Influence of myeloperoxidase-catalyzing reaction on the binding between myeloperoxidase and anti-myeloperoxidase antibodies

In the current study, whether myeloperoxidase (MPO)–catalyzing reaction could influence the antigenicity of MPO was investigated. Hypochlorite acid, the main product of the catalytic reaction, could lower the binding between MPO–antineutrophil cytoplasmic antibodies (ANCA) and MPO when the available chlorine was higher than 0.031×10−3 g/l. After MPO-catalyzing reaction with H2O2 lower than 0.469 g/l, the binding level between MPO–ANCAcontaining plasma and MPO increased slightly. The peak binding level was 1.135 ± 0.205 (expressed by the absorbance value at 405 nm). However, with the existence of hydrogen donor (o-phenylenediamine) in the reaction system, the peak binding level between MPO-ANCA–containing plasma and post-catalyzing MPO was significantly higher (1.367 ± 0.321 vs 1.135 ± 0.205, p = 0.023). Moreover, at the approximately physical concentration of H2O2 (0.02 g/l), MPO-ANCA exhibited higher titer to post-catalyzing MPO than to pre-catalyzing MPO (3.91 ± 0.84 vs 3.57 ± 0.84, p < 0.001, expressed as the lgT). These data demonstrated that MPO-catalyzing reaction could potentially increase the antigenicity of MPO.