Elevated serum Krebs von den Lungen-6 in systemic sclerosis: a marker of lung fibrosis and severity of the disease

Identification and management of interstitial lung disease associated with systemic sclerosis (SSc-ILD), rheumatoid arthritis (RA-ILD), and polymyositis/dermatomyositis (PM/DM-ILD): development of expert consensus-based clinical algorithms

BACKGROUND

Clinical guidance on the identification and management of connective tissue disease-associated interstitial lung disease (CTD-ILD) is needed for optimal clinical practice. We aimed to develop clinical algorithms for identifying and managing three common CTD-ILDs: those associated with systemic sclerosis (SSc-ILD), rheumatoid arthritis (RA-ILD), and polymyositis/dermatomyositis (PM/DM-ILD).

RESEARCH DESIGN AND METHODS

Meetings were held October - November 2023 to create consensus-based algorithms for identifying and managing SSc-ILD, RA-ILD, and PM/DM-ILD in clinical practice, based on expert consensus statements for identification and management of CTD-ILD previously derived from a Delphi process.

RESULTS

We developed clinical algorithms for SSc-ILD, RA-ILD, and PM/DM-ILD that highlight both commonalities and differences in the identification and management of these CTD-ILDs. Importantly, ILD should be suspected in patients with SSc, RA, or PM/DM who have respiratory symptoms. Chest high-resolution computed tomography has utility for screening, diagnosis and assessment of severity. Furthermore, regular follow-up and multidisciplinary management are important. Disease-specific considerations include unique risk factors such as anti-topoisomerase I antibodies in SSc-ILD, high-titer cyclic citrullinated peptide antibodies in RA, anti-aminoacyl tRNA synthetase antibodies in PM/DM, and anti-melanoma differentiation-associated gene 5 antibody in DM.

CONCLUSIONS

These algorithms may help physicians to identify and manage patients with SSc-ILD, RA-ILD, or PM/DM-ILD.

Undercover lung damage in pediatrics - a hot spot in morbidity caused by collagenoses

Connective tissue represents the support matrix and the connection between tissues and organs. In its composition, collagen, the major structural protein, is the main component of the skin, bones, tendons and ligaments. Especially at the pediatric age, its damage in the context of pathologies such as systemic lupus erythematosus, scleroderma or dermatomyositis can have a significant negative impact on the development and optimal functioning of the body. The consequences can extend to various structures (e.g., joints, skin, eyes, lungs, heart, kidneys). Of these, we retain and reveal later in our manuscript, mainly the respiratory involvement. Manifested in various forms that can damage the chest wall, pleura, interstitium or vascularization, lung damage in pediatric systemic inflammatory diseases is underdeveloped in the literature compared to that described in adults. Under the threat of severe evolution, sometimes rapidly progressive and leading to death, it is necessary to increase the popularization of information aimed at physiopathological triggering and maintenance mechanisms, diagnostic means, and therapeutic directions among medical specialists. In addition, we emphasize the need for interdisciplinary collaboration, especially between pediatricians, rheumatologists, infectious disease specialists, pulmonologists, and immunologists. Through our narrative review we aimed to bring up to date, in a concise and easy to assimilate, general principles regarding the pulmonary impact of collagenoses using the most recent articles published in international libraries, duplicated by previous articles, of reference for the targeted pathologies.

Diagnostic Value of Krebs von den Lungen (KL-6) for Interstitial Lung Disease: A European Prospective Cohort

INTRODUCTION

Krebs von den Lungen 6 (KL-6) is a mucin-1 glycoprotein produced by type II pneumocytes. High levels of KL-6 in blood may be found in patients with lung fibrosis. In Asia this biomarker is used for diagnosis and prognosis in interstitial lung diseases (ILD). There is a lack of information regarding KL-6 cut-off point for diagnosis and prognosis in European population. The aim of this study was to establish the cut-off point for serum KL-6 associated with the presence of ILD in the Spanish population.

METHODS

Prospective study including subjects who underwent chest HRCT, PFTs and autoimmune blood analysis. Two groups were created: non-ILD subjects and ILD patients. Serum KL-6 concentrations were measured using a Lumipulse KL-6 reagent assay and the optimal cut-off value was evaluated by a ROC analysis. Data on demographics and smoking history was also collected.

RESULTS

One hundred seventy-nine patients were included, 102 with ILD. Median serum KL-6 values overall were 762U/mL, 1080 (±787)U/mL for the ILD group vs 340 (±152)U/mL for the non-ILD group (p<0.0001). The main radiological pattern was NSIP (43%). ROC analysis showed greater specificity (86%) and sensitivity (82%) for KL-6 465U/mL for detecting ILD patients. The multivariate logistic regression model pointed to the male sex, higher KL-6 values, lower FVC and low DLCO values as independent factors associated with ILD.

CONCLUSION

Serum KL-6 values greater than 465U/mL have excellent sensitivity and specificity for detecting ILD in our Spanish cohort. Multicentre studies are needed to validate our results.

Heterogeneity of determining disease severity, clinical course and outcomes in systemic sclerosis-associated interstitial lung disease: a systematic literature review

Objective The course of systemic sclerosis-associated interstitial lung disease (SSc-ILD) is highly variable and different from continuously progressive idiopathic pulmonary fibrosis (IPF). Most proposed definitions of progressive pulmonary fibrosis or SSc-ILD severity are based on the research data from patients with IPF and are not validated for patients with SSc-ILD. Our study aimed to gather the current evidence for severity, progression and outcomes of SSc-ILD.Methods A systematic literature review to search for definitions of severity, progression and outcomes recorded for SSc-ILD was performed according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines in Medline, Embase, Web of Science and Cochrane Library up to 1 August 2023.Results A total of 9054 papers were reviewed and 342 were finally included. The most frequent tools used for the definition of SSc-ILD progression and severity were combined changes of carbon monoxide diffusing capacity (DLCO) and forced vital capacity (FVC), isolated FVC or DLCO changes, high-resolution CT (HRCT) extension and composite algorithms including pulmonary function test, clinical signs and HRCT data. Mortality was the most frequently reported long-term event, both from all causes or ILD related.Conclusions The studies presenting definitions of SSc-ILD 'progression', 'severity' and 'outcome' show a large heterogeneity. These results emphasise the need for developing a standardised, consensus definition of severe SSc-ILD, to link a disease specific definition of progression as a surrogate outcome for clinical trials and clinical practice.PROSPERO registration number CRD42022379254.Cite Now.

