Hypersensitivity pneumonitis: insights in diagnosis and pathobiology

Contemporary Concise Review 2023: Environmental and occupational lung diseases

Air pollutants have various effects on human health in environmental and occupational settings. Air pollutants can be a risk factor for incidence, exacerbation/aggravation and death due to various lung diseases, including asthma, chronic obstructive pulmonary disease (COPD), hypersensitivity pneumonitis or pneumonia (HP), pulmonary fibrosis such as pneumoconiosis and malignant respiratory diseases such as lung cancer and malignant pleural mesothelioma. Environmental and occupational respiratory diseases are crucial clinical and social issues worldwide, although the burden of respiratory disease due to environmental and occupational causes varies depending on country/region, demographic variables, geographical location, industrial structure and socioeconomic situation. The correct recognition of environmental and occupational lung diseases and taking appropriate measures are essential to their effective prevention.

Deregulated immune cell recruitment orchestrated by c-MET impairs pulmonary inflammation and fibrosis

BACKGROUND

Pulmonary fibrosis (PF) represents the pathologic end stage of several interstitial lung diseases (ILDs) associated with high morbidity and mortality rates. However, current treatments can only delay disease progression rather than provide a cure. The role of inflammation in PF progression is well-established, but new insights into immune regulation are fundamental for developing more efficient therapies. c-MET signaling has been implicated in the migratory capacity and effector functions of immune cells. Nevertheless, the role of this signaling pathway in the context of PF-associated lung diseases remains unexplored.

METHODS

To determine the influence of c-MET in immune cells in the progression of pulmonary fibrosis, we used a conditional deletion of c-Met in immune cells. To induce pulmonary fibrosis mice were administered with bleomycin (BLM) intratracheally. Over the course of 21 days, mice were assessed for weight change, and after euthanasia at different timepoints, bronchoalveolar lavage fluid cells and lung tissue were assessed for inflammation and fibrosis. Furthermore, c-MET expression was assessed in cryobiopsy sections, bronchoalveolar lavage fluid cells samples and single cell RNA-sequencing dataset from human patients with distinct interstitial lung diseases.

RESULTS

c-MET expression was induced in lung immune cells, specifically in T cells, interstitial macrophages, and neutrophils, during the inflammatory phase of BLM-induced PF mouse model. Deletion of c-Met in immune cells correlated with earlier weight recovery and improved survival of BLM-treated mice. Moreover, the deletion of c-Met in immune cells was associated with early recruitment of the immune cell populations, normally found to express c-MET, leading to a subsequent attenuation of the cytotoxic and proinflammatory environment. Consequently, the less extensive inflammatory response, possibly coupled with tissue repair, culminated in less exacerbated fibrotic lesions. Furthermore, c-MET expression was up-regulated in lung T cells from patients with fibrosing ILD, suggesting a potential involvement of c-MET in the development of fibrosing disease.

CONCLUSIONS

These results highlight the critical contribution of c-MET signaling in immune cells to their enhanced uncontrolled recruitment and activation toward a proinflammatory and profibrotic phenotype, leading to the exacerbation of lung injury and consequent development of fibrosis.

Interstitial Lung Abnormalities: Current Understanding

Interstitial lung abnormalities (ILAs) are incidental findings on computed tomography scans, characterized by nondependent abnormalities affecting more than 5% of any lung zone. They are associated with factors such as age, smoking, genetic variants, worsened clinical outcomes, and increased mortality. Risk stratification based on clinical and radiological features of ILAs is crucial in clinical practice, particularly for identifying cases at high risk of progression to pulmonary fibrosis. Traction bronchiectasis/bronchiolectasis index has emerged as a promising imaging biomarker for prognostic risk stratification in ILAs. These findings suggest a spectrum of fibrosing interstitial lung diseases, encompassing from ILAs to pulmonary fibrosis.

Fibrotic lung diseases in children

In children, pulmonary fibrosis (PF) is an extremely unusual entity that can be observed in some types of interstitial lung disease (ILD). Defining whether ILD is accompanied by PF is important for targeted therapy. Algorithm for the diagnosis of PF in children is not clearly established. Besides, the clinical, radiological, and histological definitions commonly used to diagnose particularly the cases of idiopathic PF in adult patients, is not applicable to pediatric cases. However, a few studies conducted in children offer good exemplary diagnostic approach to fibrosing ILD. Thorax high resonance computed tomography and/or lung biopsy scanning can provide valuable information about PF. Another issue that has not been clearly established is when to start antifibrotic treatment in pediatric patients with PF. The objective of this current review is to provide a comprehensive overview of pediatric PF by drawing upon adult research, particularly focusing on the areas of uncertainty.

A Case of Immunomodulator-Responsive Hypersensitivity Pneumonitis Secondary to Chronic Passive Smoke Inhalation

Hypersensitivity pneumonitis (HP) is a pulmonary disease characterized by inflammation and fibrosis of the lung parenchyma following chronic exposure to immunogenic antigens. The pathophysiology of HP involves type 3 and type 4 hypersensitivity reactions leading to acute and chronic manifestations, respectively. Clinically, it manifests as exertional dyspnea and wheezing. Pulmonary function tests display a pattern of restrictive lung disease, and high-resolution CT scans display a pattern of ground glass opacities, centrilobular nodules, and mosaic attenuation. Antigen avoidance remains the only method for primary prevention. Alternative therapy may be needed due to either the inability to avoid antigens or the lack of antigen identification. Prednisone 0.5 mg/kg per day is the first-line treatment for acute non-fibrotic forms of HP. In chronic or fibrotic HP, the immunomodulator mycophenolate mofetil (MMF) was shown to be an effective treatment in improving the diffusing capacity of the lungs for carbon monoxide and forced vital capacity, but not overall survival. The following study aims to bring to attention the need for additional prospective multicenter clinical trials to clarify the role of MMF as an immunomodulator in fibrosing HP.

Survival and Lung Function Changes in Hypersensitivity Pneumonitis According to Radiological Phenotypes Compared With Idiopathic Pulmonary Fibrosis

INTRODUCTION

The main objective of this study was to estimate survival and changes in lung function in patients with chronic hypersensitivity pneumonitis (HP), both fibrotic (f-HP) and nonfibrotic (nf-HP), and to compare them with those in patients with idiopathic pulmonary fibrosis (IPF).

METHODS

HP was diagnosed based on antigen exposure, HRCT (high-resolution CT scan), BAL (bronchoalveolar lavage), and histology. According to HRCT, HP was classified into fibrotic and non-fibrotic phenotypes. In most cases, IPF was diagnosed based on HRCT findings.

RESULTS

We identified 84 patients: 46 with IPF, 18 with f-HP, and 20 with nf-HP. Five-year survival was 23.9% in IPF, 72% in f-HP, and 100% in nf-HP (p <0.0001). Honeycombing was associated with decreased survival in IPF (p <0.001) and in f-HP (p <0.0001). The mean loss of FVC (forced vital capacity) % pred. (percent predicted) was -18.3% in IPF (p =0.001), -4.8% in f-HP, and -6.0% in nf-HP. The mean change in DLCO (diffusion capacity for carbon monoxide) % pred. was -10.2% in IPF (p <0.002), -0.5% in f-HP, and +1.9% in nf-HP. The agreement between radiological phenotypes and histology in HP was 89.6%.

CONCLUSIONS

We found shorter survival in IPF, followed by f-HP, and nf-HP. Over time, we did not find significant changes in FVC% pred. or DLCO% pred. in HP, while a significant decline in IPF was noted. In HP, we found strong agreement between radiological phenotypes and histology. Radiological signs suggestive of lung fibrosis in HP were reliable for the diagnosis of f-HP and seem to have intrinsic prognostic value.

