Association of gut microbiome with COPD in Japanese male residents: the SESSA study.

Background: Altered gut microbiota may contribute to COPD development or progression. Herein, we investigated the association of gut microorganisms with COPD, taking into account the impact of smoking status. Methods: This cross-sectional observational study was a part of the Shiga Epidemiological Study of Subclinical Atherosclerosis, a population-based cohort study of Japanese men aged 46-76 years, conducted from 2010 to 2016. The gut microbiome, determined using 16S rRNA gene sequencing, was compared among 99 never-smokers, 306 non-COPD ever-smokers and 76 patients with COPD while adjusting for age, body mass index, ethanol consumption and treatment for type 2 diabetes mellitus. Results: The abundance of phylum Firmicutes was comparable between patients with COPD and non-COPD ever-smokers but tended to be higher in never-smokers. Similarly, the α- and ß-diversity analysis showed similarity between patients with COPD and non-COPD ever-smokers, which tended to differ from never-smokers. Discriminant analysis identified the genus [Prevotella] to be more prevalent in patients with COPD than in never-smokers or non-COPD ever-smokers. Post hoc analysis confirmed similarity of gut microbiome between COPD Global Initiative for Chronic Obstructive Lung Disease (GOLD) I and non-COPD ever-smokers, which was different from GOLD II. Conclusion: Smoking may alter the overall gut microbial composition, but gut microbial composition itself may not play a role in the development of COPD. Rather, specific gut bacteria, such as [Prevotella], could be a risk factor for the development of COPD; this may be a potential therapeutic target.

Autobullectomy with COVID-19 in a patient with chronic obstructive pulmonary disease.

A 72-year-old man with chronic obstructive pulmonary disease (COPD) was admitted for coronavirus disease 2019 (COVID-19). He was discharged on day 30; however, he was readmitted 6 days later due to a left lung organizing pneumonia secondary to COVID-19. After methylprednisolone treatment, the patient was discharged on day 15. One year later, computed tomography showed shrinkage of emphysematous lesions, and both total lung capacity measured using computed tomography and fraction of low attenuation volume decreased in the left lung compared to that before COVID-19. Here, we report a rare case of autobullectomy with COVID-19 in a patient with COPD.

Predictors of longitudinal changes in body weight, muscle and fat in patients with and ever-smokers at risk of COPD.

BACKGROUND AND OBJECTIVE: Weight and muscle loss are predictors of poor outcomes in chronic obstructive pulmonary disease. However, to our knowledge, no study has investigated the predictors of longitudinal weight loss or its composition from functional and morphological perspectives. METHODS: This longitudinal observational study with a median follow-up period of 5 years (range: 3.0-5.8 years) included patients with COPD and ever-smokers at risk of COPD. Using chest computed tomography (CT) images, airway and emphysematous lesions were assessed as the square root of the wall area of a hypothetical airway with an internal perimeter of 10 mm (√Aaw at Pi10) and the percentage of low attenuation volume (LAV%). Muscle mass was estimated using cross-sectional areas (CSAs) of the pectoralis and erector spinae muscles, and fat mass was estimated using the subcutaneous fat thickness at the level of the 8th rib measured using chest CT images. Statistical analyses were performed using the linear mixed-effects models. RESULTS: In total, 114 patients were enrolled. Their body mass index remained stable during the study period while body weight and muscle CSA decreased over time and the subcutaneous fat thickness increased. Reduced forced expiratory volume in 1 s and peak expiratory flow (PEF) at baseline predicted the future decline in muscle CSA. CONCLUSION: Severe airflow limitation predicted future muscle wasting in patients with COPD and ever-smokers at risk of COPD. Airflow limitation with a PEF slightly below 90% of the predicted value may require intervention to prevent future muscle loss.

Inspiratory and Expiratory Computed Tomography Imaging Clusters Reflect Functional Characteristics in Chronic Obstructive Pulmonary Disease.