Mediators of systemic sclerosis-associated interstitial lung disease (SSc-ILD): systematic review and meta-analyses

Systemic sclerosis-associated interstitial lung disease (SSc-ILD) is rare, poorly understood, with heterogeneous characteristics resulting in difficult diagnosis. We aimed to systematically review evidence of soluble markers in peripheral blood or bronchoalveolar lavage fluid (BALF) as biomarkers in SSc-ILD.

METHOD

Five databases were screened for observational or interventional, peer-reviewed studies in adults published between January 2000 and September 2021 that assessed levels of biomarkers in peripheral blood or BALF of SSc-ILD patients compared with healthy controls. Qualitative assessment was performed using Critical Appraisal Skills Programme (CASP) checklists. Standardised mean difference (SMD) in biomarkers were combined in random-effects meta-analyses where multiple independent studies reported quantitative data.

RESULTS

768 published studies were identified; 38 articles were included in the qualitative synthesis. Thirteen studies were included in the meta-analyses representing three biomarkers: KL6, SP-D and IL-8. Greater IL-8 levels were associated with SSc-ILD in both peripheral blood and BALF, overall SMD 0.88 (95% CI 0.61 to 1.15; I2=1%). Greater levels of SP-D and KL-6 were both estimated in SSc-ILD peripheral blood compared with healthy controls, at an SMD of 1.78 (95% CI 1.50 to 2.17; I2=8%) and 1.66 (95% CI 1.17 to 2.14; I2=76%), respectively.

CONCLUSION

We provide robust evidence that KL-6, SP-D and IL-8 have the potential to serve as reliable biomarkers in blood/BALF for supporting the diagnosis of SSc-ILD. However, while several other biomarkers have been proposed, the evidence of their independent value in diagnosis and prognosis is currently lacking and needs further investigation.

PROSPERO REGISTRATION NUMBER

CRD42021282452.

Circulatory Serum Krebs von Den Lungen-6 and Surfactant Protein-D Concentrations Predict Interstitial Lung Disease Progression and Mortality

There is a need for biomarkers to predict outcomes, including mortality, in interstitial lung disease (ILD). Krebs von den Lungen-6 (KL-6) and surfactant protein D (SP-D) are associated with lung damage and fibrosis in all ILDs and are related to important clinical outcomes. Though these two biomarkers have been associated with ILD outcomes, there are no studies that have evaluated their predictive potential in combination. This study aims to determine whether KL-6 and SP-D are linked to poor disease outcomes and mortality. Additionally, we plan to examine whether changes in KL-6 and SP-D concentrations correspond with changes in lung function and whether serial measurements improve their predictive potential to identify disease progression and mortality. Forty-four patients with ILD participated in a prospective 6-month longitudinal observational study. ILD patients who succumbed had the highest KL-6 levels (3990.4 U/mL (3490.0-4467.6)) and highest SP-D levels (256.1 ng/mL (217.9-260.0)), followed by those who deteriorated: KL-6 levels 1357.0 U/mL (822.6-1543.4) and SP-D levels 191.2 ng/mL (152.8-210.5). The generalized linear model (GLM) analysis demonstrated that changes in forced vital capacity (FVC), diffusing capacity of lungs for carbon monoxide (DLCO), forced expiratory volume in 1 s (FEV1), and partial pressure of arterial oxygen (PaO₂) were correlated to changes in KL6 (p = 0.016, 0.014, 0.027, 0.047) and SP-D (p = 0.008, 0.012, 0.046, 0.020), respectively. KL-6 (odds ratio (OR): 2.87 (1.06-7.79)) and SPD (OR: 1.76 (1.05-2.97)) were independent predictors of disease progression, and KL-6 (hazard ratio (HR): 3.70 (1.46-9.41)) and SPD (HR: 2.58 (1.01-6.59)) were independent predictors of death by Cox regression analysis. Combined biomarkers (KL6 + SPD + CT + FVC) had the strongest ability to predict disease progression (AUC: 0.797) and death (AUC: 0.961), on ROC analysis. Elevated KL-6 and SPD levels are vital biomarkers for predicting the severity, progression, and outcomes of ILD. High baseline levels or an increase in levels over a six-month follow-up despite treatment indicate a poor prognosis. Combining KL6 and SPD with conventional measures yields a more potent prognostic indicator. Clinical studies are needed to test additional interventions, and future research will determine if this combined biomarker benefits different ethnicities globally.

Diagnosing lung involvement in inflammatory rheumatic diseases-Where do we currently stand?

Lung involvement is the most common and serious organ manifestation in patients with inflammatory rheumatic disease (IRD). The type of pulmonary involvement can differ, but the most frequent is interstitial lung disease (ILD). The clinical manifestations of IRD-ILD and severity can vary from subclinical abnormality to dyspnea, respiratory failure, and death. Consequently, early detection is of significant importance. Pulmonary function test (PFT) including diffusing capacity of the lungs for carbon monoxide (DLCO), and forced vital capacity (FVC) as well as high-resolution computed tomography (HRCT) are the standard tools for screening and monitoring of ILD in IRD-patients. Especially, the diagnostic accuracy of HRCT is considered to be high. Magnetic resonance imaging (MRI) and positron emission tomography/computed tomography (PET/CT) allow both morphological and functional assessment of the lungs. In addition, biomarkers (e.g., KL-6, CCL2, or MUC5B) are being currently evaluated for the detection and prognostic assessment of ILD. Despite the accuracy of HRCT, invasive diagnostic methods such as bronchoalveolar lavage (BAL) and lung biopsy are still important in clinical practice. However, their therapeutic and prognostic relevance remains unclear. The aim of this review is to give an overview of the individual methods and to present their respective advantages and disadvantages in detecting and monitoring ILD in IRD-patients in the clinical routine.

