Generation of IgG Polymers by the Myeloperoxidase-H2o2-Catechol System and Their Stimulatory Effect on Oxygen Radical Production from Human Polymorphonuclear Leukocytes

Abstract

Polymerization of native human IgG by myeloperoxidase (MPO)-H202-catechol sytem and ability of the resulting polymers to stimulate polymorphonuclear neutrophils (PMNs) to produce oxygen radicals were studied. Incubation of the human IgG with PMN granules (as a source of MPO) and H202 in the presence of catechol as a hydrogen donor resulted in polymerization of this protein, which was confirmed by Sephacryl 200 column chromatography and polyethylene glycol precipitation method. The polymer formation was completely abolished by omission of PMN granules, H202 or catechol, and addition of catalase or azide to the complete system containing the three components. Among the various hydrogen donors tested, only dopamine was able to replace catechol in the polymerization (about 75% of that of catechol). The polymerization was not affected by the quenchers for 0 ~, OH· or 102 and antioxidants but markedly inhibited by benzenesulfinic acid and some compounds acting as a hydrogen donor. These results suggest that the polymerization was due to oxidation of catechol to orthoquinone mediated by MPO and H202 with ruling out the involvement of the oxygen radicals. The IgG polymers obtained stimulated human PMNs to proudce O~ and H202 while native IgG was much less effective in this respect. The stimulatory effect was even higher than (about 1.5 times) that of heat-aggregated IgG having many properties similar to typical immune complexes. Thus, it can be expected that the IgG polymers generated in the present study will also behave as immune complexes in stimulation of PMNs. The result was discussed in terms of a possible role of the IgG polymers in the pathogenesis of tissue injury in many acute and chronic inflammatory conditions.