Excessive apoptosis of lung epithelial cells occurs in pulmonary fibrosis acute exacerbation. We recently identified corisin, a proapoptotic peptide that triggers acute exacerbation of pulmonary fibrosis. Here, we provide insights into the mechanism underlying the processing and release of corisin. Furthermore, we demonstrate that an anticorisin monoclonal antibody ameliorates lung fibrosis by significantly inhibiting acute exacerbation in the human transforming growth factorβ1 model and acute lung injury in the bleomycin model. By investigating the impact of the anticorisin monoclonal antibody in a general model of acute lung injury, we further unravel the potential of corisin to impact such diseases. These results underscore the role of corisin in the pathogenesis of acute exacerbation of pulmonary fibrosis and acute lung injury and provide a novel approach to treating this incurable disease.

The Interaction Between Pulmonary Fibrosis and COVID-19 and the Application of Related Anti-Fibrotic Drugs

COVID-19 is a highly contagious respiratory disease, which mainly affects the lungs. Critically ill patients are easily complicated by cytokine storms, acute respiratory distress syndrome (ARDS), and respiratory failure, which seriously threaten their lives. Pulmonary fibrosis (PF) is a common interstitial lung disease, and its pathogenesis may involve the participation of a variety of immune cells and inflammatory factors. Current studies have shown that patients with COVID-19 may be complicated by pulmonary fibrosis, and patients with pulmonary fibrosis may also be at higher risk of contracting COVID-19 than healthy people. Pulmonary fibrosis is an important risk factor leading to the aggravation of COVID-19 disease. COVID-19 complicated by cytokine storm and ARDS mechanism pathways are similar to the pathogenesis of pulmonary fibrosis. The potential interaction between pulmonary fibrosis and COVID-19 can cause acute exacerbation of the patient’s condition, but the potential mechanism between the two has not been fully elucidated. Most of the drug treatment programs for COVID-19-related pulmonary fibrosis are currently formulated about the relevant guidelines for idiopathic pulmonary fibrosis (IPF), and there is no clear drug treatment program recommendation. This article aims to summarize the relevant mechanism pathways of COVID-19 and pulmonary fibrosis, explore the interrelationships and possible mechanisms, and discuss the value and risks of existing and potential COVID-19-related pulmonary fibrosis treatment drugs, to provide reference for anti-fibrosis treatment for patients.

Lung Microbiome in Idiopathic Pulmonary Fibrosis and Other Interstitial Lung Diseases

Interstitial lung diseases represent a heterogeneous and wide group of diseases in which factors leading to disease initiation and progression are not fully understood. Recent evidence suggests that the lung microbiome might influence the pathogenesis and progression of interstitial lung diseases. In recent years, the utilization of culture-independent methodologies has allowed the identification of complex and dynamic communities of microbes, in patients with interstitial lung diseases. However, the potential mechanisms by which these changes may drive disease pathogenesis and progression are largely unknown. The aim of this review is to discuss the role of the altered lung microbiome in several interstitial lung diseases. Untangling the host–microbiome interaction in the lung and airway of interstitial lung disease patients is a research priority. Thus, lung dysbiosis is a potentially treatable trait across several interstitial lung diseases, and its proper characterization and treatment might be crucial to change the natural history of these diseases and improve outcomes.

Deleterious Role of Th9 Cells in Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a progressive and fatal lung disease of unknown etiology. Immune disorders play an important role in IPF pathogenesis. Here, we show that Th9 cells differentiate and activate in the lung tissue of patients with IPF and bleomycin (BLM)-induced lung fibrosis mice. Moreover, we found that Th9 cells promote pulmonary fibrosis in two ways. On the one hand, Th9 cells promote fibroblast differentiation, activation, and collagen secretion by secreting IL-9. On the other hand, they promote differentiation of Th0 cells into Th2 cells by secreting IL-4. Th9 cells and Th2 cells can promote each other, accelerating the Th1/Th2 imbalance and eventually forming a positive feedback of pulmonary fibrosis. In addition, we found that neutralizing IL-9 in both preventive and therapeutic settings ameliorates bleomycin-induced pulmonary fibrosis. Furthermore, we identified several critical signaling pathways involved in the effect of neutralizing IL-9 on pulmonary fibrosis by proteomics study. From an immunological perspective, we elucidated the novel role and underlying mechanism of Th9 cells in pulmonary fibrosis. Our study suggested that Th9-based immunotherapy may be employed as a treatment strategy for IPF.

