The respiratory burst of phagocytic cells is associated with a rise in vacuolar pH

Superoxide modulates the activity of myeloperoxidase and optimizes the production of hypochlorous acid

Myeloperoxidase catalyses the conversion of H2O2 and Cl- to hypochlorous acid (HOCl). It also reacts with O2- to form the oxy adduct (compound III). To determine how O2- affects the formation of HOCl, chlorination of monochlorodimedon by myeloperoxidase was investigated using xanthine oxidase and hypoxanthine as a source of O2- and H2O2. Myeloperoxidase was mostly converted to compound III, and H2O2 was essential for chlorination. At pH 5.4, superoxide dismutase (SOD) enhanced chlorination and prevented formation of compound III. However, at pH 7.8, SOD inhibited chlorination and promoted formation of the ferrous peroxide adduct (compound II) instead of compound III. We present spectral evidence for a direct reaction between compound III and H2O2 to form compound II, and for the reduction of compound II by O2- to regenerate native myeloperoxidase. These reactions enable compound III and compound II to participate in the chlorination reaction. Myeloperoxidase catalytically inhibited O2- -dependent reduction of Nitro Blue Tetrazolium. This inhibition is explained by myeloperoxidase undergoing a cycle of reactions with O2-, H2O2 and O2-, with compounds III and II as intermediates, i.e., by myeloperoxidase acting as a combined SOD/catalase enzyme. By preventing the accumulation of inactive compound II, O2- enhances the activity of myeloperoxidase. We propose that, under physiological conditions, this optimizes the production of HOCl and may potentiate oxidant damage by stimulated neutrophils.

The effect of the NADPH oxidase inhibitor diphenyleneiodonium on aerobic and anaerobic microbicidal activities of human neutrophils

NADPH-dependent superoxide production by intact human neutrophils is inhibited by DPI (diphenyleneiodonium), when stimulated by either FMLP (N-formylmethionyl-leucyl-phenylalanine) or PMA (phorbol 12-myristate 13-acetate). Addition of 10 microM-DPI abolished the reduction of both the FAD and the cytochrome b components of the NADPH oxidase. DPI inhibition of the oxidase was associated with defective aerobic killing of staphylococci by human neutrophils. Anaerobic killing, phagocytosis, chemotaxis and motility were relatively unaffected by 10 microM-DPI. Degranulation of the azurophil and specific granules, induced by the soluble stimuli FMLP or PMA, and by particulate stimuli was decreased by the presence of DPI. The above effects of DPI on human neutrophils are similar to those found in chronic granulomatous disease.

Internal pH changes associated with the activity of NADPH oxidase of human neutrophils. Further evidence for the presence of an H+ conducting channel

The internal pH (pHi) of cytoplasts, derived from human neutrophils, falls 0.05 pH units upon activation of the superoxide-generating NADPH oxidase. The decrease in pHi is absent in diphenyleneiodonium-treated cytoplasts and therefore it is likely to arise directly from the activity of the oxidase. The addition of amiloride, to diminish the Na+/H+ exchanger, enhanced the extent of the internal acidification but not the initial rate. However the electroneutral Na+/H+ exchanger cannot be a contributor to H+ efflux to compensate for charge translocated by the oxidase. In the presence of Cd ions or valinomycin, phorbol-induced acidification of the cytosol was greatly increased, suggesting an inability to translocate the cytosolic H+ generated by an electrogenic oxidase. In the presence of both Cd and valinomycin the cytoplasts retained 0.8 H+ per O2-. generated. The rate of acidification of the external medium by stimulated cytoplasts is greatly reduced in the presence of Zn and valinomycin. Our results support the view that the plasma membrane of neutrophils contains Zn2+- or Cd2+-sensitive proton-conducting channels which maintain a stable membrane potential and pHi during the activity of the electrogenic NADPH oxidase.

Lithium movements in resting and chemotactic factor-activated human neutrophils

The ability of the chemotactic factor-activated Na+-H+ exchange system of human neutrophils to bind and transport other cations of the alkali metal series was investigated. After exposure of cells to the tripeptide N-formyl-methionyl-leucyl-phenylalanine (FMLP), the influx of Li+ was measured by flame photometry and correlated with changes in intracellular pH (pHi) derived from the equilibrium distribution of 5,5-dimethyloxazolidine-2,4-dione. In Na+-depleted cells, Li+ (Km approximately equal to 14 mM) could substitute effectively for Na+ (Km approximately equal to 23 mM) at the external translocation site of the carrier, though the maximal transport rate for Li+ (approximately 8 meq.l-1.min-1) was roughly half that for Na+ (approximately 15 meq.l-1.min-1). On the other hand, the carrier lacked appreciable affinity for K+, Rb+, and Cs+. The influx of Li+ from the external solution was accompanied by an equivalent counterefflux of H+ from the internal milieu. The H+ efflux thus induced led to an intracellular alkalinization of approximately 0.7 units, the pHi rising from approximately 7.20 to approximately 7.90. The influx of Li+, as well as the increase in pHi in 140 mM Li+ medium, was competitively inhibited by amiloride (Ki approximately equal to 9 microM). Extracellular H+ also behaved as a competitive inhibitor of Li+ with a Ki of approximately 30 nM (pK'a approximately 7.50). These studies indicate that the FMLP-activated alkali metal cation-H+ exchange mechanism of neutrophils shares a number of features in common with those of Na+-H+ exchangers in a variety of different cells.