Purpose: Disease probability measure (DPM) is a useful voxel-wise imaging assessment of gas-trapping and emphysematous lesions in patients with chronic obstructive pulmonary disease (COPD). To elucidate the progression of COPD, we performed a cluster analysis using the following DPM parameters: normal (DPMNormal), gas-trapping (DPMGasTrap), and emphysematous lesions (DPMEmph). Our findings revealed the characteristics of each cluster and the 3-year disease progression using imaging parameters. Patients and Methods: Inspiratory and expiratory chest computed tomography (CT) images of 131 patients with COPD were examined, of which 84 were followed up for 3 years. The percentage of low attenuation volume (LAV%) and the square root of the wall area of a hypothetical airway with an internal perimeter of 10 mm (√Aaw at Pi10) were quantitatively measured using inspiratory chest CT. A hierarchical cluster analysis was performed using the DPM parameters at baseline. Five clusters were named according to the dominant DPM parameters: normal (NL), normal-GasTrap (NL-GT), GasTrap (GT), GasTrap-Emphysema (GT-EM), and Emphysema (EM). Results: Women were predominantly diagnosed with GT. Forced expiratory volume in 1 s gradually decreased in the following order: NL, NL-GT, GT, GT-EM, and EM. DPMEmph correlated well with LAV%. Four clusters other than NL showed significantly higher values of √Aaw at Pi10 than NL; however, no significant differences were observed among them. In all clusters, DPMEmph increased after 3 years. DPMNormal only increased in the GT cluster. Conclusion: Clusters using DPM parameters may reflect the characteristics of COPD and help understand the pathophysiology of the disease.

Risk factors for pneumonitis in advanced extrapulmonary cancer patients treated with immune checkpoint inhibitors.

BACKGROUND: Immune-mediated pneumonitis has a high mortality rate; however, information regarding the related risk factors remains limited. This study aimed to analyze risk factors for pneumonitis, including smoking and lung metastasis (LM), in patients with extrapulmonary primary tumors. METHODS: Data of 110 patients treated with immune checkpoint inhibitors (ICIs) (nivolumab/pembrolizumab) for treating extrapulmonary primary tumors at the Shiga University of Medical Science Hospital between January 2015 and December 2019 were retrospectively collected. The association between the onset of pneumonitis and treatment-related factors was analyzed by logistic regression. The severity of pneumonitis was graded according to the Common Terminology Criteria for Adverse Events version 5.0. Risk factors, such as the absence or presence of interstitial lung disease (ILD) and LM, or other clinical factors, including smoking status before ICI administration, were analyzed. RESULTS: Multivariate analyses indicated that the amount of smoking was significantly associated with an increase in the development of all-grade pneumonitis types (odds ratio (OR) = 20.33, 95% confidence interval (CI) = 20.03-20.66; p = 0.029). LM and ILD were significantly related to an increase in the development of symptomatic pneumonitis (≥ Grade 2) (OR = 10.08, 95% CI = 1.69-199.81; p = 0.076, and OR = 6.76, 95% CI = 1.13-40.63; p = 0.037, respectively). CONCLUSIONS: Pre-screening for ILD and LM and recognizing patients' smoking history is important for determining the risk of ICI-induced pneumonitis and allowing safe ICI administration.

The molecular and cellular mechanisms associated with the destruction of terminal bronchioles in COPD.

