Human platelets damage Aspergillus fumigatus hyphae and may supplement killing by neutrophils.

Neutropenia is considered a significant risk factor for invasive aspergillosis but is almost always associated with concurrent thrombocytopenia. Studies determined that platelets, like neutrophils, attached to cell walls of the invasive hyphal form of Aspergillus fumigatus. Organisms were damaged as shown by loss of cell wall integrity in scanning laser confocal microscopy and release of defined hyphal surface glycoproteins. Rapid expression appearance of surface antigen CD63 and release of markers of platelet degranulation confirmed activation during attachment to hyphae. Optimal platelet activation required opsonization of hyphae with fresh or heat-inactivated whole plasma. These effects of opsonization with whole plasma could not be duplicated by pooled human serum, immunoglobulin G, or fibrinogen, whether used separately or combined. Thus, platelets in the presence of whole plasma have the potential to play an important role in normal host defenses against invasive aspergillosis.

Mechanisms and target sites of damage in killing of Candida albicans hyphae by human polymorphonuclear neutrophils.

Target sites of fungal cell damage were studied to define mechanisms of neutrophil-mediated killing of Candida albicans hyphae. Neutrophils induced hyphal cell wall damage, as evidenced by release of cell wall glycoproteins and confocal microscopic changes. Damage occurred in the presence of neutrophil granule extracts and did not require oxidants. However, oxidation of hyphal surface glycoproteins correlated strongly with parallel increments in fungicidal activity, suggesting that oxidants did contribute to maximal cell wall damage. Neutrophil oxidants also induced hyphal DNA fragmentation, primarily single-strand breakage, as shown by increased electrophoretic migration after nuclease-S1 DNA digestion at single-strand break sites. The onset of damage to hyphal cell walls and DNA preceded detectable neutrophil-mediated fungicidal effects. Likewise, hyphal amino acid and nucleotide turnover as well as ATP initially rose, then declined as lethal effects became detectable. Thus, preceding detectable fungal cell death, neutrophil oxidative and oxygen-independent mechanisms damaged defined targets.

A simplified new assay for assessment of fungal cell damage with the tetrazolium dye, (2,3)-bis-(2-methoxy-4-nitro-5-sulphenyl)-(2H)-tetrazolium-5-carboxanil ide (XTT).

Studies of antimycotic host defenses have been limited by the paucity of rapid, reproducible quantitative assays for fungal cell damage. Prior studies defined a colorimetric method that uses MTT, a tetrazolium dye, to quantify polymorphonuclear leukocyte (PMNL)-mediated damage to fungi. These relatively simple, rapid, and reproducible assays require cumbersome extraction of precipitated MTT-formazan and high cell densities to overcome relatively low sensitivity. In experiments that compared assays with MTT and another tetrazolium dye, 2,3-bis-(2-methoxy-4-nitro-5-sulphenyl)-(2H)-tetrazolium-5-+ ++carboxanilide (XTT), estimates of damage to Aspergillus fumigatus hyphae by human PMNL were similar with both dyes. However, XTT reduction was more rapid and sensitive, yielding accurate results with fewer organisms and PMNL. The water-soluble XTT-formazan product also simplified measurements by eliminating the need for solvent-extraction steps that are obligatory in MTT assays. Thus, XTT is advantageous for quantitative assessment of fungal cell damage, although MTT remains useful for assessing fungal cell viability by direct microscopic visualization of precipitated formazan.

Role of the Fc gamma R subclasses Fc gamma RII and Fc gamma RIII in the activation of human neutrophils by low and high valency immune complexes.

