Oxygen-dependent modulation of release and activity of polymorphonuclear leukocyte granule products

Polymorphonuclear leukocytes are important in the defense against the anaerobic microflora of infected gingival pockets. One part of this defense is release of antibacterial granule products by polymorphonuclear leukocytes into the pockets. The aim of the present study was to compare the efficiency of polymorphonuclear leukocytes in releasing granule products under aerobic and anaerobic conditions. Polymorphonuclear leukocytes were exposed to serum-opsonized zymosan under aerobic and anaerobic conditions. The levels of released granule products were determined by combining measurements of activity with enzyme-linked immunosorbent assays. The level of released elaslase was twice as high in anaerobic as in aerobic reaction mixtures. A similar difference was not detected for mycloperoxidase. However, mycloperoxidase was inactivated after its release under aerobic conditions. The release of lactoferrin was as efficient under aerobic as under anaerobic conditions. The effect of aerobic conditions on the release of elastase and the inactivation of myeloperoxidase could be ascribed to oxidants formed in the mycloperoxidase-H₂O₂-chloride system. Also, the activity of the released cytoplasmic enzyme lactate dehydrogenase was inactivated by oxidants formed in the myeloperoxidase-H₂O₂-chloride system. These findings suggest that, in the anaerobic environment of the gingival pocket, elastase and possibly also other azurophilic granule products are released in higher amounts than under fully oxygenated conditions. In this environment, the released products may also escape inaclivation by the myeloperoxidase- H₂O₂-chloride system.