EFFECT OF ANAEROBIOSIS AND SULFIDE ON KILLING OF BACTERIA BY POLYMORPHONUCLEAR LEUKOCYTES

Anaerobic microorganisms in periodontal pockets produce toxic amounts of hydrogen sulfide. The capacity of polymorphonuclear leukocytes to k ill a capsulated and a non-capsulated variant of a group B streptococc al strain was studied in presence and absence of sulfide. The killing was equally efficient under aerobic and anaerobic conditions. However, in presence of sulfide the killing of the capsulated variant of the s train was significantly inhibited. Since this strain required higher s erum concentrations to be killed by the polymorphonuclear leukocytes, it suggested that sulfide interfered with the opsonization of the bact eria. The capacity of sulfide to split the disulfide bonds of compleme nt factor 3 and immunoglobulin G, deposited on the bacterial surface, was evaluated by sodium dodecyl sulfate-polyacrylamide gel electrophor esis. There was no detectable effect of 2 mM sulfide on immunoglobulin G. However, sulfide released from opsonized bacteria the beta-chain o f C3b C3bi, and the C-terminal part of the alpha-chain of C3bi. This r egion of the alpha-chain of C3bi has been suggested to bind to the com plement receptor 3 of polymorphonuclear leukocytes. The beta-chain of C3b/C3bi may augment the binding of opsonized bacteria to the compleme nt receptors of polymorphonuclear leukocytes. The formation of sulfide by the microflora of the periodontal pockets may provide conditions f or the bacteria to escape important parts of the host immune, system.