Clinical characteristics and prognostic risk factors of mortality in patients with interstitial lung diseases and viral infection: a retrospective cohort study

Introduction. Patients with interstitial lung disease (ILD) who subsequently develop a viral infection have high rates of morbidity and mortality.Hypothesis/Gap Statement. Few large-scale epidemiological studies have investigated potential prognostic factors for morbidity and mortality in this patient group.Aim. To evaluate the risk factors for morbidity and mortality in hospitalized patients with ILD and viral infection, as well as the clinical characteristics.Methodology. This retrospective cohort study included patients with ILD who were hospitalized for a viral infection in two tertiary academic hospitals in China, between 1 January 2013 and 31 December 2019. We analysed the prevalence of comorbidities, clinical characteristics, 30 day mortality rates, and prognostic risk factors.Results. A total of 282 patients were included; 195 and 87 were immunocompromised and immunocompetent, respectively. The most common underlying interstitial diseases were idiopathic pulmonary fibrosis (42.9 %) and connective tissue disease (36.9 %). The 30 day mortality rate was 20.6 %. During the influenza season, an increase in influenza virus (IFV) (25.7 %), respiratory syncytial virus (14.9 %) and cytomegalovirus (CMV) (11.3 %) cases was observed in the immunocompromised group. The most frequently detected virus in the immunocompetent group was IFV (44.8 %), followed by respiratory syncytial virus (11.5 %), and human rhinovirus (9.2 %). During the non-influenza season, CMV (34.4 %) was the main virus detected in the immunocompromised group. The 30 day mortality rates of non-IFV patients were higher than those of IFV patients. Older age (>60 years), respiratory failure, persistent lymphocytopenia, invasive mechanical ventilation and non-IFV virus infection were significantly associated with increased 30 day mortality.Conclusion. Patients with ILD who develop viral infection have high rates of morbidity and mortality, which are associated with increased age (>60 years), respiratory failure, mechanical ventilation, persistent lymphocytopenia and non-IFV virus infection. These risk factors should be carefully considered when determining treatment strategies for this patient population.

Utility of illness severity scores to predict mortality in patients hospitalized with respiratory deterioration of idiopathic pulmonary fibrosis

INTRODUCTION

In the context of idiopathic pulmonary fibrosis (IPF), respiratory-related admissions to hospital are associated with a high morbidity and short-term mortality with significant burden on secondary care services. It has yet to be determined how to accurately identify patients at risk of acute respiratory deterioration (ARD) or the prognosticating factors.

AIM

We sought to define the characteristics of hospitalized ARD-IPF patients in a real-world cohort and investigate factors associated with worse outcomes. Specifically, we wished to determine the association between baseline CURB-65 and NEWS-2 and mortality in IPF, given illness severity scores have not previously been validated in this cohort.

METHODS

Single-centre retrospective observational cohort study.

RESULTS

Of 172 first hospitalizations for ARD, 27 admissions (15.7%) were due to an acute exacerbation of IPF (AE-IPF), 28 (16.3%) secondary to cardiac failure/fluid overload and 17 due to pneumonia (9.9%). Other admissions related to lower respiratory tract infection, extra-parenchymal causes and those without a specific trigger. Baseline patient characteristics were comparable for all underlying aetiologies of ARD-IPF. Treatment pathways did not differ significantly between AE-IPF and other causes of ARD-IPF. Short-term mortality was high, with ∼22% patients dying within 30 days. Illness severity scores (NEWS-2 and CURB-65) were independent predictors of mortality in multivariable logistic regression modelling.

CONCLUSIONS

Our findings suggest significant mortality related to hospitalization with ARD-IPF of any underlying cause. Our data support the use of CURB-65 and NEWS-2 scores as illness severity scores that can provide a simple tool to help future prognostication in IPF. Research should be aimed at refining the management of these episodes, to try to reduce mortality, where possible, or to facilitate palliative care for those with adverse prognostic characteristics.

