Alkalinizing the intralysosomal pH inhibits degranulation of human neutrophils

Ferrichrome, a fungal-type siderophore, confers high ammonium tolerance to fission yeast

Microorganisms and plants produce siderophores, which function to transport environmental iron into cells as well as participate in cellular iron use and deposition. Their biological functions are diverse although their role in primary metabolism is poorly understood. Ferrichrome is a fungal-type siderophore synthesized by nonribosomal peptide synthetase (NRPS). Herein we show that ferrichrome induces adaptive growth of fission yeast on high ammonium media. Ammonium is a preferred nitrogen source as it suppresses uptake and catabolism of less preferred nitrogen sources such as leucine through a mechanism called nitrogen catabolite repression (NCR). Therefore, the growth of fission yeast mutant cells with leucine auxotrophy is suppressed in the presence of high concentrations of ammonium. This growth suppression was canceled by ferrichrome in a manner dependent on the amino acid transporter Cat1. Additionally, growth retardation of wild-type cells by excess ammonium was exacerbated by deleting the NRPS gene sib1, which is responsible for the biosynthesis of ferrichrome, suggesting that intrinsically produced ferrichrome functions in suppressing the metabolic action of ammonium. Furthermore, ferrichrome facilitated the growth of both wild-type and sib1-deficient cells under low glucose conditions. These results suggest that intracellular iron regulates primary metabolism, including NCR, which is mediated by siderophores.

Metabolic-scale gene activation screens identify SLCO2B1 as a heme transporter that enhances cellular iron availability

Iron is the most abundant transition metal essential for numerous cellular processes. Although most mammalian cells acquire iron through transferrin receptors, molecular players of iron utilization under iron restriction are incompletely understood. To address this, we performed metabolism-focused CRISPRa gain-of-function screens, which revealed metabolic limitations under stress conditions. Iron restriction screens identified not only expected members of iron utilization pathways but also SLCO2B1, a poorly characterized membrane carrier. SLCO2B1 expression is sufficient to increase intracellular iron, bypass the essentiality of the transferrin receptor, and enable proliferation under iron restriction. Mechanistically, SLCO2B1 mediates heme analog import in cellular assays. Heme uptake by SLCO2B1 provides sufficient iron for proliferation through heme oxygenases. Notably, SLCO2B1 is predominantly expressed in microglia in the brain, and primary Slco2b1-/- mouse microglia exhibit strong defects in heme analog import. Altogether, our work identifies SLCO2B1 as a microglia-enriched plasma membrane heme importer and provides a genetic platform to identify metabolic limitations under stress conditions.

Heterogeneity of ferrous iron-containing endolysosomes and effects of endolysosome iron on endolysosome numbers, sizes, and localization patterns

Endolysosomes are key regulators of iron metabolism and are central to iron trafficking and redox signaling. Iron homeostasis is linked to endolysosome acidity and inhibition of endolysosome acidity triggers iron dysregulation. Because of the physiological importance and pathological relevance of ferrous iron (Fe2+ ), we determined levels of Fe2+ specifically and quantitatively in endolysosomes as well as the effects of Fe2+ on endolysosome morphology, distribution patterns, and function. The fluorescence dye FeRhoNox-1 was specific for Fe2+ and localized to endolysosomes in U87MG astrocytoma cells and primary rat cortical neurons; in U87MG cells the endolysosome concentration of Fe2+ ([Fe2+ ]el ) was 50.4 μM in control cells, 73.6 μM in ferric ammonium citrate (FAC) treated cells, and 12.4 μM in cells treated with the iron chelator deferoxamine (DFO). Under control conditions, in primary rat cortical neurons, [Fe2+ ]el was 32.7 μM. Endolysosomes containing the highest levels of Fe2+ were located perinuclearly. Treatment of cells with FAC resulted in endolysosomes that were less acidic, increased in numbers and sizes, and located further from the nucleus; opposite effects were observed for treatments with DFO. Thus, FeRhoNox-1 is a useful probe for the study of endolysosome Fe2+ , and much more work is needed to understand better the physiological significance and pathological relevance of endolysosomes classified according to their heterogeneous iron content Cover Image for this issue: https://doi.org/10.1111/jnc.15396.

Environmental impacts of COVID-19 treatment: Toxicological evaluation of azithromycin and hydroxychloroquine in adult zebrafish

