Inhibition of oxidative activity of myeloperoxidase by anti-myeloperoxidase antibodies from patients with microscopic polyangiitis

To investigate the inhibitory effects on myeloperoxidase (MPO) oxidation activity by affinity-purified anti-MPO antibodies from patients with microscopic polyangiitis (MPA) and to further investigate the interaction between MPO, ceruloplasmin and anti-MPO antibodies.Human IgG fractions were purified from plasma of 11 patients with anti-MPO antibody positive MPA and sera of 12 normal controls. Anti-MPO antibodies were further purified from anti-MPO antibody containing IgG fractions using MPO affinity chromatography. The enzyme activity of MPO was measured, in the presence of anti-MPO antibodies and normal IgG preparations, using a classical MPO oxidation assay. Interaction between ceruloplasmin, MPO and anti-MPO antibodies was further investigated using ELISA.Anti-MPO antibodies from 7/11 patients with MPA could inhibit the MPO activity as non-competitive inhibitors in a dose-dependent manner. Ceruloplasmin could competitively inhibit the oxidation activity of MPO in a dose-dependent and time-dependent manner. Anti-MPO antibodies could inhibit the binding between MPO and ceruloplasmin to a maximum of (75.4+/-11.6)%.Anti-MPO antibodies, from the majority of patients with MPA, could inhibit the oxidation activity of MPO and interfere with the binding between MPO and ceruloplasmin.PubMed02155-94