RATIONALE: Peripheral airway obstruction is a key feature of chronic obstructive pulmonary disease (COPD), but the mechanisms of airway loss are unknown. This study aims to identify the molecular and cellular mechanisms associated with peripheral airway obstruction in COPD. METHODS: Ten explanted lung specimens donated by patients with very severe COPD treated by lung transplantation and five unused donor control lungs were sampled using systematic uniform random sampling (SURS), resulting in 240 samples. These samples were further examined by micro-computed tomography (CT), quantitative histology and gene expression profiling. RESULTS: Micro-CT analysis showed that the loss of terminal bronchioles in COPD occurs in regions of microscopic emphysematous destruction with an average airspace size of ≥500 and <1000 µm, which we have termed a "hot spot". Based on microarray gene expression profiling, the hot spot was associated with an 11-gene signature, with upregulation of pro-inflammatory genes and downregulation of inhibitory immune checkpoint genes, indicating immune response activation. Results from both quantitative histology and the bioinformatics computational tool CIBERSORT, which predicts the percentage of immune cells in tissues from transcriptomic data, showed that the hot spot regions were associated with increased infiltration of CD4 and CD8 T-cell and B-cell lymphocytes. INTERPRETATION: The reduction in terminal bronchioles observed in lungs from patients with COPD occurs in a hot spot of microscopic emphysema, where there is upregulation of IFNG signalling, co-stimulatory immune checkpoint genes and genes related to the inflammasome pathway, and increased infiltration of immune cells. These could be potential targets for therapeutic interventions in COPD.

The transition from normal lung anatomy to minimal and established fibrosis in idiopathic pulmonary fibrosis (IPF).

BACKGROUND: The transition from normal lung anatomy to minimal and established fibrosis is an important feature of the pathology of idiopathic pulmonary fibrosis (IPF). The purpose of this report is to examine the molecular and cellular mechanisms associated with this transition. METHODS: Pre-operative thoracic Multidetector Computed Tomography (MDCT) scans of patients with severe IPF (n = 9) were used to identify regions of minimal(n = 27) and established fibrosis(n = 27). MDCT, Micro-CT, quantitative histology, and next-generation sequencing were used to compare 24 samples from donor controls (n = 4) to minimal and established fibrosis samples. FINDINGS: The present results extended earlier reports about the transition from normal lung anatomy to minimal and established fibrosis by showing that there are activations of TGFBI, T cell co-stimulatory genes, and the down-regulation of inhibitory immune-checkpoint genes compared to controls. The expression patterns of these genes indicated activation of a field immune response, which is further supported by the increased infiltration of inflammatory immune cells dominated by lymphocytes that are capable of forming lymphoid follicles. Moreover, fibrosis pathways, mucin secretion, surfactant, TLRs, and cytokine storm-related genes also participate in the transitions from normal lung anatomy to minimal and established fibrosis. INTERPRETATION: The transition from normal lung anatomy to minimal and established fibrosis is associated with genes that are involved in the tissue repair processes, the activation of immune responses as well as the increased infiltration of CD4, CD8, B cell lymphocytes, and macrophages. These molecular and cellular events correlate with the development of structural abnormality of IPF and probably contribute to its pathogenesis.

Prediction of radiation pneumonitis using dose-volume histogram parameters with high attenuation in two types of cancer: A retrospective study.

The constraint values of dose-volume histogram (DVH) parameters for radiation pneumonitis (RP) prediction have not been uniform in previous studies. We compared the differences between conventional DVH parameters and DVH parameters with high attenuation volume (HAV) in CT imaging in both esophageal cancer and lung cancer patients to determine the most suitable DVH parameters in predicting RP onset. Seventy-seven and 72 patients who underwent radiation therapy for lung cancer and esophageal cancer, respectively, were retrospectively assessed. RP was valued according to the Common Terminology Criteria for Adverse Events. We quantified HAV with quantitative computed tomography analysis. We compared conventional DVH parameters and DVH parameters with HAV in both groups of patients. Then, the thresholds of DVH parameters that predicted symptomatic RP and the differences in threshold of DVH parameters between lung cancer and esophageal cancer patient groups were compared. The predictive performance of DVH parameters for symptomatic RP was compared using the area under the receiver operating characteristic curve. Mean lung dose, HAV30% (the proportion of the lung with HAV receiving ≥30 Gy), and HAV20% were the top three parameters in lung cancer, while HAV10%, HAV5%, and V10 (the percentage of lung volume receiving 10 Gy or more) were the top three in esophageal cancer. By comparing the differences in the threshold for parameters predicting RP between the two cancers, we saw that HAV30% retained the same value in both cancers. DVH parameters with HAV showed narrow differences in the threshold between the two cancer patient groups compared to conventional DVH parameters. DVH parameters with HAV may have higher commonality than conventional DVH parameters in both patient groups tested.