One of the most impact issues in recent years refers to the COVID-19 pandemic, the consequences of which thousands of deaths recorded worldwide, are still inferior understood. Its impacts on the environment and aquatic biota constitute a fertile field of investigation. Thus, to predict the impact of the indiscriminate use of azithromycin (AZT) and hydroxychloroquine (HCQ) in this pandemic context, we aim to assess their toxicological risks when isolated or in combination, using zebrafish (Danio rerio) as a model system. In summary, we observed that 72 h of exposure to AZT and HCQ (alone or in binary combination, both at 2.5 μg/L) induced the reduction of total protein levels, accompanied by increased levels of thiobarbituric acid reactive substances, hydrogen peroxide, reactive oxygen species and nitrite, suggesting a REDOX imbalance and possible oxidative stress. Molecular docking analysis further supported this data by demonstrating a strong affinity of AZT and HCQ with their potential antioxidant targets (catalase and superoxide dismutase). In the protein-protein interaction network analysis, AZT showed a putative interaction with different cytochrome P450 molecules, while HCQ demonstrated interaction with caspase-3. The functional enrichment analysis also demonstrated diverse biological processes and molecular mechanisms related to the maintenance of REDOX homeostasis. Moreover, we also demonstrated an increase in the AChE activity followed by a reduction in the neuromasts of the head when zebrafish were exposed to the mixture AZT + HCQ. These data suggest a neurotoxic effect of the drugs. Altogether, our study demonstrated that short exposure to AZT, HCQ or their mixture induced physiological alterations in adult zebrafish. These effects can compromise the health of these animals, suggesting that the increase of AZT and HCQ due to COVID-19 pandemic can negatively impact freshwater ecosystems.

A second Warburg-like effect in cancer metabolism: The metabolic shift of glutamine-derived nitrogen: A shift in glutamine-derived nitrogen metabolism from glutaminolysis to de novo nucleotide biosynthesis contributes to malignant evolution of cancer

Carbon and nitrogen are essential elements for life. Glucose as a carbon source and glutamine as a nitrogen source are important nutrients for cell proliferation. About 100 years ago, it was discovered that cancer cells that have acquired unlimited proliferative capacity and undergone malignant evolution in their host manifest a cancer-specific remodeling of glucose metabolism (the Warburg effect). Only recently, however, was it shown that the metabolism of glutamine-derived nitrogen is substantially shifted from glutaminolysis to nucleotide biosynthesis during malignant progression of cancer-which might be referred to as a "second" Warburg effect. In this review, address the mechanism and relevance of this metabolic shift of glutamine-derived nitrogen in human cancer. We also examine the clinical potential of anticancer therapies that modulate the metabolic pathways of glutamine-derived nitrogen. This shift may be as important as the shift in carbon metabolism, which has long been known as the Warburg effect.

Rethinking the role of hydroxychloroquine in the treatment of COVID-19

There are currently no proven or approved treatments for coronavirus disease 2019 (COVID-19). Early anecdotal reports and limited in vitro data led to the significant uptake of hydroxychloroquine (HCQ), and to lesser extent chloroquine (CQ), for many patients with this disease. As an increasing number of patients with COVID-19 are treated with these agents and more evidence accumulates, there continues to be no high-quality clinical data showing a clear benefit of these agents for this disease. Moreover, these agents have the potential to cause harm, including a broad range of adverse events including serious cardiac side effects when combined with other agents. In addition, the known and potent immunomodulatory effects of these agents which support their use in the treatment of auto-immune conditions, and provided a component in the original rationale for their use in patients with COVID-19, may, in fact, undermine their utility in the context of the treatment of this respiratory viral infection. Specifically, the impact of HCQ on cytokine production and suppression of antigen presentation may have immunologic consequences that hamper innate and adaptive antiviral immune responses for patients with COVID-19. Similarly, the reported in vitro inhibition of viral proliferation is largely derived from the blockade of viral fusion that initiates infection rather than the direct inhibition of viral replication as seen with nucleoside/tide analogs in other viral infections. Given these facts and the growing uncertainty about these agents for the treatment of COVID-19, it is clear that at the very least thoughtful planning and data collection from randomized clinical trials are needed to understand what if any role these agents may have in this disease. In this article, we review the datasets that support or detract from the use of these agents for the treatment of COVID-19 and render a data informed opinion that they should only be used with caution and in the context of carefully thought out clinical trials, or on a case-by-case basis after rigorous consideration of the risks and benefits of this therapeutic approach.

Differential role of vacuolar (H+)-ATPase in the expression and activity of cyclooxygenase-2 in human monocytes

Monocytes are professional immune cells that produce abundant levels of pro-inflammatory eicosanoids including prostaglandins and leukotrienes during inflammation. Vacuolar (H⁺)-ATPase (V-ATPase) is critically involved in a variety of inflammatory processes including cytokine trafficking and lipid mediator biosynthesis. However, its role in eicosanoid biosynthetic pathways in monocytes remains elusive. Here, we present a differential role of V-ATPase in the expression and in the activity of cyclooxygenase (COX)-2 in human monocytes. Pharmacological targeting of V-ATPase increased the expression of COX-2 protein in lipopolysaccharide-stimulated primary monocytes, which was paralleled by enhanced phosphorylation of p38 MAPK and ERK-1/2, without impacting the NF-κB and SAPK/JNK pathways. Targeting of both p38 MAPK and ERK-1/2 pathways showed that the kinase pathways are crucial for COX-2 expression in human monocytes. Despite increased COX-2 protein levels, however, suppression of V-ATPase activity impaired the biosynthesis of COX- and also of 5-lipoxygenase (LOX)-derived lipid mediators in monocytes without affecting 12-/15-LOX products, assessed by a metabololipidomics approach using UPLC-MS-MS analysis. Our results indicate that changes in the intracellular pH may contribute to suppression of COX-2 and 5-LOX activities. We suggest that V-ATPase on one hand limits COX-2 protein levels via restricting p38 MAPK and ERK-1/2 activation, while on the other hand it governs the cellular activity of COX-2 through appropriate adjustment of the intracellular pH.