Bird-related non-fibrotic hypersensitivity pneumonitis with bronchoalveolar lavage fluid eosinophilia that developed after COVID-19 vaccination: A case report

A 60-year-old man who had been keeping seven budgerigars and four cockatiels in his house for 2 years developed dyspnea and was admitted to our hospital the day after receiving the second dose of the messenger RNA coronavirus disease 2019 vaccination. Chest high resolution computed tomography (HRCT) showed bilateral ground glass opacities without nodules or mosaic attenuation. IgG specific for budgerigars was positive. Although his respiratory symptoms were resolved without corticosteroid therapy, he developed severe dyspnea soon after the discharge to his home. The results of bronchial alveolar lavage fluid obtained at the initial admission and after the provocation challenge showed elevation of lymphocytes (34%) and eosinophils (37%). We finally diagnosed him with non-fibrotic bird-related hypersensitivity pneumonitis. His condition and HRCT findings were improved by corticosteroid treatment. All his birds were given away. He has not experienced any recurrence or deterioration of respiratory function even after withdrawal of corticosteroid.

Aspergillus and the Lung

The filamentous fungus Aspergillus causes a wide spectrum of diseases in the human lung, with Aspergillus fumigatus being the most pathogenic and allergenic subspecies. The broad range of clinical syndromes that can develop from the presence of Aspergillus in the respiratory tract is determined by the interaction between host and pathogen. In this review, an oversight of the different clinical entities of pulmonary aspergillosis is given, categorized by their main pathophysiological mechanisms. The underlying immune processes are discussed, and the main clinical, radiological, biochemical, microbiological, and histopathological findings are summarized.

The Unveiled Triad: Clinical, Radiological and Pathological Insights into Hypersensitivity Pneumonitis

Hypersensitivity pneumonitis (HP) is a diffuse parenchymal lung disease (DLPD) characterized by complex interstitial lung damage with polymorphic and protean inflammatory aspects affecting lung tissue targets including small airways, the interstitium, alveolar compartments and vascular structures. HP shares clinical and often radiological features with other lung diseases in acute or chronic forms. In its natural temporal evolution, if specific therapy is not initiated promptly, HP leads to progressive fibrotic damage with reduced lung volumes and impaired gas exchange. The prevalence of HP varies considerably worldwide, influenced by factors like imprecise disease classification, diagnostic method limitations for obtaining a confident diagnosis, diagnostic limitations in the correct processing of high-resolution computed tomography (HRCT) radiological parameters, unreliable medical history, diverse geographical conditions, heterogeneous agricultural and industrial practices and occasionally ineffective individual protections regarding occupational exposures and host risk factors. The aim of this review is to present an accurate and detailed 360-degree analysis of HP considering HRCT patterns and the role of the broncho-alveolar lavage (BAL), without neglecting biopsy and anatomopathological aspects and future technological developments that could make the diagnosis of this disease less challenging.

Hypersensitivity Pneumonitis: Challenges of a Complex Disease

Hypersensitivity pneumonitis (HP) is a complex interstitial lung disease caused by chronic inhalation of a wide variety of antigens in susceptible and sensitized individuals, commonly associated with an occupational exposure. An impressive number of inciting antigens causing hypersensitivity pneumonitis have been found to cover a wide range of occupations. As working practices have changed over time, especially in industrialized countries, new names for occupational HP have emerged. This review emphasizes the main diagnostic issues arising from the high variability of clinical presentation and the broad spectrum of causal antigens. Furthermore, it provides an overview of current methods to unveil possible causes of hypersensitivity pneumonitis, highlights HP's current diagnostic and treatment challenges and the remaining areas of uncertainty, and presents prevention strategies.

[Morphology of hypersensitivity pneumonitis]

Hypersensitivity pneumonitis (HP) is one of the most common interstitial lung diseases, the manifestations of which are diverse, and the diagnosis is complex and requires a multidisciplinary approach. HP is an immunologically determined disease in response to inhaled antigens. The main feature of the disease is terminal bronchiole's involvement accompanied by interstitial inflammation and/or fibrosis together with the presence of non-necrotizing granulomas in the interalveolar septa and bronchioles. The article presents the histological features of non-fibrous and fibrotic variants of the disease. Well-defined diagnostic criteria were formulated on the basis of published international recommendations and the authors' own experience.

Japanese clinical practice guide 2022 for hypersensitivity pneumonitis

Considering recently published two guidelines for the diagnosis of hypersensitivity pneumonitis (HP), the Japanese Respiratory Society (JRS) has now published its own Japanese clinical practice guide for HP. Major types of HP in Japan include summer-type, home-related, bird-related, farmer's lung, painter's lung, humidifier lung, and mushroom grower's lung. Identifying causative antigens is critical for increasing diagnostic confidence, as well as improving prognosis through appropriate antigen avoidance. This guide proposes a comprehensive antigen questionnaire including the outbreak sources reported in Japan. Drawing on the 2021 CHEST guideline, this guide highlights the antigen identification confidence level and adaptations for environmental surveys. The detection of specific antibodies against causative antigens is an important diagnostic predictor of HP. In Japan, the assessments of bird-specific IgG (pigeons, budgerigars) and the Trichosporon asahii antibody are covered by medical insurance. Although this guide adopts the 2020 ATS/JRS/ALAT guideline diagnostic criteria based on the combination of imaging findings, exposure assessment, bronchoalveolar lavage lymphocytosis, and histopathological findings, it added some annotations to facilitate the interpretation of the content and correlate the medical situation in Japan. It recommends checking biomarkers; seasonal changes in the KL-6 concentration (increase in winter for bird-related HP/humidifier lung and in summer for summer-type HP) and high KL-6 concentrations providing a basis for the suspicion of HP. Antigen avoidance is critical for disease management of HP. This guide also addresses the pharmacological management of HP, highlighting the treatment strategy for fibrotic HP including combination therapies with anti-inflammatory/immunosuppressive and antifibrotic drugs.

Distinct TNF-alpha and HLA polymorphisms associate with fibrotic and non-fibrotic subtypes of hypersensitivity pneumonitis

INTRODUCTION

Since Hypersensitivity Pneumonitis (HP) categorization in fibrotic and nonfibrotic/inflammatory types seems to be more consistent with the distinctive clinical course and outcomes, recent international guidelines recommended the use of this classification. Moreover, fibrotic subtype may share immunogenetic and pathophysiological mechanisms with other fibrotic lung diseases.

AIM

To investigate HLA -A, -B, -DRB1 and TNF-α -308 gene polymorphisms among fibrotic and nonfibrotic HP patients due to avian exposure, also in comparison with asymptomatic exposed controls.

METHODS

We prospectively enrolled 40 HP patients, classified as fibrotic or nonfibrotic/inflammatory, and 70 exposed controls. HLA and TNF-α polymorphisms were determined by polymerase chain reaction-sequence specific primer amplification.

RESULTS

While HLA alleles were not associated to HP susceptibility, fibrotic HP patients showed increased frequencies of HLA A*02 (46.7% vs 25.7%; OR=2.53, p = 0.02) and HLA DRB1*14 (10.0% vs 0.7%; OR=15.44, p=0.02) alleles when compared with exposed controls, although not statistically significant after correction for multiple comparisons. TNF-α G/G genotype (associated with low TNF-α production) frequencies were significantly increased among the non-fibrotic/inflammatory HP patients comparatively to fibrotic presentations (88% vs 60%; RR=0.44; p=0.04) and controls (88% vs 63%, OR 4.33, p=0.037). Also, these patients had a significantly increased frequency of the G allele (94.0% vs 73.3%, RR=0.44, p=0.01), while fibrotic HP patients predominantly presented the A allele (26.7% vs 6.0%, RR=2.28, p=0.01).

CONCLUSIONS

Our results support the hypothesis that fibrotic and non-fibrotic HP subtypes exhibit a distinct profile of TNF-α and HLA polymorphisms, which may be relevant to predict disease course and better define treatment strategies.