Comprehensive stereological assessment of the human lung using multiresolution computed tomography.

The application of stereology to lung casts and two-dimensional microscopy images is the gold standard for quantification of the human lung anatomy. However, these techniques are labor intensive, involving fixation, embedding, and histological sectioning of samples and thus have prevented comprehensive studies. Our objective was to demonstrate the application of stereology to volumetric multiresolution computed tomography (CT) to efficiently and extensively quantify the human lung anatomy. Nontransplantable donor lungs from individuals with no evidence of respiratory disease (n = 13) were air inflated, frozen at 10 cmH2O, and scanned using CT. Systematic uniform random samples were taken, scanned using micro-CT, and assessed using stereology. The application of stereology to volumetric CT imaging enabled comprehensive quantification of total lung volume, volume fractions of alveolar, alveolar duct, and tissue, mean linear intercept, alveolar surface area, alveolar surface area density, septal wall thickness, alveolar number, number-weighted mean alveolar volume, and the number and morphometry of terminal and transitional bronchioles. With the use of this data set, we found that women and men have the same number of terminal bronchioles (last generation of conducting airways), but men have longer terminal bronchioles, a smaller wall area percentage, and larger lungs due to a greater number of alveoli per acinus. The application of stereology to multiresolution CT imaging enables comprehensive analysis of the human lung parenchyma that identifies differences between men and women. The reported data set of normal donor lungs aged 25-77 yr provides reference data for future studies of chronic lung disease to determine exact changes in tissue pathology.NEW & NOTEWORTHY Stereology has been the gold standard to quantify the three-dimensional lung anatomy using two-dimensional microscopy images. However, such techniques are labor intensive. This study provides a method that applies stereology to volumetric computed tomography images of frozen whole human lungs and systematic uniform random samples. The method yielded a comprehensive data set on the small airways and parenchymal lung structures, highlighting morphometric sex differences and providing a reference data set for future pathological studies.

An index of the fractal characteristic of an airway tree is associated with airflow limitations and future body mass index reduction in COPD patients.

Disorders of the fractality of an airway tree and a vessel tree have been studied in pulmonary diseases. Here we successfully applied Mishima's D to the bronchial minimal inner cross-sectional area (iCSA) measured in multidetector computed tomography (MDCT) images of chronic obstructive pulmonary disease (COPD) and non-COPD smokers (n = 162), by defining D in the following formula: logN(≥X) = -D × logX + c, where X is a certain iCSA value, N(≥X) is the number of airway branches having iCSA greater than or equal to X, and c is a constant. Mathematically, this D of iCSA was associated with the expected reduction ratio of iCSA at bifurcations, which can be estimated by 2-1/D. This D of iCSA also correlated weakly with the box-counting fractal dimension and Weibel's reduction ratio over airway generations, which indicated that the airway tree was not a perfect fractal object and that the branch bifurcation was asymmetric. The D of iCSA showed positive correlations with lung function measurements of airflow limitation in study participants. In addition, D of iCSA representing the periphery showed an association with future body mass index reduction, most likely as an indicator of energy efficacy for breathing as predicted by Hess-Murray's law. D of iCSA may be helpful to understanding the pathogenesis of obstructive lung diseases.NEW & NOTEWORTHY An airway tree is a fractal object. We showed that the distribution of minimal inner cross-sectional area (iCSA) of airway branches can be expressed by a fractal index, D, of minimal iCSA. This D was correlated with airflow limitation and future body mass index reduction in chronic obstructive pulmonary disease patients, as predicted by Hess-Murray's law.