Maintaining Iron Homeostasis Is the Key Role of Lysosomal Acidity for Cell Proliferation

The lysosome is an acidic multi-functional organelle with roles in macromolecular digestion, nutrient sensing, and signaling. However, why cells require acidic lysosomes to proliferate and which nutrients become limiting under lysosomal dysfunction are unclear. To address this, we performed CRISPR-Cas9-based genetic screens and identified cholesterol biosynthesis and iron uptake as essential metabolic pathways when lysosomal pH is altered. While cholesterol synthesis is only necessary, iron is both necessary and sufficient for cell proliferation under lysosomal dysfunction. Remarkably, iron supplementation restores cell proliferation under both pharmacologic and genetic-mediated lysosomal dysfunction. The rescue was independent of metabolic or signaling changes classically associated with increased lysosomal pH, uncoupling lysosomal function from cell proliferation. Finally, our experiments revealed that lysosomal dysfunction dramatically alters mitochondrial metabolism and hypoxia inducible factor (HIF) signaling due to iron depletion. Altogether, these findings identify iron homeostasis as the key function of lysosomal acidity for cell proliferation.

Determination of glucose deficiency-induced cell death by mitochondrial ATP generation-driven proton homeostasis

Glucose is one of major nutrients and its catabolism provides energy and/or building bricks for cell proliferation. Glucose deficiency results in cell death. However, the underlying mechanism still remains elusive. By using our recently developed method to monitor real-time cellular apoptosis and necrosis, we show that glucose deprivation can directly elicit necrosis, which is promoted by mitochondrial impairment, depending on mitochondrial adenosine triphosphate (ATP) generation instead of ATP depletion. We demonstrate that glucose metabolism is the major source to produce protons. Glucose deficiency leads to lack of proton provision while mitochondrial electron transfer chain continues consuming protons to generate energy, which provokes a compensatory lysosomal proton efflux and resultant increased lysosomal pH. This lysosomal alkalinization can trigger apoptosis or necrosis depending on the extent of alkalinization. Taken together, our results build up a metabolic connection between glycolysis, mitochondrion, and lysosome, and reveal an essential role of glucose metabolism in maintaining proton homeostasis to support cell survival.

Amyloid β peptide promotes lysosomal degradation of clusterin via sortilin in hippocampal primary neurons

Progressive accumulation of amyloid-β peptide (Aβ) in the brain is implicated as the central event in the development of Alzheimer's disease (AD). It is thought that extracellular Aβ triggers toxic signals leading to neurodegeneration. The events downstream of Aβ however are not entirely clear. Clusterin (Apo J) is one of the major risk factors for sporadic form of AD. Clusterin binds to Aβ and prevents Aβ aggregation. In addition, clusterin promotes Aβ degradation and accelerates Aβ clearance from the brain. Clusterin thus protects neurons from Aβ and loss of clusterin level in the brain is implicated as promoting AD pathology. In this study, we found that the level of clusterin protein but not mRNA is reduced in the brains of 3xTg-AD mice. When rat hippocampal primary neurons were treated with Aβ1-42, level of clusterin protein but not mRNA was downregulated. Aβ1-42-induced downregulation of clusterin was blocked by lysosome inhibitors bafilomycin A1 and ammonium chloride. In neurons, Aβ1-42 induced expression of sortilin, a lysosomal sorting protein that targets proteins to lysosome for degradation. In BE(2) M17 human neuroblastoma cells, clusterin bound to sortilin and when sortilin expression was silenced, Aβ1-42-induced clusterin downregulation was almost completely blocked. Our data demonstrate that in neurons, Aβ1-42 promotes lysosomal degradation of clusterin by inducing expression of sortilin and provide a novel mechanism by which Aβ promotes AD pathogenesis.

Mechanisms of the Macrolide-Induced Inhibition of Superoxide Generation by Neutrophils

The effect of macrolides on the superoxide (O2 (-)) production by neutrophils was studied. Resting neutrophils become primed by lipopolysaccharide (LPS) or N-formyl-methionyl-leucyl-phenylalanine (fMLP), and primed neutrophils generate O2 (-) in response to fMLP or adhesion, respectively. Both LPS-primed fMLP-stimulated O2 (-) generation by macrolide-treated neutrophils and adhesion-stimulated O2 (-) generation by macrolide-treated fMLP-primed neutrophils were inhibited. Macrolide inhibition of O2 (-) generation was dependent on serum or pH. Serum could be substituted by NaHCO3. The intensity of inhibition was azithromycin = roxithromycin > clarithromycin > erythromycin, in that order. Non-antimicrobial derivatives of erythromycin, that is, EM703 and EM900, inhibited O2 (-) generation at pH 7.4. NH4Cl abolished the activity of azithromycin (AZ) only when added to neutrophils with AZ but not after incubation with AZ, suggesting that NH4Cl prevented the influx of AZ. AZ did not affect the expression of alkaline phosphatase, CD11b, and cytochrome b558 in both resting and LPS-primed neutrophils. These results suggested that macrolides did not affect granule mobilization but inhibited O2 (-) generation selectively.