Systemic sclerosis associated interstitial lung disease: a survey of current practices in France

Background

Interstitial lung disease (ILD) is the leading cause of mortality in systemic sclerosis (SSc).

Objective

We performed an overview of the diagnostic approaches, follow-up and treatment strategies used in France for the management of SSc-associated ILD (SSc-ILD).

Design Structured nationwide online surveyMethods

A structured nationwide online survey was submitted to participants via the French Medical Societies for Internal Medicine and Pneumology, and research groups on SSc-ILD from May 2018 to June 2020. The 79 multiple-choice and 9 open-ended questions covered the screening of ILD at baseline, monitoring of patients with established SSc-ILD and its management. Fourteen optional vignettes exploring different clinical phenotypes of SSc-ILD were submitted to evaluate therapeutic decisions.

Results

All of the 93 participants screened SSc patients for ILD at baseline with 83 (89%) participants relying on a systematic chest computed tomography (CT) scan. Pulmonary function tests (PFT) were prescribed by 87 (94%) participants at baseline and during follow-up. Treatment was started based on abnormal PFT (95%), chest CT scan characteristics (89%), worsening dyspnoea (72%) and drop in SpO₂ during 6-min walk tests (66%). First-line therapy was cyclophosphamide (CYC) (89%), mycophenolate mofetil (MMF) (83%) and prednisone (73%). Rituximab as second-line immunosuppressive therapy (41%) was preferred to antifibrotic agents (18%), and a median daily prednisone dose of 10 mg (interquartile range, 10-15) was prescribed by 73% participants. Extensive SSc-ILD with worsening PFT (95%), regardless of diffusing capacity for carbon monoxide values and skin extension, were more likely to be treated, and CYC was favoured over MMF (p < 0.01). Extensive SSc-ILD with disease duration of less than 5 years was also a criterium for treatment initiation.

Conclusion

This overview of practices in diagnosis, follow-up and treatment of SSc-ILD in France describes real-life management of patients. It highlights heterogeneity in this management and gaps in current strategies that should be addressed to improve and harmonize clinical practices in SSc-ILD.

Tumor markers are associated with rapidly progressive interstitial lung disease in adult-dermatomyositis

OBJECTIVES

DM-associated rapidly progressive interstitial lung disease (DM-RP-ILD) has been the clinical conundrum. We assess the serum levels of tumor markers (TMs) in different types of ILD, and explore the diagnostic utility of TMs for DM/ADM-RP-ILD.

METHODS

This was a retrospective cohort study, data including clinical and laboratory records were collected from the first affiliated hospital of Zhengzhou University from December 2015, to June 2020. Tumor markers (TMs) include CEA, CA153, CA724, CA125, and CA199. Spearman analysis, ROC, and Kaplan-Meier curve were used for data analysis.

RESULTS

Total 272 patients (149 DM and 123 ADM) were enrolled, 152 (55.88%) with ILD (116 with chronic ILD, 36 with RP-ILD) and 120 (44.12%) without ILD among them. The serum levels of CEA and ferritin were significantly higher in patients with RP-ILD than in the other two groups. Serum CA125, CA199, and CA153 levels in patients with RP-ILD were higher than those without ILD. CEA levels were associated with the ferritin, KL-6 and anti-MDA5 levels, and CEA concentration was significantly negatively correlated with DLco (P = 0.016, R² =  - 0.281). CEA [AUC = 0.7, 95% CI = (0.594, 0.806)] and ferritin [AUC = 0.737, 95% CI = (0.614, 0.860)] had diagnosed value for patients developing RP-ILD. Patients with high serum CEA levels had higher mortality rate within the DM-ILD population.

CONCLUSIONS

TMs and ferritin were increased in DM/ADM-RP-ILD, and serum CEA and CA153 levels can evaluate disease severity of DM. And CEA and ferritin can be used as noninvasive diagnostic biomarkers for patients with DM-RP-ILD. Key Points • Interstitial lung disease (ILD) is a serious complication of DM, and is a leading cause of mortality, especially rapidly progressive ILD. • Tumor markers as a kind of noninvasive detection can reflect the disease severity of DM, and CEA and ferritin can be used to identify patients with RP-ILD.

The Prognostic Value of Krebs von den Lungen-6 and Surfactant Protein-A Levels in the Patients with Interstitial Lung Disease

Background and Objectives

The highly variable clinical course of interstitial lung disease (ILD) makes it difficult to predict patient prognosis. Serum surfactant protein-A (SP-A) and Krebs von den Lungen-6 (KL-6) are known prognostic biomarkers. However, the clinical or pathophysiological differences in patients with these biomarkers have not been well evaluated. We investigated the clinical and pathophysiological differences through the comparison of SP-A and KL-6 levels before and after treatment.

Methods

This study included retrospective data from 91 patients who were treated for ILD between August 2015 and September 2019. Serum SP-A and KL-6 levels were measured before and after treatment. The patients were followed up for 3 months.