When to panic about a panic attack: A challenging case of hypersensitivity pneumonitis

The COVID-19 pandemic has created diagnostic difficulties with the increase in mental health illnesses that often present with nonspecific symptoms, like hypersensitivity pneumonitis. Hypersensitivity pneumonitis is a complex syndrome of varying triggers, onset, severity, and clinical manifestations that can be challenging to diagnose in many cases. Typical symptoms are nonspecific and can be attributed to other entities. There are no pediatric guidelines, which contributes to diagnostic difficulties and delays in treatment. It is particularly important to avoid diagnostic biases, have an index of suspicion for hypersensitivity pneumonitis, and to develop pediatric guidelines as outcomes are excellent when diagnosed and treated promptly. This article discusses hypersensitivity pneumonitis with a focus on the causes, pathogenesis, diagnostic approach, outcomes, and prognosis while using a case to illustrate the diagnostic difficulties worsened by the COVID-19 pandemic.

Recurrent episodes of febrile dyspnoea: hypersensitivity pneumonitis caused by a household ultrasonic humidifier

Hypersensitivity pneumonitis is an immune-mediated interstitial lung disease that presents with respiratory symptoms, with or without systemic symptoms, following exposure to an identified or unidentified external factor. It can be caused by extrinsic factors including household items such as ultrasonic humidifiers.We present an intriguing case of a previously healthy 50-year-old man who displayed recurrent episodes of progressive dyspnoea and fever after repeated exposure to his household ultrasonic humidifier. He was treated with corticosteroids, followed by the removal of the humidifier, resulting in total recovery and absence of recurrence of further episodes.The clinical presentation of hypersensitivity pneumonitis can be dramatic, and the differential diagnosis is broad. The correct diagnosis is achieved by combining clinical, radiological and histopathological patterns. The key to finding the aetiology lies in a thorough history, with an important role for household investigations to identify the external factor.

Single-Cell Profiling of Cells in the Lung of a Patient with Chronic Hypersensitivity Pneumonitis Reveals Inflammatory Niche with Abundant CD39+ T Cells with Functional ATPase Phenotype: A Case Study

This study investigated immune cell characteristics in chronic hypersensitivity pneumonitis (HP), focusing on CD39-expressing cells' impact on inflammation and tissue remodelling. Lung tissue from an HP patient was analysed using single-cell transcriptomics, flow cytometry, and gene expression profiling. The tissue revealed diverse cell types like macrophages, T cells, fibroblasts, and regulatory T cells (Tregs). CD39-expressing Tregs exhibited heightened ATP hydrolysis capacity and regulatory gene expression. CD39hi cells displayed markers of both Tregs and proinflammatory Th17 cells, suggesting transitional properties. Communication networks involving molecules like SPP1, collagen, CSF1, and IL-1β were identified, hinting at interactions between cell types in HP pathogenesis. This research provides insights into the immune response and cell interactions in chronic HP. CD39-expressing cells dual nature as Tregs and Th17 cells suggests a role in modulating lung inflammation, potentially affecting disease progression. These findings lay the groundwork for further research, underscoring CD39-expressing cells as potential therapeutic targets in HP.

Evaluation and Exploration of Machine Learning and Convolutional Neural Network Classifiers in Detection of Lung Cancer from Microarray Gene-A Paradigm Shift

Microarray gene expression-based detection and classification of medical conditions have been prominent in research studies over the past few decades. However, extracting relevant data from the high-volume microarray gene expression with inherent nonlinearity and inseparable noise components raises significant challenges during data classification and disease detection. The dataset used for the research is the Lung Harvard 2 Dataset (LH2) which consists of 150 Adenocarcinoma subjects and 31 Mesothelioma subjects. The paper proposes a two-level strategy involving feature extraction and selection methods before the classification step. The feature extraction step utilizes Short Term Fourier Transform (STFT), and the feature selection step employs Particle Swarm Optimization (PSO) and Harmonic Search (HS) metaheuristic methods. The classifiers employed are Nonlinear Regression, Gaussian Mixture Model, Softmax Discriminant, Naive Bayes, SVM (Linear), SVM (Polynomial), and SVM (RBF). The two-level extracted relevant features are compared with raw data classification results, including Convolutional Neural Network (CNN) methodology. Among the methods, STFT with PSO feature selection and SVM (RBF) classifier produced the highest accuracy of 94.47%.

Real-Life Diagnostic Performance of the Hypersensitivity Pneumonitis Guidelines: A Multicenter Cohort Study

Hypersensitivity pneumonitis (HP) is a heterogeneous interstitial lung disease (ILD) that may be difficult to confidently diagnose. Recently, the 2020 ATS/JRS/ALAT HP diagnostic guidelines were published, yet data validating their performance in real-life settings are scarce. We aimed to assess the diagnostic performance of the HP guidelines compared to the gold-standard multidisciplinary discussion (MDD). For this purpose, we included consecutive ILD patients that underwent diagnostic bronchoscopy between 2017 and 2020 in three large medical centers. Four diagnostic factors (antigen exposure history, chest computed tomography pattern, bronchoalveolar lavage lymphocyte count, and histology results) were used to assign guidelines-based HP diagnostic confidence levels for each patient. A sensitivity analysis was performed, with MDD diagnosis as the reference standard. Overall, 213 ILD patients were included, 45 (21%) with an MDD diagnosis of HP. The guidelines' moderate (≥70%) confidence threshold produced optimal performance with 73% sensitivity for HP, 89% specificity, and a J-index of 0.62. The area under the receiver operating characteristic curve (AUC) for a correct guidelines-based diagnosis was 0.86. The guidelines had better performance for non-fibrotic than fibrotic HP (AUC 0.92 vs. 0.82). All diagnostic factors, except bronchoalveolar lavage lymphocyte count, were independent predictors for MDD diagnosis of HP in a multivariate analysis. In conclusion, the HP guidelines exhibited a good diagnostic performance compared to MDD diagnosis in real-life setting.

Bagassosis- An Infrequent Type of Hypersensitivity Pneumonitis: A Case Report

Hypersensitivity pneumonitis (HP) is an umbrella term for a spectrum of disorders caused by the inhalation of organic dust or low molecular weight chemicals. Bagassosis, a rare form of HP, is an allergic reaction caused by inhalation of bagasse dust, which is used in manufacturing several products. Very few cases of bagassosis have been reported in India, owing to the growing industrialization adapting organized sectors for preventing occupational health disorders. Nevertheless, a small population is being exposed to bagasse dust, shadowed by inadequate protective equipment, leading to the occurrence of this occupational disease. Here, we report a case of bagassosis in a 25-year-old male, brick-kiln worker, who presented with respiratory complaints. He underwent a transbronchial lung biopsy that aided in confirmation of the disease, but developed pneumothorax as a complication, which was managed with an Intercostal drain. He was started on corticosteroids, following which his symptoms improved significantly.

The Characteristic of Transbronchial Lung Cryobiopsy in the Pathological Diagnosis of Hypersensitivity Pneumonitis

BACKGROUND

Transbronchial lung cryobiopsy (TBLC) has widely used for the diagnosis of diffuse lung disease. However, it remains unclear whether TBLC is useful for the diagnosis in hypersensitivity pneumonitis (HP).

METHODS

We investigated 18 patients who underwent TBLC and were diagnosed with HP based on pathology or multidisciplinary discussion (MDD). Of the 18 patients, 12 had fibrotic HP (fHP), 2 had non-fibrotic HP (non-fHP) diagnosed with MDD. The remaining 4 patients were diagnosed with fHP by pathology but not by MDD because of clinical features. The radiology and pathology of these cases were compared.