Chloroquine modulates the fungal immune response in phagocytic cells from patients with chronic granulomatous disease

Invasive aspergillosis is a major threat to patients with chronic granulomatous disease (CGD). Fungal pathogenesis is the result of a diminished antifungal capacity and dysregulated inflammation. A deficient NADPH-oxidase complex results in defective phagolysosomal alkalization. To investigate the contribution of defective pH regulation in phagocytes among patients with CGD during fungal pathogenesis, we evaluated the effect of the acidotropic, antimalarial drug chloroquine (CQ) on the antifungal capacity of polymorphonuclear cells (PMNs) and on the inflammatory response of peripheral blood mononuclear cells (PBMCs). Chloroquine exerted a direct pH-dependent antifungal effect on Aspergillus fumigatus and Aspergillus nidulans; it increased the antifungal activity of PMNs from patients with CGD at a significantly lower concentration, compared with the concentration for PMNs from healthy individuals; and decreased the hyperinflammatory state of PBMCs from patients with CGD, as observed by decreased tumor necrosis factor α and interleukin 1β release. Chloroquine targets both limbs of fungal pathogenesis and might be of great value in the clearance of invasive aspergillosis in patients with CGD.

Human β-cell killing by autoreactive preproinsulin-specific CD8 T cells is predominantly granule-mediated with the potency dependent upon T-cell receptor avidity

The end-stage immunopathology of type 1 diabetes resulting in β-cell destruction appears to be strongly dominated by cytotoxic CD8 T lymphocytes (CD8 T cells). However, the mechanism of cytotoxicity used by autoreactive CD8 T cells in the human setting remains unknown. Using type 1 diabetes patient-derived preproinsulin-specific CD8 T-cell clones recognizing either an HLA-A2 (A*0201) or HLA-A24 (A*2402)-restricted epitope (peptide of preproinsulin [PPI](15-24), ALWGPDPAAA; or PPI(3-11), LWMRLLPLL), we assessed the use of conventional mediators of cytotoxicity in the destruction of human β-cells in vitro compared with virus-specific cytotoxic CD8 T-cell clones. We show that PPI-specific CD8 T-cell clones are mainly reliant upon cytotoxic degranulation for inducing β-cell death. Furthermore, we find that in comparison with virus-specific CD8 T cells, there are differences in the killing potency of PPI-specific CD8 T cells that are not due to cell-intrinsic differences, but rather are mediated by differences in strength of signaling by peptide-HLA ligands. The study highlights the regulation of β-cell killing as a potential point for therapeutic control, including the possibility of blocking autoreactive CD8 T-cell function without impacting upon general immune competence.

Lysosome vacuolation disrupts the completion of autophagy during norephedrine exposure in SH-SY5Y human neuroblastoma cells

In our current study, we examined the mechanism underlying neuronal cell injuries caused by norephedrine in SH-SY5Y human neuroblastoma cells. Norephedrine was found to induce cytoplasmic vacuolation and a resultant loss of cell viability. In the cells treated with norephedrine also, an autophagic marker LC3 was converted to its LC3-II activated form, suggesting the induction of autophagy. In cells transfected with RFP-LC3 and GFP-LAMP1, a punctate patterning of LC3 expression and colocalization of LAMP1 with the formed vacuoles were observed, highlighting the lysosomal nature of the vacuoles and their association with autophagosomes. An autophagic flux assay using tfLC3 (mRFP-GFP-LC3) indicated the formation of autophagosomes and autolysosomes by norephedrine stimulation at an early timepoint (∼3 h). However, at a later timepoint (∼6 h), both the dilation of autolysosomes/lysosomes and the neutralization of the vacuolar pH were also observed. These results thus indicate that norephedrine induces autophagy at an early timepoint and cell death with lysosomal dysfunction and autophagy disruption at a later timepoint.

CpG-induced secretion of MHCIIbeta and exosomes from salmon (Salmo salar) APCs

Major histocompatibility complex class II (MHCII) is encoded by polymorphic genes present in vertebrates and expressed predominately in leukocytes. Upon leukocyte differentiation, intracellular MHCII is dynamically redistributed within the cells and it is expressed at maximal levels on mature antigen presenting cells (APCs). In addition, APCs secrete MHCII within endosome-derived vesicles known as exosomes which possess diverse immunomodulatory properties. Genetic and biochemical data have confirmed that piscine leukocytes express the MHCII components as well as costimulatory molecules that are necessary for the function of APCs. However data concerning the biosynthesis and the distribution of the MHCII complex within leukocytes of lower vertebrates is scarce. The presented data demonstrates for the first time that salmon leukocytes secrete vesicles that contain exosomal markers and the abundance of MHCII indicates that these exosomes are released by APCs. The secretion was specifically induced by CpG stimulation in vitro and it was observed only in head kidney leukocytes but not in splenocyte cultures. Flow cytometry revealed that, unlike splenocytes, the majority of the MHCII-positive head kidney leukocytes were Ig-negative and a population of cells expressing high levels of surface MHCII underwent degranulation upon CpG stimulation suggesting that the MHCII-containing exosomes were derived from maturing salmon APCs. Gene expression analyses have further demonstrated that CpG-B, despite its relatively weak proinflammatory activity compared to LPS, induced expression of a larger group of genes involved in regulation of the adaptive immune response.