Results

Changes in the serum biomarkers (Delta SP-A and Delta KL-6) were found to be significantly correlated (rs = 0.523, P < 0.001); Delta SP-A and Delta KL-6 were inversely correlated with changes in pulmonary function (% predicted values of diffusing capacity for carbon monoxide [DLCO], forced vital capacity [FVC], and forced expiratory volume in 1 s [FEV1]). Patients were divided into four groups based on their Delta SP-A and Delta KL-6 levels in a cluster analysis (G1, G2, G3, and G4). Both SP-A and KL-6 were elevated in the G1 group, with all the patients enrolled classified as progressive or unchanged, and 86.4% of patients showed improved disease activity in the G4 group, where both SP-A and KL-6 levels were reduced. In the G2 group, only SP-A levels decreased post-treatment, indicating an improvement in respiratory function; the patients were not at the end stage of the disease. Only the SP-A levels increased in the G3 group with immunosuppressive treatment.

Conclusions

Reduced serum SP-A and/or KL-6 levels are associated with improved lung function in patients with ILD. Some patients only showed a decrease in SP-A levels could prognosis an improvement in respiratory function. When only SP-A is increased, it may imply that the patients are at an early stage of disease progression. As a result, for proper disease monitoring, measuring both markers is important.

Serum KL-6 as predictive and prognostic marker of interstitial lung disease in childhood connective tissue diseases: a pilot study

This study was aimed to evaluate serum KL-6 levels to determine if this marker can be used for diagnosing and assessing severity of interstitial lung disease (ILD) in children with connective tissue disorders. In total, 40 patients [18 patients with juvenile systemic lupus erythematosus (JSLE), 10 patients with juvenile idiopathic arthritis (JIA), 8 patients with juvenile mixed connective tissue disease (JMCTD), 3 patients with juvenile systemic sclerosis (JSSc), and 1 patient with juvenile dermatomyositis (JDM)] and 20 healthy controls were included in this study. Age, sex, and duration of CTD and ILD (if any) were recorded. Blood samples from all the patients and controls were examined by ELISA. 20 of the 40 patients with CTD (50%) had ILD, 12 were mild and 8 were severe as assessed by spirometry. The median serum KL-6 level was 102.7 U/mL (76.1-180.8) in the CTD with severe ILD group, 72.2 U/mL (58.4- 100.5) in the CTD with mild ILD group, 56.7 U/mL (35.8-68.5) in the CTD without ILD group, and 52.3 U/mL (32.8-62.4) in the control group. KL-6 levels were significantly higher in the CTD with ILD (p<0.05), at a cutoff of 63.4 U/ml identified by ROC curve, serum KL-6 showed a sensitivity of 95.2% and specificity of 89.7%. KL-6 is a valuable biomarker for diagnostic purposes and to detect severity in ILD in childhood CTD.

Prognostic role of KL-6 in SSc-ILD patients with pleuroparenchymal fibroelastosis

BACKGROUND

Krebs von den Lungen-6 (KL-6) is a high-molecular-weight (200kDa) glycoprotein proposed as a diagnostic biomarker for differentiating interstitial lung disease (ILD). Systemic sclerosis (SSc) is a rare immune-mediated disorder, and ILD is the leading cause of morbidity and mortality. Pleuroparenchymal fibroelastosis (PPFE) has been described to have a poor prognosis in SSc-ILD patients. This study undertook to compare serial changes in KL-6 in SSc-ILD patients with and without PPFE, to verify its prognostic value as a disease biomarker.

MATERIALS AND METHODS

Twenty-five SSc-ILD patients (median IQR, 62 (56-58); 20% males) were retrospectively enrolled. 12 SSc-ILD patients (48%) had also a radiological diagnosis of PPFE. Serum KL-6 concentrations were measured by KL-6 reagent assay (Fujirebio Europe, Ghent, Belgium).

RESULTS

Serum KL-6 measurements were increased in SSc-ILD patients with and without PPFE compared with healthy controls (P < .0001). Comparative analysis of the rate of variation of KL-6 over the 6 years of follow-up was performed by serial two-yearly KL-6 measurements: Δ1(t1-t0), Δ2(t2-t1) and Δ3(t3-t2). In SSc-ILD patients with PPFE pattern, Δ3 was significantly different than those without PPFE pattern (P = .0020). Serum KL-6 levels were significantly different (P = .0455) either at Δ2 and Δ3 in the PPFE group. In SSc-ILD patients with PPFE, at t3 serum KL-6 concentrations were inversely correlated with FEV1 (r = -.76; P = .037) and FVC percentages (r = -.79; P = .028).

CONCLUSION

These results suggest that serial measurements of KL-6 in the follow-up of these patients may help to monitor disease progression. In real life, in SSc-ILD patients PPFE should be always evaluated at CT and when present should suggest a tight follow-up to monitor its evolution.

Interstitial Lung Disease in Connective Tissue Disease: A Common Lesion With Heterogeneous Mechanisms and Treatment Considerations

Connective tissue disease (CTD) related interstitial lung disease (CTD-ILD) is one of the leading causes of morbidity and mortality of CTD. Clinically, CTD-ILD is highly heterogenous and involves rheumatic immunity and multiple manifestations of respiratory complications affecting the airways, vessels, lung parenchyma, pleura, and respiratory muscles. The major pathological features of CTD are chronic inflammation of blood vessels and connective tissues, which can affect any organ leading to multi-system damage. The human lung is particularly vulnerable to such damage because anatomically it is abundant with collagen and blood vessels. The complex etiology of CTD-ILD includes genetic risks, epigenetic changes, and dysregulated immunity, which interact leading to disease under various ill-defined environmental triggers. CTD-ILD exhibits a broad spectra of clinical manifestations: from asymptomatic to severe dyspnea; from single-organ respiratory system involvement to multi-organ involvement. The disease course is also featured by remissions and relapses. It can range from stability or slow progression over several years to rapid deterioration. It can also present clinically as highly progressive from the initial onset of disease. Currently, the diagnosis of CTD-ILD is primarily based on distinct pathology subtype(s), imaging, as well as related CTD and autoantibodies profiles. Meticulous comprehensive clinical and laboratory assessment to improve the diagnostic process and management strategies are much needed. In this review, we focus on examining the pathogenesis of CTD-ILD with respect to genetics, environmental factors, and immunological factors. We also discuss the current state of knowledge and elaborate on the clinical characteristics of CTD-ILD, distinct pathohistological subtypes, imaging features, and related autoantibodies. Furthermore, we comment on the identification of high-risk patients and address how to stratify patients for precision medicine management approaches.