Interaction of macrophage cationic proteins with the outer membrane of Pseudomonas aeruginosa

The interaction of the polycationic rabbit alveolar macrophage cationic proteins MCP-1 and MCP-2 (or their identical neutrophil equivalents NP-1 and NP-2) with the surface of Pseudomonas aeruginosa was investigated. Both proteins bound avidly to purified lipopolysaccharide, as judged by their ability to competitively displace the probe dansyl polymyxin with 50% inhibition (I50) values of 2 to 3 microM. Similar I50 were measured with dansyl polymyxin as a probe for cell surface binding, suggesting that the initial binding site for MCP-1 and MCP-2 on the surface of cells was lipopolysaccharide. Both MCP-1 and MCP-2 permeabilized outer membranes to the hydrophobic fluorescent probe 1-N-phenylnaphthylamine (NPN). The initial rate of NPN uptake plotted against the concentration of MCP-1 or MCP-2 gave sigmoidal curves, suggesting cooperative permeabilization of the outer membrane. Replotting the data as a Hill plot gave an affinity parameter, S0.5, the concentration of MCP giving a half-maximal increase in the rate of NPN uptake, of 5 and 25 microM for MCP-1 and MCP-2, respectively, and thus subsequent studies concentrated on the more active permeabilizer MCP-1. Permeabilization of outer membranes to NPN was a function of buffer pH, with lower pH considerably favoring the permeabilizing effects of MCP-1. Thin-section electron microscopic visualization of MCP-1-treated cells showed production of extended blebs. Further evidence of an altered cell surface after MCP-1 treatment was obtained by demonstrating that treated unopsonized cells were more efficiently phagocytosed by unelicited rabbit alveolar macrophages. The data overall suggest that macrophage cationic proteins interact with the P. aeruginosa outer membrane in a manner typical of other polycations and suggest that one of their major functions may be to permeabilize the outer membrane.

Assessment of Na+-H+ exchange activity in phagosomal membranes of human neutrophils

To assess the presence of Na+-H+ exchange in internalized membranes, the phagosomal pH was monitored in suspensions of intact human neutrophils by measuring the fluorescence of ingested bacteria (Micrococcus lysodeikticus) prelabeled with a pH-sensitive dye. Uptake of fluoresceinated bacteria was confirmed by flow cytometry and by phase-contrast and electron microscopy. Manipulation of the cytoplasmic ion content was accomplished by permeabilization of the plasma membrane with nystatin, which did not alter phagosomal permeability. At 37 degrees C, the phagosomal interior acidified at a maximal rate of 0.135 +/- 0.003 pH units/min (n = 10). The endogenous Na+-H+ exchanger does not affect phagosomal acidification, since the rate and extent of the pH change were not altered by 1) omission of intraphagosomal Na+ and 2) addition of the permeant inhibitor methylisobutylamiloride or by trapping amiloride in the phagosome during bacterial ingestion. Moreover, amiloride-sensitive Na+-H+ exchange was not detectable when Na+ or H+ gradients were imposed across the phagosomal membrane. Under comparable conditions, Na+-H+ exchange could be readily detected across the surface membrane. These data imply that the Na+-H+ antiporters are either inactivated in the phagosome or are segregated and not internalized into the phagosomal membrane.

Intraphagosomal pH in alveolar macrophages after phagocytosis in vivo and in vitro of fluorescein-labeled yeast particles

The pH in phagolysosomes of rabbit alveolar macrophages was studied using yeast particles labeled with fluorescein isothiocyanate (FITC). The yeast particles were added to the macrophages in vitro a few hours or 1 day after they had been lavaged from the lung and in vivo 3 h or 1 day before the lungs were lavaged. Intracellular pH was estimated from the ratio between the fluorescence intensity at wavelength 519 nm with excitation at wavelengths of 495 and 450 nm. In both the in vitro and in vivo experiments pH decreased significantly during the first hours after lavage, but after a few hours reached almost the day-2 levels, i.e., 4.9-5.4. The decrease in pH was related to time after lavage and not to time after phagocytosis of the particles. It is suggested that intracellular measurements of pH in alveolar macrophages should be combined with determinations of lung clearance of metal particles.

Nonoxidative antimicrobial effects of human polymorphonuclear leukocyte granule proteins on Chlamydia spp. in vitro

Proteins from isolated granules of human polymorphonuclear leukocytes were assessed for their nonoxidative microbicidal effect on chlamydiae by two different methods: a radioisotope assay for elementary body integrity and a biological assay for inclusion development. Crude granule extract, which consisted of a mixture of all granule proteins, caused a 20 to 30% decrease in infectivity and a 52% decrease in infectivity when incubated with Chlamydia psittaci CAL-10 and Chlamydia trachomatis serovar E, respectively. To define more specifically the components that were damaging to chlamydiae, crude granule extract was subjected to Sephadex G-75 column chromatography and isolated granule fractions were obtained. Only fractions containing lysozyme as the major component consistently caused reductions in infectivity of C. trachomatis elementary bodies. In contrast, fractions collected after the lysozyme fraction, containing proteins with molecular masses of 13,000 daltons or less, had detrimental effects on C. psittaci infectivity. Additional experiments using highly purified human polymorphonuclear leukocyte lysozyme confirmed its infectivity-reducing action upon C. trachomatis but not upon C. psittaci.

Respiratory burst facilitates the digestion of Escherichia coli killed by polymorphonuclear leukocytes

We examined factors that may limit degradation of bacterial protein of Escherichia coli S15 killed by polymorphonuclear leukocytes (PMN). Both human and rabbit PMN degraded up to 40% of [14C]amino acid-labeled protein of ingested and killed E. coli in 2 h as determined by loss of acid-precipitable radioactivity. In contrast, equally bactericidal broken-PMN preparations or isolated granules degraded only about 10% of bacterial protein regardless of pH. To determine whether activation of the respiratory burst contributes to digestion, we compared degradation by intact PMN in room air and under N2. Depletion of O2 by N2 flushing had no effect on the bactericidal activity of either human or rabbit PMN but reduced degradation by approximately 50%. Protein degradation during phagocytosis was also reduced in the presence of cyanide or azide, inhibitors of myeloperoxidase (MPO). PMN of two patients with chronic granulomatous disease ingested and killed E. coli S15 as well as did normal PMN but degraded bacterial protein as did normal PMN incubated under N2. The low degradative activity of PMN disrupted by sonication could be raised to nearly the level of intact PMN incubated in room air by preincubation of the PMN with 10(-7) M formyl-methionyl-leucyl-phenylalanine (fMLP) before sonication and by pretreatment of E. coli with MPO. Depletion of O2 or chloride during these preincubations with formyl-methionyl-leucyl-phenylalanine respectively, virtually abolished and markedly diminished stimulation of bacterial protein degradation. We conclude that enhanced MPO-mediated O2 metabolism of intact PMN plays a role in the digestion of killed E. coli.