Spectral properties and mechanisms that underlie autofluorescent accumulations in Batten disease

Neuronal Ceroid Lipofuscinoses (NCLs) have an incidence of 1 in 12,500 live births. These devastating neurodegenerative lysosomal storage diseases are characterized by the lysosomal accumulation of autofluorescent storage material (AFSM) similar to that seen in aging cells. Using patient derived lymphoblasts from three genetically distinct NCLs we report that AFSM for each NCL has distinct spectral properties. Moreover, by using pharmacological inhibitors to disrupt various biochemical pathways in normal control lymphoblasts we have determined that disruptions in microtubule assembly and non-muscle myosin II function results in accumulation of lysosomal AFSM. Interestingly, inhibition of autophagy did not result in AFSM. We conclude that cellular disturbances outside the lysosome in addition to compromised function of this organelle can result in accumulation of lysosomal AFSM in NCLs and possibly as a result of cellular aging.

Rat Urinary Bladder Carcinogenesis by Dual-Acting PPARalpha + gamma Agonists

Despite clinical promise, dual-acting activators of PPARalpha and gamma (here termed PPARalpha+gamma agonists) have experienced high attrition rates in preclinical and early clinical development, due to toxicity. In some cases, discontinuation was due to carcinogenic effect in the rat urothelium, the epithelial layer lining the urinary bladder, ureters, and kidney pelvis. Chronic pharmacological activation of PPARalpha is invariably associated with cancer in rats and mice. Chronic pharmacological activation of PPARgamma can in some cases also cause cancer in rats and mice. Urothelial cells coexpress PPARalpha as well as PPARgamma, making it plausible that the urothelial carcinogenicity of PPARalpha+gamma agonists may be caused by receptor-mediated effects (exaggerated pharmacology). Based on previously published mode of action data for the PPARalpha+gamma agonist ragaglitazar, and the available literature about the role of PPARalpha and gamma in rodent carcinogenesis, we propose a mode of action hypothesis for the carcinogenic effect of PPARalpha+gamma agonists in the rat urothelium, which combines receptor-mediated and off-target cytotoxic effects. The proposed mode of action hypothesis is being explored in our laboratories, towards understanding the human relevance of the rat cancer findings, and developing rapid in vitro or short-term in vivo screening approaches to faciliate development of new dual-acting PPAR agonist compounds.

Macrophage cholesterol efflux and the active domains of serum amyloid A 2.1

Serum amyloid A 2.1 (SAA2.1) suppresses ACAT and stimulates cholesteryl ester hydrolase (CEH) activities in cholesterol-laden macrophages, and in the presence of a cholesterol transporter and an extracellular acceptor, there is a marked increase in the rate of cholesterol export in culture and in vivo. The stimulation of CEH activity by SAA2.1 is not affected by chloroquine, suggesting that it operates on neutral CEH rather than the lysosomal form. With liposomes containing individual peptides of SAA2.1, residues 1-20 inhibit ACAT activity, residues 74-103 stimulate CEH activity, and each of residues 1-20 and 74-103 promotes macrophage cholesterol efflux to HDL in culture media. In combination, these peptides exhibit a profound effect, so that 55-70% of cholesterol is exported to media HDL in 24 h. The effect is also demonstrable in vivo. [3H]cholesterol-laden macrophages injected intravenously into mice were allowed to establish themselves for 24 h. Thereafter, the mice received a single intravenous injection of liposomes containing intact SAA1.1, SAA2.1, peptides composed of SAA2.1 residues 1-20, 21-50, 51-80, 74-103, or SAA1.1 residues 1-20. Only liposomes containing intact SAA2.1 or its residues 1-20 or 74-103 promoted the efflux of cholesterol in vivo. A single injection of each of the active peptides is effective in promoting cholesterol efflux in vivo for at least 4 days.

Secretory granules are recaptured largely intact after stimulated exocytosis in cultured endocrine cells

Classical cell biology teaches that exocytosis causes the membrane of exocytic vesicles to disperse into the cell surface and that a cell must later retrieve by molecular sorting whatever membrane components it wishes to keep inside. We have tested whether this view applies to secretory granules in intact PC-12 cells. Three granule proteins were labeled with fluorescent proteins in different colors, and two-color evanescent-field microscopy was used to view single granules during and after exocytosis. Whereas neuro-peptide Y was lost from granules in seconds, tissue plasminogen activator (tPA) and the membrane protein phogrin remained at the granule site for over 1 min, thus providing markers for postexocytic granules. When tPA was imaged simultaneously with cyan fluorescent protein (CFP) as a cytosolic marker, the volume occupied by the granule appeared as a dark spot where it excluded CFP. The spot remained even after tPA reported exocytosis, indicating that granules failed to flatten into the cell surface. Phogrin was labeled with GFP at its luminal end and used to sense the pH in granules. When exocytosis caused the acidic granule interior to neutralize, GFP-phogrin at first brightened and later dimmed again as the interior separated from the extracellular space and reacidified. Reacidification and dimming could be reversed by application of NH(4)Cl. We conclude that most granules reseal in <10 s after releasing cargo, and that these empty or partially empty granules are recaptured otherwise intact.

