Journal
RHEUMATOLOGY
Volume 50, Issue 7, Pages 1236-1243Publisher
OXFORD UNIV PRESS
DOI: 10.1093/rheumatology/ker085
Keywords
Natural autoantibodies; Myeloperoxidase; Anti-neutrophil cytoplasm antibodies; Microscopic polyangitis; Vasculitis
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Funding
- National Natural Science Foundation of China [30700752, 30725034]
- Beijing Municipal Natural Science Foundation [7082094]
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Methods. MPO-NAAs were affinity purified from normal plasma of five healthy blood donors and one batch of IVIG. MPO-ANCAs were purified from plasma of 10 patients with MPA. Antigen specificity of the antibodies was tested by western blot analysis. The titre, the avidity, the Immunoglobulin G (IgG) subclasses and the effect of the antibodies towards the binding between ceruloplasmin and MPO were tested using ELISAs. The MPO-NAA-induced production of reactive oxygen species was assessed using oxidation of dihydrorhodamine (DHR) to rhodamine. Results. MPO-NAA recognized epitope(s) in the heavy chains of MPO with conformation-dependent structure, the same as MPO-ANCA. The median titre of MPO-NAA was lower than that of MPO-ANCA (1 : 40 vs 1 : 4800, P < 0.001). The median avidity of MPO-NAA was lower than that of MPO-ANCA (2.2 x 10(7) vs 8.7 x 10(7)/M, P = 0.014). The IgG subclasses of MPO-NAA were mainly restricted to IgG1 (100%) and lack of IgG3. The inhibition effect on the binding between ceruloplasmin and MPO was lower for MPO-NAA than MPO-ANCA (P = 0.046). The MPO-NAA-induced respiratory burst of neutrophils was significantly weaker than that of MPO-ANCA (P = 0.036). Conclusion. The lower titre, lower avidity and lack of IgG3 subclass compared with MPO-ANCA may contribute to the non-pathogenic co-existence of MPO-NAA with MPO in serum.
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