Burn wound sepsis may be promoted by a failure of local antibacterial host defenses

Little attention has been focused on the local burn wound environment, even though burn wound sepsis is a common cause of death in the burn victim. To characterize the effect of the local burn wound environment on neutrophil function and metabolism, the opsonic activity of blister fluid specimens against Pseudomonas aeruginosa was measured as was the effect of blister fluid on control neutrophil oxygen consumption using preopsonized zymosan and f-met-leu-phe (FMLP) as stimuli. Blister fluid did not support the killing of P. aeruginosa by normal neutrophils as well as normal serum. Additionally, blister fluid inhibited zymosan-stimulated, but not FMLP-stimulated, neutrophil oxygen consumption. The inhibitory effect of blister fluid on zymosan-stimulated oxygen consumption correlated with the extent of complement activation, measured as C3d or C3AI (p less than 0.01). That blister fluid did not inhibit the FMLP-mediated respiratory burst supports the concept that the blister fluid inhibitory effect on the zymosan-mediated respiratory burst was mediated through the complement receptor. These findings that blister fluid can affect the bactericidal and metabolic activity of normal neutrophils support the concept that cellular function can be altered by the microenvironment in which the cells are bathed. This potential impairment of host defenses within the burn wound could predispose the burn victim to burn wound sepsis.

Absence of both cytochrome b-245 subunits from neutrophils in X-linked chronic granulomatous disease

Phagocytosis by neutrophils and other 'professional' phagocytic cells is accompanied by a microbicidal burst of non-mitochondrial respiration. Cytochrome b-245 is the only clearly defined component of this oxidase system and its absence provides the molecular basis of X-linked chronic granulomatous disease (CGD), in which a profound predisposition to infection results from complete failure of this respiratory burst. Purification of the cytochrome has proved difficult, with uniform disagreement regarding the identity of its apoprotein, descriptions of its relative molecular mass (Mr) on SDS-polyacrylamide gel electrophoresis (PAGE) ranging from 10,000 to 127,000 (10-127K). I report here that it has two subunits, a 23K protein and the previously described 76-92K glycoprotein. These subunits are closely linked and remain associated with the haem of the cytochrome through affinity and gel filtration chromatography and sucrose gradient centrifugation, and exhibit a similar distribution in a pH gradient. Neither protein was detected in the cells of five patients with X-linked CGD whereas both were present in two with the form of this disease with autosomal recessive inheritance.

Antigonococcal activity of human neutrophil cathepsin G

We have shown that lysosomal cathepsin G, prepared from acid extracts of granules derived from human polymorphonuclear granulocytes, exhibits potent in vitro antimicrobial activity against Neisseria gonorrhoeae. An isolated isozyme of cathepsin G was found to exhibit antigonococcal activity by a nonenzymatic mechanism in a time-dependent manner. Moreover, we observed that the antigonococcal activity of cathepsin G was relatively independent of pH and evident over a pH range resembling that invoked for maturing phagolysosomes. Using a number of isogenic strains, we determined that certain mutations known to alter cell envelope structure rendered gonococci more susceptible to cathepsin G. This suggests that the susceptibility of gonococci to cathepsin G, and possibly other antimicrobial proteins derived from PMN granules, is genetically determined and possibly related to the structure of the gonococcal cell envelope.

The influence of extracellular and phagolysosomal pH changes on the bactericidal activity of bovine neutrophils against Staphylococcus aureus

The influence of the pH of suspending medium on bovine neutrophil (PMN) function was assessed in tests of phagocytosis and killing of Staphylococcus aureus. Intracellular killing was markedly inhibited by moderate extracellular acidification whereas phagocytosis was little affected, except at the lowest pH level (pH 5.0). The killing of S. aureus by extracts of isolated PMN lysosomal granules showed a similar pH dependence and was optimal at pH levels above neutrality. Survival of S. aureus within PMN from different cows varied significantly and the relative differences in PMN bactericidal efficiency were maintained at all pH levels. The acidification of extracellular medium during incubation which resulted from metabolic activity of the PMN themselves, increased with increasing ratios of bacteria:PMN and varied significantly among cows. Addition of methylamine (10 mM) to elevate phagolysosomal pH inhibited phagocytosis and had no effect on intracellular survival of S. aureus. However, a lower concentration (1.5 mM) did not affect phagocytosis, but reduced bacterial survival without altering the relative differences in efficiency of PMN from different cows. It is suggested that the acidity of the extracellular medium may both reflect and influence the pH changes occurring within PMN phagosomes and, thereby, modulate the efficiency of intracellular destruction of S. aureus.

Late intraphagosomal hydrogen ion concentration favors the in vitro antimicrobial capacity of a 37-kilodalton cationic granule protein of human neutrophil granulocytes

We described previously (W.M. Shafer, L.E. Martin, and J.K. Spitznagel, Infect. Immun. 45:29-35, 1984) the presence of a 37-kilodalton cationic antimicrobial protein (37K CAP) in extracts of granules prepared from human polymorphonuclear granulocytes (PMN). In this investigation, we prepared 37K CAP from PMN granule extracts by sequential ion-exchange and molecular-sieve chromatography and examined its antimicrobial activity against a number of gram-negative and gram-positive bacteria. At concentrations of 5 micrograms/ml or lower, 37K CAP exerted selective antimicrobial activity against gram-negative bacteria. These bacteria included Acinetobacter lwoffii, Escherichia coli, Neisseria gonorrhoeae, Pseudomonas aeruginosa, Pseudomonas cepacia, Salmonella typhi, Salmonella typhimurium, and Shigella sonnei. However, at 5 micrograms of 37K CAP per ml, Proteus mirabilis, Proteus vulgaris, and Serratia marcescens resisted this antimicrobial activity. The bactericidal activity of 37K CAP was greatest in acidic (pH 5.5) as opposed to alkaline (pH 7.5) media. The level of S. typhimurium resistance to 37K CAP correlated with the presence of O antigen in the lipopolysaccharide. In the absence of O antigen repeat units, resistance was proportional to the length of the core oligosaccharide. These results suggest that 37K CAP may contribute significantly to the ability of PMN to kill gram-negative bacteria by nonoxidative means, particularly as the maturing phagolysosome becomes acidified.