Two Fc gamma receptor (Fc gamma R) subclasses on human neutrophils, Fc gamma RII and Fc gamma RIII, activate different cellular functions. To examine the involvement of each receptor subtype in polymorphonuclear leukocyte activation, Fab and F(ab')2 fragments of subclass-specific monoclonal antibodies ([mAbs] mAb IV.3 against Fc gamma RII and mAb 3G8 against Fc gamma RIII, respectively) were used to block the binding of low valency immune complexes (LICs) and high valency immune complexes (HICs). Flow cytometry then permitted the simultaneous quantitation of antibody and ligand binding, the elicited intracellular Ca2+ concentration (delta[Ca2+]int), initiation of the oxidative burst, and/or the phospholipase A activation in the same cell. We have previously demonstrated that subsaturating dosages of HIC bind uniformly to all the cells but elicit an "all-or-none" (i.e., dose independent) maximal delta[Ca2+]int in a dose-dependent subpopulation of the cells. In contrast, both the proportion of cells responding and the magnitude of the delta[Ca2+]int transient depend on the subsaturating dose of LIC, even though it too binds uniformly to all the cells, nonresponding as well as responding. These earlier findings have here been extended by single cell flow cytometric analysis to demonstrate that F(ab')2 Fc gamma RIII is the major Fc gamma R involved in HIC binding (and [Ca2+]int mobilization), as well as in oxidative burst and phospholipase A activation. In contrast, both receptor subclasses must be available for LIC-elicited delta[Ca2+]int, as blockage by either of the mAb Fab or F(ab')2 fragments abrogates this response, even though LIC binding to the receptors is not decreased. Furthermore, LIC elicited little oxidative burst activity and failed to activate phospholipase A but cross-linking to achieve multivalency, previously shown to induce [Ca2+]int and oxidative burst responses, elicited phospholipase A activity via Fc gamma RIII. Fc gamma RII's role appears to be modulation of the small, late Ca2+ influx observed at > 1 min, whereas Fc gamma RIII modulates all the earlier larger events. Thus, simultaneous observation of receptor identity, receptor occupancy, and consequent activation parameters in the same cell by flow cytometry permits use to demonstrate that Fc gamma RII is necessary for the small signal transduction elicited by LIC; it plays a relatively small role in polymorphonuclear leukocyte stimulation by HIC. Fc gamma RIII is the main receptor responsible for immune complex-elicited polymorphonuclear leukocyte responses; its efficacy is greatly enhanced when the receptors are cross-linked, either by preequilibrated multivalent complexes or by in situ cross-linking of bound LIC with excess antibody.

Relationship of phospholipase C- and phospholipase D-mediated phospholipid remodeling pathways to respiratory burst activation in human neutrophils stimulated by Candida albicans hyphae.

Neutrophil (PMN) oxidant release, a key component of defenses against disseminated candidiasis, was preceded by oxidant generation after stimulation by Candida albicans hyphae. Opsonized or unopsonized hyphae triggered phospholipase D (PLD) activation within 5 or 30 s, respectively, forming 1-O-alkyl-phosphatidic acid (alkyl-PA) or 1-O-alkyl-phosphatidyl-ethanol in the presence of ethanol. Ethanol, which competitively lowers phosphatidic acid (PA) production, caused dose-dependent inhibition of superoxide (O2-) generation after hyphal stimulation but altered neither baseline-unstimulated O2- production nor responses to phorbol myristate acetate. PA rises evoked by unopsonized hyphae began 2 min before significant O2- release, also preceding both phospholipase C activation and cytosolic Ca2+ rises. Diacylglycerol (DAG) rose in two distinct phases after stimulation by opsonized or unopsonized hyphae, peaking briefly after 60 or 120 s, respectively, followed by prolonged secondary rises. Initial DAG rises preceded inositol triphosphate elevations evoked by unopsonized hyphae. Though PA rose before DAG, no dephosphorylation of PA to form 1-O-alkyl-DAG was noted. Propranalol, which increases PA accumulation by inhibiting PA phosphohydrolase, lowered PMN O2- responses to hyphae. Early DAG rises temporally overlapped respiratory burst initiation but PMN responses to hyphae were unchanged by a DAG kinase inhibitor, R59022, which blocks phosphorylation of DAG to PA and enhances DAG accumulation. Thus, neither PA nor DAG accumulation individually accounted for triggering PMN O2- responses to hyphae. PLD activation and PA production may facilitate PMN fungicidal responses to hyphae but play an indirect role in initiating the respiratory burst.

Flow cytometric kinetic measurements of neutrophil phospholipase A activation.

