Barbara Styrt

Alkalinizing the intralysosomal pH inhibits degranulation of human neutrophils.

Degranulation of lysosomes is one of the consequences of neutrophil activation. Regulatory mechanisms of lysosomal secretion are thought to be localized largely in the plasma membrane and cytosol, with the lysosome playing a passive role in secretion. Recent evidence indicates that the intralysosomal pH is highly acidic (pH congruent to 5.5) and is maintained by active transport of H+. We investigated whether changes in the intralysosomal pH altered the availability of lysosomes for exocytosis. Intralysosomal pH in intact neutrophils was monitored with the weakly basic fluorescent probe, 9-aminoacridine (9AA). The weak bases, methylamine, chloroquine, clindamycin, propanolol, and ammonium chloride (0.1-50 mM), caused an alkalinization of the intralysosomal pH as determined by reversal of quenching of 9AA fluorescence. Similarly, each of the weak bases, including ammonium chloride, methylamine, chloroquine, ethylamine, propylamine, propanolol, clindamycin, and dansylcadaverine, inhibited neutrophil degranulation in response to the calcium ionophore A23187, phorbol myristate acetate, or the chemotactic peptide, formyl-methionine-leucine-phenylalanine plus cytochalasin B. These studies indicate that an acid intralysosomal pH is important to the neutrophil secretory response and suggest that the lysosome may play an active part in control of degranulation.

Characterization of the neutrophil respiratory burst in atopy

Activated neutrophils may play a part in atopic disorders. In these studies, neutrophils were obtained from atopic and nonatopic adults for assessment of respiratory-burst activity. Superoxide production was measured in the resting state and after stimulation with phorbol myristate acetate, formyl-methionyl-leucyl-phenylalanine (f-met-leu-phe), or calcium ionophore A23187. Inhibition of this response by histamine was also measured. Neutrophils from atopic subjects produced more superoxide in the basal state, or in response to calcium ionophore A23187, or submaximal concentrations of f-met-leu-phe, than cells from control subjects. Histamine inhibition of f-met-leu-phe-stimulated superoxide production was less in atopic subjects than in control subjects. These findings suggest that neutrophils from atopic subjects may be hyperreactive in that they produce more superoxide in response to stimuli of low potency and are less readily inhibited than cells from control subjects. These properties may reflect a general attribute of cellular function in atopy and may contribute directly to tissue damage in allergic diseases.

Internal pH of human neutrophil lysosomes

The ingestion of microorganisms by human neutrophils involves the formation of a particlecontaining phagocytic vacuole (the phagosome). Several studies [l, 21 using microorganisms labelled with pH indicator dyes have demonstrated a progressive fall in pH of the phagocytic vacuole (possibly after a transient initial rise [3]) after phagocytosis. This acidification of the phagocytic vacuole is considered an important antimicrobial event, but its mechanism has not been elucidated. Several possibilities have been offered, including local production of lactate [4,5], a carbonic anhydrase-dependent proton-translocating system [6], NADPH-oxidase dependent formation of perhydroxyl radicals (’ 02H) which then dissociate into superoxide radicals (Oi -) and protons [7], and the discharge of lysosomal contents into the phagosome [8]. Two observations favor the possibility that the lysosome is the source of acidification: (i) The kinetics of the decline in phagosome pH coincide with the kinetics of lysosome fusion with the phagosome to form the phagolysosome [9]; (ii) In other cells wherein the intralysosomal pH has been measured, it is decidedly acidic [lO,ll]. In an attempt to elucidate the role of the lysosome in phagosome acidification, we measured the intralysosomal pH of isolated neutrophil lysosomes, and the effect of varying external ion concentrations. Neutrophil pH Phagocytic vacuole

Effects of pH on killing of Staphylococcus aureus and Escherichia coli by constituents of the neutrophil phagolysosome.

Lysosomotropic weak bases impair in-vitro neutrophil functions including intracellular killing of Staphylococcus aureus strain 502a. To investigate whether prevention of phagosomal acidification could account for impaired microbicidal activity, a model phagosome was formulated with a freeze-thawed granule extract as a source of lysosomal enzymes and H2O2 as a source of toxic oxygen metabolites. The lysosomal extract alone killed Escherichia coli strain S15 efficiently at pH 5.5 and 7.0, but had little activity against S. aureus 502a. Sublethal concentrations of the two agents, when combined, acted synergically against either organism. Each organism was killed more effectively at pH 5.5 than at pH 7.0 by the lysosome extract-H2O2 combination, but the killing of E. coli was more rapid than that of S. aureus in the same conditions. These findings suggest that impairment of neutrophil antistaphylococcal activity by weak bases may be mediated by their ability to raise phagosomal pH, and that persistence of E. coli in similar conditions does not occur because the latter is killed by lysosomal constituents in a non-pH-dependent fashion.

