Systemic autoimmune rheumatic disease-associated interstitial lung disease (SARD-ILD) occurs across a spectrum of systemic autoimmune rheumatic diseases—including rheumatoid arthritis (RA), systemic sclerosis (SSc), microscopic polyangiitis (MPA), Sjögren’s disease (SjD), idiopathic inflammatory myopathies (IIM), and mixed connective tissue disease (MCTD)—and represents a major driver of morbidity and mortality. Conventional models emphasize dysregulated fibroblast activation as the proximate cause of fibrotic remodeling, and currently used therapies primarily aim to inhibit fibroblast activation but generally delay rather than reverse fibrosis.
Recent work highlights the potential contribution of immune–microenvironment imbalance and oxidative stress to disease progression. Within this context, regulatory T cells (Tregs)—defined by CD4+ CD25+ phenotype and Foxp3 expression—are central mediators of immune tolerance and control of excessive inflammation. The reviewed article distinguishes four related but non-equivalent dimensions of Treg abnormality: numerical changes in abundance; alterations in regulatory phenotype or molecular programs (for example, CD25/CTLA-4 pathways and IL-10/IL-35 production); loss of lineage stability (unstable Foxp3 expression or acquisition of effector-like features); and impaired suppressive capacity as measured by functional assays. The term “Treg dysfunction” is reserved mainly for loss of lineage stability or demonstrable loss of suppressive function, whereas isolated changes in cell counts or marker expression are treated as associated observations unless supported by functional data.
Evidence for Treg involvement in SARD-ILD is heterogeneous and derives from human SARD-ILD studies, other ILD cohorts (including IPF), related autoimmune diseases, and experimental models. For example, observations that hilar lymphadenopathy correlates with worse survival in fibrotic ILD suggest altered adaptive immune responses in lung-draining lymph nodes, but direct attribution to Treg dysfunction remains unproven.
Loss of Foxp3 stability is a key mechanism by which Tregs can lose regulatory function and acquire effector-like properties. Foxp3 is a master transcriptional regulator of Treg development and suppressive function; however, changes in Foxp3 expression alone do not inevitably equate to functional loss. Multiple regulatory elements within the Foxp3 locus (CNS0, CNS2, CNS3) coordinate development and maintenance of lineage stability.
Experimental studies implicate specific regulators of Foxp3 stability. The transcription factor BATF supports Foxp3 transcription and Treg lineage maintenance partly via interaction with the CNS2 enhancer; Treg-specific BATF deficiency in mice produces “ex-Treg” cells with Th17/effector-like characteristics and prominent lung immune-cell infiltration in experimental settings. Other perturbations—such as IL-18–mediated enhancement of Foxp3 ubiquitination, or loss of IKZF1 function disrupting Foxp3-associated regulatory complexes—have been described in autoimmune contexts and can shift Tregs toward unstable or proinflammatory phenotypes. These mechanistic insights are mainly derived from non-pulmonary or experimental autoimmune models and have not been directly validated as causal in human SARD-ILD.
Altered Treg stability can favor increased Th1 responses and IFN-γ production, thereby sustaining inflammatory injury. The review emphasizes that while these mechanisms plausibly link Foxp3 instability to tissue inflammation and remodeling, a direct causal chain from Foxp3 instability to pulmonary fibrosis in human SARD-ILD has not been established.
Tregs exert context-dependent effects in lung injury and repair. Experimental models show that impaired Treg homeostasis can associate with immune imbalance, pulmonary fibrosis, and vascular remodeling, whereas restoration of Tregs (for example, by adoptive transfer or low-dose IL-2) ameliorates pulmonary abnormalities in some models. Conversely, certain Treg phenotypes or mediators can have pro-remodeling effects:
Human IPF studies illustrate the complexity: peripheral blood and bronchoalveolar lavage Tregs in IPF showed globally impaired suppressive function correlated with disease severity, and certain expanded Treg subsets in progressive IPF expressed reduced regulatory genes (including IL-10) and promoted fibrosis in experimental transfers. These data underscore that increased Treg abundance does not imply preserved function and that selected Treg phenotypes may acquire pro-remodeling properties in fibrotic lung environments.
Overall, the evidence supports a potentially important but context- and stage-dependent role for Tregs in pulmonary fibrotic remodeling. Importantly, much of the mechanistic insight arises from animal models, IPF cohorts, or non-pulmonary autoimmune research rather than direct human SARD-ILD tissue-based mechanistic studies.
Oxidative stress—characterized by excess reactive oxygen species (ROS) and reactive nitrogen species (RNS)—is implicated in pulmonary fibrotic remodeling through alveolar epithelial cell injury, macrophage polarization, myofibroblast differentiation, and extracellular-matrix remodeling. Treg homeostasis and function are metabolically and redox-sensitive: Tregs rely substantially on oxidative phosphorylation (OXPHOS) and fatty acid oxidation (FAO) for metabolic fitness and suppressive programs, and mitochondrial integrity is important for Treg suppressive capacity.
The review integrates experimental evidence suggesting that oxidative stress can destabilize Tregs through multiple interrelated mechanisms, including redox-sensitive regulation of Foxp3 expression and stability, disruption of IL-2 signaling, metabolic perturbations of mitochondrial function, and remodeling of the inflammatory microenvironment via pro-inflammatory macrophage responses. Specific mechanistic examples cited in related settings include ACC1-regulated mitochondrial metabolism influencing Treg suppression and ROS-dependent SOCS3 upregulation destabilizing Tregs in experimental autoimmune contexts. These interactions may contribute to a self-reinforcing cycle whereby oxidative stress impairs Tregs, leading to heightened effector T-cell activation, macrophage-driven inflammation, and fibroblast proliferation that further promotes fibrosis.
However, the review repeatedly notes that the majority of mechanistic evidence for oxidative stress–driven Treg dysregulation comes from experimental models, IPF, or other autoimmune conditions, and direct validation in human SARD-ILD—particularly from lung tissue or bronchoalveolar lavage samples—is limited.
The authors emphasize heterogeneity in the evidence base and caution that findings extrapolated from experimental models or non-pulmonary autoimmune diseases should be viewed as hypothesis-generating for SARD-ILD rather than definitive proof. Direct mechanistic data from patients with SARD-ILD, especially tissue-level analyses, remain sparse. Consequently, the proposed oxidative stress–Treg dysregulation framework is presented as a potentially convergent but subtype-dependent hypothesis rather than a unified pathogenic mechanism proven across all SARD-ILD subtypes.
The review proposes an integrated framework in which oxidative stress perturbs Treg lineage stability and suppressive function via redox-sensitive molecular pathways (including Foxp3 regulatory elements and metabolic regulators), thereby favoring effector T-cell activation, dysregulated macrophage responses, and fibroblast proliferation that contribute to pulmonary fibrotic remodeling. Experimental interventions that restore Treg numbers or function (for example, adoptive transfer or low-dose IL-2 in animal models) can ameliorate pulmonary abnormalities, suggesting potential therapeutic avenues.
Nevertheless, the article underscores the need for focused, disease- and tissue-specific mechanistic studies in human SARD-ILD to validate targets and inform precision therapeutic strategies. Where the provided source text ends, further sections on oxidative stress mechanisms and additional translational recommendations were not reported in the excerpt and therefore cannot be summarized here.