Background/Aims: To clarify the clinical significance of tumor necrosis factor (TNF) receptors in patients with myeloperoxidase (MPO)-anti-neutrophil cytoplasmic autoantibody (ANCA)-associated vasculitis, we evaluated the cell surface expression of TNF receptor 1 (TNFR1) and TNF receptor 2 (TNFR2). Patients and Methods: 43 patients with MPO-ANCA-associated vasculitis, 16 patients with chronic renal failure, 10 patients with sepsis, 15 patients with systemic lupus erythematosus, and 18 healthy controls were enrolled in this study, and the surface expression levels of TNFR1, TNFR2, CD63, and CD64 on granulocytes were assessed. In 21 patients with MPO-ANCA-associated vasculitis, soluble TNFR1 (sTNFR1), soluble TNFR2 (sTNFR2), and TNF-alpha in the serum were also measured. Results: The surface expression levels of TNFR1 and TNFR2 on granulocytes were significantly higher in patients with MPO-ANCA-associated vasculitis than in the healthy controls, and positively correlated with the Birmingham Vasculitis Activity Score (BVAS). The levels of sTNFR1, sTNFR2, and TNF-alpha in the serum were also significantly higher in patients with MPO-ANCA-associated vasculitis than in the healthy controls. Serum levels of sTNFR1 and sTNFR2 correlated with serum creatinine, while the surface expression of TNFR1 and TNFR2 on the granulocytes did not. There was no significant correlation between the BVAS and CD63 or BVAS and CD64. Conclusion: The surface expression levels of TNFR1 and TNFR2 on granulocytes were upregulated in patients with MPO-ANCA-associated vasculitis and reflected disease activity. Copyright (C) 2009 S. Karger AG, Basel