Contributions of ultrastructural cytochemistry to the analysis of stimlus-response patterns in neutrophils

Abstract

Upon stimulation neutrophils undergo a complex series of biochemical and morphological changes. Phagocytosis by polymorphonuclear leukocytes (PMN) is accompanied by enhanced cyanide-insensitive respiration and hexose monophosphate shunt activity. H2O2 and O2 free radicals, such as superoxide O2-, are produced in increased amounts. H2O2, myeloperoxidase, and halide ions constitute a potent microbicidal system (Klebanoff system), via halogenation, e.g., chlorination, of microorganisms. Intermediate reaction products of oxidation, e.g., aldehydes, might themselves be microbicidal, or act as substrates for further H2O2 production. We have examined these aspects of phagocytosis with specially developed techniques of oxidative cytochemistry and correlated cytochemical, biochemical, and functional data.Utilizing diaminobenzidine (DAB) as a substrate for myeloperoxidase, we were able to confirm, at the EM level, that myeloperoxidase, present in the azurophil granules, enters the phagosome upon degranulation. We also showed, using a modified DAB reaction, that endogenous H2O2 was present in the phagosome. Intracellular halide, probably chloride, is presumed to be freely available.