Correction: Quantitative CT analysis of honeycombing area predicts mortality in idiopathic pulmonary fibrosis with definite usual interstitial pneumonia pattern: A retrospective cohort study.

[This corrects the article DOI: 10.1371/journal.pone.0214278.].

Quantitative CT analysis of honeycombing area predicts mortality in idiopathic pulmonary fibrosis with definite usual interstitial pneumonia pattern: A retrospective cohort study.

BACKGROUND: Honeycombing on high-resolution computed tomography (HRCT) images is a key finding in idiopathic pulmonary fibrosis (IPF). In IPF, honeycombing area determined by quantitative CT analysis is correlated with pulmonary function test findings. We hypothesized that quantitative CT-derived honeycombing area (HA) might predict mortality in patients with IPF. MATERIALS AND METHODS: Chest HRCT images of 52 IPF patients with definite usual interstitial pneumonia (UIP) pattern were retrospectively evaluated. Mortality data up to July 31, 2016, were recorded. Using a computer-aided system, HA and percentage of HA (%HA) were measured quantitatively. Predictors of 3-year mortality were evaluated using logistic regression models. RESULTS: The median %HA, %predicted forced vital capacity (FVC) and composite physiologic index (CPI) were 3.8%, 83.6%, and 33.6, respectively. According to GAP (gender, age, and physiology) stage, 20, 14, and 5 patients were classified under stages I-II-III, respectively. Percentage of HA was significantly correlated with %FVC, CPI, and GAP stage (all, p < 0.001). In univariate analysis, %HA, %FVC, and CPI were statistically significant predictors of mortality. In multivariate analysis using the stepwise regression method, only %HA (odds ratio [OR], 1.27; p = 0.011) was a significant independent predictors of mortality. Patients with %HA ≥ 4.8% had significantly lower survival rates than those with lesser %HA (median survival time, 1.3 vs 5.0 years; log-rank test; p < 0.001). CONCLUSION: Quantitative CT-derived HA might be an important and independent predictor of mortality in IPF patients with definite UIP pattern.

Novel Respiratory Impedance-Based Phenotypes Reflect Different Pathophysiologies in Chronic Obstructive Pulmonary Disease Patients.

Purpose: The forced oscillation technique (FOT) is a non-invasive method to measure respiratory impedance, the respiratory resistance (Rrs) and reactance (Xrs). The disease probability measure (DPM) is a useful computed tomography (CT) imaging variable for the assessment of gas trapping and emphysema in patients with chronic obstructive pulmonary disease (COPD) using pairs of inspiratory and expiratory CT images. We aimed to develop FOT-based phenotypes and determine whether the phenotypes and their imaging characteristics could facilitate the understanding of COPD pathophysiology. Patients and methods: FOT and spirometry were examined in 164 COPD patients and 22 non-COPD smokers. COPD patients were divided into four FOT-based phenotypes (NL, normal group; RD, resistance-dominant group; XD, reactance-dominant group; and MIX, mixed group) based on the 3rd quartile values of R5 (Rrs at 5Hz) and X5 (Xrs at 5Hz) in the non-COPD group. The emphysematous lesions and the airway lesions were quantitatively assessed in CT images by low attenuation volume and the square root of the wall area of a hypothetical airway with an internal perimeter of 10 mm (√Aaw at Pi10), respectively. DPM imaging analysis was also performed in 131 COPD patients. We investigated the differences in COPD parameters between the FOT-based phenotypes. Results: √Aaw at Pi10 were significantly higher in the RD, XD, and MIX groups than in the NL group. The XD group showed lower pulmonary function and higher dyspnea scores than the RD group. No significant changes in DPM values were observed between the RD and the NL groups. The gas-trapping area was significantly higher in the XD group than in the NL group. The MIX group showed the highest dyspnea score, most emphysematous lesions, and the lowest forced expiratory volume in 1 s % predicted value. Conclusion: The FOT-based phenotyping may be useful to assess pathophysiological changes of COPD with CT assessments.

