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Histochemical detection of oxidative stress in synovial tissue: spontaneous reactive oxygen species (ROS) production by rheumatoid arthritis T cells

Background

Oxidative stress is thought to underlie the altered pathogenic behavior of T cells in rheumatoid arthritis (RA). We recently demonstrated that intracellular signaling by Ras family GTPases leads to ROS production in RA synovial fluid (SF) T cells. However, other cellular sources of ROS may cause oxidative stress in RA synovial tissue (ST).

Objectives

The study was conducted to determine whether T cells or other cells spontaneously produce ROS in RA ST, to determine the specificity of T cell ROS production in long-standing RA versus early RA and osteoarthritis (OA) T cells, and to identify signaling pathways producing ROS in RA ST and SF T cells.

Methods

ROS production was assessed using ROS-dependent polymerization of diaminobenzidine (DAB) on cryostat sections of ST from patients with long-standing RA, early RA, and OA (n = 10 patients in each group), purified RA patient peripheral blood (PB) and SF mononuclear cells, and purified T cells (n = 4), and oxidation of the dye DCF by FACS analysis of purified RA PB and SF T cells (n = 10), in the absence or presence of pharmacological inhibitors. Cryostat sections were double labelled with DAB and cell-specific antibodies to quantify ROS-producing cells.

Results

ROS production was observed in both longstanding and early RA, but not OA ST. ROS production was observed only in T cells (68%) and neutrophils (15%). In RA ST, ROS producing T cells were observed in the synovial sublining and perivascular tissue. Catalase and BAPTA-AM, but not other ROS inhibitors, blocked ROS production in ST and SF T cells. Intracellular ROS production is detected in ST of patients with RA but not OA. T cells are the major source of intra-cellular ROS production in RA ST. Conserved signaling pathways regulate ROS production in ST, SF and Jurkat T cells. ROS production is observed in recently extravasated T cells, indicating that oxidative stress is an early event affecting T cell function in the RA synovial joint.

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Keywords

  • Rheumatoid Arthritis
  • Synovial Fluid
  • Reactive Oxygen Species Production
  • Synovial Tissue
  • Early Rheumatoid Arthritis