Pulmonary fibrosis (PF) refers to a heterogeneous group of chronic, progressive, and irreversible interstitial lung diseases (ILDs) (1, 2). The pathological characteristics of PF are diffuse interstitial inflammation, structural destruction of lung tissue, and pulmonary parenchymal fibrosis, which ultimately leads to irreversible loss of lung function, and the clinical manifests including reduced lung compliance, impaired gas exchange, progressive dyspnea, and even respiratory failure (1, 3, 4). When the lungs are damaged, under the continuous action of damaging stimuli, lung tissue is repeatedly damaged, excessive deposition of extracellular matrix (ECM) components (including collagen, fibronectin, and proteoglycans) in the alveolar spaces and pulmonary interstitium, accompanied by abnormal activation, proliferation and differentiation of fibroblasts (4–6). PF encompasses a spectrum of disorders with distinct etiologies, including idiopathic pulmonary fibrosis (IPF), cystic pulmonary fibrosis (CF), asthma, silicosis, chronic obstructive pulmonary disease (COPD), etc. (1, 3, 7). Among them, IPF is the most common and severe form with unknown pathogenesis, and secondary PF associated with multiple factors, including, aging, environmental factors, toxic, autoimmune, drug-induced, infectious, or traumatic injuries (1, 3, 7) (Figure 1).

Currently, the prevalence of PF is on the rise worldwide, imposing a heavy disease burden with a notably high case fatality rate (8, 9). Despite the application of current antifibrotic therapies, the disease still carries a poor prognosis, with a median survival time of merely 5 to 7 years following diagnosis (10).

The clinical challenges associated with pulmonary fibrosis (PF) are mainly manifested in four key aspects: Firstly, the early clinical manifestations of PF are non-specific, which predisposes to misdiagnosis and thus delays the implementation of targeted therapeutic interventions (11, 12). Secondly, there is still no curative treatment for PF to date, and the available clinical medications only exert a disease-modifying effect to slow down its progressive course (13). Thirdly, the lack of sensitive and specific biomarkers has become a major bottleneck restricting the early diagnosis of PF (14). Fourthly, the clinical management of PF is further complicated by the presence of various comorbidities in affected patients (15).

Clinically, the currently recognized global classification system categorizes pulmonary fibrosis (PF) into two major subtypes: idiopathic pulmonary fibrosis (IPF) and non-idiopathic pulmonary fibrosis (non-IPF-PF) (1, 10). IPF represents the most common, typical and well-characterized subtype in clinical practice and basic research (16). By contrast, non-IPF-PF refers to fibrotic lesions with identifiable etiologies or triggering factors, encompassing cases induced by occupational exposure, underlying systemic diseases, pharmaceutical agents and physical-chemical insults (7).

Notably, these subtypes exhibit distinct core pathological features. IPF is pathologically defined by usual interstitial pneumonia (UIP) pattern, featured by patchy interstitial fibrosis, alternating fibroblastic foci, honeycomb lung formation, and minimal inflammatory cell infiltration (16). For environmental/occupational exposure-related PF—exemplified by silicosis fibrosis—the disease is initiated by long-term inhalation of free silica dust, with pathological hallmarks including pulmonary interstitial dust deposition, silicotic nodule formation, and nodule-centric progressive interstitial fibrosis, accompanied by prominent neutrophil-predominant inflammatory infiltration and extensive collagen deposition (17). Disease-associated PF displays heterogeneous pathological characteristics that vary with the primary disorder, and lacks the typical UIP pattern (1). PF induced by drugs or physical-chemical factors is predominantly characterized by diffuse alveolar and interstitial lung injury (18). In addition, recent research in the PF field have reported that progressive fibrotic interstitial lung disease (PF-ILD) characterized by persistent, progressive pulmonary fibrotic progression and a concomitant progressive decline in lung function (19).

The core pathological distinctions between IPF and non-IPF-PF subtypes are manifested in two key aspects: First, the immune microenvironment profiles differ substantially—IPF is characterized by a mild inflammatory infiltrative immune microenvironment, whereas non-IPF-PF features a robust inflammatory state with prominent infiltration of neutrophils and other inflammatory cells. Second, the rates of fibrotic progression vary: IPF typically presents with slow, progressive interstitial remodeling, while fibrotic progression in non-IPF-PF is closely coupled to the activity of the underlying primary disease (1, 16, 17).