RESULTS

All patients with fHP showed radiological findings of inflammation, fibrosis, and airway disease. Conversely, pathology showed fibrosis and inflammation in 11 of 12 cases (92%), but airway disease was significantly less common with 5 cases (42%) (p = 0.014). Non-fHP showed inflammatory cell infiltration mainly in the centrilobule on pathology, which was consistent with radiology. Granulomas were found in 5 patients with HP (36%). In the non-HP group, airway-centered interstitial fibrosis was observed in 3 patients (75%) with pathology.

CONCLUSIONS

The pathology with TBLC is difficult to evaluate airway disease of HP. We need to understand this characteristic of TBLC to make a MDD diagnosis of HP.

Enhanced immune complex formation in the lungs of patients with dermatomyositis

BACKGROUND

Interstitial lung disease is frequently comorbid with dermatomyositis and has a poor prognosis, especially in patients with the anti-melanoma differentiation-associated gene 5 (MDA5) autoantibody. However, the pathogenesis of dermatomyositis-related interstitial lung disease remains unclear.

METHODS

We examined 18 and 19 patients with dermatomyositis-related interstitial lung disease and idiopathic pulmonary fibrosis (control), respectively. Lung tissues obtained from these patients were semi-quantitatively evaluated by immunohistochemical staining with in-house anti-human MDA5 monoclonal antibodies, as well as anti-human immunoglobulin (Ig) G, IgM, IgA, and complement component 3(C3) antibodies. We established human MDA5 transgenic mice and treated them with rabbit anti-human MDA5 polyclonal antibodies, and evaluated lung injury and Ig and C3 expression.

RESULTS

MDA5 was moderately or strongly expressed in the lungs of patients in both groups, with no significant differences between the groups. However, patients with dermatomyositis-related interstitial lung disease showed significantly stronger expression of C3 (p < 0.001), IgG (p < 0.001), and IgM (p = 0.001) in the lungs than control. Moreover, lung C3, but IgG, IgA, nor IgM expression was significantly stronger in MDA5 autoantibody-positive dermatomyositis-related interstitial lung disease (n = 9) than in MDA5 autoantibody-negative dermatomyositis-related interstitial lung disease (n = 9; p = 0.022). Treatment with anti-MDA5 antibodies induced lung injury in MDA5 transgenic mice, and strong immunoglobulin and C3 expression was observed in the lungs of the mice.

CONCLUSION

Strong immunoglobulin and C3 expression in the lungs involve lung injury related to dermatomyositis-related interstitial lung disease. Enhanced immune complex formation in the lungs may contribute to the poor prognosis of MDA5 autoantibody-positive dermatomyositis-related interstitial lung disease.

Database analysis of hypersensitivity pneumonitis in Japan

BACKGROUND

Three epidemiological small-scale studies on hypersensitivity pneumonitis (HP) have been performed in Japan to date. Herein, we aimed to clarify the clinical characteristics of various types of HP diseases using a large nationwide database in Japan.

METHODS

We used the Japanese Diagnostic Procedure Combination database that includes data from 1,031 participant hospitals. Patients with HP from 2011 to 2017 were identified using International Classification of Diseases 10th Revision codes. We analyzed patient characteristics, the yearly transition of the number of HP cases, rate per one million hospitalizations, geographical distribution, seasonality, and risk factors for in-hospital mortality.

RESULTS

In total, 3,634 patients with HP were identified, including summer-type HP (SHP) (n = 490), bird fancier's lung (BFL) (n = 199), ventilation pneumonitis (n = 106), farmer's lung (n = 48), and unspecified HP (n = 2761). The length of hospital stay was significantly longer in patients with BFL (19 days) than in patients with SHP (15 days). SHP was more prevalent in the southwestern region of Japan, and hospitalization occurred mainly in summer (37.8%) and fall (37.3%). Ventilation pneumonitis was predominant in winter (28.6%) and spring (38.7%). In-hospital mortality was significantly associated with old age (p < 0.001), low body mass index (p = 0.016), severe dyspnea (p < 0.001), and BFL diagnosis on admission (p = 0.031).

CONCLUSIONS

This study revealed the clinical characteristics of SHP and BFL, including the frequency of causative antigens, geographical distribution, seasonality, and risk factors for mortality, which may help in diagnosing HP and identifying causative antigens.

Diagnosis of Fibrotic Hypersensitivity Pneumonitis: Is There a Role for Biomarkers?

Hypersensitivity pneumonitis is a complex interstitial lung syndrome and is associated with significant morbimortality, particularly for fibrotic disease. This condition is characterized by sensitization to a specific antigen, whose early identification is associated with improved outcomes. Biomarkers measure objectively biologic processes and may support clinical decisions. These tools evolved to play a crucial role in the diagnosis and management of a wide range of human diseases. This is not the case, however, with hypersensitivity pneumonitis, where there is still great room for research in the path to find consensual diagnostic biomarkers. Gaps in the current evidence include lack of validation, validation against healthy controls alone, small sampling and heterogeneity in diagnostic and classification criteria. Furthermore, discriminatory accuracy is currently limited by overlapping mechanisms of inflammation, damage and fibrogenesis between ILDs. Still, biomarkers such as BAL lymphocyte counts and specific serum IgGs made their way into clinical guidelines, while others including KL-6, SP-D, YKL-40 and apolipoproteins have shown promising results in leading centers and have potential to translate into daily practice. As research proceeds, it is expected that the emergence of novel categories of biomarkers will offer new and thriving tools that could complement those currently available.

Fibrotic Hypersensitivity Pneumonitis Diagnosed by a Re-evaluation with Bronchoalveolar Lavage at Disease Deterioration

A 79-year-old man was admitted with worsening cough, dyspnea, and increased ground-glass opacity on chest computed tomography (CT). He had been diagnosed with idiopathic pulmonary fibrosis given the absence of an identifiable cause of interstitial pneumonia, chest CT findings, and absence of lymphocytosis in bronchoalveolar lavage (BAL) fluid. Meticulous history taking revealed extensive exposure to inciting antigens contained in chicken fertilizer before symptom worsening. A re-evaluation with BAL showed lymphocytosis, and clinical improvement with antigen avoidance confirmed the diagnosis of fibrotic hypersensitivity pneumonitis (fHP). A re-evaluation with BAL at disease deterioration after possible exposure to inciting antigen can facilitate a correct fHP diagnosis.

Immunopathological Mechanisms of Bird-Related Hypersensitivity Pneumonitis

Bird-related hypersensitivity pneumonitis (BRHP) is an interstitial lung disease induced by avian proteins. The immunopathological pathways involved in the disease are still unknown. This study assesses the cellular immune response and the cytokine pattern in a mouse model of BRHP. On days -3 and -1, mice were intraperitoneally sensitized with commercial pigeon serum (PS) or saline. Intranasal instillations with PS or saline were carried out on three consecutive days/week over either 3 weeks (Group 1) or 12 weeks (Group 2). Leukocyte and cytokine patterns in lung tissue and pulmonary inflammation in bronchoalveolar lavage (BAL) were analysed. Both groups presented increases in resident monocytes, interstitial macrophages and type 2 dendritic cells (DCs), but also reductions in inflammatory monocytes, alveolar macrophages and tolerogenic DCs compared with their control groups. Group 1 had increased levels of eosinophils and T cells with reductions in neutrophils and B cells, while Group 2 showed high levels of B cells. Both groups exhibited increases in Th1 and Th2 cytokines. Group 2 also showed increased levels of IL-23, a Th17 cytokine. Increased levels of neutrophils, eosinophils and lymphocytes were observed in BAL samples of both groups compared with controls. In the first stages of BRHP, there is a mixed Th1/Th2 immune response, while during the progression of the disease, although there is a Th1 response, the cytokine levels seem to indicate a switch towards a Th2/Th17 mixed response.

Interstitial Lung Disease: A Focused Review for the Emergency Clinician

BACKGROUND

Interstitial lung disease (ILD) is a group of restrictive pulmonary diseases associated with diffuse interstitial and parenchymal inflammation. Patients can present to the emergency department with severe exacerbation.