Improved Prognostic Prediction by Combination of Early Initiation of Polymyxin B Hemoperfusion with Modified Gender-Age-Physiology Index in Acute Exacerbation of Idiopathic Pulmonary Fibrosis

INTRODUCTION

Respiratory failure from acute exacerbation of idiopathic pulmonary fibrosis (AE-IPF) is associated with high mortality. Direct hemoperfusion with polymyxin B-immobilized fiber column (PMX-DHP) has been reported to have beneficial effects on patients with AE-IPF. Whether patient characteristics influence the extent of this benefit remains unclear.

METHODS

We retrospectively examined the records of 30 patients with AE-IPF who underwent PMX-DHP. The favorable factors of survival were determined using Cox proportional hazards analyses.

RESULTS

The 1- and 12-month survival rates after PMX-DHP were 70.0% and 50.0%, respectively. The multivariate analysis revealed that low modified Gender-Age-Physiology (GAP) index (≤8 points) (hazard ratio [HR] 0.317, p = 0.015) and PMX-DHP received within 48 h of steroid pulse (HR 0.289, p = 0.012) were favorable factors. Notably, even in the patients with high modified GAP index (>8 points), that is, more advanced IPF, those who received PMX-DHP within 48 h of steroid pulse had a better prognosis than those who did after 48 h of the steroid pulse (p = 0.032).

CONCLUSIONS

Early PMX-DHP initiation in patients with AE-IPF, specifically within 48 h after the steroid pulse therapy, may improve prognosis regardless of the severity of chronic phase of IPF before AE-IPF.

The Role of Herpes Viruses in Pulmonary Fibrosis

Pulmonary fibrosis (PF) is a serious lung disease which can result from known genetic or environmental exposures but is more commonly idiopathic (IPF). In familial PF (FPF), the majority of identified causal genes play key roles in the maintenance of telomeres, the protective end structures of chromosomes. Recent evidence suggests that short telomeres may also be implicated causally in a significant proportion of idiopathic cases. The possible involvement of herpes viruses in PF disease incidence and progression has been examined for many years, with some studies showing strong, statistically significant associations and others reporting no involvement. Evidence is thus polarized and remains inconclusive. Here we review the reported involvement of herpes viruses in PF in both animals and humans and present a summary of the evidence to date. We also present several possible mechanisms of action of the different herpes viruses in PF pathogenesis, including potential contributions to telomere attrition and cellular senescence. Evidence for antiviral treatment in PF is very limited but suggests a potential benefit. Further work is required to definitely answer the question of whether herpes viruses impact PF disease onset and progression and to enable the possible use of targeted antiviral treatments to improve clinical outcomes.

Neutrophils Modulate Fibrogenesis in Chronic Pulmonary Diseases

Chronic inflammatory pulmonary diseases are characterized by recurrent and persistent inflammation of the airways, commonly associated with poor clinical outcomes. Although their etiologies vary tremendously, airway neutrophilia is a common feature of these diseases. Neutrophils, as vital regulators linking innate and adaptive immune systems, are a double-edged sword in the immune response of the lung involving mechanisms such as phagocytosis, degranulation, neutrophil extracellular trap formation, exosome secretion, release of cytokines and chemokines, and autophagy. Although neutrophils serve as strong defenders against extracellular pathogens, neutrophils and their components can trigger various cascades leading to inflammation and fibrogenesis. Here, we review current studies to elucidate the versatile roles of neutrophils in chronic pulmonary inflammatory diseases and describe the common pathogenesis of these diseases. This may provide new insights into therapeutic strategies for chronic lung diseases.

