Review: Serum Biomarkers of Lung Fibrosis in Interstitial Pneumonia with Autoimmune Features—What Do We Already Know?

Ewa Miądlikowska,Adam Jerzy Białas,Patrycja Rzepka-Wrona,Joanna Miłkowska-Dymanowska,Wojciech Jerzy Piotrowski

doi:10.3390/jcm11010079

Abstract

Interstitial pneumonia with autoimmune features (IPAF) belongs to a group of diseases called interstitial lung diseases (ILDs), which are disorders of a varied prognosis and course. Finding sufficiently specific and sensitive biomarkers would enable the progression to be predicted, the natural history to be monitored and patients to be stratified according to their treatment. To assess the significance of pulmonary fibrosis biomarkers studied thus far, we searched the PubMed, Medline and Cochrane Library databases for papers published between January 2015 and June 2021. We focused on circulating biomarkers. A primary review of the databases identified 38 articles of potential interest. Overall, seven articles fulfilled the inclusion criteria. This review aims to assess the diagnostic and prognostic value of molecules such as KL-6, SP-A, SP-D, circulating fibrocytes, CCL2, CXCL13, CXCL9, CXCL10 and CXCL11. All of these biomarkers have previously been studied in idiopathic pulmonary fibrosis (IPF) and connective tissue disease-associated interstitial lung disease (CTD-ILD). IPAF is a disorder of a heterogeneous nature. It explains the lack of coherent observations in terms of correlations with functional parameters. There is still no meta-analysis of pulmonary fibrosis biomarkers in IPAF. This is mainly due to the heterogeneity of the methodology and groups analysed in the research. More research in this area is needed.

Highlights

Interstitial pneumonia with autoimmune features (IPAF) is a relatively novel disorder developed in 2015 by the European Respiratory Society/American Thoracic Society Task Force on Undifferentiated Forms of Connective Tissue Disease-Associated Interstitial Lung Disease [1]
The Krebs von den Lungen-6 (KL-6), SP-A and SP-D levels were higher in IPAF than in a healthy group and non-fibrotic lung diseases
The serum levels of CXCL13, CXCL-9, CXCL10 and CXCL11 in IPAF patients were elevated compared to idiopathic pulmonary fibrosis (IPF) patients

Summary

Introduction

Interstitial pneumonia with autoimmune features (IPAF) is a relatively novel disorder developed in 2015 by the European Respiratory Society/American Thoracic Society Task Force on Undifferentiated Forms of Connective Tissue Disease-Associated Interstitial Lung Disease [1]. The mentioned publication aimed to identify, describe and study patients with interstitial lung disease (ILD) who display some symptoms of autoimmunity, but do not meet established criteria for any connective tissue disease. It is estimated that approximately 7% of ILD patients may be diagnosed with IPAF [2]. It affects mostly women in the 6–7th decades of their lives. Distinct results were described in Oldham’s research—the cohort study reports a high proportion of usual interstitial pneumonia (UIP). This is mostly likely due to the fact that the study was conducted retrospectively in the reference centre for IPF patients

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Discussion

Conclusion