The interrelationships between activation of phospholipases and neutrophil stimulus-induced Ca2+ responses remain unclear. We report here that immune complexes activate a phosphatidylcholine-specific phospholipase A in a neutrophil only after the cytoplasmic Ca2+ transient has been initiated in the same cell, while chemotactic peptide activation does not proceed via such a phospholipase A-mediated mechanism. Measurements of [Ca2+] changes and of phosphatidylcholine-specific phospholipase A activity were made by flow cytometry, using Indo-1 for Ca2+ indication, and a new fluorescent probe, bis-BODIPY-phosphatidylcholine, localized in the inner leaflet of the plasma membrane, to measure phospholipase A activation. Both 100 nM formyl-methionyl-leucyl-phenylalanine (with or without cytochalasin B) and 60 micrograms/ml insoluble immune complexes elicited cytoplasmic Ca2+ transients, but only insoluble immune complexes stimulated phospholipase A activation in a subpopulation of cells exhibiting an elevation of [Ca2+]in. Phospholipase A activation followed the Ca2+ transient, starting, in each cell, after [Ca2+]in had begun to decrease as Ca2+ redistributed in the activated cell. The products of this phospholipase activation were confirmed by thin layer chromatography. We conclude that neutrophils respond to immune complexes with an elevated cytoplasmic Ca(2+)-requiring phosphatidylcholine-specific phospholipase A activation and to chemotactic peptides by a different mechanism.

In vitro, Candida albicans releases the immune modulator adenosine and a second, high-molecular weight agent that blocks neutrophil killing.

We previously described a lyophilized supernatant from germinated Candida albicans that blocks human neutrophil (PMN) O2- production and degranulation stimulated by several PMN agonists but does not block stimulation by PMA. In studies to further characterize this Candida hyphal inhibitory product (CHIP), we noted several physicochemical parallels with the purine nucleoside adenosine (Ado). A Sephadex G-10 semipurified fraction of CHIP had an absorption peak near 260 nm, an apparent m.w. of less than 400, and was resistant to boiling and proteases. Maximally effective doses of CHIP (100 micrograms/ml) and Ado (100 microM) blocked 0.1 microM FMLP-stimulated O2- production by 76.8 +/- 4.1 and 81.7 +/- 4.8%, respectively. Ado deaminase, known to inactivate Ado, reversed inhibition by both Ado and CHIP. Results were comparable for the effect of CHIP and Ado on FMLP-stimulated beta-glucuronidase and lactoferrin release. Activation of the respiratory burst by opsonized C. albicans yeast was also inhibited by CHIP and Ado, but the extent of inhibition was less than for FMLP. At yeast:PMN ratios of 4:1, 10:1, and 40:1, CHIP inhibited O2- by -3.8%, 14.3%, and 12.8%, respectively; Ado blocked production by 32.9%, 24.2%, and 11.5%, respectively. The effect of CHIP and Ado on Candida killing by PMN was compared using two viability assays in each of four experiments. Ado (100 microM) had no effect on killing, although CHIP (100 micrograms/ml) inhibited killing in the MTT assay at 15 and 45 min by 81.6 +/- 6.3 and 24.7 +/- 6.2%, respectively; as assayed by CFU, CHIP inhibited killing by 34.1 +/- 6.2 and 10.3 +/- 2.5%, respectively. The ability of CHIP to inhibit killing was not affected by adding Ado deaminase, providing additional evidence that an Ado-like effect by CHIP is not essential for killing inhibition. Killing of opsonized Streptococcus pneumoniae was also inhibited in a concentration-dependent manner. Reverse-phase HPLC of the semipurified fraction revealed a peak, eluting identically to authentic Ado, which was eliminated by adding Ado deaminase. Ado content of the G-10 fraction was sufficient to account fully for the FMLP-inhibitory activity. The antikilling activity was resistant to boiling and proteases but was eliminated by mild periodation. Fractions eluting from a Sephadex CL6B column between 0.8 and 2.0 x 10(6) m.w. had increased sp. act. for killing inhibition. Sp. act. increased as carbohydrate content increased, but killing inhibition by various Candida cell wall constituents was absent to modest compared to inhibition induced by CHIP.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of cilofungin (LY121019), a fungal cell wall synthesis inhibitor, on interactions of Candida albicans with human neutrophils.