Characteristics and mechanisms of azithromycin accumulation and efflux in human polymorphonuclear leukocytes

Azithromycin achieves prolonged, high tissue concentrations in spite of low serum levels and obviously must be active at tissue sites of infection to be effective. These unique features prompted us to evaluate the interactions of azithromycin and human polymorphonuclear leukocytes (PMN). Uptake of radiolabeled antibiotic by PMN was determined by a velocity-gradient centrifugation technique and expressed as the ratio of cellular to extracellular drug concentration (C/E). Azithromycin was massively accumulated by human PMN (C/E=387.2 at 2 h). Uptake was not influenced by inhibitors of cellular metabolism, but phagocytosis slightly inhibited the entry of azithromycin into PMN. After removal of extracellular drug, the release (efflux) of azithromycin from PMN was extremely slow. Agents which neutralize lysosomal pH, preventing protonation and trapping of azithromycin, markedly increased antibiotic efflux. Active concentration and prolonged retention of azithromycin by phagocytic cells should allow delivery and subsequent release of accumulated drug at sites of infection.

Omeprazole inhibits phagocytosis and acidification of phagolysosomes of normal human neutrophils in vitro

We postulated omeprazole inhibition of the neutrophil proton pump, impairing phagocytosis and phagolysosomal acidification. Neutrophils from healthy human beings were treated with omeprazole prodrug 0.5 mM/l or acid activated omeprazole 0.5 mM/l, then incubated with killed Saccharomyces cerevisiae stained with bromcresol purple. Wet mounts were done at 10, 30 and 60 minutes. Percent neutrophils phagocytosing, percent yeast phagocytosed, and yeast per phagocytosing neutrophil were significantly decreased in acid activated omeprazole compared to controls and omeprazole prodrug. In contrast, percent acidification of intracellular yeast was significantly lower in both omeprazole prodrug and acid activated omeprazole compared to controls. Over time, control neutrophils showed an increase in percent yeast phagocytosed and yeast per phagocytosing neutrophil. When treated with acid activated omeprazole, the percent of neutrophils phagocytosing progressively decreased over time. We observed 1) omeprazole prodrug does not inhibit neutrophil phagocytosis but does inhibit phagolysosomal acidification, whereas 2) acid activated omeprazole inhibits both neutrophil phagocytosis and phagolysosome acidification. We conclude that omeprazole impairs these neutrophil functions in vitro.

Effects of in vitro atmospheric ammonia exposure on recovery rate and luminol-dependent chemiluminescence of bovine neutrophils and bronchoalveolar macrophages

The effects of atmospheric ammonia, a major pollutant in animal confinement facilities, on bovine neutrophils and bronchoalveolar macrophages were evaluated in vitro. Ammonia exposure at concentrations 50, 100 and 200 ppm for one hour impaired recovery rates of neutrophils dose-dependently but enhanced their chemiluminescence activity per cell at lower concentrations (50 and 100 ppm). Macrophages were resistant to the exposure. Their recovery rates and chemiluminescence remained unaffected even at 200 ppm exposure. The present results suggest that ammonia exposure is unfavorable for bovine neutrophils in vitro, and probably in vivo also, in light of causing cell damage and triggering wider inflammatory responses.

Intracellular accumulation, subcellular distribution, and efflux of tilmicosin in chicken phagocytes

Tilmicosin is a semi-synthetic macrolide antibiotic, currently approved for veterinary use in cattle and swine respiratory disease, and is in development for use in poultry mycoplasma air sacculitis. In order to provide an understanding of clinical efficacy, the in vitro interaction of tilmicosin with three types of chicken phagocytes (MQ-NCSU macrophages, monocyte-macrophages, and heterophils) was evaluated. After incubation with radiolabeled tilmicosin, uptake was determined and expressed as the ratio of the cellular (Cc) to the extracellular (Ce) drug concentration (Cc:Ce). Tilmicosin was avidly accumulated by heterophils (Cc: Ce 138 at 4 h incubation vs 32 and 66, respectively, in MQ-NCSU and monocyte-macrophages) with 61 to 88% localized in the lysosomes. Uptake was dependent on cell viability, temperature, and pH, but was not influenced by metabolic inhibitors. However, phagocytosis of Pasteurella multocida and lipopolysaccharide exposure increased tilmicosin uptake by the chicken phagocytes. Upon removal of extracellular tilmicosin, 50% of the intracellular tilmicosin was effluxed within the first 30 min, but after 4 h of incubation in antibiotic-free medium, 30% remained cell-associated. Opsonized P. multocida significantly enhanced the release of tilmicosin from all three types of chicken phagocytes. Tilmicosin uptake was observed to increase lysosomal enzyme (acid phosphatase, lysozyme, avidin, and beta-glucuronidase) production. Finally, neutrophils were shown to transport and efflux bioactive tilmicosin in a test system measuring both neutrophil chemotaxis under agarose and a bioassay measuring inhibition of bacterial growth in the presence of antibiotic in agar. These in vitro observations of cellular pharmacology suggest a complex interaction between phagocytes and tilmicosin that contribute to clinical efficacy.