In the human body, neutrophils are involved in innate immunity and adaptive immunity, and can interconnect and interact with a variety of immune cells, which is the first line of the body’s defense (20). NET is one kind of complex released by neutrophil that made up of DNA and a variety of granule proteins and peptides (21). These proteins and peptides include citrullinated histone (Cit-H3), neutrophil elastase (NE) and myeloperoxidase (MPO) etc. and them can be important markers and detection indicators in the detection of NET (22, 23).

At the site of inflammation, neutrophils release large numbers of NETs, which surround the invading pathogen and help leucocytes clear and engulf pathogens and other microorganisms (21). However, the overexpression of NETs will cause tissue damage and inflammation progress (24). Recent studies have shown that abnormally activated NETs can be used as key inflammatory mediators to participate in the pathological process of chronic inflammatory and fibrotic diseases by releasing pro-inflammatory factors, inducing cell activation, and damaging the tissue microenvironment (25). By blocking the formation of NETs or promoting the clearance of NETs, the progression of inflammation and tissue fibrosis can be effectively suppressed (23, 26). Therefore, we consider that NETs may be significant and vital target for investigate the mechanism of pathology, developing drugs and treating pulmonary fibrosis (Figure 2).

However, the crosstalk between NETs and fibroblasts/immune cells, potential NET-targeted therapeutic strategies, and the associated risks remain largely elusive—key questions that this review seeks to systematically clarify and address.

The formation of NETs is generally called NETosis and it’s actually a novel mode of death that distinguished from apoptosis and necrosis. There are three way of formation of NET according to different stimuli (21).

The first way, known as suicidal NETosis, is dependent on the involvement of NADPH oxidase and Raf/MEPK/ERK signaling pathway. This pathway causes plasma membrane rupture and cell death (23, 27). Neutrophil under the stimulation of phorbol ester (PMA), interleukin-1β (IL-1β) or others to activate protein kinase C (PKC) (28). NADPH oxidase will activated by Raf/MEPK/ERK signaling pathway and then stimulate the generation of reactive oxygen species (ROS) and Cit-H3 (27). The final cause rupture of nuclear membrane and release of NETs. On the contrary, the second way is vital NETosis, which independent on the involvement of NADPH and Raf/MEPK/ERK signaling pathway (29). The pathological feature of the formation is relatively intact nuclear membrane and cell membrane, and the activity and function of neutrophil are maintained (30). Some new studies of the third type of NETosis in recent years and it occur when neutrophil stimulated by Lipopolysaccharides (LPS) or Granulocyte-macrophage colony-stimulating factor (GM-CSF) (30, 31).

The core pathological feature of pulmonary fibrosis is the aberrant conversion of early inflammatory responses to late-stage irreversible fibrosis, with NETs acting as key regulators driving this process (53). NETs bridge the inflammation-fibrosis transition via three core nodes. First, NE, MPO, and other components released by NETs directly damage pulmonary epithelial cells, induce the infiltration of innate immune cells, and trigger the early inflammatory cascade (54, 55). Second, NETs modulate the polarization of immune cells toward profibrotic phenotypes (e.g., M2 macrophage polarization), shift the inflammatory microenvironment from an anti-inflammatory to a profibrotic state, and drive the secretion of fibrosis-related factors such as TGF-β1 and IL-17 (55–57). Third, NETs crosslink with ECM to form stable NET-ECM complexes; these complexes not only impede inflammatory resolution but also provide sustained microenvironmental signals for fibroblast activation, ultimately facilitating the irreversible conversion of inflammatory responses to fibrosis (56, 58, 59). In summary, NETs are not merely inflammatory mediators but core bridging molecules linking early inflammation to late-stage tissue remodeling in pulmonary fibrosis.

The central target of NETs to achieve bridging is fibroblasts. It precisely drives fibroblast activation and ECM deposition through direct contact and indirect signal regulation, and the specific mechanism is as follows (53, 58) (Figure 3).

On the one hand, NETs can bind directly to fibroblast surface receptors to initiate activation signals. In many related studies, it has been reported that NETs bind TLR9 receptors and RAGE receptors on the surface of fibroblasts, activating NF-kB pathway within fibroblasts, thereby promoting the secretion of pro-inflammatory factors (such as IL-6) and the deposition of ECM (53, 60, 61).

