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D Roos

Publications and source records attributed to D Roos.

24 records · Page 2Linked to original sources
PubMed1975

Complement and immunoglobulins stimulate superoxide production by human leukocytes independently of phagocytosis.

Human peripheral blood polymorphonuclear leukocytes, when exposed to appropriate stimuli, generate significant amounts of superoxide anion (O-.2), a highly reactive molecule which is possibly involved in bacterial killing. Since the subcellular localization and mechanism of activation of O-.2 generating systems are unknown, we have investigated superoxide dismutase-inhibitable cytochrome c reduction (attributable to O-.2) by, and lysosomal enzyme release from, normal polymorphonuclear leukocytes and cells rendered incapable of ingesting particles by treatment with cytochalasin B. Neither phagocytosis nor lysosomal degranulation were prerequisites for enhanced O-.2 generation. Cytochalasin B-treated cells exposed to (a) serum-treated zymosan, a C3b receptor stimulus; (b) heat aggregated human IgG, an Fc receptor stimulus; and (c) the complement component, C5a, generated enhanced amounts of O-.2 in a time and concentration-dependent fashion. These cells also responded by releasing lysosomal enzymes, but there was no correlation between the ability of any immune reactant to provoke enzyme release and its ability to stimulate O-.2 generation. The three stimuli also enhanced O-.2 generation by normal (untreated) polymorphonuclear leukocytes, but only serum-treated zymosan and aggregated IgG were capable of provoking lysosomal enzyme release from normal cells. Untreated zymosan and native IgG neither stimulated O-.2 production nor provoked lysomal enzyme release. Since enhanced O-.2 production was stimulated by immune reactants in the absence of phagocytosis, the O-.2 generating system is very likely associated with the external plasma membrane of the polymorphonuclear leukocyte. Leukocyte membrane receptors for complement and immunoglobulins may therefore not only serve in particle recognition but also may initiate biochemical events which accompany phagocytosis and killing.

Adult↗
PubMed1975

Production of hydrogen peroxide by phagocytizing human granulocytes.

A rapid and sensitive method is described for the quantitative determination of H202 produced by phagocytizing human granulocytes. For this purpose, the method of Keston and Brandt was mechanized, which is based on the oxidation of nonfluorescent leukociacetyl-2,7-dichlorofluorescein to a fluorescent compound by H202 in the presence of peroxidase. The optimal conditions for this test were determined. H202 in water can be measured in the range of 0.05 to 0.5 muM, with a standard deviation of 1.2 per cent at 0.4 muM (n = 1-). The production of H2O2 by phagocytizing granulocytes could only be measured in a medium which contained phosphate-buffered salt, albumin, glucose, NaN3, and IgG-coated latex particles. The fluorescence signal was catalase-sensitive. Of known amounts of H202, added to this medium, 97 per cent were recovered. Under optimal conditions we found a H2O2 production of 970 plus or minus 170 mumoles per 10-10 cells per hour (10 different healthy donors), corresponding to 50 to 70 per cent of the observed increase in O2 consumption. No H2O2 was produced by phagocytizing granulocytes from 2 patients with chronic granulomatous disease, while intermediate values were found in the cells from heterozygotes.

Female↗
PubMed1975

Quantitative aspects of the production of superoxide radicals by phagocytizing human granulocytes.

The production of superoxide radicals (O2-) by human granulocytes after phagocytosis of latex particles has been studied as a function of cell, latex, and cytochrome c concentration. Under the chosen conditions, latex phagocytosis stimulated the reduction of cytochrome c by O2- sevenfold to 420 mumoles per 10-10 granulocytes per hour. At high cytochrome c concentrations, this value increased to 800 to 1,000 mumoles per 10-10 granulocytes per hour. These amounts suggest that O2- plays an important role in the formation of H2O2 during the phagocytic process. We propose that the extra oxygen consumed in the respiratory burst is first reduced to O2-, possibly by ascorbate, before being converted to H2O2. No stimulation of the superoxide radical formation was found in the phagocytizing granulocytes of two patients with chronic granulomatous disease, and intermediate values were found for the heterozygotes of this deficiency.

Animals↗
PubMedDate not supplied

Defects in the oxidative killing of microorganisms by phagocytic leukocytes.

One of the most important mechanisms of phagocytic killing of ingested microorganisms by leukocytes is the generation of toxic oxygen products. During phagocytosis, neutrophils, as well as monocytes and macrophages, display a strongly increased cell respiration. Quantitatively the most important product of this reaction is hydrogen peroxide. Superoxide is also generated in large amounts, probably as an intermediate in the formation of hydrogen peroxide. Indications exist that singlet oxygen and hydroxyl radicals are also formed in this process. Some of these oxygen products have microbicidal properties by themselves. The effect of hydrogen peroxide is greatly enhanced by the enzyme myeloperoxidase. Several dysfunctions of this sytem are known. In chronic granulomatous disease the enzyme system that produces superoxide is not operative. Thus, no superoxide or hydrogen peroxide is generated, leading to a severely decreased bacterial killing capacity. The exact molecular defects in the X-linked and the autosomal form are as yet undefined. Two variants are also known: lipochrome histiocytosis, with different clinical and histological manifestations, and a 'triggering defect' where only strongly opsonized particles trigger the respiratory burst. Myeloperoxidase deficiency leads to slightly decreased killing capacity, especially for yeasts. In glucose-6-phosphate dehydrogenase deficiency no oxygen radicals or hydrogen peroxide are produced because no equivalents for oxygen reduction can be generated in the hexose-monophosphate shunt. Deficiencies in the glutathione redox system also result in impaired phagocyte function, probably because the cells have to be protected against their own toxic oxygen products.

Blood Bactericidal Activity↗