OBJECTIVE

This narrative review provides emergency clinicians with the most recent evidence concerning acute exacerbation of ILD (AE-ILD).

DISCUSSION

AE-ILD can present as acute respiratory distress in a patient with a pre-existing ILD diagnosis or as a de novo presentation of ILD, and is associated with significant morbidity and mortality. A variety of underlying triggers may result in AE-ILD. Emergency clinicians must first assess for extraneous causes of respiratory decompensation prior to diagnosing AE-ILD. For a de novo presentation of ILD, emergency physicians should also assess for possible reversible causes. AE-ILD is managed with systemic steroids, immunosuppressants, intravenous antibiotics, supplemental oxygen, and extracorporeal membrane oxygenation in severe cases. Given the high mortality rates in the absence of lung transplantation, early referral to transplant centers is essential to increase chances of survival.

CONCLUSIONS

Emergency clinician knowledge of AE-ILD can improve the evaluation and management of these patients.

Impact of diagnostic guidelines on the diagnosis of hypersensitivity pneumonitis

Introduction

Hypersensitivity pneumonitis (HP) is an immune-mediated interstitial lung disease from exposure to environmental antigens. Diagnosing HP could be challenging. The American College of Chest Physicians (CHEST) and American Thoracic Society/Japanese Respiratory Society/and Asociación Latinoamericana del Tórax (ATS/JRS/ALAT) have published diagnostic guidelines in 2021 and 2020 respectively. The CHEST guideline uses four grades of confidence: confident (>90%), provisional high (70-89%), provisional low (51-69%), and unlikely (≤50%). The ATS/JRS/ALAT guideline uses five grades of confidence: definite (>90%), high (80-89%), moderate (70-79%), low (51-69%) and not excluded (≤50%). In this study, we determined how these two guidelines could have affected the diagnosis of HP made before the guidelines.

Methods

Two hundred and fifty-nine adult patients from a previous cohort with HP (ICD-9:495) made between Jan. 1, 2008, and Dec. 31, 2013, at Duke University Medical Center were included. We simplified the diagnostic confidence into three categories so we could compare the guidelines: high (≥90%), intermediate (51-89%), and low (≤50%).

Results

There were 156 female and 103 male. Mean age was 58 (range: 20-90). 68.8% of the patients had restrictive defects (FVC < 80% pred) and 48.6% had lung biopsy. The CHEST guideline classified 33.6% of the patients into high, 59.5% into intermediate and 6.9% into low confidence categories. The ATS/JRS/ALAT guideline classified 29.7% of the patients into high, 21.2% into intermediate and 49.0% into low confidence categories (p < 0.0001 vs. CHEST). Cohen's kappa was 0.331. In patients with identifiable inciting agents (IAs) (N = 168), the CHEST guideline classified 32.1% of the patients into high, 64.3% into intermediate and 3.6% into low confidence categories. The ATS/JRS/ALAT guideline classified 29.2% of the patients into high, 20.8% into intermediate, and 50.0% into low confidence categories. Cohen's kappa was 0.314.

Discussion

In our HP cohort with two-thirds of the patients with restrictive defects, we found the two guidelines had fair agreement in diagnosing HP with or without identifiable IAs. They agreed more when the diagnostic confidence was high. When the diagnostic confidence was lower, however, the ATS/JRS/ALAT guideline was more stringent. Clinicians should be aware of the differences between the two guidelines when evaluating patients suspicious of HP.

Criteria for progressive fibrotic hypersensitivity pneumonitis in a Portuguese patient cohort

Background

Hypersensitivity pneumonitis (HP) is a syndrome caused by sensitisation to inhaled antigens that leads to an abnormal immune response in the airways and lung parenchyma. Some patients previously diagnosed with certain types of fibrotic interstitial lung diseases (f-ILDs), including fibrotic HP (f-HP), are susceptible to develop a progressive fibrosing phenotype (PF-ILD), despite initial state-of-the-art management.

Objectives

To characterise a cohort of patients with a multidisciplinary diagnosis (MTD) of chronic f-HP, who were followed up in an ILD outpatient clinic of a hospital in Portugal, and to assess the prevalence of PF-ILD criteria in these patients.

Methods

Data were collected from all patients with a definite or provisional diagnosis of f-HP after a multidisciplinary team discussion. Patients were followed up between December 2014 and July 2019. Data included clinical characteristics, high-resolution chest tomography (HRCT) disease patterns, lung function tests, bronchoalveolar lavage and further immunological work-up, biopsy reports (conventional transbronchial lung biopsy, transbronchial lung cryobiopsy or surgical video-assisted thoracoscopic lung biopsy), all ILD multidisciplinary team records and diagnostic confidence levels. Patients were assessed according to PF-ILD criteria as defined in the INBUILD trial.

Results

We identified 83 patients with an MTD of HP, who had been followed up for at least 12 months. Of these, 63 (75.9%) were diagnosed with f-HP. Of the 63 f-HP patients, 33.3% (n=21) fulfilled the predefined criteria for PF-HP: 66.7% had a relative decline of ≥10% forced vital capacity (FVC); 5% a relative decline of 5 - 9% FVC, with worsening symptoms or increased fibrosis on HRCT; and 23.8% had worsening respiratory symptoms with radiological progression.

Conclusion

This single-centre cohort study demonstrated that a third of f-HP patients presented with PF-ILD, as determined by progression during initial standard-of-care treatment. A usual interstitial pneumonia (UIP)/UIP-like pattern was present in >70% of patients with f-HP, and two-thirds of these patients had an FVC decline of ≥10%. PF-HP patients were also more exacerbation prone. According to recent trial data, this segment of patients can be considered possible candidates for antifibrotic treatment, with a reasonable prospect of effectiveness. Further efforts should focus on refining knowledge of longitudinal behaviour of large multicentric cohorts of f-HP patients, establishing a consensual and uniform definition of progression for use in clinical practice, as well as developing prognostic prediction tools to better (and early) inform the disease course.

Hypersensitivity Pneumonitis: A Pictorial Review Based on the New ATS/JRS/ALAT Clinical Practice Guideline for Radiologists and Pulmonologists

Hypersensitivity pneumonitis (HP) is a complicated and heterogeneous interstitial lung disease (ILD) caused by an excessive immune response to an inhaled antigen in susceptible individuals. Accurate diagnosis of HP is difficult and necessitates a detailed exposure history, as well as a multidisciplinary discussion of clinical, histopathologic, and radiologic data. We provide a pictorial review based on the latest American Thoracic Society (ATS)/Japanese Respiratory Society (JRS)/Asociación Latinoamericana del Tórax (ALAT) guidelines for diagnosing HP through demonstrating new radiologic terms, features, and a new classification of HP which will benefit radiologists and pulmonologists.

Co-modulation of T cells and B cells enhances the inhibition of inflammation in experimental hypersensitivity pneumonitis

Background

Hypersensitivity pneumonitis (HP) is an interstitial lung disease characterized by antigen-triggered neutrophilic exacerbations. Although CD4⁺ T cells are sufficient for HP pathogenesis, this never translated into efficient T cell-specific therapies. Increasing evidence shows that B cells also play decisive roles in HP. Here, we aimed to further define the respective contributions of B and T cells in subacute experimental HP.

Methods

Mice were subjected to a protocol of subacute exposure to the archaeon Methanosphaera stadmanae to induce experimental HP. Using models of adoptive transfers of B cells and T cells in Rag1-deficient mice and of B cell-specific S1P₁ deletion, we assessed the importance of B cells in the development of HP by evaluating inflammation in bronchoalveolar lavage fluid. We also aimed to determine if injected antibodies targeting B and/or T cells could alleviate HP exacerbations using a therapeutic course of intervention.