Intracellular accumulation, subcellular distribution and efflux of tilmicosin in swine phagocytes

Tilmicosin is a semi-synthetic macrolide antibiotic, currently approved for veterinary use in cattle and swine respiratory disease. As the concentrations of tilmicosin are generally low in swine lung tissue, the interaction of tilmicosin with three types of swine phagocytes (monocyte-macrophages, alveolar macrophages, and neutrophils) was evaluated to provide an understanding of clinical efficacy. After incubation with radiolabelled tilmicosin, uptake was determined and expressed as the ratio of the intracellular (Ci) to the extracellular (Ce) drug concentration (Ci/Ce). Tilmicosin was avidly accumulated by the swine phagocytes (Ci/Ce 48-69 at 4 h incubation) with 51 to 85% localized in the lysosomes. Uptake was dependent on cell viability, temperature and pH, but was not influenced by the metabolic inhibitors, sodium cyanide or potassium fluoride. However, lipopolysaccharide (LPS) exposure increased tilmicosin uptake by the swine phagocytes. In neutrophils, upon removal of extracellular tilmicosin, 60% of the intracellular tilmicosin was effluxed within the first 30 min, but after 4 h of incubation in drug-free medium, 25% remained cell-associated. In contrast, after 4 h of incubation in drug-free medium, 60% and 45% of tilmicosin remained cell-associated, within alveolar macrophages and monocyte-derived macrophages, respectively. Tilmicosin uptake was observed to increase lysosomal enzyme (acid phosphatase, lysozyme and beta-glucuronidase) production. Finally, neutrophils were shown to transport and efflux bioactive tilmicosin in a test system measuring both neutrophil chemotaxis under agarose and a bioassay measuring inhibition of bacterial growth in the presence of antibiotic in agar. These in vitro interactions of tilmicosin with swine phagocytes suggest an integral role in effecting clinical efficacy.

Attachment, ingestion and intracellular killing of Helicobacter pylori by human peripheral blood mononuclear leukocytes and mouse peritoneal inflammatory macrophages

The different steps of phagocytosis, attachment, ingestion and intracellular killing of cells of Helicobacter pylori strain 17874 (expressing sialic acid-specific haemagglutinin) and cells of H. pylori strain 17875 (expressing non-sialic acid-specific haemagglutinin) have been studied. More cells of sialopositive H. pylori strain 17874 have been found attached to human peripheral blood mononuclear leukocytes (PBM) and mouse peritoneal inflammatory macrophages (PIM) than cells of sialonegative H. pylori strain 17875. Binding of cells of H. pylori strain 17874 has been significantly inhibited by treatment of phagocytes with neuraminidase. Inhibition of adhesion of these bacteria preincubated with foetuin to normal phagocytic cells has also been found. Well adhering cells of H. pylori strain 17874 were more resistant to killing mechanisms of human PBM and mouse PIM than cells of strain 17875. Good, probably sialic acid-specific haemagglutinin dependent, adhesion of H. pylori bacteria to phagocytes can be considered as an important virulence factor which facilitates the pathogen to avoid the defence mechanisms.

The evolutionarily conserved ribosomal protein L23 and the cationic urease beta-subunit of Yersinia enterocolitica O:3 belong to the immunodominant antigens in Yersinia-triggered reactive arthritis: implications for autoimmunity

BACKGROUND

Reactive arthritis (ReA) is a T cell mediated inflammatory process. The immune response is primarily directed against a triggering organism, although autoimmunity has been invoked in long-lasting, antibiotic-resistant disease. Although a variety of different species are known to trigger Reactive arthritis, the clinical manifestations are strikingly similar as well as closely associated to the HLA-B27 (70%).

MATERIALS AND METHODS

Various antigenic fractions and single antigens of Yersinia enterocolitica were prepared, and their immunological activity was assessed by proliferation of synovial fluid mononuclear cells from 10 Reactive arthritis patients. The gene encoding one hitherto unknown antigen has been sequenced. Nonapeptides deduced from sequences of the target antigens were tested in an assembly assay.

RESULTS

Two immunodominant proteins of Yersinia enterocolitica were found, one being the urease beta-subunit and the other the 50 S ribosomal protein L23. The latter has been sequenced and belongs to the evolutionarily conserved ribosomal proteins with homology to procaryotes and eucaryotes. One nonapeptide derived from the urease beta-subunit was identified as a possible epitope for HLA-B27-restricted cytotoxic T cells by its high affinity. This epitope is also highly conserved.

CONCLUSION

Sharing of conserved immunodominant proteins between different disease triggering microorganisms could provide an explanation of the shared clinical picture in Reactive arthritis. Moreover, autoimmunity in Reactive arthritis might be mediated by antigen mimicry between evolutionarily conserved epitopes of ribosomal proteins and their host analogs.