Effects of the putative neutrophil-generated toxin, hypochlorous acid, on membrane permeability and transport systems of Escherichia coli

Titrimetric addition of hypochlorous acid (HOCl) or chloramine (NH2Cl) to suspensions of Escherichia coli decreases their ability to accumulate 14C-labeled glutamine, proline, thiomethylgalactoside, and leucine in a manner that approximately coincides with loss of cell viability; quantitative differences in cellular response are observed with the two oxidants. Inhibition of beta-galactosidase activity in E. coli ML-35, a strain lacking functional lactose permease, is complex and also depends upon the identity of the oxidant. Membrane proton conductivities and glycerol permeabilities are unchanged by addition of HOCl or NH2Cl in excess of that required for inactivation. The combined results are interpreted to indicate that the locus of HOCl attack is the cell envelope, that HOCl inactivation does not occur by loss of membrane structural integrity, that loss of transport function can be identified with either selective oxidative inhibition of the transport proteins or loss of cellular metabolic energy, and that different mechanisms of inactivation may exist for HOCl and NH2Cl.

Cytoplasmic pH regulation in phorbol ester-activated human neutrophils

Activation of neutrophils by 12-O-tetradecanoylphorbol-13-acetate (TPA) is accompanied by an initial cytoplasmic acidification, followed by an alkalinizing phase due to Na+-H+ countertransport. The source of the acidification, which is fully expressed by activation with TPA in Na+-free or amiloride-containing media, was investigated. The acidification phase was detected also in degranulated and enucleated cytoplasts, ruling out a major contribution by the nucleus or secretory vesicles. Cytoplasmic acidification was found to be associated with an extracellular acidification, suggesting metabolic generation of H+. Two principal metabolic pathways are stimulated in activated neutrophils: the reduction of O2 by NADPH-oxidase and the hexose monophosphate shunt. A good correlation was found between the activity of these pathways and the changes in cytoplasmic pH. Inhibition of superoxide synthesis prevented the TPA-induced cytoplasmic acidification. Moreover, activation of the hexose monophosphate shunt with permeable NADPH-oxidizing agents (in the absence of TPA) also produced a cytoplasmic acidification. Cytoplasmic acidification was also elicited by exogenous diacylglycerol and by other beta-phorbol diesters, which are activators of the kinase, but not by unesterified phorbol or by alpha-phorbol diesters, which are biologically inactive. The results suggest that the cytoplasmic acidification induced by phorbol esters in neutrophils reflects accumulation of H+ liberated during the metabolic burst that follows activation.

Influence of human monocytes on the antibacterial activity of kanamycin and gentamicin for Staphylococcus aureus

The present study was performed to compare the antibacterial activities of kanamycin and gentamicin on Staphylococcus aureus phagocytosed by human monocytes and on nonphagocytosed S. aureus. The method used permitted the measurement of the effect of antibiotics on intracellular bacteria independent of phagocytosis and intracellular killing by the monocytes. A morphological assay with lysostaphin established the intracellular localization of about 70% of the cell-associated S. aureus in the monocyte-bacterium suspension. After 1 h of incubation, the antibacterial activity of both aminoglycosides was greater against intracellular than against nonphagocytosed S. aureus, but after 3 h, the reverse was true. The maximal effect on phagocytosed S. aureus, i.e., killing of about 98% of the bacteria, was reached in the first hour of incubation at kanamycin and gentamicin concentrations of 5 and 1 microgram/ml, respectively. A cell-free medium in which monocytes had been incubated increased the antibacterial activity of kanamycin, indicating that monocytes secrete a factor that enhances the antibacterial activity of aminoglycosides.

Abnormalities of neutrophil phagocytosis, intracellular killing and metabolic activity in alcoholic cirrhosis and hepatitis

Neutrophil functions of phagocytosis and intracellular killing of bacteria were examined in 40 patients with alcoholic cirrhosis of whom 18 had a superimposed acute alcoholic hepatitis. In 65% of these, defective neutrophil phagocytosis was demonstrable, and in 62.5% there was a defect of intracellular killing of either Staphylococcus aureus or Escherichia coli. Studies of the patients' serum failed to reveal inhibitors of neutrophil function. Additional assays of superoxide (O2-) and hydrogen peroxide production, hexose monophosphate shunt activity, degranulation and cellular levels of granule enzymes and glutathione revealed that these neutrophil defects are caused by both reduced production of superoxide and defects of degranulation. The hydrogen peroxide/superoxide molar ratio was raised in patients' neutrophils, and the strong inverse correlation found between the value of this ratio and intracellular levels of reduced glutathione would be consistent with the hypothesis that the neutrophils from patients with cirrhosis are unable to detoxify hydrogen peroxide effectively and that this is a result of reduced levels of glutathione in the cells. The consequent increase in oxidant stress, both intra- and extracellularly, may be the cause of phagocytic and degranulation defects. The reduced responses of patients' neutrophils may be caused by previous exposure of the cells to activating stimuli in circulation, as evidenced by depleted intracellular levels of granule enzymes and glutathione. Neutrophils from the patients with a superimposed acute alcoholic hepatitis had depressed phagocytosis in the early stages of incubation but, on the whole, neutrophils from these patients had a greater capacity for ingestion and killing of bacteria than neutrophils from patients with cirrhosis alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Similarity of kinetics of three types of myeloperoxidase from human leukocytes and four types from HL-60 cells

Km values for H2O2 and Vmax values for three types of myeloperoxidase (MPO) from human leukocytes (MPO-I, -II, and -III) and four types from human myeloid leukemia HL-60 cells (MPO-IA, -IB, -II, and -III) were determined. Km values of human leukocyte MPOs decreased with increasing pH from 4.4 to 6.2 and increased with increasing NaCl concentration from 0.025 to 0.14 M. There was no significant difference among Km values of leukocyte MPO-I, -II, and -III. NaBr also showed a tendency similar to that of NaCl with regard to the effects of pH and halide concentration on Km values. However, Km values in the presence of NaBr were lower than those in the presence of NaCl. Effects of pH and NaCl concentration on Vmax values of MPO-I, -II, and -III were also examined. Vmax values of MPO-I, -II, and -III were higher at pH 4.9 and 5.4 and increased with increasing NaCl concentration. In addition, no difference was observed between Km values of leukocyte and those of HL-60 cells. MPO-IB, the half-molecular-weight enzyme of HL-60 cells, also had the same Km values as the others. Furthermore, inhibition of the activities of seven MPOs of leukocytes and HL-60 cells by H2O2 was similarly observed at concentrations above 1 mM at pH 5.4 but not at pH 4.4. These results indicate that there is no difference in the affinity to H2O2 among leukocyte MPO-I, -II, and -III and HL-60 cell MPO-IA, -IB, -II, and -III.