The Role of Microbiome and Virome in Idiopathic Pulmonary Fibrosis

The interest in the lung microbiome and virome and their contribution to the pathogenesis, perpetuation and progression of idiopathic pulmonary fibrosis (IPF) has been increasing during the last decade. The utilization of high-throughput sequencing to detect microbial and/or viral genetic material in bronchoalveolar lavage fluid or lung tissue samples has amplified the ability to identify and quantify specific microbial and viral populations. In stable IPF, higher microbial burden is associated with worse prognosis but no specific microbe has been identified to contribute to this. Additionally, no causative relation has been established. Regarding viral infections, although in the past they have been associated with IPF, causation has not been proved. Although in the past the diagnosis of acute exacerbation of IPF (AE-IPF) was not considered in patients with overt infection, this was amended in the last few years and infection is considered a cause for exacerbation. Besides this, a higher microbial burden has been found in the lungs of patients with AE-IPF and an association with higher morbidity and mortality has been confirmed. In contrast, an association of AE-IPF with viral infection has not been established. Despite the progress during the last decade, a comprehensive knowledge of the microbiome and virome in IPF and their role in disease pathogenesis are yet elusive. Although association with disease severity, risk for progression and mortality has been established, causation has not been proven and the potential use as a biomarker or the benefits of antimicrobial therapeutic strategies are yet to be determined.

Role of ILC2 in Viral-Induced Lung Pathogenesis

Innate lymphoid type-2 cells (ILC2) are a population of innate cells of lymphoid origin that are known to drive strong Type 2 immunity. ILC2 play a key role in lung homeostasis, repair/remodeling of lung structures following injury, and initiation of inflammation as well as more complex roles during the immune response, including the transition from innate to adaptive immunity. Remarkably, dysregulation of this single population has been linked with chronic lung pathologies, including asthma, chronic obstructive pulmonary disease (COPD) and idiopathic pulmonary fibrotic diseases (IPF). Furthermore, ILC2 have been shown to increase following early-life respiratory viral infections, such as respiratory syncytial virus (RSV) and rhinovirus (RV), that may lead to long-term alterations of the lung environment. The detrimental roles of increased ILC2 following these infections may include pathogenic chronic inflammation and/or alterations of the structural, repair, and even developmental processes of the lung. Respiratory viral infections in older adults and patients with established chronic pulmonary diseases often lead to exacerbated responses, likely due to previous exposures that leave the lung in a dysregulated functional and structural state. This review will focus on the role of ILC2 during respiratory viral exposures and their effects on the induction and regulation of lung pathogenesis. We aim to provide insight into ILC2-driven mechanisms that may enhance lung-associated diseases throughout life. Understanding these mechanisms will help identify better treatment options to limit not only viral infection severity but also protect against the development and/or exacerbation of other lung pathologies linked to severe respiratory viral infections.

Role of interleukins in the pathogenesis of pulmonary fibrosis

Interleukins, a group of cytokines participating in inflammation and immune response, are proved to be involved in the formation and development of pulmonary fibrosis. In this article, we reviewed the relationship between interleukins and pulmonary fibrosis from the clinical, animal, as well as cellular levels, and discussed the underlying mechanisms in vivo and in vitro. Despite the effects of interleukin-targeted treatment on experimental pulmonary fibrosis, clinical applications are lacking and unsatisfactory. We conclude that intervening in one type of interleukins with similar functions in IPF may not be enough to stop the development of fibrosis as it involves a complex network of regulation mechanisms. Intervening interleukins combined with other existing therapy or targeting interleukins affecting multiple cells/with different functions at the same time may be one of the future directions. Furthermore, the intervention time is critical as some interleukins play different roles at different stages. Further elucidation on these aspects would provide new perspectives on both the pathogenesis mechanism, as well as the therapeutic strategy and drug development.

The role of viral and bacterial infections in the pathogenesis of IPF: a systematic review and meta-analysis

Background

Idiopathic pulmonary fibrosis (IPF) is a chronic progressive lung disease. Several risk factors such as smoking, air pollution, inhaled toxins, high body mass index and infectious agents are involved in the pathogenesis of IPF. In the present study, this meta-analysis study investigates the prevalence of viral and bacterial infections in the IPF patients and any possible association between these infections with pathogenesis of IPF.