The effects of cilofungin, a lipopeptide antifungal agent active against several species of Candida, on human neutrophil candidacidal activity were investigated. While no increase or decrease in neutrophil killing of blastospores was observed when cilofungin was simultaneously incubated with neutrophils and yeasts, preincubation of yeasts with serum containing cilofungin resulted in approximately 90% decrease in killing of five of six strains. Attachment/phagocytosis of these strains was unchanged from controls. We conclude that cilofungin interferes with opsonization of most strains of C. albicans, resulting in a marked decrease in neutrophil candidacidal activity, a phenomenon which may be of significance in vivo in certain tissues where access to antibodies and/or complement is limited.

Defective leukocyte fungicidal activity in end-organ resistance to 1,25-dihydroxyvitamin D.

Recent studies have shown 1,25(OH)2D3 receptor-mediated modulation of leukocyte proliferation, differentiation, and function. We examined the phagocytosis and killing of microorganisms by neutrophils and monocytes from five patients of three families with hereditary resistance to 1,25(OH)2D3. Phagocytosis of microorganisms by patients' neutrophils and monocytes was normal. However, defective neutrophil killing activity toward Candida albicans (30-40% of controls) was found in all patients. The killing of Staphylococcus aureus was normal. The neutrophil chemiluminescence, nitroblue tetrazolium (NBT) dye reduction, and the generation of superoxide ions and hydrogen peroxide by neutrophils and monocytes after induction by either soluble stimuli or zymozan particles, did not differ from those in controls. The neutrophil myeloperoxidase activity was also normal. Monocytes obtained from two patients of different families before long-term calcium infusion therapy and after they became normocalcemic, demonstrated a similar impaired fungicidal activity toward Saccharomyces cerevisiae, indicating that hypocalcemia itself was not the cause of the killing defect. However, the addition of the Ca+2 ionophore A23187 (1 microM) to the test medium restored the monocyte fungicidal activity to normal. As patients' neutrophil cytosolic free calcium concentration was similar to that in controls, it is suggested that 1,25-(OH)2D3 exerts its effect on leukocyte function by a putative receptor-mediated regulation of subcellular calcium localization which may be important for fungicidal activity.

Clostridium difficile toxin A stimulates intracellular calcium release and chemotactic response in human granulocytes.

Clostridium difficile, a common enteric pathogen, mediates tissue damage and intestinal fluid secretion by release of two protein exotoxins: toxin A, an enterotoxin, and toxin B, a cytotoxin. Because toxin A elicits an intense inflammatory reaction in vivo, we studied the effects of highly purified C. difficile toxins on activation of human granulocytes. Toxin A at concentrations of 10(-7) to 10(-6) M, but not toxin B, elicited a significant chemotactic and chemokinetic response by granulocytes that was comparable with that induced by the chemotactic factor N-FMLP (10(-7) M). Neither toxin stimulated release of superoxide anion from granulocytes. Toxin A produced a rapid, transient rise in cytosolic [Ca2+]i, as measured by quin 2 fluorescence. Pertussis toxin and depletion of intra- and extracellular calcium blocked the toxin A effect on cytosolic [Ca2+]i. These findings suggest that the inflammatory effects of C. difficile toxin A in the intestine may be related to its ability to mobilize intracellular Ca2+ and elicit a chemotactic response by granulocytes.

Temporal association of calcium mobilization, inositol trisphosphate generation, and superoxide anion release by human neutrophils activated by serum opsonized and nonopsonized particulate stimuli.

We have investigated the involvement of phospholipase C mediated polyphosphoinositide turnover in activation of polymorphonuclear leukocytes by particulate stimuli. Results showed that stimulation of leukocytes with serum opsonized zymosan (ingestible particle), serum opsonized Candida albicans hyphae (noningestible particle), or nonopsonized hyphae was followed by a transient rise in cellular inositol phosphates as has been described for neutrophil activation via the formyl peptide receptor. The kinetics of inositol trisphosphate generation paralleled both the time course of changes in cytosolic calcium concentration and the onset of superoxide anion generation, suggesting that these may be related events.

