Oxidative inhibition of polymorphonuclear leukocyte motility mediated by the peroxidase/H2O2/halide system: studies on the reversible nature of the inhibition and mechanism of protection of migratory responsiveness by ascorbate, levamisole, thiamine and cysteine.

The antimicrobial oxidative system (myeloperoxidase (MPO), H2O2 and a halide) produced by stimulated PMNLs is simulated in vitro using horseradish peroxidase (HRP), H2O2 and NaI. Ascorbate, thiamine, levamisole and cysteine prevent and reverse the PMNL motility inhibiting effects of the HRP/H2O2/NaI system. The ability of these agents to protect the PMNL specifically from the known iodinating and oxidising abilities of this system was investigated. All four agents protect the PMNL from iodination by HRP/H2O2/NaI. However, only ascorbate and thiamine are able to reverse this process after it has occurred. Thiamine is seen on thin layer chromatography followed by autoradiography to be iodinated by this system. Ascorbate, thiamine and cysteine are able to protect the neutrophil sulfhydryl groups from oxidation by the system. One can therefore conclude that ascorbate and cysteine protect neutrophil motility from inhibition by the HRP/H2O2/NaI system by acting as reducing agents which maintain the neutrophil sulfhydryl groups. Thiamine also acts as a reducing agent, though not as effectively as ascorbate or cysteine. In addition, thiamine protects the PMNL from iodination by a competitive mechanism. The mechanism of levamisole protection is less clear but may involve scavenging of free radicals generated by the HRP/H2O2/NaI system. Protease enzymes, glycolysis and adherence are found not to be target sites for the PMNL motility inhibiting effects of the HRP/H2O2/NaI system. Further, increasing concentrations of the synthetic leukoattractant FMLP were shown to increase the auto-iodination of PMNLs without addition of extraneous peroxidase or peroxide. This data was compared with optimal FMLP concentrations for chemotaxis.