Neutrophils are found in abundance in the synovial fluid of patients with rheumatoid arthritis (RA), where they are activated and show high reactive oxygen species (ROS) production. However, there is limited data on circulating neutrophils in peripheral blood of patients with RA in terms of ROS production, expression of activation markers and the effect of treatment with methotrexate (MTX) on ROS.
This single-centre prospective study recruited patients of RA classified as per the 2010 ACR/EULAR criteria. In the cross-sectional arm, we included three groups, treatment-naïve RA (naïve-RA), MTX-treated RA (MTX-RA) and healthy controls, and compared ROS production and surface markers of neutrophil activation. In the longitudinal arm, we studied the change in neutrophil ROS production after 8 weeks of MTX treatment in naïve-RA patients. Neutrophil ROS production was measured by flow cytometry using dihydrorhodamine-123 (DHR) and by chemiluminescence using luminol. Surface expression of CD177, CD11b and CD64 was measured by flow cytometry.
This study included 103 patients (50 naïve-RA, 53 MTX-RA) and 20 controls. Both naïve-RA and MTX-RA patients showed higher ROS production than healthy controls in unstimulated neutrophils in the DHR assay (p<0.001 and p=0.004). MTX-RA patients showed significantly lower ROS production than naive-RA, in both unstimulated (p=0.004) and PMA-stimulated neutrophils in the DHR assay (p=0.03). On longitudinal follow-up of 24 naïve-RA patients, there was a significant reduction of neutrophil ROS production (by 55% from baseline) (p<0.001) after 8 weeks of MTX. Neutrophil CD177 expression was higher in both naïve-RA and MTX-RA (trend) than controls (p=0.001 and p=0.09). MTX-RA neutrophils showed lower expression of CD177 than naïve-RA (p=0.01). CD11b expression was higher in MTX-RA compared to controls (p=0.01).
Circulating neutrophils in RA showed higher ROS production and higher expression of CD177 and CD11b compared to controls. MTX treatment was associated with a reduction in ROS production and CD177 expression, which may be one of the mechanisms by which MTX works in RA.