Krebs von den Lungen 6 (KL-6) as a marker for disease severity and persistent radiological abnormalities following COVID-19 infection at 12 weeks

INTRODUCTION

Acute presentations of COVID-19 infection vary, ranging from asymptomatic carriage through to severe clinical manifestations including acute respiratory distress syndrome (ARDS). Longer term sequelae of COVID-19 infection includes lung fibrosis in a proportion of patients. Krebs von den Lungen 6 (KL-6) is a mucin like glycoprotein that has been proposed as a marker of pulmonary epithelial cell injury. We sought to determine whether KL-6 was a marker of 1) the severity of acute COVID-19 infection, or 2) the persistence of symptoms/radiological abnormalities at medium term follow up.

METHODS

Prospective single centre observational study.

RESULTS

Convalescent KL-6 levels were available for 93 patients (male 63%, mean age 55.8 years) who attended an 12-week follow up appointment after being admitted to hospital with COVID-19. For 67 patients a baseline KL-6 result was available for comparison. There was no significant correlations between baseline KL-6 and the admission CXR severity score or clinical severity NEWS score. Furthermore, there was no significant difference in the baseline KL-6 level and an initial requirement for oxygen on admission or the severity of acute infection as measured at 28 days. There was no significant difference in the 12-week KL-6 level and the presence or absence of subjective breathlessness but patients with abnormal CT scans at 12 weeks had significantly higher convalescent KL-6 levels compared to the remainder of the cohort (median 1101 IU/ml vs 409 IU/ml).

CONCLUSIONS

The association between high KL-6 levels at 12 weeks and persisting CT abnormalities (GGO/fibrosis), is a finding that requires further exploration. Whether KL-6 may help differentiate those patients with persisting dyspnoea due to complications rather than deconditioning or dysfunctional breathing alone, is an important future research question.

Krebs von den Lungen-6 and surfactant protein-A in interstitial pneumonia with autoimmune features

Interstitial pneumonia with autoimmune features (IPAF) is a special subtype of interstitial lung disease that has received worldwide attention. Krebs von den Lungen-6 (KL-6) and surfactant protein-A (SP-A) can be used as an important biomarker of interstitial lung disease, but its exact relationship with IPAF is poorly understood.A total of 65 IPAF patients were included in the study and were followed up for 52 weeks. The KL-6 and SP-A were evaluated by chemiluminescence enzyme immunoassay. The above indicators were tested at 2 time points, baseline (the first admission of patients) and 52 weeks. We also collected the indicators of antinuclear antibodies and rheumatoid factor. Based on high-resolution computed tomography evaluations, patients were divided into: aggravation, stable, and improvement group. At same time, 30 age-matched normal people as normal control were recruited, the same information was collected. Correlations among the groups were compared and analyzed.The KL-6 and SP-A level in IPAF patients were significantly higher than normal controls (fold increase = 11.35 and 1.39, both P < .001) and differed significantly at baseline and 52 weeks in IPAF (difference ratio = 37.7% and 21.3%, P < .05, both). There were significant differences at baseline and 52 weeks (r values of aggravation, improvement, and stable groups for KL-6 were 0.705, 0.770, and 0.344, P = .001, .001, and .163, and for SP-A the r value were 0.672, 0.375, and 0.316, P = .001, .126, and .152). In aggravation group, KL-6 and SP-A were correlated with CT scores (both P < .05). Diffusing capacity of the lung for carbon monoxide (DLCO) and forced vital capacity (FVC), % predicted showed a progressive downward trend, with a significant difference at baseline and 52 weeks in IPAF patients (difference ratio = 23.8% and 20.6%, both P < .05). There was a significant correlation between KL-6 and FVC % predicted and DLCO (both P < .05), SP-A showed negatively correlated with DLCO, but not significantly correlated with FVC % predicted (P < .05 and .47).This study demonstrated that KL-6 and SP-A can reflect disease progression, and both 2 play a key role at reflection of lung epithelial cell injury and fibrosis degree in IPAF.

Serum Krebs von den Lungen-6 and lung ultrasound B lines as potential diagnostic and prognostic factors for rheumatoid arthritis-associated interstitial lung disease

INTRODUCTION

Rheumatoid arthritis (RA)-associated interstitial lung disease (ILD) (RA-ILD) is a serious systemic RA manifestation with high mortality that needs proper, accurate, and sensitive assessment tools.

OBJECTIVES

Firstly, evaluate serum Krebs von den Lungen-6 (KL-6) levels and lung ultrasound B lines (LUS B lines) score in RA-ILD correlating them with the severity of ILD assessed by high-resolution computed tomography (HRCT) and pulmonary function tests (PFTs). Secondly, determine cut-off values for LUS and KL-6 in RA-ILD assessment and outcome prediction.

METHODS

A case-control study included seventy-five RA-ILD patients with an equal number of matched RA patients without ILD. Clinical assessment includes DAS-28 and PFTs, laboratory assessment of serum KL-6 by latex-enhanced immunoturbidimetric assay, and radiological evaluation of ILD using semiquantitative CT grade and LUS B lines.

RESULTS

RA-ILD patients had significantly higher serum KL6 compared to those without ILD (1025.5 ± 419.6 vs. 237.5 ± 51.9, p ≤ 0.001). Serum KL6 was positively correlated with HRCT and LUS scores (r = 0.93, r = 0.97, respectively) with negative correlation with FVC% and FEV1% (r = - 0.93, r = - 0.91, respectively). LUS was positively correlated with KL6 and HRCT (r = 0.97, r = 0.944, respectively) while, negatively correlated with PFTs. Cut-off values of KL6 and LUS were 277.5 U/ml and < 5.5, with AUC 0.878 and 1, sensitivity 86.7% and 100%, and specificity 88% and 100%, respectively.