Effects of recombinant human granulocyte and macrophage colony-stimulating factors on signal transduction pathways in human granulocytes.

We studied the ability of the recombinant human-active hemopoietic growth factors granulocyte-macrophage colony-stimulating factor (GM-CSFrh) and granulocyte colony-stimulating factor (G-CSFrh) to activate receptor-mediated transduction pathways which have been implicated in the stimulation of cytotoxic functions in granulocytes. With the use of a panel of fluorescent probes, we found that these two growth factors exerted no detectable immediate effect on the resting transmembrane electrical potential, the intracellular concentration of free calcium ions, or the cytosolic pH of isolated, mature granulocytes. However, when granulocytes were "primed" by preincubation for 90 min with GM-CSFrh or G-CSFrh, the rate of membrane depolarization induced by 10(-7) M N-formyl-methionyl-leucyl-phenylalanine, but not the rate of rise in free calcium ions, was greatly accelerated. In examining potential mechanisms to account for the priming effect of these growth factors, we found that although they did not induce translocation of protein kinase C or stimulate significant degranulation, they each directly caused prompt release of arachidonic acid from plasma membrane phospholipids. Our data indicate that although GM-CSFrh and G-CSFrh do not activate the transduction signals that have most clearly been implicated in receptor-mediated activation of cytotoxic functions in granulocytes--namely, those coupled to membrane depolarization or release of intracellular calcium ions--they appear directly to induce the release of arachidonic acid esterified to membrane phospholipids, an event which may represent the receptor-mediated activation of membrane phospholipases and which may contribute to the "priming" of the cells for enhancement of their functional responsiveness.

Intralipid effects on preterm neonate serum: chemoattractant and opsonizing capacities.

The effects of Intralipid (IL) administration of preterm infants have been investigated. For this purpose, adult neutrophils were stimulated by infant sera collected before and after IL treatment. A definite decrease (p less than 0.0005) in chemoattractant capacity of zymosan-activated serum was observed after IL. On the other hand, no difference in the opsinizing abilities of untreated versus treated sera could be demonstrated by measuring the chemiluminescence responses to serum-opsonized zymosan. This study emphasized the need of caution in the use of IL treatment for preterm infants.

The effects of phorbol myristate acetate and chemotactic peptide on transmembrane potentials and cytosolic free calcium in mature granulocytes evolve sequentially as the cells differentiate.

We isolated myeloid precursors from human marrow and studied the effects of phorbol myristate acetate (PMA) and N-formyl-methionyl-leucyl-phenylalanine (fMLP) upon transmembrane potentials and cytosolic calcium ([Ca2+]i) as the cells matured. Using a panel of fluorescent probes, we found that membrane depolarization induced by PMA and fMLP in granulocytes, and elevation in [Ca2+]i stimulated by fMLP, were absent in myeloblasts. When we induced differentiation with granulocyte-macrophage colony-stimulating factors, we found that both ionic responses appeared at approximately the promyelocyte stage. By using di-O-C5(3), we detected an initial phase of fMLP-induced hyperpolarization which appeared ontogenetically earlier than depolarization and which could be evoked in mature granulocytes with lower concentrations of the ligand. Hyperpolarization was partially dependent on extracellular Na+, was abrogated by increasing the external K+ concentration, and was accompanied by mild acidification of the cytoplasm. Bordetella pertussis toxin abolished both hyperpolarization and depolarization. Our findings indicate that shifts in [Ca2+]i and membrane potential changes in response to PMA and fMLP evolve as granulocytes mature. In addition, transmembrane ionic fluxes induced by fMLP appear to be more complex than previously considered, involving at least two separable phases of membrane potential change.

Calcium modulation and chemotactic response: divergent stimulation of neutrophil chemotaxis and cytosolic calcium response by the chemotactic peptide receptor.

