Senescent Lung Fibroblasts in Pulmonary Fibrosis Mount a Broken Antiviral Response

Senescent fibroblasts from lungs scarred by idiopathic pulmonary fibrosis respond to influenza A virus in a way that looks antiviral on paper but fails in practice, according to a new laboratory study of primary human cells. Although the fibrotic cells switched on many of the same virus-response genes as senescent healthy lung fibroblasts, they produced lower viral titers, secreted less of a key inflammatory messenger, and proved largely independent of the IRF3 and STAT1 signaling axes that healthy senescent cells rely on to control infection. The findings portray these fibrotic stromal cells as trapped in a state that is transcriptionally activated yet functionally incompetent, offering a mechanistic clue to why patients with idiopathic pulmonary fibrosis are so vulnerable to respiratory viral infections.

Idiopathic pulmonary fibrosis is a progressive and irreversible scarring disease of the lung that is increasingly understood as an age-associated disorder rather than one in which aging is merely a demographic backdrop. Cellular senescence, one of the hallmarks of aging, has emerged as a central process in this pathology. Senescent cells accumulate in fibrotic lung tissue, and experimental work has shown that clearing them can attenuate pulmonary fibrosis in animal models. Fibroblasts, the cells responsible for depositing excess extracellular matrix in the diseased lung, display senescence-associated phenotypes including resistance to apoptosis, mitochondrial dysfunction, telomere abnormalities, and a pro-inflammatory secretory program known as the senescence-associated secretory phenotype.

Respiratory infections matter enormously in this disease. They have been implicated not only as cofactors of progression but also as potential triggers of acute exacerbations, the most devastating complication of idiopathic pulmonary fibrosis, in which reported mortality often exceeds 50 percent despite therapeutic intervention. Influenza A virus, a major cause of viral lower respiratory tract infection worldwide, has been among the pathogens implicated in these episodes. This clinical vulnerability suggested to the researchers that impaired local host defense might be a relevant component of fibrotic lung disease, and that the fibroblast compartment, far from being a passive bystander, could be an active participant in antiviral defense gone wrong.

To test this, the team worked with primary lung fibroblasts from healthy donors and from patients with idiopathic pulmonary fibrosis, derived from adult donors aged 37 to 61. Senescence was induced by exposing the cells to 15 Grays of gamma irradiation, a well-established method that triggers senescence primarily through DNA double-strand breaks. Ten days later, the senescent cells, along with quiescent controls maintained by serum starvation, were infected with influenza A virus of the H1N1 Puerto Rico/8/1934 strain at a multiplicity of infection of 1 for 24 hours, a time point chosen because prior work in human lung fibroblasts showed robust viral load and broad interferon-stimulated gene expression at that stage. The researchers then profiled gene expression by bulk RNA sequencing and measured viral replication and cytokine secretion directly.

Before any senescence or infection, an important baseline difference was already visible. In quiescent fibroblasts from fibrotic lungs, viral-associated gene pathways, including interferon response signaling, negative regulation of viral processes, and viral genome replication, were repressed relative to healthy fibroblasts. Transcription factor enrichment analysis predicted reduced activity of antiviral regulators such as IRF1, STAT1, and STAT3 in the fibrotic cells. This dampened starting point raised the possibility that fibrotic fibroblasts might respond to infection with an exaggerated compensatory reaction, a hypothesis the study ultimately did not confirm in its simplest form.

After senescence and infection, the two cell types activated broadly similar canonical viral response programs at the pathway level, and both upregulated more genes than they downregulated. But the fibrotic cells mounted a larger individual-gene response, with 176 uniquely and significantly upregulated genes, including antiviral effectors such as OAS1, OAS2, MX1, RSAD2, and the chemokine CXCL10, several of which rose only in the infected senescent fibrotic condition. Metabolic pathways told a different story: fibrotic fibroblasts showed persistent depletion of mitochondrial translation, respiratory electron transport, and oxidative phosphorylation programs both before and after senescence and infection, while healthy fibroblasts enriched for these pathways after infection, hinting at a metabolic constraint that could limit the translation of antiviral transcripts into protein.