CONCLUSIONS

The non-invasive, radiation-free LUS with a score < 5.5 combined with serum KL6 could be helpful for RA-ILD assessment correlating with HRCT and disease severity. Serum KL6 combined with LUS is important new and potential prognostic factor predicting poor outcomes in RA-ILD. Further large-scale, multi-center, and prospective studies are needed to confirm these findings.

KEY POINTS

• Combination of the non-invasive, radiation-free LUS with a score < 5.5 and serum KL6 levels of 277.5 U/ml is recommended as prognostic tools for RA-ILD. • Easily obtainable tests such as serum KL-6, inflammatory markers, and LUS are sensitive for assessing RA-ILD and the risk of poor outcomes in patients with RA-ILD. • RA-ILD patients with higher KL6 levels, higher LUS scores had a poor prognosis with short survival. • LUS B lines could be used as the first imaging tool for the evaluation of RA-ILD decreasing the risk of HRCT radiation exposure in asymptomatic or mild RA-ILD patients.

Serum markers of pulmonary epithelial damage in systemic sclerosis-associated interstitial lung disease and disease progression

BACKGROUND AND OBJECTIVE

The course of systemic sclerosis-associated interstitial lung disease (SSc-ILD) is highly variable, and accurate prognostic markers are needed. KL-6 is a mucin-like glycoprotein (MUC1) expressed by type II pneumocytes, while CYFRA 21-1 is expressed by alveolar and bronchiolar epithelial cells. Both are released into the blood from cell injury.

METHODS

Serum KL-6 and CYFRA 21-1 levels were measured in a retrospective (n = 189) and a prospective (n = 118) cohort of SSc patients. Genotyping of MUC1 rs4072037 was performed. Linear mixed-effect models were used to evaluate the relationship with change in lung function parameters over time, while association with survival was evaluated with Cox proportional hazard analysis.

RESULTS

In both cohorts, KL-6 and CYFRA 21-1 were highest in patients with lung involvement, and in patients with extensive rather than limited ILD. KL-6 was higher in patients carrying the MUC1 rs4072037 G allele in both cohorts. In patients with SSc-ILD, serum KL-6, but not CYFRA 21-1, was significantly associated with DL_CO decline in both cohorts (P = 0.001 and P = 0.004, respectively), and with FVC decline in the retrospective cohort (P = 0.005), but not the prospective cohort. When combining the cohorts and subgrouping by severity (median CPI = 45.97), KL-6 remained predictive of decline in DL_CO in both milder (P = 0.007) and more severe disease (P = 0.02) on multivariable analysis correcting for age, gender, ethnicity, smoking history and MUC1 allele carriage.

CONCLUSION

Our results suggest serum KL-6 predicts decline in lung function in SSc, suggesting its clinical utility in risk stratification for progressive SSc-ILD.

Pulmonary involvement in systemic sclerosis: exploring cellular, genetic and epigenetic mechanisms

Systemic sclerosis (SSc) is a chronic progressive autoimmune disease characterized by immune inflammation, vasculopathy, and fibrosis. There are still numerous uncertainties in the understanding of disease initiation and progression. Pulmonary involvement in SSc, and particularly pulmonary fibrosis, is critical for all organ systems affections in this disease. This review is aimed to describe and analyze new findings in the pathophysiology of SSc-associated pulmonary involvement and to explore perspective diagnostic and therapeutic strategies. A myriad of cellular interactions is explored in the dynamics of progressive interstitial lung disease (ILD) and pulmonary hypertension (PH) in SSc. The role of exosomes, microvesicles, and apoptotic bodies is examined and the impact of micro and long non-coding RNAs, DNA methylation, and histone modification in SSc is discussed.

Comparative diagnostic efficacy of serum Krebs von den Lungen-6 and surfactant D for connective tissue disease-associated interstitial lung diseases: A meta-analysis

PURPOSE

The aim of the study was to estimate and compare the diagnostic accuracy of serum Krebs von den Lungen-6 (KL-6) and surfactant protein D (SP-D) for identifying interstitial lung disease (ILD) from non-ILD among connective tissue disease (CTD) patients.

MATERIALS AND METHODS

Original articles on the diagnostic accuracy of serum KL-6 and SP-D in differentiating CTD-ILD from CTD-nonILD were identified from three public databases. The overall quality of evidence and methodologic quality of each eligible study were assessed by the Grading of Recommendations, Assessment, Development and Evaluation approach and Quality Assessment of Diagnostic Accuracy Studies, respectively. We used the bivariate model to calculate random-effect sensitivity, specificity, likelihood ratios, and area under curve. Furthermore, trial sequential analysis (TSA) was used to determine whether sample sizes incorporated in the meta-analysis were powerful for evaluating the diagnostic utility. Bayesian network analysis was performed to compare the diagnostic accuracy of 2 serum biomarkers in differentiating ILD among CTD patients and various subgroups.

RESULTS

Twenty-nine studies were included in the quantitative synthesis. No threshold effects were observed (all P values >.05). For diagnosis of ILD among CTD patients, overall sensitivity and specificity of serum KL-6 were 0.76 (95% confidence interval [CI]: 0.68-0.82) and 0.89 (95% CI: 0.83-0.93), whereas those for serum SP-D were 0.65 (95% CI: 0.45-0.80) and 0.88 (95% CI: 0.80-0.93). Comprehensive comparison of 2 circulating biomarkers using back-calculated likelihood ratio (LR) demonstrated that serum KL-6 corresponded to a higher LR+ and a lower LR- in comparison to serum SP-D, as well as in SSc-ILD. TSA indicated that evidence for serum KL-6 and SP-D in identifying CTD-ILD is powerful; nonetheless, more trials were needed for validation of serum KL-6 and SP-D in differentiating CTD-ILD subtypes, including different CTD and ethnicities.

