Elevated ST2⁺ Tregs in RA-ILD: correlation with pulmonary fibrosis and the IL-33/ST2/AREG axis

Interstitial lung disease (ILD) represents a significant extra-articular complication associated with rheumatoid arthritis (RA), contributing substantially to the morbidity and mortality observed in affected patients. Despite its clinical relevance, the underlying mechanisms driving the pathogenesis of RA-ILD remain poorly understood, necessitating further investigation into the immunological factors that may play a role in this condition.

This study aimed to elucidate the role of ST2⁺ regulatory T cells (Tregs) in the progression of RA-ILD. To achieve this, we developed a composite murine model that integrated collagen-induced arthritis (CIA) with intratracheal bleomycin (BLM) administration, thereby simulating the pathophysiological features of RA-ILD. Concurrently, using flow cytometric and artificial intelligence-based quantitative analysis of high-resolution computed tomography (HRCT), we analyzed a clinical cohort consisting of healthy controls, RA patients without ILD (RA-nonILD), and RA patients with ILD (RA-ILD).

Histopathological assessment confirmed that the composite model exhibited exacerbated lung inflammation and fibrosis. Notably, flow cytometry revealed a marked expansion of ST2⁺ Tregs in both the lungs of CIA + BLM mice and the peripheral blood of RA-ILD patients. Moreover, quantitative HRCT analysis indicated a positive correlation between the frequency of ST2⁺ Tregs and fibrotic lung volume in patients. RA-ILD patients exhibited elevated serum levels of IL-33 and amphiregulin (AREG), which correlated with disease severity. In vitro studies further demonstrated that IL-33 stimulation significantly upregulated AREG expression at both the mRNA and protein levels in Tregs.

These results highlight the potential involvement of the IL-33/ST2 axis in mediating a pathogenic Tregs response characterized by AREG production, thereby linking systemic autoimmunity to the progression of lung fibrosis in RA-ILD. Importantly, this study identifies the IL-33/ST2/AREG axis and ST2⁺ Tregs as promising biomarkers and therapeutic targets for RA-ILD, laying the groundwork for future mechanistic studies and translational research endeavors.