Analysis of airway pathology in COPD using a combination of computed tomography, micro-computed tomography and histology.

The small conducting airways are the major site of obstruction in chronic obstructive pulmonary disease (COPD). This study examined small airway pathology using a novel combination of multidetector row computed tomography (MDCT), micro-computed tomography (microCT) and histology.Airway branches visible on specimen MDCT were counted and the dimensions of the third- to fifth-generation airways were computed, while the terminal bronchioles (designated TB), preterminal bronchioles (TB-1) and pre-preterminal bronchioles (TB-2) were examined with microCT and histology in eight explanted lungs with end-stage COPD and seven unused donor lungs that served as controls.On MDCT, COPD lungs showed a decrease in the number of 2-2.5 mm diameter airways and the lumen area of fifth-generation airways, while on microCT there was a reduction in the number of terminal bronchioles as well as a decrease in the luminal areas, wall volumes and alveolar attachments to the walls of TB, TB-1 and TB-2 bronchioles. The combination of microCT and histology showed increased B-cell infiltration into the walls of TB-1 and TB-2 bronchioles, and this change was correlated with a reduced number of alveolar attachments in COPD.Small airways disease extends from 2 mm diameter airways to the terminal bronchioles in COPD. Destruction of alveolar attachments may be driven by a B-cell-mediated immune response in the preterminal bronchioles.

Exclusion of emphysematous lung from dose-volume estimates of risk improves prediction of radiation pneumonitis.

BACKGROUND: The risk factors for radiation pneumonitis (RP) in patients with chronic obstructive pulmonary disease (COPD) are unclear. Mean lung dose (MLD) and percentage of irradiated lung volume are common predictors of RP, but the most accurate dosimetric parameter has not been established. We hypothesized that the total lung volume irradiated without emphysema would influence the onset of RP. METHODS: We retrospectively evaluated 100 patients who received radiotherapy for lung cancer. RP was graded according to the Common Terminology Criteria for Adverse Events (version 4.03). We quantified low attenuation volume (LAV) using quantitative computed tomography analysis. The association between RP and traditional dosimetric parameters including MLD, volume of the lung receiving a dose of ≥2 Gy, ≥ 5 Gy, ≥ 10 Gy, ≥ 20 Gy, and ≥30 Gy, and counterpart measurements of the lung without LAV, were analyzed by logistic regression. We compared each dosimetric parameter for RP using multiple predictive performance measures including area under the receiver operating characteristic curve (AUC) and integrated discrimination improvement (IDI). RESULTS: Of 100 patients, RP of Grades 1, 2, 3, 4, and 5 was diagnosed in 24, 12, 13, 1, and 1 patients, respectively. Compared with traditional dosimetric parameters, counterpart measurements without LAV improved risk prediction of symptomatic RP. The ratio of the lung without LAV receiving ≥30 Gy to the total lung volume without LAV most accurately predicted symptomatic RP (AUC, 0.894; IDI, 0.064). CONCLUSION: Irradiated lung volume without LAV predicted RP more accurately than traditional dosimetric parameters.

Micro-Computed Tomography Comparison of Preterminal Bronchioles in Centrilobular and Panlobular Emphysema.

