Two types of myeloperoxidase-antineutrophil cytoplasmic autoantibodies with a high affinity and a low affinity in small vessel vasculitis

M Yoshida, M Sasaki, I Nakabayashi, M Akashi, T Tomiyasu, N Yoshikawa, T Kojima, N Ohno, M Yamada
Clinical and Experimental Rheumatology 2009, 27 (1 Suppl 52): S28-32

OBJECTIVE: Myeloperoxidase (MPO) -anti-neutrophil cytoplasmic autoantibodies (ANCAs) are detected at a high rate in microscopic polyangiitis and renal-limited vasculitis. MPO-ANCA titers are not always reflected in the disease activity. We studied the titer and affinity of MPO-ANCA in sera from patients in relation to vasculitis activity.

METHODS: Blood samples were collected from 27 newly diagnosed or relapsed patients with MPO-ANCA-associated vasculitides. The MPO-ANCA titer was determined by a direct enzyme-linked immunosorbent assay (ELISA) using homogeneously purified human MPO of leukocytes. The MPO-ANCA affinity was expressed as IC50 that was determined by a competitive inhibition method using the ELISA.

RESULTS: The MPO-ANCA affinity of 27 sera from 27 patients could be classified into a high-affinity type (14 sera) and a low-affinity type (13 sera). The mean values for IC50 in the two types were 0.15+/-0.06 microg/ml and 0.54+/-0.15 microg/ml, and the difference was statistically significant (p<0.0000000684). Between the two groups of patients divided by the affinity, there were differences in the Birmingham Vasculitis Activity Score (BVAS): and in C-reactive protein (CRP): (p<0.00093 and p<0.00129, respectively). However, the difference in titer was not statistically significant (p<0.0265). The affinity remained steady from the disease onset to remission or relapse.

CONCLUSIONS: The affinity of MPO-ANCA from patients with MPO-ANCA-associated vasculitides were largely distinguished into a high and a low affinity, irrespective of the level of MPO-ANCA titers, and may be helpful for assessment of vasculitis activity affecting mainly the kidney and the lung.

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