Methods

The authors carried out this systematic literature review from different reliable databases such as PubMed, ISI Web of Science, Scopus and Google Scholar to December 2020.Keywords used were the following “Idiopathic pulmonary fibrosis”, “Infection”, “Bacterial Infection” and “Viral Infection”, alone or combined together with the Boolean operators "OR”, “AND” and “NOT” in the Title/Abstract/Keywords field. Pooled proportion and its 95% CI were used to assess the prevalence of viral and bacterial infections in the IPF patients.

Results

In this systematic review and meta-analyses, 32 studies were selected based on the exclusion/inclusion criteria. Geographical distribution of included studies was: eight studies in American people, 8; in European people, 15 in Asians, and one in Africans. The pooled prevalence for viral and bacterial infections w ere 53.72% (95% CI 38.1–69.1%) and 31.21% (95% CI 19.9–43.7%), respectively. The highest and lowest prevalence of viral infections was HSV (77.7% 95% CI 38.48–99.32%), EBV (72.02%, 95% CI 44.65–90.79%) and Influenza A (7.3%, 95% CI 2.66–42.45%), respectively. Whereas the highest and lowest prevalence in bacterial infections were related to Streptococcus sp. (99.49%, 95% CI 96.44–99.9%) and Raoultella (1.2%, 95% CI 0.2–3.08%), respectively.

Conclusions

The results of this review were confirmed that the presence of viral and bacterial infections are the risk factors in the pathogenesis of IPF. In further analyses, which have never been shown in the previous studies, we revealed the geographic variations in the association strengths and emphasized other methodological parameters (e.g., detection method). Also, our study supports the hypothesis that respiratory infection could play a key role in the pathogenesis of IP.

High-Expressed Macrophage Scavenger Receptor 1 Predicts Severity Clinical Outcome in Transplant Patient in Idiopathic Pulmonary Fibrosis Disease

Background

Lung transplantation has been performed worldwide and admitted as an effective treatment for patients with various end-stage lung diseases. However, limit reliable clinical indicators exist to identify patients at high risk for allograft failure in lung transplant recipients. The recent advances in the knowledge of immunological aspects of the pulmonary diseases, for that innate macrophage activation, are induced by pathogen or pathogen-derived molecules and widely accepted as the critical evidence among the pathogenesis of lung inflammation and fibrosis. This study was aimed at evaluating the clinical significance of CD86- and macrophage scavenger receptor 1- (MSR1-) positive cells during the development of idiopathic pulmonary fibrosis (IPF) and pulmonary arterial hypertension (PAH), and their potential roles in the prediction of the outcomes after lung transplantation were examined.

Methods

Tissues from lung transplantation for 37 IPF and 15 PAH patients from the Department of Cardiothoracic Surgery in Wuxi People's Hospital from December 2015 to December 2016 were analyzed by immunohistochemistry (IHC) for detecting the expression and CD86 and MSR1 and correlated with clinical events after lung transplantation.

Results

IHC results showed that the expression of MSR1, IL-13, and arginase-1 (Arg1) but not CD86 in the lung section of IPF patients was dramatically enhanced when compared with that of PAH patients. The expression of MSR1, IL-13, and Arg1 but not CD86 in the lung from IPF patients with smoking was significantly increased when compared with that from nonsmoking subjects. In addition, the expression of MSR1-positive cells in IPF subjects with Klebsiella pneumoniae infection was dramatically enhanced than that in noninfection subjects. MSR1-positive macrophages were negatively associated with FEV1 and with FVC but not associated with TLC and with TL_CO. However, CD86-positive macrophages were not significantly associated with the above lung function-related factors. Furthermore, MSR1 had a higher area under the ROC curve (AUC) than CD86 for IPF diagnosis. Survival analysis indicated that high levels of MSR1-positive macrophages had a worse prognostic effect for IPF patients with lung transplantation.

Conclusion

Our study indicates the clinical significance of Klebsiella pneumoniae infection-related MSR1-positive cells in IPF progression, and it could be a prognostic marker in IPF after the lung transplant; development strategies to reduce the expression of MSR1-positive macrophages in IPF may be beneficial for the lung transplant.

