Preferential adsorption of human neutrophil myeloperoxidase isoform III by oral bacteria.

Neutrophil myeloperoxidase (MPO) adsorbs to bacteria as a pre-requisite for killing by the MPO/hydrogen-peroxide/chloride system. Three chromatographically distinct isoforms of MPO (MPO I, MPO II, and MPO III) have been isolated from human neutrophils. The purpose of this study was to determine whether oral bacteria--including Actinobacillus actinomycetemcomitans, Capnocytophaga sputigena, Haemophilus aphrophilus, and Eikenella corrodens--differentially adsorb the three major isoforms of MPO from a mixture of MPO I, II, and III, and to assess the effect of pH and normal human serum (NHS) on MPO adsorption. MPO III adsorbed preferentially (i) at high bacterial concentrations, (ii) in the pH range of 6.0-8.0, and (iii) in the presence and absence of NHS. These results support the role of MPO III in the killing of oral bacteria.