Pulmonary Fibrosis and COVID-19 Impacts

Pulmonary fibrosis has emerged as a significant long-term complication of severe COVID-19, characterised by irreversible distortion of lung architecture and persistent impairment of gas exchange. Following acute viral injury, a subset of patients develops chronic interstitial remodelling marked by extracellular matrix deposition, fibroblast activation and loss of normal alveolar structure. The interplay between dysregulated immune responses, vascular injury and profibrotic signalling pathways underpins this process. Clinically, survivors may experience diminished exercise tolerance, reduced diffusing capacity and persistent radiographic abnormalities, posing challenges for rehabilitation and long-term care. Globally, the burden of post-COVID fibrosis underscores the need for early identification of at-risk individuals, monitoring strategies and interventions to mitigate progression.

Research from Nature Portfolio

Recent studies have elucidated local immune–stromal interactions that sustain lung injury beyond viral clearance. In severe cases, specialised peri-vascular zones known as adventitial niches become activated, up-regulating chemokines such as CCL18 and CCL21. This chemokine milieu promotes endothelial-to-mesenchymal transition, driving fibroblast accumulation and matrix deposition, while exhausted T-cell aggregates form ectopic lymphoid structures that perpetuate inflammation and remodelling. Another body of work has revealed that in critically ill patients, B-cell precursors termed plasmablasts are instructed by transforming growth factor-β to produce non-protective immunoglobulin isotypes, notably IgA2, instead of targeting the virus. This chronic TGF-β-dominated response appears to divert immune resources towards fibrotic pathways rather than viral neutralisation, linking sustained immune activation to tissue fibrosis.

Pulmonary Fibrosis and COVID-19 Impacts publication trend

The graph below shows the total number of articles in pulmonary fibrosis and covid-19 impacts across all publications each year (not limited to Nature Index journals).

Technical terms

Endothelial-to-mesenchymal transition (EndMT): A process by which endothelial cells lose their specialised characteristics and acquire a mesenchymal, fibroblast-like phenotype, contributing to tissue fibrosis.

Adventitial niche: Functional microenvironments in the outer layer of blood vessels where immune, stromal and vascular cells interact to regulate tissue homeostasis and pathology.

Transforming growth factor-β (TGF-β): A multifunctional cytokine that orchestrates cell proliferation, differentiation and extracellular matrix production, pivotal in fibrotic disease.

Plasmablast: An activated B-cell derivative that rapidly secretes antibodies but has limited longevity compared with mature plasma cells.

High-resolution computed tomography (HRCT): An imaging modality that provides detailed cross-sectional views of lung parenchyma, essential for detecting and monitoring interstitial changes.

References

1. Distinct tissue niches direct lung immunopathology via CCL18 and CCL21 in severe COVID-19. Nature Communications (2023).
2. Diverse roles of SARS-CoV-2 Spike and Nucleocapsid proteins in EndMT stimulation through the TGF-β-MRTF axis inhibited by aspirin. Cell Communication and Signaling (2024).
3. SARS-CoV-2 in severe COVID-19 induces a TGF-β-dominated chronic immune response that does not target itself. Nature Communications (2021).
4. The characteristics and evolution of pulmonary fibrosis in COVID-19 patients as assessed by AI-assisted chest HRCT. PLOS ONE (2021).
5. Pulmonary fibrosis and its related factors in discharged patients with new corona virus pneumonia: a cohort study. Respiratory Research (2021).