[Epitope mapping of myeloperoxidase antibodies in propylthiouracil-induced vasculitis and microscopic polyangiitis]

To compare the epitopes of antibodies for myeloperoxidase (MPO) in the serum from patients with propylthiouracil (PTU) induced vasculitis and microscopic polyangiitis (MPA).

Serum samples from patients with PTU-induced vasculitis (n = 10) and MPA (n = 10) were collected and used to inhibit monoclonal antibodies against human MPO 3D8 and 6B9 and then affinity was purified, horseradish peroxidase conjugated and human MPO antibodies determined (Pab1-HRP, Pab2-HRP) in a competitive inhibition ELISA system using soluble human MPO as solid phase ligands. The Pab1-HRP and Pab2-HRP were affinity purified from plasma exchanges of a patient with PTU-induced vasculitis and a patient with MPA. The inhibition rates were evaluated and compared between PTU group and primary MPA group.

In PTU group, all the 10 serum samples could inhibit 3D8; the average inhibition rate was 44.7%, 9/10 of the serum samples could inhibit 6B9; the average inhibition rate was 35.6%; In MPA group, all 10 serum samples could inhibit 3D8 and 6B9; the average inhibition rates were 68.4% and 62.2%. Serum in both groups could inhibit Pab1-HRP and the inhibition rates were both more than 80%; the average inhibition rate for Pab2-HRP in MPA group was significantly higher than that in PTU group (76.3% vs 58.9%, P < 0.01).

MPO antibodies from patients with PTU-induced vasculitis and patients with primary MPA could recognize more than one epitopes on native MPO molecule. Although the epitopes were overlapping between the two groups, the epitopes of MPO antibodies from patients with PTU-induced vasculitis might be more restricted.