NOX2-deficient neutrophils facilitate joint inflammation in immune-mediated arthritis

Abstract

Abstract Immune-mediated inflammatory arthritis, including rheumatoid arthritis (RA), is characterized chronic inflammatory in the joints. NADPH oxidases 2 (NOX2) complex in phagocytes mediates the generation of high concentrations of reactive oxygen species (ROS) to kill the engulfed microbes. Inherited mutations in the subunits of NOX2 result in chronic granulomatous disease (CGD). CGD patients experience recurrent infections and diverse autoimmune conditions including arthritis. In our previous studies, we found that NOX2-deficient mice tended to have more severe inflammatory arthritis and neutrophils accumulation. Based on the hypothesis that NOX2-deficient neutrophils play a role in facilitating immune-mediated arthritis, we investigated the activity of neutrophil from inflamed joints. We found that while neutrophils from both NOX2-deficient and WT mice weakened the anti-CD3 and anti-CD28 induced T lymphocyte responses, NOX2-deficient neutrophils were less suppressive. Down-regulated PD-L1 expression on NOX2-deficient neutrophils was observed, which could be a cause for their impaired suppressive function. Moreover, pro-inflammatory genes, including IL-1b, NOS2, and Cxcl3 were up-regulated in NOX2-deficient neutrophils according to our RNA-seq results. In humans, neutrophils from RA joints were found to suppress the T cell proliferation. Consistent with our mice model, carbonylated protein and total GSH level, the oxidative markers, were lower in synovial fluid of RA patients. Our results implicate that neutrophil-mediated immune regulation may be an important factor in controlling inflammation in the joints, and this regulation is affected by the NOX2-produced ROS.