On the other hand, NETs indirectly activate fibroblast signaling pathways by regulating immune cell secretion of profibrotic cytokines. First, NETs induce macrophages to polarize toward the M2 phenotype, and M2 macrophages secrete TGF-β1. This cytokine binds to TGF-β receptors (TGF-βR) on the fibroblast surface, initiates Smad3 phosphorylation, and promotes fibroblast activation as well as collagen I/III synthesis (62–64). Second, NETs-mediated immune networks induce Th17 cells to secrete IL-17, and this cytokine binds to IL-17 receptors (IL-17R) on fibroblasts, activates NF-κB nuclear translocation, and enhances fibroblast proliferation and α-SMA expression (65, 66).

The mechanisms by which NETs drive pulmonary fibrosis exhibit marked heterogeneity across distinct pulmonary fibrosis subtypes, owing to differences in their immune microenvironment, etiology, and disease progression characteristics (67). NETs display subtype-specificity in their functional targets, core mechanisms, and effector intensity, as follows.

First, idiopathic pulmonary fibrosis (IPF) is characterized by low-grade inflammation, prominent fibrosis, and slow progression (1). The pathological effects of NETs in IPF are dominated by direct actions on fibroblasts and indirect effects mediated via the TGF-β1/Smad3 pathway (56). Given the mild inflammatory cell infiltration in IPF lung tissue, NETs do not depend on a robust inflammatory microenvironment, instead, they bind directly to fibroblasts via TLR9/RAGE receptors and synergize with M2 macrophage-secreted TGF-β1 to augment fibrotic effects (60, 61, 64). Additionally, NETs form complexes with dense ECM in IPF lung tissue, which acts as a persistent driver of fibrosis and constitutes a key underlying cause of the irreversible progression of IPF (58).

Second, non-IPF-PF, represented by silicosis, are characterized by robust inflammation, rapid progression, and a well-defined etiology (1). The pathological effects of NETs in this subtype are primarily mediated by the inflammation-fibrosis transition and indirect activation of the IL-17/NF-κB pathway (66, 68). Exogenous stimuli such as silica dust directly activate neutrophils to release NETs, provoking a vigorous early inflammatory response. NETs then rapidly drive the conversion of inflammation to fibrosis by augmenting the pro-fibrotic bias of the inflammatory response (54). Concurrently, NETs drive robust Th17 cell proliferation, which sustains the amplification of both inflammatory and fibrotic effects (69). Furthermore, NETs can bind to silica dust particles to form NET-dust complexes, thereby prolonging inflammatory stimulation and accelerating fibrotic progression (70).

As key innate immune inflammatory mediators, NETs directly or indirectly regulate the functions of macrophages and DCs, and the crosstalk between neutrophils and these two cell types further amplifies NETs production. NETs activate macrophages to release inflammatory factors, which in turn promotes neutrophil activation and NETosis (71). Meanwhile, NETs promote DC maturation and migration to lymph nodes and thus triggering subsequent adaptive immune activation (72, 73). DNA-Cit-H3 complexes bind to TLR4/TLR9 on the macrophage surface, activating the NF-κB pathway and inducing macrophages to secrete abundant pro-inflammatory factors (IL-6, IL-1β) and pro-fibrotic cytokines (TGF-β, IL-10), thereby initiating a pro-fibrotic inflammatory microenvironment and driving fibroblast activation (56, 74–76).

Mature DCs present NET-associated antigens to naïve T cells, and NETs directly activate T cell receptors via DNA-LL37 complexes, lowering T cell activation thresholds and selectively inducing Th17 cell differentiation. IL-17 secreted by Th17 cells in turn fuels this vicious circle (65). IL-17 not only promotes neutrophil activation and NETosis, but also directly activates the IL-17R-NF-κB pathway in fibroblasts to enhance their proliferation and ECM synthesis (66, 77, 78). This crosstalk is notably pronounced in autoimmune disease-associated PF and silicosis, serving as a key driver of sustained inflammatory amplification and accelerated fibrotic progression (79).

Innate-adaptive immune crosstalk ultimately forms a fibrosis-promoting closed-loop network via two pathways. First, various immune cell-secreted cytokines synergistically amplify profibrotic signals, encompassing multiple steps in fibroblast activation (77). Second, NETs co-bind with immune cell-secreted cytokines to fibroblast surface receptors, activating downstream signaling cascades (60). The core feature of this network is the sustained amplification of fibrotic signals, and elevated NETs sustain long-term profibrotic effects through this immune network (80).

