Exaggerated neutrophil activation and formation of neutrophil extracellular traps (NETs) are linked to inflammation and autoimmunity, including rheumatoid arthritis (RA). However, whether NETs are present in the circulation of RA patients and contribute to inflammation and disease progression has not been carefully addressed. Here we assess markers of neutrophil activation and NET formation in plasma samples, asking whether they add clinical value in improving on determination of prognosis and monitoring in RA patients.
Markers of neutrophil activation (calprotectin) and cell death (NET) were analyzed in plasma from three cross-sectional RA cohorts and healthy individuals using ELISA. A longitudinal inception cohort (n=247), seen for follow-up a median of 8 years later was used for predictive analyses.
Markers of neutrophil activation and cell death were increased in RA patients compared to healthy individuals (p<0.0001). Calprotectin levels correlated with CDAI (r=0.53, p<0.0001) and distinguished between patients in remission and active disease, an observation not seen with CRP. A biomarker panel consisting of ACPA and calprotectin could predict erosive disease (OR=7.5, p<0.0001) and joint space narrowing (OR=4.9, p=0.001). Levels of NETs were associated with heightened levels of cell-free citrulline (p=0.02) and inflammation (p=0.0002). Furthermore, NETs, and a ‘neutrophil activation signature’ biomarker panel, had good predictive value in identifying patients developing extra-articular nodules (OR=5.6, p=0.006).
Neutrophils undergo marked activation and cell death in RA. Neutrophil biomarkers provide added clinical value in monitoring and prognosis of RA patients, and may allow for early preventive treatment intervention.