Results

Even though B cells are not sufficient to induce HP, they strongly potentiate CD4⁺ T cell-induced HP‑associated neutrophilic inflammation in the airways. However, the reduction of 85% of lung B cells in mice with a CD19-driven S1P₁ deletion does not dampen HP inflammation, suggesting that lung B cells are not necessary in large numbers to sustain local inflammation. Finally, we found that injecting antibodies targeting B cells after experimental HP was induced does not dampen neutrophilic exacerbation. Yet, injection of antibodies directed against B cells and T cells yielded a potent 76% inhibition of neutrophilic accumulation in the lungs. This inhibition occurred despite partial, sometimes mild, depletion of B cells and T cells subsets.

Conclusions

Although B cells are required for maximal inflammation in subacute experimental HP, partial reduction of B cells fails to reduce HP-associated inflammation by itself. However, co-modulation of T cells and B cells yields enhanced inhibition of HP exacerbation caused by an antigenic rechallenge.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12931-022-02200-9.

Updates in Hypersensitivity Pneumonitis: A Narrative Review

Purpose of Review

Hypersensitivity pneumonitis (HP) is an immune-mediated disease triggered by a known or unknown antigen. While reversible in the early stages of disease, progression toward irreversible pulmonary fibrosis may occur. This narrative review summarizes recent publications highlighting a methodical approach toward the diagnosis, classification, and management of fibrotic and nonfibrotic HP.

Recent Findings

Establishing the diagnosis of HP is often challenging given its variable clinical course, extensive inciting agents, and overlapping features with other interstitial lung diseases. Recently, HP has been re-classified into nonfibrotic and fibrotic subtypes based on radiographic and histopathological features. Chronic fibrotic HP is associated with significant functional impairment and increased mortality. In addition to antigen avoidance, immunosuppression is the cornerstone of management in nonfibrotic HP. Antifibrotic agents have emerged as a therapeutic option in halting the progression of chronic fibrotic HP.

Summary

The combination of clinical, radiographical, and histopathological data will assist in increasing the diagnostic certainty of HP. The new dichotomization of HP is thought to provide better prognostication for patients. This review provides clinicians with a current and evidence-based approach toward the management of patients with HP.

Impact of number and type of identified antigen on transplant-free survival in hypersensitivity pneumonitis

Background

Identification of inciting antigen can affect diagnostic confidence, quality of life, and prognosis in patients with HP. It is unknown whether the number and type of antigen affect results of diagnostic testing or prognosis, whether antigen identified by clinical history alone affects prognosis, and whether feather exposure is associated with outcomes similar to those of other antigens.

Methods

To evaluate whether the number or type of antigen identified by clinical history alone affects clinical outcomes, we evaluated a retrospective cohort of patients with a high or definite probability of HP based on recent guidelines.

Results

In our retrospective cohort, 136 patients met high or definite probability of HP and were included in the analysis. Median transplant-free survival was better in patients with antigen identified on clinical history alone than patients without identified antigen. Feather exposure was associated with improved TFS compared to patients without antigen identified; there was no difference in TFS between patients with feather exposure and either mold or live bird exposure. Mold antigen was associated with increased risk of fibrotic HP compared to avian antigen. Among patients with identified antigen, the number and type of antigen did not affect TFS.

Discussion

Our study suggests that clinical history is adequate for providing prognostic information to patients with HP and classifying the diagnostic probability of HP according to recent guidelines. Feather exposure should be considered an inciting antigen in patients with ILD.

A Scoping Analysis of Cathelicidin in Response to Organic Dust Exposure and Related Chronic Lung Illnesses

Over two billion people worldwide are exposed to organic dust, which can cause respiratory disorders. The discovery of the cathelicidin peptide provides novel insights into the lung’s response to organic dust; however, its role in the lung’s response to organic dust exposure and chronic lung diseases remains limited. We conducted a scoping review to map the current evidence on the role of cathelicidin LL-37/CRAMP in response to organic dust exposure and related chronic lung diseases: hypersensitivity pneumonitis (HP), chronic obstructive pulmonary disease (COPD) and asthma. We included a total of n = 53 peer-reviewed articles in this review, following the process of (i) a preliminary screening; (ii) a systematic MEDLINE/PubMed database search; (iii) title, abstract and full-text screening; (iv) data extraction and charting. Cathelicidin levels were shown to be altered in all clinical settings investigated; its pleiotropic function was confirmed. It was found that cathelicidin contributes to maintaining homeostasis and participates in lung injury response and repair, in addition to exerting a positive effect against microbial load and infections. In addition, LL-37 was found to sustain continuous inflammation, increase mucus formation and inhibit microorganisms and corticosteroids. In addition, studies investigated cathelicidin as a treatment modality, such as cathelicidin inhalation in experimental HP, which had positive effects. However, the primary focus of the included articles was on LL-37’s antibacterial effect, leading to the conclusion that the beneficial LL-37 activity has not been adequately examined and that further research is required.

Relevance of RNA N6-Methyladenosine Regulators for Pulmonary Fibrosis: Implications for Chronic Hypersensitivity Pneumonitis and Idiopathic Pulmonary Fibrosis

N6-methyladenosine (m6A) modification plays a pivotal role in post-transcriptionally regulating gene expression and biological functions. Nonetheless, the roles of m6A modification in the regulation of chronic hypersensitivity pneumonitis (CHP) and idiopathic pulmonary fibrosis (IPF) remain unclear. Twenty-two significant m6A regulators were selected from differential gene analysis between the control and treatment groups from the GSE150910 dataset. Five candidate m6A regulators (insulin-like growth factor binding protein 2, insulin-like growth factor binding protein 3, YTH domain-containing protein 1, zinc finger CCCH domain-containing protein 13, and methyltransferase-like 3) were screened by the application of a random forest model and nomogram model to predict risks of pulmonary fibrosis. The consensus clustering method was applied to divide the treatment samples into two groups with different m6A patterns (clusters A and B) based on the 22 m6A regulators. Our study performed principal component analysis to obtain the m6A-related score of the 288 samples to quantify the two m6A patterns. The study reveals that cluster A was linked to T helper cell (Th) 2-type cytokines, while the immune infiltration of Th1 cytokines was higher in cluster B. Our results suggest that m6A cluster A is likely related to pulmonary fibrosis, indicating m6A regulators play notable roles in the occurrence of pulmonary fibrosis. The m6A patterns could be considered as biomarkers to identify CHP and IPF, which will be helpful to develop immunotherapy strategies for pulmonary fibrosis in the future.

Do Not Miss Acute Diffuse Panbronchiolitis for Tree-in-Bud: Case Series of a Rare Lung Disease

Acute bronchiolitis is a common disease of infants affecting the small airways. Rarely, acute bronchiolitis may occur in adolescents and adults. Here, we present four unrelated adolescent patients with severe clinical presentation and unique CT imaging with extensive tree-in-bud pattern, representing a rare clinical phenotype of acute diffuse panbronchiolitis. This characteristic disease pattern caused by inhalation injury from waterpipes, smoked tobacco, and cannabinoids must be differentiated from e-cigarette or vaping product-use-associated lung injury (EVALI). Visual diagnosis of CT and an early diagnostic procedure for detection and differentiation of inhaled hazards, including sample storage for future identification of novel noxious agents, are warranted.

Advances in the management of idiopathic pulmonary fibrosis and progressive pulmonary fibrosis

Similarly to idiopathic pulmonary fibrosis (IPF), other interstitial lung diseases can develop progressive pulmonary fibrosis (PPF) characterized by declining lung function, a poor response to immunomodulatory therapies, and early mortality. The pathophysiology of disordered lung repair involves common downstream pathways that lead to pulmonary fibrosis in both IPF and PPF. The antifibrotic drugs, such as nintedanib, are indicated for the treatment of IPF and PPF, and new therapies are being evaluated in clinical trials. Clinical, radiographic, and molecular biomarkers are needed to identify patients with PPF and subgroups of patients likely to respond to specific therapies. This article reviews the evidence supporting the use of specific therapies in patients with IPF and PPF, discusses agents being considered in clinical trials, and considers potential biomarkers based on disease pathogenesis that might be used to provide a personalized approach to care.

