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Hirohito Kanemitsu, Mizuho Matsunawa, Kuninobu Wakabayashi, Michihito Sato, Ryo Takahashi, Tsuyoshi Odai, Takeo Isozaki, Nobuyuki Yajima, Yusuke Miwa, Tsuyoshi KasamaDivision of Rheumatology, Department of Medicine, Showa University School of Medicine, Tokyo, JapanObjective: To test the hypothesis that macrophage migration inhibitory factor (MIF) is involved in the disease activity of systemic vasculitis.Methods: Patients with systemic vasculitis were divided into three groups based on the size of the affected vessels. Microscopic polyangiitis (MPA) was considered as small vessel vasculitis (SVV), polyarteritis nodosa as medium-sized vessel vasculitis (MVV), and giant cell arteritis and Takayasu arteritis as large vessel vasculitis (LVV). Sera from patients with systemic vasculitis and healthy individuals were collected, and MIF levels were measured using an enzyme-linked immunosorbent assay. Disease activity of vasculitis was assessed using the Birmingham Vasculitis Activity Score (BVAS).Results: Serum MIF levels were significantly higher in the vasculitis patients than in healthy individuals. Among the vasculitis patients, MIF levels were significantly higher in patients in the SVV group (median; 4161.7 pg/ml) than in the other groups (MVV; 1443.2 pg/ml and LVV; 1576.7 pg/ml). In patients with MPA, a positive correlation was observed between serum MIF levels and CRP levels and disease activity (BVAS). Notably, serum MIF levels were significantly diminished after clinical improvement.Conclusions: Our findings suggest that MIF may have an important role in small vessel vasculopathy and serve as a useful serologic marker of MPA disease activity.Keywords: macrophage migration inhibitory factor, systemic vasculitis, microscopic polyangiitis, cytokine