Systemic neutrophil activation and N-formyl methionine-formyl peptide receptor-1 signaling define inflammatory endotypes in rheumatoid arthritis-associated lung involvement.

Abstract

Background: Neutrophil activation plays a crucial role in the pathogenesis of rheumatoid arthritis (RA), but its involvement in RA-associated interstitial lung disease (RA-ILD) remains unclear. This study investigated the involvement of N-formyl methionine (fMET) and its receptor formyl peptide receptor-1 (FPR1) in neutrophil-mediated inflammation in RA-ILD.

Methods: Plasma and sputum levels of fMET and neutrophil activation markers were measured by ELISA in two cohorts (n = 269 and 314) spanning multiple disease subgroups. Neutrophil activation was assessed by flow cytometry following plasma stimulation, with or without FPR1 inhibitors.

Results: Calprotectin levels were significantly elevated in both plasma and sputum of RA-ILD patients compared to controls and RA-noILD patients (p < 0.05 for all analyses) and were negatively correlated with pulmonary function in RA (forced vital capacity [FVC], r = -0.39, p = 0.0002; diffusing capacity for carbon monoxide [DLCO], r = -0.39, p = 0.001). Plasma fMET levels were higher in RA-ILD patients compared to healthy controls (p < 0.0001) as well as compared to RA-noILD patients (p < 0.01), with a significant inverse correlation to pulmonary function in RA patients (FVC, r = -0.42, p < 0.0001; DLCO, r = -0.31, p = 0.01). Plasma from RA-ILD patients induced neutrophil activation through FPR1-dependent mechanisms (p < 0.0001). Hierarchical clustering identified reproducible subgroups defined by fMET and calprotectin, with the high-fMET cluster enriched for RA-ILD and associated with lower DLCO (p < 0.05).

Conclusions: The fMET-FPR1 axis is associated with neutrophil activation in RA-ILD and defines inflammatory endotypes associated with lung impairment. Neutrophil-based biomarkers may enable early risk stratification and provide rationale for targeting the fMET-FPR1 axis in RA-ILD.