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

CER3588
2009 Vol.27, N°1 ,Suppl.52
PI 0028, PF 0032
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PMID: 19646343 [PubMed]

Abstract

OBJECTIVES:
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 µg/ml and 0.54±0.15 µg/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.