Uptake, intracellular activity, and influence of rifampin on normal function of polymorphonuclear leukocytes

Quinone and hydroquinone forms of rifampin accumulated in normal polymorphonuclear leukocytes (PMN) (maximal cellular to extracellular concentration ratio [C/Emax] +/- standard error of the mean, 9.36 +/- 0.54 and 8.82 +/- 0.65, respectively, after 5 to 10 min) and chronic granulomatous disease PMN (C/Emax, 13.76 +/- 0.77 and 14.29, respectively). Uptake of rifampin was influenced by incubation temperature and extracellular pH but not by phorbol myristate acetate stimulation or metabolic inhibitors. At extracellular concentrations between 0.06 and 5.0 mg/liter, rifampin significantly reduced the number of staphylococci surviving inside chronic granulomatous disease PMN, thus compensating for the bactericidal defect inherent with this disease. Spontaneous migration and chemotaxis of normal PMN were unaffected by rifampin. However, phagocytosis of yeast particles and oxygen consumption of stimulated PMN were moderately depressed, and O2- production and chemiluminescence were significantly depressed in a dose-dependent manner. The bactericidal activity of normal PMN was not impaired. Inhibition of chemiluminescence and O2- release were also observed in a cell-free system. We conclude that rifampin possesses favorable characteristics for the effective elimination of intracellular microorganisms. Further studies are needed to evaluate the in vivo significance of ion scavenging by rifampin, which could be hazardous to immunocompromised patients.

Modification of interactions between neutrophils and staphylococci by lysosomotropic weak bases

Weak bases that alkalinize the pH within neutrophil lysosomes inhibit in vitro cell functions, including lysosomal enzyme release and superoxide production. To determine the relevance of this inhibition to microbicidal activity, the effect of lysosomotropic weak bases on interactions between human neutrophils and Staphylococcus aureus 502a was studied. After treatment with 1 mM chloroquine, neutrophils showed significantly impaired phagocytosis of 14C-labeled S. aureus. However, 50 mM ammonium chloride had no effect on phagocytosis, although we have previously shown that this concentration raises lysosomal pH and inhibits degranulation and superoxide production. This base was therefore used to study effects on intracellular microbicidal activity. Incubation of neutrophils with 50 mM ammonium chloride diminished killing of S. aureus (22.9 +/- 6.3% of bacteria surviving versus 8.2 +/- 1.3% in suspensions without ammonium chloride). At 1 mM, ammonium chloride had no significant effect. The inhibition of cellular function could be neither explained as a function of neutrophil death, as measured by trypan blue dye exclusion, nor attributed to direct promotion of bacterial growth (in the absence of neutrophils, colony counts were similar in the presence or absence of ammonium chloride) or enhanced resistance to neutrophil microbicidal mechanisms (bacteria treated with ammonium chloride and washed before neutrophil exposure showed no improvement in survival). Ammonium chloride at 50 mM also impaired neutrophil killing of S. aureus in an anaerobic chamber, but microbicidal activity against Escherichia coli S15 was not affected. These findings suggest that optimal neutrophil killing of staphylococci requires a highly acid intralysosomal compartment, but ingestion of bacteria does not. This may reflect primary failure of acidification of the phagocytic vacuole or differential pH requirements for fusion of the plasma membrane with itself and with lysosome membranes. The difference between effects on killing of S. aureus and E. coli is probably a result of the relative importance of the components of neutrophil microbicidal activity against the two organisms.

Intracellular pH modulates the generation of superoxide radicals by human neutrophils

The relationship of intracellular pH (pHi) to superoxide radical (O2-) generation was investigated in chemotactic factor-stimulated human neutrophils. Exposure of cells to 100 nM N-formylmethionyl-leucyl-phenylalanine (FMLP) caused activation of Na/H exchange which, in 140 mM Na medium (pH0 7.40), led to a rise in pHi from 7.22 to 7.80. This pHi change was sensitive to amiloride (apparent Ki 78 microM), an inhibitor of Na/H countertransport. The time course of the alkalinization was similar to that of FMLP-stimulated O2- production, which was complete by 5 min. In the presence of 1 mM amiloride, which nearly blocked the pHi transient elicited by FMLP, or in the absence of external Na, where intracellular acidification was observed in FMLP-stimulated cells, O2- release was still roughly 25-45% of normal. Thus, an alkalinization cannot be an obligatory requirement for O2- generation. By independently varying either pH0, pHi, or the internal or external concentrations of Na, both the direction and magnitude of the FMLP-induced pHi transients could be altered. In each instance, the amount of O2- release correlated directly with pHi and was enhanced by intracellular alkalinization. In the absence of FMLP, a rise in pHi to 7.7-7.8 by exposure of cells to 30 mM NH4Cl, 10 microM monensin (a Na/H exchanging ionophore), or after a prepulse with 18% CO2 did not result in O2- generation. Thus, these results imply that an alkalinization per se is not a sufficient trigger. Neutrophils exposed to 4 nM FMLP exhibited a threefold slower rate of alkalinization (reaching pHi approximately 7.80 by 20-30 min) as compared to that obtained with 100 nM FMLP and did not release significant amounts of O2- under normal incubation conditions. However, these cells could be induced to generate O2- when the degree of alkalinization was enhanced by internal Na depletion or by pretreatment with 18% CO2. Together, these results indicate a modulating effect of pHi on O2- production and suggest that other functional responses of neutrophils may be regulated by their pHi.

Comparative reactivities of various biological compounds with myeloperoxidase-hydrogen peroxide-chloride, and similarity of the oxidant to hypochlorite

The reactivities of myeloperoxidase-H2O2-Cl- and sodium hypochlorite with amino acids, uric acid, NADH, ascorbic acid, ADP, albumin, haemoglobin, alpha 1-antitrypsin and some hydroxyl radical scavengers have been compared. The ability of each compound to inhibit chlorination of monochlorodimedon by both oxidants was measured. Relative reaction rates varied over a range of 10(5), but the reactivities of the two oxidants with each compound were very similar, from which it is concluded that the reactions of hypochlorite accurately reflect those of the myeloperoxidase system. Thiol compounds (cysteine and GSH) and methionine were more than 100-times more reactive than other amino acids, which had comparable reactivity to NADH and uric acid. Benzoate, dimethylsulphoxide and formate were very much less reactive. The significance of these reactions of myeloperoxidase in microbial killing and inflammation is discussed.