The functional measurements, however, inverted expectations. Senescence increased viral titers relative to quiescent controls in both healthy and fibrotic cells, supporting the idea that senescent cell states can promote viral permissiveness. Yet senescent fibrotic fibroblasts carried significantly lower viral titers than senescent healthy fibroblasts 24 hours after infection, a pattern mirrored by intracellular viral RNA. At the same time, a multiplex cytokine assay revealed a general trend toward reduced pro-inflammatory cytokine production in the infected fibrotic cells, with IP-10, the protein encoded by CXCL10 and critical to the inflammatory response to influenza, significantly lower in both quiescent and senescent fibrotic fibroblasts. The cells that transcribed the most antiviral genes were thus not the cells that produced the strongest inflammatory output.

Network-level analysis sharpened this picture. Weighted gene correlation network analysis identified two gene modules, one enriched for viral response genes including the RNA sensor RIG-I and another enriched for cell-cycle genes, that were significantly correlated with the infected senescent healthy fibroblast state but not with the infected senescent fibrotic state. Transcription factor inference predicted higher activity of STAT1 and IRF3, each with an activity score roughly five points higher, in the infected senescent fibrotic cells than in healthy ones. When the researchers knocked down IRF3 or STAT1 with siRNA before infection, senescent healthy fibroblasts showed clear dependence on these nodes: IRF3 depletion was accompanied by a lack of increase in viral plaque formation, and depletion of either factor significantly reduced interferon-beta secretion. In senescent fibrotic fibroblasts, the same knockdowns produced only milder changes, and interferon-stimulated gene induction appeared largely independent of IRF3 and STAT1, indicating that residual antiviral control in these cells does not run through the canonical interferon signaling axis.

Taken together, the results define senescent fibrotic lung fibroblasts as a dysfunctional antiviral stromal state in which viral sensing remains inducible but its downstream execution is disabled. The authors note that this uncoupling of transcriptional activation from functional defense is consistent with broader patterns in aging biology, in which cellular stress responses persist but fail to trigger appropriate effector function. In the lung, such a state could blunt paracrine immune signaling, delay recruitment of immune cells, and prolong viral persistence, feeding a detrimental feedback loop of injury and aberrant repair. Because influenza infection has been shown to trigger acute exacerbations in idiopathic pulmonary fibrosis, impaired viral clearance in the fibroblast compartment could plausibly worsen outcomes through prolonged cellular injury or increased secretion of profibrotic factors such as TGF-beta, although the study itself did not test these downstream clinical consequences directly.

The authors also flag important limitations. Only one mode of senescence induction, irradiation, was used, and other triggers such as oncogene-induced or mitochondrial dysfunction-induced senescence can produce distinct senescent phenotypes. Protein-level confirmation of the knockdown was limited to two senescent healthy replicates because of cell availability, and phosphorylated IRF3 was inconsistently reduced in those samples. The senescence-associated secretory phenotype findings rest on gene expression alone and require protein-level verification, and the network analysis was performed on a sample size below the commonly recommended threshold for full statistical power. Even so, the study’s central message stands: senescence in fibrotic lung fibroblasts does not simply amplify inflammation, but produces a partially activated yet biologically incompetent antiviral state, pointing toward therapeutic strategies that restore coordinated interferon responsiveness rather than indiscriminately boosting inflammatory signaling in the aging fibrotic lung.

Subject of Research: Dysregulated antiviral interferon responses in senescent lung fibroblasts from idiopathic pulmonary fibrosis patients infected with influenza A virus

Article Title: Cellular Senescence Dysregulates Antiviral Interferon Responses in Idiopathic Pulmonary Fibrosis

Article References: Hughes, J.-W. B., Reisser, Y., Hornung, F., Hilsabeck, T. A. U., Senchyna, F., Coelho, A. L., Ho, T.-C., Schneider, K., Furman, D., Hogaboam, C. M., Le Saux, C. J., Desprez, P.-Y., & Deinhardt‐Emmer, S. (2026). Cellular Senescence Dysregulates Antiviral Interferon Responses in Idiopathic Pulmonary Fibrosis. Aging Cell, 25(11), Article e70763. https://doi.org/10.1111/acel.70763

Image Credits: AI Generated

DOI: 10.1111/acel.70763

Keywords: idiopathic pulmonary fibrosis, cellular senescence, influenza A virus, lung fibroblasts, IRF3, STAT1, interferon, antiviral response, acute exacerbation, RNA sequencing, senescence-associated secretory phenotype, innate immunity