CONCLUSIONS

This meta-analysis suggested that serum KL-6 had superior diagnostic accuracy to SP-D for differentiating ILD from non-ILD among CTD patients, providing a convenient and non-invasive approach for screening and management of ILD among CTD patients.

Circulating biomarkers of systemic sclerosis - interstitial lung disease

Interstitial lung disease is a frequent organ manifestation in systemic sclerosis and is associated with high mortality. It is crucial to diagnose interstitial lung disease in systemic sclerosis and to assess severity and identify patients prone to progression at an early stage to ultimately decrease organ damage and improve outcome. Circulating anti-topoisomerase-I autoantibodies have long been associated with the presence and development of systemic sclerosis - interstitial lung disease, evidence on their potential to further predict the clinical course of systemic sclerosis is however conflicting. C-reactive protein is a marker of infection and systemic inflammation with widespread clinical application and is elevated in systemic sclerosis with a tendency towards higher abundancy in patients with early disease. The role of other circulating biomarkers is promising but hampered by the lack of standardized criteria and guidelines for sample/data collection, analyses, reporting and validation and has not reached prime time for clinical application. However, epithelial markers including Krebs von den Lungen-6 and surfactant protein D and several cytokines and chemokines including CCL2 and CCL18 for severity assessment of systemic sclerosis - interstitial lung disease patients at the time of interstitial lung disease diagnosis and to predict interstitial lung disease progression have been reported and seem to be promising candidate biomarkers in the future.

Circulating lung biomarkers in idiopathic lung fibrosis and interstitial lung diseases associated with connective tissue diseases: Where do we stand?

Interstitial lung diseases (ILDs) are complex diseases with various courses where personalized medicine is highly expected. Biomarkers are indicators of physiological, pathological processes or of pharmacological response to therapeutic interventions. They can be used for diagnosis, risk-stratification, prediction and monitoring of treatment response. To better delineate the input and pitfalls of biomarkers in ILDs, we performed a systematic review and meta-analysis of literature in MEDLINE and Embase databases from January 1960 to February 2019. We focused on circulating biomarkers as having the highest generalizability. Overall, 70 studies were included in the review and 20 studies could be included in the meta-analysis. This review highlights that ILD associated with connective tissue diseases (CTD-ILD) and idiopathic pulmonary fibrosis (IPF) share common biomarkers, suggesting common pathophysiological pathways. KL-6 and SP-D, could diagnose lung fibrosis in both IPF and CTD-ILD, with KL-6 having the strongest value (OR: 520.95[110.07-2465.58], p<0.001 in IPF and OR:26.43[7.15-97.68], p<0.001 in CTD-ILD), followed by SPD (OR: 33.81[3.20-357.52], p = 0.003 in IPF and 13.24 [3.84-45.71] in SSc-ILD), MMP7 appeared as interesting for IPF diagnosis (p<0.001), whereas in SSc, CCL18 was associated with ILD diagnosis. Both CCL18 and KL-6 were predictive for the outcomes of ILDs, with higher predictive values for CCL18 in both IPF (OR:10.22[4.72-22.16], p<0.001 and in SSc [2.62[1.71-4.03], p<0.001). However, disease specific biomarkers are lacking and large longitudinal studies are needed before the translational use of the potential biomarkers in clinical practice. With the recent availability of new effective therapies in ILDs, further studies should assess response to treatment.

Interstitial Lung Disease in Systemic Sclerosis: Focus on Early Detection and Intervention

Systemic sclerosis (SSc) is a progressive and often devastating disease characterized by autoimmune dysfunction, vasculopathy, and fibrosis. Interstitial lung disease (ILD) is identified in the majority of patients with SSc and is the leading cause of SSc-related mortality. Although clinical manifestations and ILD severity vary among patients, lung function typically declines to the greatest extent during the first 3-4 years after disease onset. We aim to provide an overview of SSc-associated ILD (SSc-ILD) with a focus on current and emerging tools for early diagnosis of ILD and current and novel treatments under investigation. Early detection of ILD provides the opportunity for early therapeutic intervention, which could improve patient outcomes. Thoracic high-resolution computed tomography is the most effective method of identifying ILD in patients with SSc; it enables detection of mild lung abnormalities and plays an important role in monitoring disease progression. Cyclophosphamide and mycophenolate mofetil are the most commonly prescribed treatments for SSc-ILD. Recently, nintedanib (an antifibrotic) was approved by the Food and Drug Administration for patients with SSc-ILD; it is indicated for slowing the rate of decline in pulmonary function. However, there is a need for additional effective and well-tolerated disease-modifying therapy. Ongoing studies are evaluating other antifibrotics and novel agents. We envision that early detection of lung involvement, combined with the emergence and integration of novel therapies, will lead to improved outcomes in patients with SSc-ILD.

Progression of Interstitial Lung Disease in Systemic Sclerosis: The Importance of Pneumoproteins Krebs von den Lungen 6 and CCL18

OBJECTIVE

To investigate the relationship between Krebs von den Lungen 6 (KL-6) and CCL18 levels and the severity and progression of systemic sclerosis (SSc)-related interstitial lung disease (ILD).

METHODS

Patients enrolled in the Scleroderma Lung Study II (cyclophosphamide [CYC] versus mycophenolate mofetil [MMF]) were included. Baseline and 12-month plasma samples were analyzed by enzyme-linked immunosorbent assay to assess CCL18 and KL-6 levels. The forced vital capacity (FVC) and the diffusing capacity for carbon monoxide (DLco) were measured every 3 months. Joint models were created to investigate the relationship between baseline CCL18 and KL-6 levels and the course of the FVC and DLco over 1 year according to treatment arm.

