Review: Surfactant Protein D and KL-6 in Scleroderma-Related Interstitial Lung Disease

Introduction

Systemic sclerosis (scleroderma, SSc) is a rheumatic disease of unknown etiology. It is a connective tissue disorder characterized by three major processes: organ fibrosis, small vessel vasculopathy, and disease-specific autoantibodies. Fibrosis can affect virtually any organ system, and the respiratory system is the leading cause of mortality and considerable morbidity. Although the pulmonary system can be affected in a variety of ways in SSc, interstitial lung disease is the most common manifestation. Virtually any patient with SSc can develop ILD, including those patients with diffuse cutaneous SSc (dcSSc), limited cutaneous systemic sclerosis (lcSSc, formerly CREST syndrome), SSc sine scleroderma, and overlap conditions.

Abstract

This article will review the clinical background and significance of two promising serum biomarkers that have been studied in relation to systemic sclerosis (scleroderma, SSc). Systemic sclerosis is a rare and difficult to treat connective tissue disease, with pulmonary involvement being the leading cause of mortality. The most common pulmonary manifestation in SSc is interstitial lung disease (SSc-ILD), and noninvasive serum markers to evaluate and monitor patients and their lung disease are being sought. Krebs von den Lungen-6 (KL-6) and surfactant protein D (SP-D) are glycoproteins secreted by type II pneumocytes. Serum levels of KL-6 and SP-D have been shown in several studies to correlate with the presence of interstitial lung disease in patients with a variety of lung conditions including SSc-ILD. In this article, we will examine the background and significance of these glycoproteins and assess their role to this point as biomarkers of SSc-ILD.

Keywords

systemic sclerosis, scleroderma, interstitial lung disease, biomarkers, KL-6, surfactant protein D