An Abnormal Calcium Uptake Pump in Chediak-Higashi Neutrophil Lysosomes

Calcium is mobilized from intracellular stores during phagocyte activation and appears to be involved in stimulus‐response coupling in these and other cell types. Because the lysosome is a calcium‐sequestering organelle in the neutrophil and abnormal lysosome morphology is associated with defective neutrophil function in Chediak‐Higashi syndrome (CHS), we examined ATP‐dependent calcium uptake in neutrophil lysosomes from the beige mouse model of CHS. We present findings indicating that CHS lysosomes have an enhanced capacity for ATP‐dependent calcium uptake relative to control lysosomes. Kinetic analysis showed differences in Vmax and in the Km for both ATP and calcium, suggesting that both the number of lysosomal calcium uptake pumps and their substrate affinity may be altered in CHS. We conclude that a genetically determined abnormality of a subcellular calcium transport system may contribute to the structural and functional defects of CHS cells.

Differential lysis of plasma membranes and granules of human neutrophilis by digitonin

The effect of the detergent digitonin on lysis of granule and plasma membranes of human neutrophils was studied. Either linear or sigmoid dose-response for release of the cytoplasmic marker lactate dehydrogenase and the granule markers lysozyme, beta-glucuronidase, lactoferrin, and myeloperoxidase was noted using digitonin concentrations ranging from 0.001 to 0.1 mM. However, release of the cytosol compartment was far more sensitive to the detergent than the granule compartment, with more release of lactate dehydrogenase than of lysozyme at 0.01-0.08 mM digitonin. Distinction between the two compartments was optimal at 0.025 mM digitonin. By examining in parallel the digitonin-induced release of exogenous fluorescent or luminescent indicators, a granule location was demonstrated for the pH indicator 9-aminoacridine, while the calcium probes aequorin and Quin 2 were released coincident with release of the cytosolic enzyme lactate dehydrogenase. These findings were employed to validate use of the indicators for monitoring of ion translocation in the intact cell. The differential effect of this detergent on subcellular membranes provides a broadly applicable technique for rapid assessment of the subcellular localization of tracer substances. Rapid monitoring may help to avoid problems of redistribution during cell fractionation.

Inhibition of neutrophil superoxide production by fanetizole

The effects on neutrophil function of the new immunomodulatory agent fanetizole mesylate were studied. Fanetizole did not affect random or stimulated migration, phagocytosis, or degranulation by normal human neutrophils. Production of superoxide in response to the chemotactic factor formyl-methionyl-leucyl-phenylalanine (f-Met-Leu-Phe) was markedly inhibited (41.3±3.9%) by 250μM fanetizole. This inhibition was not due to scavenging of superoxide by fanetizole, as there was no impairment of superoxide detection in a cell-free xanthine-xanthine oxidase system. Inhibition was dose dependent (no effect seen with 1 or 10μM fanetizole) and stimulus specific (no impairment of superoxide production in response to phorbol myristate acetate). Washing the cells after fanetizole treatment partially restored their superoxide response to f-Met-Leu-Phe. Suppression of neutrophil production of toxic oxygen metabolites may partially explain the antiarthritic effect of fanetizole, and study of such selective inhibitors may be useful in probing the contribution of neutrophils to inflammatory tissue damage.

Calcium release associated with discharge of specific granule contents from human neutrophils.

Neutrophil discharge of calcium into the ambient medium was measured, using an ion-sensitive electrode, after cells were stimulated with phorbol myristate acetate. Dose-dependent calcium efflux was observed over the same range of stimulus concentrations associated with specific granule marker release. Calcium efflux was preserved when cells were treated with vanadate to inhibit the plasma membrane calcium ATPase. However, less calcium was released than in previous studies employing a complete secretagogue to discharge both specific and azurophil granule contents. These studies suggest that calcium is stored in both the azurophil and the specific granules of the neutrophil, and can be mobilized from both sites during degranulation.

Linkage between neutrophil degranulation and calcium discharge

Calcium flux across organelle and plasma membranes is an important event in neutrophil activation. We measured calcium discharge into the media from neutrophils stimulated with formyl-methionyl-leucyl-phenylalanine after treatment with cytochalasin b. Cytochalasin markedly potentiated calcium efflux from stimulated neutrophils, and similarly promoted release of lysosomal enzymes into the media. Colchicine neither reproduced nor modified the cytochalasin effect. Neutrophil cytoplasts discharged very little calcium in response to stimulation, and discharge was not significantly altered by cytochalasin b. These findings indicate that neutrophil degranulation is accompanied by efflux of calcium into the media, and suggest that the neutrophil granules constitute a source of mobilizable calcium which could be used to modify the extracellular microenvironment.

Comparison of prostaglandins E2 and D2 as inhibitors of respiratory burst in neutrophils from atopic and nonatopic subjects

Neutrophils from atopic and nonatopic donors were treated with prostaglandins D2 and E2 before stimulation of the respiratory burst. Both agents inhibited neutrophil response to formyl-methionyl-leucyl-phenylalanine, but superoxide production was inhibited much more profoundly by D2 than by E2. Inhibition was similar in atopics and nonatopics. Phorbol myristate acetate stimulation of superoxide production was not significantly altered by prostaglandins. These findings suggest that minor alterations in pathways of prostaglandin synthesis may have major effects on modulation of neutrophil function, and exploration of the mechanism of stimulusspecific inhibition may further elucidate the role of neutrophils in the inflammatory response.