Glucocorticoid therapy in respiratory illness: bench to bedside

Each year, hundreds of millions of individuals are affected by respiratory disease leading to approximately 4 million deaths. Most respiratory pathologies involve substantially dysregulated immune processes that either fail to resolve the underlying process or actively exacerbate the disease. Therefore, clinicians have long considered immune-modulating corticosteroids (CSs), particularly glucocorticoids (GCs), as a critical tool for management of a wide spectrum of respiratory conditions. However, the complex interplay between effectiveness, risks and side effects can lead to different results, depending on the disease in consideration. In this comprehensive review, we present a summary of the bench and the bedside evidence regarding GC treatment in a spectrum of respiratory illnesses. We first describe here the experimental evidence of GC effects in the distal airways and/or parenchyma, both in vitro and in disease-specific animal studies, then we evaluate the recent clinical evidence regarding GC treatment in over 20 respiratory pathologies. Overall, CS remain a critical tool in the management of respiratory illness, but their benefits are dependent on the underlying pathology and should be weighed against patient-specific risks.

Title-Inflammatory Signaling Pathways in Allergic and Infection-Associated Lung Diseases

Lung inflammation can be caused by pathogen infection alone or by allergic disease, leading to pneumonitis. Most of the allergens (antigens) that cause allergic lung diseases, including asthma and hypersensitivity pneumonitis (HP), are derived from microorganisms, such as bacteria, viruses, and fungi, but some inorganic materials, such as mercury, can also cause pneumonitis. Certain allergens, including food and pollen, can also cause acute allergic reactions and lead to lung inflammation in individuals predisposed to such reactions. Pattern recognition-associated and damage-associated signaling by these allergens can be critical in determining the type of hypersensitization and allergic disease, as well as the potential for fibrosis and irreversible lung damage. This review discusses the signs, symptoms, and etiology of allergic asthma, and HP. Furthermore, we review the immune response and signaling pathways involved in pneumonitis due to both microbial infection and allergic processes. We also discuss current and potential therapeutic interventions for infection-associated and allergic lung inflammation.

Diagnosis, course and management of hypersensitivity pneumonitis

Hypersensitivity pneumonitis (HP) is a complex and heterogeneous interstitial lung disease (ILD) that occurs when susceptible individuals develop an exaggerated immune response to an inhaled antigen. In this review, we discuss the latest guidelines for the diagnostic evaluation of patients with suspected HP, the importance of identifying patients with fibrotic and progressive disease, and the evidence supporting the drugs commonly used in the treatment of HP. Differential diagnosis of HP can be challenging and requires a thorough exposure history, multidisciplinary discussion of clinical and radiologic data, and, in some cases, assessment of bronchoalveolar lavage lymphocytosis and histopathologic findings. Patients with HP may be categorised as having non-fibrotic or fibrotic HP. The presence of fibrosis is associated with worse outcomes. A proportion of patients with fibrotic HP develop a progressive phenotype, characterised by worsening fibrosis, decline in lung function and early mortality. There are no established guidelines for the treatment of HP. Antigen avoidance should be implemented wherever possible. Immunosuppressants are commonly used in patients with HP but have not been shown to slow the worsening of fibrotic disease. Nintedanib, a tyrosine kinase inhibitor, has been approved by the US Food and Drug Administration for slowing the progression of chronic fibrosing ILDs with a progressive phenotype, including progressive fibrotic HP. Non-pharmacological interventions, such as oxygen therapy, pulmonary rehabilitation and supportive care, may be important components of the overall care of patients with progressive HP.

Pediatric hypersensitivity pneumonitis: literature update and proposal of a diagnostic algorithm

Hypersensitivity pneumonitis (HP) is a rare disease in childhood with the prevalence of 4 cases per 1 million children and an incidence of 2 cases per year. The average age of diagnosis at pediatric age is approximately 10 years. The pathogenesis of HP is characterized by an immunological reaction caused by recurrent exposure to triggering environmental agents (mostly bird antigens in children). The clinical picture of HP is complex and variable in children, often presenting in subacute forms with cough and exertion dyspnea. A diagnosis of HP should be considered in patients with an identified exposure to a triggering antigen, respiratory symptoms, and radiologic signs of interstitial lung disease. Blood tests and pulmonary function tests (PFT) support the diagnosis. Bronchoscopy (with bronchoalveolar lavage and tissue biopsy) may be needed in unclear cases. Antigen provocation test is rarely required. Of note, the persistence of symptoms despite various treatment regimens may support HP diagnosis. The avoidance of single/multiple triggers is crucial for effective treatment. No evidence- based guidelines for treatment are available; in particular, the role of systemic glucocorticoids in children is unclear. With adequate antigen avoidance, the prognosis in children with HP is generally favorable.

The Impact of Ambient Environmental and Occupational Pollution on Respiratory Diseases

Ambient pollutants and occupational pollutants may cause and exacerbate various lung and respiratory diseases. This review describes lung and respiratory diseases in relation to ambient pollutants, particularly particulate matter (PM_2.5), and occupational air pollutants, excluding communicable diseases and indoor pollutants, including tobacco smoke exposure. PM_2.5 produced by combustion is an important ambient pollutant. PM_2.5 can cause asthma attacks and exacerbations of chronic obstructive pulmonary disease in the short term. Further, it not only carries a risk of lung cancer and death, but also hinders the development of lung function in children in the long term. It has recently been suggested that air pollution, such as PM_2.5, is a risk factor for severe coronavirus disease (COVID-19). Asbestos, which causes asbestosis, lung cancer, and malignant mesothelioma, and crystalline silica, which cause silicosis, are well-known traditional occupational pollutants leading to pneumoconiosis. While work-related asthma (WRA) is the most common occupational lung disease in recent years, many different agents cause WRA, including natural and synthetic chemicals and irritant gases. Primary preventive interventions that increase awareness of pollutants and reduce the development and exacerbation of diseases caused by air pollutants are paramount to addressing ambient and occupational pollution.

Hypersensitivity pneumonitis: Current concepts in pathogenesis, diagnosis, and treatment

Hypersensitivity pneumonitis is an immune-mediated interstitial lung disease caused by an aberrant response to an inhaled exposure, which results in mostly T cell-mediated inflammation, granuloma formation, and fibrosis in some cases. HP is diagnosed by exposure identification, HRCT findings of ground-glass opacities, centrilobular nodules, and mosaic attenuation, with traction bronchiectasis and honeycombing in fibrotic cases. Additional testing including serum IgG testing for the presence of antigen exposure, bronchoalveolar lavage lymphocytosis, and lung biopsy demonstrating granulomas, inflammation, and fibrosis, increases the diagnostic confidence. Treatment for HP includes avoidance of the implicated exposure, immunosuppression, and anti-fibrotic therapy in select cases. This narrative review presents the recent literature in the understanding of the immunopathological mechanisms, diagnosis, and treatment of HP.

Timber-colonizing gram-negative bacteria as potential causative agents of respiratory diseases in woodworkers

Occurrence

Gram-negative bacteria occur commonly in the inner tissues of stored coniferous and deciduous timber, showing a marked variation in numbers. The greatest maximal numbers are found in the sapwood of coniferous timber. The common constituents of the Gram-negative biota are potentially pathogenic species of Enterobacteriaceae family of the genera Rahnella, Pantoea, Enterobacter, and Klebsiella. The air of wood-processing facilities is polluted with the wood-borne Gram-negative bacteria and produced by them endotoxin, as demonstrated worldwide by numerous studies.