Production of the superoxide adduct of myeloperoxidase (compound III) by stimulated human neutrophils and its reactivity with hydrogen peroxide and chloride

Examination of the spectra of phagocytosing neutrophils and of myeloperoxidase present in the medium of neutrophils stimulated with phorbol myristate acetate has shown that superoxide generated by the cells converts both intravacuolar and exogenous myeloperoxidase into the superoxo-ferric or oxyferrous form (compound III or MPO2). A similar product was observed with myeloperoxidase in the presence of hypoxanthine, xanthine oxidase and Cl-. Both transformations were inhibited by superoxide dismutase. Thus it appears that myeloperoxidase in the neutrophil must function predominantly as this superoxide derivative. MPO2 autoxidized slowly (t 1/2 = 12 min at 25 degrees C) to the ferric enzyme. It did not react directly with H2O2 or Cl-, but did react with compound II (MP2+ X H2O2). MPO2 catalysed hypochlorite formation from H2O2 and Cl- at approximately the same rate as the ferric enzyme, and both reactions showed the same H2O2-dependence. This suggests that MPO2 can enter the main peroxidation pathway, possibly via its reaction with compound II. Both ferric myeloperoxidase and MPO2 showed catalase activity, in the presence or absence of Cl-, which predominated over chlorination at H2O2 concentrations above 200 microM. Thus, although the reaction of neutrophil myeloperoxidase with superoxide does not appear to impair its chlorinating ability, the H2O2 concentration in its environment will determine whether the enzyme acts primarily as a catalase or peroxidase.

Regulation of intracellular pH in human neutrophils

The intracellular pH (pHi) of isolated human peripheral blood neutrophils was measured from the fluorescence of 6-carboxyfluorescein (6-CF) and from the equilibrium distribution of [14C]5,5-dimethyloxazolidine -2,4-dione (DMO). At an extracellular pH (pHo) of 7.40 in nominally CO2-free medium, the steady state pHi using either indicator was approximately 7.25. When pHo was suddenly raised from 7.40 to 8.40 in the nominal absence of CO2, pHi slowly rose by approximately 0.35 during the subsequent hour. A change of similar magnitude in the opposite direction occurred when pHo was reduced to 6.40. Both changes were reversible. Intrinsic intracellular buffering power, determined by using graded pulses of CO2 or NH4Cl, was approximately 50 mM/pH over the pHi range of 6.8-7.9. The course of pHi obtained from the distribution of DMO was followed during and after imposition of intracellular acid and alkaline loads. Intracellular acidification was brought about either by exposing cells to 18% CO2 or by prepulsing with 30 mM NH4Cl, while pHo was maintained at 7.40. In both instances, pHi (6.80 and 6.45, respectively) recovered toward the control value at rates of 0.029 and 0.134 pH/min. These rates were reduced by approximately 90% either by 1 mM amiloride or by replacement of extracellular Na with N-methyl-D-glucamine. Recovery was not affected by 1 mM SITS or by 40 mM alpha-cyano-4-hydroxycinnamate (CHC), which inhibits anion exchange in neutrophils. Therefore, recovery from acid loading is probably due to an exchange of internal H for external Na. Intracellular alkalinization was achieved by exposing the cells to 30 mM NH4Cl or by prepulsing with 18% CO2, both at a constant pHo 7.40. In both instances, pHi, which was 7.65 and 7.76, respectively, recovered to the control value. The recovery rates (0.033 and 0.077 pH/min, respectively) were reduced by 80-90% either by 40 mM CHC or by replacement of extracellular Cl with p-aminohippurate (PAH). SITS, amiloride, and ouabain (0.1 mM) were ineffective.(ABSTRACT TRUNCATED AT 400 WORDS)

Adherence of lysostaphin to and penetration into human monocytes

The effect of lysostaphin on Staphylococcus aureus phagocytosed by monocytes was investigated. The results showed that lysostaphin adheres to monocytes by a temperature-independent mechanism, is not adequately removed from monocytes by washing, and penetrates by means of a temperature-dependent mechanism. In in vitro assays of monocyte function, phagocytosed S. aureus can be killed by lysostaphin after penetration of the cells during incubation or by adhering lysostaphin when the monocytes are disrupted.

Legionella pneumophila inhibits acidification of its phagosome in human monocytes

We used quantitative fluorescence microscopy to measure the pH of phagosomes in human monocytes that contain virulent Legionella pneumophila, a bacterial pathogen that multiplies intracellularly in these phagocytes. The mean pH of phagosomes that contain live L. pneumophila was 6.1 in 14 experiments. In the same experiments, the mean pH of phagosomes containing dead L. pneumophila averaged 0.8 pH units lower than the mean pH of phagosomes containing live L. pneumophila, a difference that was highly significant (P less than 0.01 in all 14 experiments). In contrast, the mean pH of phagosomes initially containing live E. coli, which were then killed by monocytes, was the same as for phagosomes initially containing dead E. coli. The mean pH of L. pneumophila phagosomes in activated monocytes, which inhibit L. pneumophila intracellular multiplication, was the same as in nonactivated monocytes. To simultaneously measure the pH of different phagosomes within the same monocyte, we digitized and analyzed fluorescence images of monocytes that contained both live L. pneumophila and sheep erythrocytes. Within the same monocyte, live L. pneumophila phagosomes had a pH of approximately 6.1 and sheep erythrocyte phagosomes had a pH of approximately 5.0 or below. This study demonstrates that L. pneumophila is capable of modifying the pH of its phagocytic vacuole. This capability may be critical to the intracellular survival and multiplication of this and other intracellular pathogens.