RATIONALE: Very little is known about airways that are too small to be visible on thoracic multidetector computed tomography but larger than the terminal bronchioles. OBJECTIVES: To examine the structure of preterminal bronchioles located one generation proximal to terminal bronchioles in centrilobular and panlobular emphysema. METHODS: Preterminal bronchioles were identified by backtracking from the terminal bronchioles, and their centerlines were established along the entire length of their lumens. Multiple cross-sectional images perpendicular to the centerline were reconstructed to evaluate the bronchiolar wall and lumen, and the alveolar attachments to the outer airway walls in relation to emphysematous destruction in 28 lung samples from six patients with centrilobular emphysema, 20 lung samples from seven patients with panlobular emphysema associated with alpha-1 antitrypsin deficiency, and 47 samples from seven control (donor) lungs. MEASUREMENTS AND MAIN RESULTS: The preterminal bronchiolar length, wall volume, total volume (wall + lumen), lumen circularity, and number of alveolar attachments were reduced in both centrilobular and panlobular emphysema compared with control lungs. In contrast, thickening of the wall and narrowing of the lumen were more severe and heterogeneous in centrilobular than in panlobular emphysema. The bronchiolar lumen was narrower in the middle than at both ends, and the decreased number of alveolar attachments was associated with increased wall thickness in centrilobular emphysema. CONCLUSIONS: These results provide new information about small airways pathology in centrilobular and panlobular emphysema and show that these changes affect airways that are not visible with thoracic multidetector computed tomography scans but located proximal to the terminal bronchioles in chronic obstructive pulmonary disease.

Nondestructive cryomicro-CT imaging enables structural and molecular analysis of human lung tissue.

Micro-computed tomography (CT) enables three-dimensional (3D) imaging of complex soft tissue structures, but current protocols used to achieve this goal preclude cellular and molecular phenotyping of the tissue. Here we describe a radiolucent cryostage that permits micro-CT imaging of unfixed frozen human lung samples at an isotropic voxel size of (11 µm)3 under conditions where the sample is maintained frozen at -30°C during imaging. The cryostage was tested for thermal stability to maintain samples frozen up to 8 h. This report describes the methods used to choose the materials required for cryostage construction and demonstrates that whole genome mRNA integrity and expression are not compromised by exposure to micro-CT radiation and that the tissue can be used for immunohistochemistry. The new cryostage provides a novel method enabling integration of 3D tissue structure with cellular and molecular analysis to facilitate the identification of molecular determinants of disease. NEW & NOTEWORTHY: The described micro-CT cryostage provides a novel way to study the three-dimensional lung structure preserved without the effects of fixatives while enabling subsequent studies of the cellular matrix composition and gene expression. This approach will, for the first time, enable researchers to study structural changes of lung tissues that occur with disease and correlate them with changes in gene or protein signatures.

Association of COPD exacerbation frequency with gene expression of pattern recognition receptors in inflammatory cells in induced sputum.

BACKGROUND: Bacteria and viruses are major causes of chronic obstructive pulmonary disease (COPD) exacerbations. Molecular components of these pathogens are recognized by pattern-recognition receptors (PRRs) expressed by various cells in the airway, which leads to initiation of inflammatory processes. Expression levels of PRRs in airway inflammatory cells are expected to affect susceptibility to COPD exacerbation. AIMS: This prospective observational study was conducted to detect any association between exacerbation and PRR expression. METHODS: Thirty-one male COPD patients were recruited. At baseline, clinical history, lung function measurements, peripheral blood samples and induced sputum were obtained. Using sputum samples, we performed gene expression analysis of TLR2, TLR3, TLR4, NOD1, NOD2, RIG-I and MDA-5 by quantitative reverse transcription-polymerase chain reaction in addition to quantitative bacterial culture. COPD exacerbations were assessed based on Anthonisen's criteria using symptom diaries for the following 1-year period. RESULTS: During 1-year follow-up period, 13 patients experienced at least one exacerbation, but 18 patients did not. Those with exacerbations tended to be more severe COPD and showed larger neutrophil fraction in their induced sputum. Among PRRs, only TLR3 gene expression was increased in COPD patients with exacerbation compared with those without exacerbations. Multivariate logistic regression analysis including neutrophil fraction and TLR3 gene expression as predictor variables demonstrated that only an increase of neutrophil fraction, but not TLR3 gene expression, was a significant predictor for COPD exacerbation. CONCLUSION: TLR3 expression in inflammatory cells might affect the susceptibility to COPD exacerbation.