Effects

There are three potential pathways of the pathogenic impact of wood-borne Gram-negative bacteria on exposed woodworkers: allergic, immunotoxic, and infectious. Allergic impact has been underestimated for a long time with relation to Gram-negative bacteria. Hopefully, the recent demonstration of the first documented case of hypersensitivity pneumonitis (HP) in woodworkers caused by Pantoea agglomerans which developed in extremely large quantities in birch sapwood, would speed up finding of new wood-related cases of HP caused by Gram-negative bacteria. The second pathway is associated with endotoxin, exerting strong immunotoxic (excessively immunostimulative) action. It has been demonstrated that endotoxin is released into wood dust in the form of nano-sized microvesicles, by peeling off the outer membrane of bacteria. Endotoxin microvesicles are easily inhaled by humans together with dust because of small dimensions and aerodynamic shape. Afterwards, they cause a nonspecific activation of lung macrophages, which release numerous inflammatory mediators causing an inflammatory lung reaction, chest tightness, fever, gas exchange disorders, and bronchospasm, without radiographic changes. The resulting disease is known as “Organic Dust Toxic Syndrome” or “toxic pneumonitis.” The potential third pathway of pathogenic impact is infection. The suspected species is Klebsiella pneumoniae that may occur commonly in wood dust; however, until now this pathway has not been confirmed.

Conclusion

Summarizing, Gram-negative bacteria-inhabiting timber should be considered, besides filamentous fungi and actinobacteria, as important risk factors of occupational disease in woodworkers that could be either HP with allergenic background or toxic pneumonitis elicited by endotoxin.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00420-021-01829-1.

Hypersensitivity Pneumonitis From Fire-Retardant Spray in a Patient With Multiple Lung Pathologies and Elevated Immunoglobulin E

Background: Hypersensitivity pneumonitis, also known as extrinsic allergic alveolitis, is a pulmonary disease with large knowledge gaps, including etiology, pathogenesis, diagnosis, and treatment.

Case Report: A 58-year-old male with a pertinent history of recurrent Mycobacterium malmoense presented to a tertiary emergency department after 1 week of difficulty breathing. He also reported a productive cough and fevers. The patient was an active smoker and was recently exposed to chemical fire-retardant spray. Chest x-ray showed extensive bilateral pulmonary infiltrates. The tertiary center initiated cefpodoxime 200 mg twice daily for 5 days and home azithromycin for possible pneumonia. However, the patient returned the next day with worsening symptoms. After the patient transferred to our institution, physical examination revealed a hypoxic patient with bibasilar crackles and wheezes. Laboratory tests revealed elevated white blood cell count, sedimentation rate, and immunoglobulin E. Chest computed tomography demonstrated growth of a previously noted right upper lobe intracavitary lesion and new onset diffuse interstitial pulmonary ground-glass airspace opacities. Hypersensitivity pneumonitis panel demonstrated positive antibodies to Aspergillus fumigatus antibody precipitin 1 and Micropolyspora faeni. The patient was given oral prednisone and advice on proper respiratory precautions in the workplace.

Conclusion: This case illustrates that hypersensitivity pneumonitis can develop via chemical fire-retardant spray. Additionally, patients with a smoking history and elevated immunoglobulin E should be evaluated for severe forms of the disease.

MIXTURE of human expertise and deep learning-developing an explainable model for predicting pathological diagnosis and survival in patients with interstitial lung disease

Interstitial pneumonia is a heterogeneous disease with a progressive course and poor prognosis, at times even worse than those in the main cancer types. Histopathological examination is crucial for its diagnosis and estimation of prognosis. However, the evaluation strongly depends on the experience of pathologists, and the reproducibility of diagnosis is low. Herein, we propose MIXTURE (huMan-In-the-loop eXplainable artificial intelligence Through the Use of REcurrent training), an original method to develop deep learning models for extracting pathologically significant findings based on an expert pathologist's perspective with a small annotation effort. The procedure of MIXTURE consists of three steps as follows. First, we created feature extractors for tiles from whole slide images using self-supervised learning. The similar looking tiles were clustered based on the output features and then pathologists integrated the pathologically synonymous clusters. Using the integrated clusters as labeled data, deep learning models to classify the tiles into pathological findings were created by transfer-learning the feature extractors. We developed three models for different magnifications. Using these extracted findings, our model was able to predict the diagnosis of usual interstitial pneumonia, a finding suggestive of progressive disease, with high accuracy (AUC 0.90 in validation set and AUC 0.86 in test set). This high accuracy could not be achieved without the integration of findings by pathologists. The patients predicted as UIP had poorer prognosis (5-year overall survival [OS]: 55.4%) than those predicted as non-UIP (OS: 95.2%). The Cox proportional hazards model for each microscopic finding and prognosis pointed out dense fibrosis, fibroblastic foci, elastosis, and lymphocyte aggregation as independent risk factors. We suggest that MIXTURE may serve as a model approach to different diseases evaluated by medical imaging, including pathology and radiology, and be the prototype for explainable artificial intelligence that can collaborate with humans.

Longstanding hypersensitivity pneumonitis and its response to roflumilast: A review of its likely immunological effects

We describe the case of a 42yr old man with evidence of hypersensitivity pneumonitis referred with cough and breathlessness for several years which had further deteriorated in the prior 12 months. He had known atopic asthma without evidence of activation.

A chest CT scan showed widespread ground glass change in his lung fields. He had feather bedding at home and in his youth cleaned aviaries. His forced vital capacity and lung volumes were reduced along with oxygen saturations at rest (92% on air), overnight (83% on air) and upon walking (78%). Steroids were commenced for a total of 6 months with little consistent improvement in symptoms or objective measures and with no change in his CT scan appearance. As a result, a trial of roflumilast (a phosphodiesterase-4 inhibitor) was commenced due to its range of immunological effects and in order to avoid long-term immune suppression with mycophenolate motefil in a young patient.

On roflumilast treatment his cough and breathlessness improved at 4 weeks and the chest crackles cleared. An interval Chest CT scan showed resolution of the ground glass change with improved CT scores that are maintained 2 yrs. All oxygen measures improved and nocturnal oxygen was discontinued. His Lung function has remained largely stable on roflumilast and symptoms of cough and breathlessness have resolved. This case report reviews the immunology of hypersensitivity pneumonitis and the likely actions of Roflumilast relevant to this condition. It is the first published case report documenting its use in hypersensitivity pneumonitis.

OUP accepted manuscript

Although a high prevalence of COVID-19-associated pulmonary aspergillosis has been reported, it is still difficult to distinguish between colonization with Aspergillus fumigatus and infection. Concomitantly, similarities between severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and hypersensitivity pneumonitis were suggested. The objective of this study was to investigate retrospectively if precipitin assays targeting A. fumigatus could have been useful in the management of SARS-CoV-2 patients hospitalized in an Intensive Care Unit (ICU) in 2020. SARS-CoV-2 ICU patients were screened for Aspergillus co-infection using biomarkers (galactomannan antigen, qPCR) and culture of respiratory samples (tracheal aspirates and bronchoalveolar lavage). For all these patients, clinical data, ICU characteristics and microbial results were collected. Electrosyneresis assays were performed using commercial A. fumigatus somatic and metabolic antigens. ELISA were performed using in-house A. fumigatus purified antigen and recombinant antigens.

Our study population consisted of 65 predominantly male patients, with a median ICU stay of 22 days, and a global survival rate of 62%. Thirty-five patients had at least one positive marker for Aspergillus species detection. The number of arcs obtained by electrosyneresis using the somatic A. fumigatus antigen was significantly higher for these 35 SARS-CoV-2 ICU patients (P 0.01, Welch's t-test). Our study showed that SARS-CoV-2 ICU patients with a positive marker for Aspergillus species detection more often presented precipitins towards A. fumigatus. Serology assays could be an additional tool to assess the clinical relevance of the Aspergillus species in respiratory samples of SARS-CoV-2 ICU patients.