Serum levels of Krebs von den Lungen-6 as a promising marker for predicting occurrence and deterioration of systemic sclerosis-associated interstitial lung disease from a Chinese cohort

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.

Evaluation of the Clinical Value of KL-6 and Tumor Markers in Primary Sjögren's Syndrome Complicated with Interstitial Lung Disease

OBJECTIVE

primary Sjögren's syndrome (pSS) is an autoimmune disease, of which the most common complication is interstitial lung disease (ILD). This study aimed to analyze the clinical value of Krebs von den Lungen-6 (KL-6), carcinoembryonic antigen (CEA), and carbohydrate antigen 153(CA153) in patients with pSS complicated with ILD (pSS-ILD), given that only few studies have evaluated this.

METHODS

This is a cross-sectional study. Serum KL-6 levels (U/mL) were measured using chemiluminescence immunoassay, and concentrations of serum tumor markers were determined using the immunofluorescence method in 64 cases of pSS-ILD (pSS-ILD group), 23 cases without ILD (non-ILD group), and 45 healthy controls. The correlation between KL-6 and tumor markers as well as lung function was analyzed, and the factors that were associated with pSS-ILD were screened.

RESULTS

The serum KL-6 was more abnormally increased in patients with pSS-ILD, and the serum KL-6, CEA, carbohydrate antigen 125 (CA125), and CA153 levels were significantly higher in the pSS-ILD group than in the non-ILD and healthy control groups (p < 0.05). KL-6, CEA, and CA153 were negatively correlated with forced vital capacity (FVC%), forced expiratory volume in 1 s (FEV1%), total lung capacity (TLC%), and diffusing capacity for carbon monoxide (DLCO%) (all p < 0.05). Multivariate logistic analysis showed that KL-6 was an independent factor associated with pSS-ILD.

CONCLUSIONS

In conclusion, we evaluated the association between clinical values of KL-6, tumor markers, and pSS-ILD, and found that KL-6 and tumor markers such as CEA, CA153, and CA125 in patients with pSS-ILD were higher than in patients with non-ILD, and KL-6 was more abnormally increased and significantly associated with ILD development in patients with pSS.

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.

Krebs von den Lungen-6 (KL-6) is a pathophysiological biomarker of early-stage acute hypersensitivity pneumonitis among pigeon fanciers

BACKGROUND

Identifying early stages of hypersensitivity pneumonitis (HP) is hampered by variable presentation, heterogeneous or undetected causal antigens and lack of gold-standard biomarkers. Krebs von den Lungen (KL)-6 is pathophysiological biomarker of alveolar epithelial damage. Pigeon fanciers, susceptible to HP, provide a model to investigate early HP.

OBJECTIVE

To test the hypothesis that plasma concentrations of KL-6 are increased in early-stage acute HP.

METHODS

Clinical history, spirometry and blood samples were obtained from pigeon fanciers, 20 with intermittent acute symptoms indicative of developing HP, 27 with no symptoms and 10 healthy subjects with no avian exposure. Plasma KL-6 (units/mL) and pigeon antigen-specific IgG antibody were quantified by enzyme immunoassay. Blood lymphocytes were quantified by flow cytometry and antigen specificity by in vitro cytokine production.

RESULTS

KL-6 was higher in fanciers than controls, median (IQR) 452 (244, 632) vs 274 (151, 377), P = .01. Although fanciers with symptoms had similar antigen exposure and lung function, they had higher KL-6 than those without, 632 (468, 1314) vs 320 (200, 480), P < .001. KL-6 correlated with IgG antibody titre in those with symptoms, r = .591, P = .006. High KL-6, irrespective of symptom category, was associated with higher antibody (P = .006) and lymphocyte proliferation (P = .041), and lower CD4+ T lymphocyte proportion (P = .032).

CONCLUSION AND CLINICAL RELEVANCE

Raised KL-6 is associated with acute symptoms of early-stage HP, and its correlation with antibody may support therapeutic strategies when HP is suspected. KL-6 may act as a mechanistic biomarker of early pathogenesis by linking lung pathophysiological changes with an endotype of immune hypersensitivity.

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.

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 levels of Krebs von den Lungen-6 as a promising marker for predicting occurrence and deterioration of systemic sclerosis-associated interstitial lung disease from a Chinese cohort

AIM

A prospective and longitudinal study to investigate the correlations between Krebs von den Lungen-6 (KL-6) serum levels and systemic sclerosis associated with interstitial lung disease (SSc-ILD).

METHOD

Blood samples of baseline and the time point at 2 years follow-up intervals were collected for the measurement of serum KL-6 levels. The baseline clinical, laboratory characteristics, and incidence density of newly diagnosed ILD during the follow up were compared between SSc patients with elevated serum KL-6 levels (KL-6 > 500 U/mL) and those with normal KL-6 levels (KL-6 ≤ 500 U/mL) at baseline. Further, we explored the association between serum KL-6 and deterioration of ILD measured by lung function parameters during follow-up of 2 years.

RESULTS

Patients with elevated baseline serum KL-6 had a significant tendency to have disappearance of the finger pad. The incidence density of new-onset ILD in SSc patients with elevated baseline serum KL-6 and those with normal baseline serum KL-6 was 1.33% and 0.51%, respectively. Among the mild lung injury group, the incidence density of ILD deterioration in SSc patients with elevated baseline serum KL-6 and those with normal serum KL-6 was 1.2% and 0.74%, respectively.

CONCLUSION

Serum KL-6 level correlates with the clinical manifestations of microvascular injury. Baseline elevated serum KL-6 may predict deterioration of lung function of SSc-ILD patients with mild lung injury.