RESULTS

Baseline KL-6 and CCL18 levels each correlated with the extent of radiographic fibrosis. Levels of both CCL18 and KL-6 declined significantly at 1 year. In both treatment arms (n = 71 for CYC, n = 62 for MMF), a higher baseline KL-6 level predicted progression of ILD based on the course of FVC (P = 0.024 for CYC; P = 0.005 for MMF) and DLco (P < 0.001 for CYC; P = 0.004 for MMF) over 1 year. A higher baseline CCL18 level predicted progression of ILD based on the course of the FVC (P < 0.001 for CYC; P = 0.007 for MMF) and DLco (P = 0.001 for CYC; P < 0.001 for MMF) over 1 year, as well as mortality (P = 0.0008 for CYC arm only).

CONCLUSION

In a rigorously conducted clinical trial for SSc-related ILD, KL-6 and CCL18 levels correlated with ILD severity and declined with immunosuppression. Patients with higher baseline KL-6 and CCL18 levels were more likely to experience disease progression despite treatment. KL-6 and CCL18 levels could be used to identify patients with a progressive ILD phenotype who may benefit from a more aggressive initial treatment approach.

Detection and classification of systemic sclerosis-related interstitial lung disease: a review

PURPOSE OF REVIEW

Systemic sclerosis (SSc) is a heterogeneous disease with a variable disease course. Interstitial lung disease (ILD) is one of the leading causes of morbidity and mortality in patients with SSc. The present review highlights recent advances in the classification, diagnosis, and early detection of SSc-associated ILD (SSc-ILD).

RECENT FINDINGS

Risk stratification through measurement of disease extent on high-resolution computed tomography (HRCT) of the chest, longitudinal declines in pulmonary function tests (PFTs), and mortality prediction models have formed the basis for classifying clinically significant ILD. HRCT may be preferred over PFTs for screening, as PFTs lack sensitivity and have a high false-negative rate. Novel imaging modalities and biomarkers hold promise as adjunct methods for assessing the presence and severity of SSc-ILD, and predicting risk for progressive disease. Further validation is required prior to their use in clinical settings.

SUMMARY

Classification of SSc-ILD has shifted to a personalized approach that considers an individual patient's probability of progressive disease through identification of risk factors, measurement of disease extent on HRCT, longitudinal declines in PFTs, and mortality prediction models. There remains an unmet need to develop screening guidelines for SSc-ILD.

Serum KL-6 is associated with the severity of interstitial lung disease in Chinese patients with polymyositis and dermatomyositis

OBJECTIVE

This cross-sectional study was designed to assess the clinical significance of the serum KL-6 in the diagnosis of interstitial lung disease (ILD) in patients with idiopathic inflammatory myopathy (IIM).

METHODS

We measured serum KL-6 levels in 184 patients with IIM using a chemiluminescent enzyme immunoassay and compared KL-6 levels between patients with and without ILD, according to other clinical features.

RESULTS

IIM patients with ILD had significantly higher serum KL-6 levels than those without ILD (776.5 [372.3-1378.8] vs. 297.5 [204.75-599.3] U/ml, P < 0.001). At a cut-off of 461.5 U/ml identified by ROC curve, serum KL-6 yielded a sensitivity of 70.2% and specificity of 73.9% for ILD in IIM patients. IIM patients with an elevated serum KL-6 were more likely to have clinical symptoms of mechanic's hands (P = 0.002), anti-Jo-1 antibody positivity (P = 0.021), dysphagia (P = 0.039), hoarseness (P < 0.001), and polyarthritis/polyarthralgia (P < 0.001). Significant inverse correlations were found between serum KL-6 levels and pulmonary function tests (P < 0.01), including forced vital capacity (FVC, %Pred), total lung capacity (TLC, %Pred), and diffusing capacity for carbon monoxide (DLCO, %Pred).

CONCLUSIONS

Serum KL-6 offers high sensitivity and specificity for the diagnosis of IIM-associated ILD and is inversely correlated with pulmonary function deterioration. Serum KL-6 may represent a promising biomarker for monitoring ILD severity in IIM patients.

Serum KL-6 levels reflect the severity of interstitial lung disease associated with connective tissue disease

Background

Biomarkers have been actively investigated to supplement functional and imaging modalities to predict the severity, therapeutic responsiveness, and progression of connective tissue disease-associated interstitial lung disease (CTD-ILD). This study aimed to evaluate Krebs von den Lungen 6 (KL-6) as a potential biomarker reflecting the severity of CTD-ILD as assessed through computed tomography (CT) and pulmonary function test (PFT) parameters.

Methods

This retrospective study included 549 Korean patients with rheumatoid arthritis, systemic sclerosis, inflammatory myositis, and other CTDs with or without concurrent ILD. Serum KL-6 concentration (U/mL) was measured using the latex-enhanced immunoturbidimetric assay method. CT and PFT results were collected within 1 year of serum collection. A semiquantitative grade of ILD extent was evaluated through CT scan (grade 1, 0–25%; grade 2, 26–50%; grade 3, 51–75%; grade 4, 76–100%).

Results

CTD-ILD patients (n = 165) had elevated serum KL-6 levels compared to CTD patients without ILD (n = 384) (p < 0.001), and those findings were preserved after adjusting for age, sex, and CTD type. The semiquantitative grade of ILD on CT scan was significantly proportional to the KL-6 level, and the optimal cut-off KL-6 value effectively differentiated each ILD grade. The percent diffusing capacity of the lung for carbon monoxide (DLCO) (p < 0.001) and forced vital capacity (FVC) (p < 0.001) parameters had a moderate, negative correlation with the KL-6 level.

Conclusion

Serum KL-6 levels were increased in CTD-ILD patients and had a positive correlation with CT grade and a negative correlation with FVC and DLCO. Serum KL-6 levels may reflect CTD-ILD severity.

Electronic supplementary material

The online version of this article (10.1186/s13075-019-1835-9) contains supplementary material, which is available to authorized users.