The detrimental effects of NETs on the fibrotic pathological process stem from an imbalance between NET formation and clearance (80). Excessive NET release coupled with impaired clearance leads to their aberrant accumulation at the site of tissue injury. Such abnormal accumulation triggers the massive release of proinflammatory cytokines, which on the one hand act on various immune cells (e.g., macrophages), and on the other hand activate multiple intracellular signaling pathways; this consequently drives the progression of pulmonary fibrosis and causes repeated damage to pulmonary tissue cells. Therefore, current research into NET-targeted therapeutic strategies for pulmonary fibrosis focuses on three key approaches: 1) Inhibition and blockade of NETosis. 2) Elimination of preformed NETs. 3) Blockade of NET-associated signaling pathways (Table 1).

Although NET targeting strategies have shown potential in basic research and early clinical practice of PF, there are still multiple common challenges from the laboratory to clinical application, which are not only due to the characteristics of the drug itself, but also closely related to the disease complexity and patient heterogeneity of PF. Based on the existing research evidence, this part will systematically sort out the core conversion obstacles and propose feasible optimization directions.

First, there is currently no uniform NETs-related biomarker for stratification and efficacy assessment in PF patients. Commonly used markers such as cit-H3 and MPO in clinical practice are elevated in PF and other inflammatory lung diseases, lacking disease specificity (14). And these markers cannot judge the patient’s disease stage, resulting in strong blindness in the choice of treatment strategy. In addition, the expression profiles of NETs-related markers for different PF subtypes have not been well determined, further hindering the clinical translation of subtype-specific therapies.

Second, NETs-related signaling pathways (such as TGF-β, NF-κB) and key molecules (such as PAD4 and NE) are involved in normal physiological functions of the body, and most of the existing inhibitors are pan-targets, and long-term use may lead to off-target effects (97). However, PF patients themselves have impaired lung function, fragile immunity, and easy co-infection, and have a lower tolerance to off-target effects.

Third, the fibrosis process of PF is driven by multipathway synergy, and a single NET targeting strategy can easily trigger pathway compensation, resulting in limited clinical benefits of existing strategies in advanced PF and difficult to meet clinical needs (119).

Finally, there are obvious limitations to traditional drug administration. Nebulized inhaled DNase has difficulty penetrating the dense ECM to reach the lung interstitium deposited by NETs, while PF patients are mostly elderly and have poor adherence to long-term intravenous administration (99, 120). These administration-level issues further hinder clinical translation.

Future research should therefore be prioritized in the following aspects. Research should focus on leveraging multi-omics technologies to decode subtype-specific NETosis regulatory circuits, validating multi-parametric NETs-fibrotic biomarker panels through large-scale multi-center cohorts, optimizing and validating subtype-adapted combination therapies in preclinical models and biomarker-stratified clinical trials, and conducting large-scale observational studies to clarify long-term safety risks while establishing personalized monitoring systems, thereby advancing the clinical translation of NET-targeted strategies and promoting precision medicine for PF.

A systematic literature search was conducted in PubMed and Web of Science from database inception to January 2026, with no initial restrictions to ensure comprehensive coverage. The search combined Medical Subject Headings (MeSH) and free-text terms using Boolean operators (AND/OR), with the core strategy formulated as (neutrophil extracellular traps OR NETs OR NETosis) AND (pulmonary fibrosis OR idiopathic pulmonary fibrosis OR IPF OR silicosis OR interstitial lung disease OR ILD) to align with the review’s focus on NETs in pulmonary fibrosis (PF) and its key subtypes. Studies were included if they were English-language peer-reviewed publications (original basic/clinical research, reviews, meta-analyses, clinical trial data) focusing on NETs-related mechanisms, biomarkers or therapeutic strategies in PF with subtype-specific analysis (IPF/non-IPF-PF). Excluded studies comprised non-English articles, conference abstracts, unpublished data, case reports without mechanistic/therapeutic insights, research unrelated to NETs, in vitro/in vivo studies without clear PF-related outcomes or subtype stratification, and duplicate publications. Two independent investigators performed literature screening via title/abstract and subsequent full-text assessment, extracted key study data (design, core findings, quantitative results) and conducted cross-validation, with discrepancies resolved by a third senior investigator to minimize selection bias.