Outcome of Hospitalization for COVID-19 in Patients with Interstitial Lung Disease. An International Multicenter Study

Rationale: The impact of coronavirus disease (COVID-19) on patients with interstitial lung disease (ILD) has not been established.Objectives: To assess outcomes in patients with ILD hospitalized for COVID-19 versus those without ILD in a contemporaneous age-, sex-, and comorbidity-matched population.Methods: An international multicenter audit of patients with a prior diagnosis of ILD admitted to the hospital with COVID-19 between March 1 and May 1, 2020, was undertaken and compared with patients without ILD, obtained from the ISARIC4C (International Severe Acute Respiratory and Emerging Infection Consortium Coronavirus Clinical Characterisation Consortium) cohort, admitted with COVID-19 over the same period. The primary outcome was survival. Secondary analysis distinguished idiopathic pulmonary fibrosis from non-idiopathic pulmonary fibrosis ILD and used lung function to determine the greatest risks of death.Measurements and Main Results: Data from 349 patients with ILD across Europe were included, of whom 161 were admitted to the hospital with laboratory or clinical evidence of COVID-19 and eligible for propensity score matching. Overall mortality was 49% (79/161) in patients with ILD with COVID-19. After matching, patients with ILD with COVID-19 had significantly poorer survival (hazard ratio [HR], 1.60; confidence interval, 1.17-2.18; P = 0.003) than age-, sex-, and comorbidity-matched controls without ILD. Patients with an FVC of <80% had an increased risk of death versus patients with FVC ≥80% (HR, 1.72; 1.05-2.83). Furthermore, obese patients with ILD had an elevated risk of death (HR, 2.27; 1.39-3.71).Conclusions: Patients with ILD are at increased risk of death from COVID-19, particularly those with poor lung function and obesity. Stringent precautions should be taken to avoid COVID-19 in patients with ILD.

"A Chain Only as Strong as Its Weakest Link": An Up-to-Date Literature Review on the Bidirectional Interaction of Pulmonary Fibrosis and COVID-19

The COVID-19 pandemic rapidly became a worldwide healthcare emergency affecting millions of people, with poor outcomes for patients with chronic conditions and enormous pressure on healthcare systems. Pulmonary fibrosis (PF) has been cited as a risk factor for a more severe evolution of COVID-19, primarily because its acute exacerbations are already associated with high mortality. We reviewed the available literature on biochemical, pathophysiological, and pharmacological mechanisms of PF and COVID-19 in an attempt to foresee the particular risk of infection and possible evolution of PF patients if infected with SARS-COV-2. We also analyzed the possible role of medication and risk factors (such as smoking) in the disease's evolution and clinical course. We found out that there is a complexity of interactions between coexisting idiopathic pulmonary fibrosis/interstitial lung disease (ILD) and COVID-19 disease. Also, patients recovering from severe COVID-19 disease are at serious risk of developing PF. Smokers seem to have, in theory, a chance for a better outcome if they develop a severe form of COVID-19 but statistically are at much higher risk of dying if they become critically ill.

Incidence and impact of extra-pulmonary organ failures on hospital mortality in acute exacerbation of idiopathic pulmonary fibrosis

To evaluate hospital mortality and associated risk factors for acute exacerbations of idiopathic pulmonary fibrosis (AEIPF). Emphases were put on incidence and impact of extra-pulmonary organ failures. Patients diagnosed with AEIPF from July 2014 to September 2018 were enrolled. Clinical data were collected. Acute physiology and chronic health evaluation II (APACHE II) and simplified acute physiological score II (SAPS II) were calculated. Extra-pulmonary organ failures were diagnosed upon criteria of sequential organ failure assessment (SOFA). Forty-five patients with AEIPF were included. Eighteen patients (40.0%) developed extra-pulmonary organ failures, and 25 patients (55.6%) died during hospitalization. Serum C-reactive protein (CRP) (p = 0.001), SAPS II (p = 0.004), SOFA (p = 0.001) were higher, whereas arterial oxygen pressure (PaO₂)/ fractional inspired oxygen (FiO₂) (p = 0.001) was lower in non-survivors than survivors. More non-survivors developed extra-pulmonary organ failures than survivors (p = 0.002). After adjustment, elevated serum CRP (OR 1.038, p = 0.049) and extra-pulmonary organ failure (OR 13.126, p = 0.016) were independent predictors of hospital mortality in AEIPF. AEIPF had high hospital mortality and occurrence of extra-pulmonary organ failure was common. Elevated serum CRP and extra-pulmonary organ failure had predictive values for mortality.