Growth of group IV mycobacteria on medium containing various saturated and unsaturated fatty acids

Seventy-one strains of 15 species of rapidly growing mycobacteria were studied for their susceptibilities to fatty acids with 2 to 20 carbons by the agar dilution method at pH 7.0. Most mycobacteria other than potential pathogens (Mycobacterium fortuitum and Mycobacterium chelonei) were resistant to saturated fatty acids, except for lauric acid (C12:0) (MIC, 6.25 to 25 micrograms/ml) and capric acid (C10:0) (MIC, 50 to 100 micrograms#ml). M. fortuitum and M. chelonei were substantially insusceptible to these fatty acids. Unsaturated fatty acids with 16 to 20 carbons, except for C20:5, were highly toxic to group IV mycobacteria other than M. fortuitum, M. chelonei, Mycobacterium smegmatis, and Mycobacterium phlei, these being highly resistant to all the unsaturated acids, except for C16:1, C18:3, and C20:5. Introduction of double bonds to C16 to C20 fatty acids caused a marked increase in their activities that depended on the increase in the number of double bonds, at least up to three or four. M. fortuitum and M. chelonei were more resistant to the unsaturated fatty acids (particularly to C20:3 and C20:4) than the other group IV mycobacteria.

Purification and antibacterial activity of antimicrobial peptides of rabbit granulocytes

Six antimicrobial peptides, corresponding to the family of "lysosomal cationic proteins" described previously by Zeya and Spitznagel (H. I. Zeya and J. K. Spitznagel, J. Bacteriol. 91:750-754, 1966; H. I. Zeya and J. K. Spitznagel, J. Bacteriol. 91:755-762, 1966), were purified from rabbit peritoneal granulocytes by preparative acrylamide gel electrophoresis and reversed-phase high-pressure liquid chromatography. Each of the peptides was of low molecular weight (ca. 4,000) as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The two most cationic peptides, NP-1 and NP-2, were active against a broad spectrum of gram-positive and gram-negative bacteria. The remaining four peptides, NP-3A, NP-3B, NP-4, and NP-5, had more selective antibacterial activity. None of the peptides was active against Bordetella bronchiseptica, a common pathogen of domestic rabbits. Antibacterial activity was best expressed at near neutral pH under conditions of low ionic strength.

Endosome pH measured in single cells by dual fluorescence flow cytometry: rapid acidification of insulin to pH 6

The acidification of various ligands was measured on a cell by cell basis for cell suspensions by correlated dual fluorescence flow cytometry. Mouse 3T3 cells were incubated with a mixture of fluorescein- and rhodamine-conjugated ligands, and the ratio of fluorescein and rhodamine fluorescence was used as a measure of endosome pH. The calibration of this ratio by both fluorometry and flow cytometry is described. Dual parameter histograms of average endosome pH per cell versus amount of internalization were calculated from this data, for samples in the absence and presence of chloroquine added to neutralize acidic cellular vesicles. The kinetics of acidification of insulin were measured and compared with previous results obtained with the chloroquine ratio technique. Rapid acidification of internalized ligand was observed both for insulin, which was mostly internalized via nonspecific pathways, and for alpha 2-macroglobulin, which was mainly internalized by specific receptor-mediated endocytosis. The average pH observed for internalized insulin was less than pH 6 within 10 min after addition of insulin. At 30 min, the average pH began to decrease to approximately pH 5, presumably because of fusion of endosomes with lysosomes.

Changes in the subcellular distribution of the cytochrome b-245 on stimulation of human neutrophils

Cytochrome b-245 of neutrophils has a bimodal distribution in sucrose density gradients. The lighter component (d = 1.14) is shown to be associated with the plasma membrane by the similarity between its density and that of markers of this organelle, as well as a parallel increase in the density of the cytochrome and plasma membrane after treatment with digitonin or dimethyl suberimidate. The cytochrome b-245 of monocytes and cytoplasts, the latter produced by the removal of nuclei and granules from neutrophils, was located only in the plasma membrane. The denser peak of cytochrome (d = 1.19), which contained approximately half of the cytochrome b of neutrophils, had a similar density-distribution profile to the specific granules. After hypo-osmotic disruption of this denser material, the cytochrome distributed with the density of membranes, suggesting an original location within the membrane of the intracellular structure. Redistribution of the cytochrome from the granules to the membranes was observed after stimulation of respiratory activity with soluble agents or opsonized particles. This translocation is not responsible for activation of the oxidase system. There was poor agreement between the kinetics of the transfer of cytochromes from the dense component to the membranes, and degranulation of specific-granule contents, suggesting that the cytochrome may be located in another intracellular structure or that its localization becomes further modified after granule fusion.

A wild and an attenuated strain of Francisella tularensis differ in susceptibility to hypochlorous acid: a possible explanation of their different handling by polymorphonuclear leukocytes

We have previously reported that a wild strain of Francisella tularensis is much less efficiently killed by human polymorphonuclear leukocytes than is an attenuated strain. In the present study, the killing of the attenuated strain was found to be strictly oxygen dependent. The wild and the attenuated strains both induced a respiratory burst in the leukocytes. The difference between the strains in susceptibility to agents produced at the burst could be explained by a difference in susceptibility to hypochlorous acid.

pH in the endosome. Measurements during pinocytosis and receptor-mediated endocytosis

By fluorescence spectroscopy, the average pH within endocytic compartments was determined during endocytosis of fluorescein conjugates by macrophages and hepatocytes. In mouse macrophages and hepatocytes fluorescein conjugates taken up either in the fluid phase or by binding to cell surface receptors were rapidly transferred to an acidic compartment (pH 5-5.5). The half-time for this process was generally less than 4 min. The pH within yeast-containing phagosomes was also rapidly reduced to similar levels, following a unique and transient increase. In each case, the acid endosomal compartments involved probably do not contain lysosomal enzymes. When fluorescein conjugates of asialoglycoproteins were internalised by hepatocytes at 20 degrees C, no proteolysis occurred within the acidic endosome until the temperature was raised. Fluorescein conjugates of concanavalin A (conA) and polylysine were relatively more slowly internalised by macrophages. The half-times for uptake, estimated by fluorescence change, were comparable with the turnover time for bulk plasma membrane. The relatively high average pH experienced by these conjugates indicated that a small proportion of these non-specific cell-surface labels was always in contact with the extracellular medium.