Stimulation of neutrophils by chemoattractants is followed by a rapid, transient rise in cytosolic calcium concentration. The role of calcium in activation of cell movement and related responses was examined by selectively chelating extracellular or both extra- and intracellular calcium. Removal of calcium from the extracellular medium did not alter the cytosolic calcium concentration (Quin 2 fluorescence, 110 to 120 nM) of unstimulated neutrophils and did not dramatically affect the rise induced by formyl peptide. Despite the intact Quin 2 response, depletion of extracellular calcium partially inhibited chemotaxis, adherence to substrate, and polarization (increased forward light scatter) in response to formyl peptide. Loading neutrophils with Quin 2 in the absence of calcium depressed cytosolic Ca2+ to 10 to 20 nM and abrogated a detectable rise with formyl peptide stimulation. Depletion of intracellular calcium further inhibited chemotaxis and polarization, although neutrophils still demonstrated significant directed migration and shape change to formyl peptide (30 to 40% of control) without an increase in Quin 2 fluorescence. Other neutrophil responses related to chemotaxis (decreased right-angle light scatter, actin polymerization) were minimally affected by depletion of calcium from either site. The data indicate that neutrophil chemotaxis and related responses to formyl peptide may be activated by intracellular signals not detectable with Quin 2.

Activation of human neutrophils by monoclonal antibody PMN7C3: cell movement and adhesion can be triggered independently from the respiratory burst.

Anti-neutrophil monoclonal antibody PMN7C3 (IgG3) recognizes glycoproteins bearing the oligosaccharide lacto-N-fucopentaose III, including the C3bi receptor, LFA-1, and p150,95 on the plasma membrane and a group of granule-associated glycoproteins. We have previously shown that binding of this antibody to polymorphonuclear leukocytes (PMNs) stimulates a transient rise in cytosolic free calcium concentration but does not trigger the neutrophil respiratory burst. We now demonstrate that binding of PMN7C3 (and five other monoclonal antibodies recognizing the same antigen) to human neutrophils activates several other cellular responses. Addition of PMN7C3 to monolayers of neutrophils induces a rapid change in cell shape followed by pseudopod formation and increased migration. With incubation at 37 degrees C, the neutrophils aggregate in clusters (leukoagglutination). Quantitation of cell movement in a multiwell chemotaxis assembly or by migration of PMNs under agarose revealed that PMN7C3 is both chemotactic and chemokinetic. Pretreatment with the antibody inhibits subsequent chemotactic response to other stimuli. Monoclonal antibodies binding to other neutrophil antigens do not mimic these effects. These data suggest that cell movement and adhesion can be triggered independently from the respiratory burst. PMN7C3 may be a useful probe with which to study the events that link receptor-ligand binding to cellular response.

Escherichia coli adherence to human transitional cell tumors: a simple research model of bacterial attachment to the lower urinary tract.

A simple model for assaying bacterial adherence to the urinary tract is presented. Cell suspensions of freshly excised transitional cell tumors were used as substrata for attachment of 3H-adenine-labeled Escherichia coli urine isolates. Quantitative radioactive counts were confirmed by microscopic observations in replicate assays of each condition tested. This model provided for species and organ specificity in studies of the bacterial adherence role in urinary tract infections.

A transient rise in intracellular free calcium is not a sufficient stimulus for respiratory burst activation in human polymorphonuclear leukocytes.

Binding of murine monoclonal antibody PMN7C3 to human neutrophils results in a large rapid, dose dependent transient increase in intracellular free calcium as measured by QUIN-2 fluorescence. Unlike other calcium mobilizing agents PMN7C3 does not induce any increase in respiratory burst activity over basal level. The PMN7C3 effect requires multivalent binding. Chelation of extracellular calcium does not significantly decrease the fluorescence transient generated by exposure to PMN7C3. Lowering of basal levels of intracellular free calcium concentration by maintaining QUIN-2-loaded PMN in calcium free medium eliminates the fluorescence transient. The observations demonstrate that a cell surface receptor mediated intracellular free calcium transient may be generated without any associated respiratory burst activation.