Biomarkers and their potential functions in idiopathic pulmonary fibrosis

Introduction: Idiopathic pulmonary fibrosis (IPF) is a chronic, devastating, and progressive lung disease that is characterized by fibrosis and respiratory failure. IPF holds high morbidity and poor prognosis and still faces considerable problems of reliable diagnosis and valid prognosis. A growing body of literature have reported changes in the level of various biomarkers in IPF patients, which means that they are expected to become a new tool for the clinical practice of IPF.Areas covered: We reviewed the recent literature about biomarkers and focus on the role they play in IPF. We systematically searched Medline/PubMed through February 2020. Many works of literature have shown that a variety of biomolecules and genomics played multiple roles in the diagnosis or differential diagnosis, prognosis, and indication of acute deterioration of IPF and so on.Expert opinion: Significant advances have been made in the role of biomarkers for IPF these years; however, current data indicate that a single biomarker is unlikely to have a transformative effect on clinical practice; therefore, the combined effect of various biomarkers can be considered to improve the accuracy of diagnosis and prognosis. Further research of biomarkers may provide new insights for the diagnosis, prognosis, and even therapy of IPF.

Acute exacerbation of idiopathic pulmonary fibrosis: who to treat, how to treat

Purpose of Review

Acute exacerbations of idiopathic pulmonary fibrosis (AE-IPF) are the most frequent cause of death among patients with IPF. Here, we review the revised definition and diagnostic criteria for AE-IPF and discuss management strategies including mechanistically targeted investigational therapies for this complex syndrome.

Recent Findings

Novel therapies targeting various pathways including inflammation, autoimmunity and coagulation cascade involved in AE-IPF have recently been reported. Although most of these reports are small and uncontrolled, they have provided evidence to design larger randomized, controlled, multicenter studies to improve outcomes among patients with AE-IPF.

Summary

AE-IPF has a dismal prognosis and current treatment consists mainly of supportive care and symptom palliation. There is a lack of consensus on current therapies for AE-IPF, including corticosteroids, but current randomized control studies for newer therapeutic strategies may hold promise.

The Role of the Lung's Microbiome in the Pathogenesis and Progression of Idiopathic Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive, fibrosing interstitial lung disease that commonly affects older adults and is associated with the histopathological and/or radiological patterns of usual interstitial pneumonia (UIP). Despite significant advances in our understanding of disease pathobiology and natural history, what causes IPF remains unknown. A potential role for infection in the disease's pathogenesis and progression or as a trigger of acute exacerbation has long been postulated, but initial studies based on traditional culture methods have yielded inconsistent results. The recent application to IPF of culture-independent techniques for microbiological analysis has revealed previously unappreciated alterations of the lung microbiome, as well as an increased bacterial burden in the bronchoalveolar lavage (BAL) of IPF patients, although correlation does not necessarily entail causation. In addition, the lung microbiome remains only partially characterized and further research should investigate organisms other than bacteria and viruses, including fungi. The clarification of the role of the microbiome in the pathogenesis and progression of IPF may potentially allow its manipulation, providing an opportunity for targeted therapeutic intervention.

The contribution of infection and the respiratory microbiome in acute exacerbations of idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) arises in genetically susceptible individuals as a result of an aberrant wound-healing response following repetitive alveolar injury. The clinical course of the disease remains both variable and unpredictable with periods of more rapid decline, termed acute exacerbation of IPF (AE-IPF), often punctuating the disease trajectory. Exacerbations carry a significant morbidity and mortality, and their exact pathogenesis remains unclear. Given the emerging evidence that disruption and alteration in the lung microbiome plays a role in the pathogenesis and progression of IPF, this review discusses the current knowledge of the contribution of infection and the respiratory microbiome to AE-IPF.