Interplay of inflammation and fibrosis in CTD-ILDs

Irrespective of the trigger for the lung injury, fibrosing connective tissue disease-associated interstitial lung diseases (CTD-ILDs) show commonalities in the pathogenic mechanisms driving fibrosis1-3

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THE PATHOGENESIS OF CTD-ILDs INVOLVES THE INTERPLAY OF INFLAMMATION AND FIBROSIS EARLY IN THE COURSE OF THE DISEASE4–6

SHARED PATHOGENIC MECHANISMS OF PULMONARY FIBROSIS IN CTD-ILDs

Learn about the pathophysiological mechanisms applicable to a broad range of fibrotic CTD-ILDs that can develop a progressive fibrosing phenotype

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The pathogenesis of fibrotic interstitial lung disease in connective tissue diseases involves a complex interplay of inflammatory and fibrotic processes. Patients with connective tissue diseases (CTDs), such as rheumatoid arthritis, systemic sclerosis and primary Sjogren’s syndrome, develop fibrotic interstitial lung disease (ILD) via common pathogenic processes, irrespective of the underlying diagnosis or trigger. Fibrotic ILD often develops early in the course of a CTD. For example, in a study of systemic sclerosis patients, approximately 24% of systemic sclerosis-associated ILD patients showed an extent of more than 10% pulmonary fibrosis on high-resolution computed tomography at their baseline systemic sclerosis diagnosis. At the cellular level, ILD in CTDs is triggered by repeated tissue injury which induces an inflammatory response, and releases probiotic mediators, including VEGF, PDGF and FGF. These contribute to the recruitment and activation of leukocytes and fibroblasts. Resulting in a complex interplay of inflammatory and fibrotic processes. Activation of leukocytes also produces profibrotic mediators leading to further activation of the fibrotic process with excessive secretion of extracellular matrix. Excess extracellular matrix increases lung tissue stiffness, further activating fibroblasts in a feed-forward loop of self-sustaining progressive pulmonary fibrosis. Pulmonary fibrosis causes irreversible destruction and architectural disruption of the lung tissue. Based on the pathogenesis of fibrotic interstitial lung disease in connective tissue diseases, a new treatment paradigm of CTD-ILDs suggests to not only target inflammation but also fibrosis.

While CTDs differ, common pathogenic pathways to fibrogenesis are shared irrespective of the trigger for the lung injury1–3,7

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Autoimmunity, and/or repetitive injury to the alveolar epithelium and/or vascular endothelium, can cause persistent fibroblast activation and progressive injury through vicious cycles of profibrotic events4,5,8,9

A complex interplay of inflammatory, fibrotic and vascular processes leads to the activation and proliferation of fibroblasts, their differentiation into myofibroblasts, and the excessive secretion of extracellular matrix4,5,10

Mechanisms behind inflammation and fibrosis in pathogenesis of CTD-ILDs4,8–16
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Fibrosis may have already affected ≥10% of your CTD patient’s lung volume on diagnosis of their ILD17,18

Find out how to diagnose ILD in your SSc patients as early as possible

Pulmonary fibrosis involves both fibrotic and inflammatory processes4,5– ensure you are targeting both in your patients with SSc-ILD and progressive fibrosing CTD-ILDs

Learn more about the management of SSc-ILD

Learn more about the management of progressive fibrosing ILD in patients with:

RA-ILD
Primary Sjögren’s syndrome-ILD

How can you identify fibrotic ILD early in your patients with CTDs?

Footnote

bFGF, basic fibroblast growth factor; CTD, connective tissue disease; CTD-ILD, connective tissue disease-associated interstitial lung disease; CTGF, connective tissue growth factor; EMT, epithelial-mesenchymal transition; HRCT, high-resolution computed tomography; ILD, interstitial lung disease; MMP, matrix metalloproteinase; PDGF, platelet-derived growth factor; PFT, pulmonary function test; TGF-β, transforming growth factor-β; TNF-α, tumor necrosis factor-α; TNF-β, tumor necrosis factor-β; VEGF, vascular endothelial growth factor.  

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