Nonoxidative antimicrobial reactions of leukocytes

Increasingly abundant evidence supports the hypothesis that PMNs and perhaps alveolar macrophages have antimicrobial mechanisms independent of the presences of molecular oxygen for effective action against an array of bacteria and against some fungi. Eosinophils have mechanisms toxic for schistosomula and Trichinella larvae. In all instances the antimicrobial substances isolated have been cationic proteins and, in PMNs, associated with the azurophil cytoplasmic granules of the PMNs. Several of these substances have thus far demonstrated no enzymic function. Two of these substances are serine proteases but in one, chymotrypsin-like protein, the antimicrobial action depends on the cationic properties of the protein and is independent of the proteolytic action of the substance. In most instances, these proteins are cationic due to relatively large proportions of arginine. In two instances, a large proportion of lysine is present. All have high proportions (about 50%) of hydrophobic amino acid. Such proteins occur in the PMNs of man, rabbit, guinea pig, rat, cow, and chicken. The present view is that they are most active against gram-negative bacteria. At least two of them-37-kd and 57-kd proteins (Shafer and Spitznagel, 1983)-act on S. typhimurium in a manner analogous to that of polymyxin B through binding to lipid A. Currently available results shows that anaerobic PMNs have substantial antimicrobial capacity. Whether this capacity is due to the O2-independent mechanisms discussed in this chapter remains to be established with greater certainty.

Fluorescein conjugates as indicators of subcellular pH. A critical evaluation

Fluorescein and tetramethylrhodamine conjugates to protein or dextran were used to determine subcellular pH. The pH dependence of fluorescence of fluorescein isothiocyanate (FITC) conjugates could be described by a single proton dissociation (pK'a approximately 6.8). This allowed pH to be derived accurately from spectra using the simple Henderson-Hasslebach equation. FITC and TRITC conjugates were delivered to mouse macrophage lysosomes by pinocytosis. Lysosomal pH was then determined in several different ways. First, by direct matching of the subcellular fluorescence spectrum with calibration spectra obtained in free solution. Secondly, monensin was used to equilibrate internal and extracellular pH. Subcellular pH could then be determined by the relative increase in fluorescence of the FITC conjugate without loss of probe from the lysosomes. This allowed the calibration of pH dependence with the probe in situ. Finally, macrophages were permitted to pinocytose FITC and TRITC dextran conjugates simultaneously. pH could be determined from the ratio of emissions from the two dyes within the lysosomes. Each of these different methods gave a similar value for lysosomal pH (4.8 +/- 0.1).

In vivo degradation of gonococcal outer membrane proteins within human leukocyte phagolysosomes

We previously showed in vitro hydrolysis of outer membrane proteins by lysosomal proteases and purified elastase. In this study we examined the in vivo relevance of the previous studies. Outer membranes were obtained from Neisseria gonorrhoeae type 3 (strain GC7) by LiCl2 extraction. Some preparations were labeled with 125I. Phagocytizable particles were prepared by coating latex beads with outer membranes, and polymorphonuclear leukocytes were allowed to phagocytize serum-opsonized particles. After homogenization of neutrophils, phagolysosomes were recovered by flotation through sucrose. Phagolysosomes were prepared for slab gel electrophoresis immediately or incubated further at 37 degrees C to allow continued degradation of outer membrane proteins. The principal protein (protein I) and minor proteins (proteins II) of outer membranes were hydrolyzed in whole neutrophils and in isolated phagolysosomes. Proteins II were more susceptible to hydrolysis than protein I. Hydrolytic products formed were nearly identical in vivo and in vitro. We also radiolabeled the surface-exposed proteins of live gonococci. Degradation of outer membrane proteins on the intact bacteria within neutrophil and monocyte phagolysosomes was shown. This indicates that our earlier in vitro model is relevant to in vivo hydrolysis of gonococcal outer membrane proteins.

Simultaneous measurement of phagocytosis and phagosomal pH by flow cytometry: role of polymorphonuclear neutrophilic leukocyte granules in phagosome acidification

Human polymorphonuclear neutrophilic leukocytes (PMNLs) phagocytosed fluorescein-isothiocyanate (FITC)-labelled Staphylococcus aureus. Free bacteria, phagocytes, and nonphagocytes were discriminated and quantified by flow cytometry (FCM). The relative fluorescence of phagocyte-associated and free bacteria (Nf:N) was calculated by dividing the mean phagocyte fluorescence by that of the free bacteria and the number of phagocytosed bacteria. Bactericidal capacity and chemiluminescence were measured by standard methods. The red-to-green fluorescence ratio of acridine orange-stained PMNLs (R/G) was measured by FCM. Degradation of bacteria was monitored by the reduction in FITC and ethidiumbromide fluorescence of bacteria liberated from the phagocytes. Bacterial FITC fluorescence was pH dependent. Nf:N was 0.5 to 0.7. Using a standard curve for the interrelationship between bacterial fluorescence and pH, phagosomal pH was 5.0-5.5. Phagocytes, kept at 4 degrees C for 24 h had Nf:N approximately 1, did not degrade bacteria, but killed them and emitted chemiluminescence. NH4Cl increased phagocyte fluorescence by 27% and decreased R/G by 50%. Cyanide and azide did not affect Nf:N. Nf:N of phagocytes from a patient with chronic granulomatous disease was 32% below, and R/G was 32% higher than the controls. Acidification of the phagosomes seems to be related to discharge of PMNL granule contents and independent of the respiratory burst.

Behavior of neutrophilic granulocytes in a case of Papillon-Lefèvre syndrome

Recently we had the opportunity to examine and follow up over a period of 2 years an unusual case of Papillon-Lefèvre syndrome (PLS). A 10 year old boy exhibited all symptoms typical of PLS except periodontitis and premature loss of deciduous teeth. The present report aimed at studying the functional capacity of his neutrophilic granulocytes. It integrates clinical observations, histopathological findings and results of in vitro tests. The bioptic material examined included one gingival biopsy, extracted teeth, suppurative material discharged from periodontal pockets, pus emanating from a mucosal abscess, and peripheral blood leucocytes. The neutrophils were sampled on two separate occasions in two independent laboratories and tested for a variety of functions, i.e. motility, random and directional locomotion (chemotaxis), phagocytosis, membrane potential depolarization, oxygen consumption, NBT reduction, and intracellular killing of bacteria and fungi. Findings and test data indicated that in this case of PLS, neutrophilic granulocytes behaved normally with respect to all these functions including margination in blood vessels, emigration, phagocytosis of a broad range of bacteria, degranulation of lysosomes, and intracellular destruction. The data imply that factors other than neutrophil defects may be responsible for rapidly destructive periodontitis in cases where PLS is not associated with an increased susceptibility to infection.