Interactions of dirithromycin with human polymorphonuclear leukocytes

Dirithromycin, a new macrolide antibiotic, achieves prolonged, high levels in tissue. We previously demonstrated that certain macrolides are highly concentrated within phagocytic cells. This background information prompted us to evaluate the interactions of dirithromycin and human polymorphonuclear leukocytes (PMNs). After incubation with radiolabeled dirithromycin, antibiotic uptake by PMNs was determined by a velocity-gradient centrifugation technique and was expressed as the ratio of the cellular to the extracellular drug concentration (C/E). Dirithromycin was avidly accumulated by PMNs (C/E, 5 at 15 min, 10 at 30 min, 19 at 1 h, and 35 at 2 h). Uptake was dependent on cell viability, physiologic environmental temperature, and pH (optimum 8.6), but was not influenced by potential competitive inhibitors of membrane transport. Incubation with sodium cyanide caused an increase in dirithromycin accumulation by PMNs. Ingestion of microbial particles (mimicking in vivo infection) modestly inhibited the entry of dirithromycin into PMNs. After removal of extracellular drug, the efflux (release) of dirithromycin from PMNs was slow; only 10% was released within the first 30 min. This prolonged retention of dirithromycin within phagocytic cells might allow delivery and release of accumulated drug at sites of infection. The impact of intraphagocytic dirithromycin on cellular function was also evaluated. In a manner similar to that of other highly concentrated, weakly basic antibiotics, dirithromycin inhibited the respiratory burst response (superoxide production) in stimulated PMNs. The presence of dirithromycin slightly increased the intraphagocytic killing of Staphylococcus aureus in human PMNs. These interactions of dirithromycin with phagocytic cells may promote the extraphagocytic, and possibly the intraphagocytic, killing of infecting organisms.

Quinine uptake by human polymorphonuclear neutrophils

The antimalarial drug quinine has been shown to impair human polymorphonuclear leukocyte (PMN) functions. To gain insight into the mechanism of this phenomenon, we investigated quinine uptake by PMN with a fluorometric assay based on the fluorescence properties of this drug. After 30 min of incubation at 37 degrees C in the presence of 1 and 10 micrograms of quinine per ml, PMN-associated quinine reached 90 +/- 6 and 780 +/- 150 ng/2.5 x 10(6) PMN, respectively, giving a cellular-to-extracellular concentration ratio of 140 to 150. A steady state was reached within 5 min. Uptake was partially dependent on temperature, cell viability, and extracellular pH. Fractionation studies showed that 30 to 40% of the PMN-associated quinine was located in the particulate fraction. The efflux of PMN-associated quinine was rapid and complete when the incubation mixture was replaced by drug-free medium. These data suggest that several mechanisms are involved in the uptake of quinine by PMN, including a viability- and energy-independent process possibly related to reversible association of quinine to cell structures (particularly the membrane). Other mechanisms could involve trapping by protonation and/or active PMN transport systems. Thus, most of the quinine taken up by resting PMN is found in the soluble fraction of disrupted cells. This may partly explain the depressive properties of quinine.

Ammonium decreases human polymorphonuclear leukocyte cytoskeletal actin

Ammonium, a weak base produced as a metabolic by-product of urea metabolism by bacterial pathogens, inhibits a variety of motile polymorphonuclear leukocyte (PMN) functions. It was initially assumed that the mechanism of leukocyte inhibition was due to cytoplasmic alkalinization. However, while it is clear that ammonium can effect cytoplasmic alkalinization, current data indicate that alterations in chemotaxis, degranulation, and receptor recycling occur independently of cytoplasmic alkalinization. Since these are motility-related events, we examined the possibility that alterations in cytoskeletal actin may account for the effects of ammonium on PMN function. The results indicate that ammonium can inhibit degranulation, decrease cytoskeletal actin, and increase actin depolymerization rates. These findings are supported by five lines of evidence. First, formylmethionyl-leucyl-phenylalanine (fMLP)-induced elastase release was inhibited by 85% +/- 3% in the presence of ammonium, and ammonium by itself did not stimulate elastase release. Second, ammonium treatment of resting PMNs caused a rapid 38% +/- 6% decrease in cytoskeletal actin. Third, ammonium treatment accelerated the fMLP-induced depolymerization phase of the cytoskeletal actin transient by 150% +/- 12%. Fourth, in resting PMNs treated with cytochalasin B or D, ammonium induced a 21% +/- 4% and a 25% +/- 5% decrease in cytoskeletal actin, respectively. Conversely, ammonium did not affect the ability of the cytochalasins to inhibit an fMLP-induced cytoskeletal actin transient. Fifth, pertussis toxin treatment of neutrophils did not affect the ammonium-stimulated decrease in cytoskeletal actin. These results suggest that ammonium can inhibit neutrophil function by altering cytoskeletal actin and therefore provide new information regarding potential pathogenic mechanisms for bacterial pathogens.

Antibiotic inhibition of the respiratory burst response in human polymorphonuclear leukocytes

Recently we found that certain antibiotics which are markedly concentrated by human polymorphonuclear leukocytes (PMN) failed to kill susceptible, intraphagocytic Staphylococcus aureus, even though cellular drug levels were quite high. The possibility that specific antibiotics might adversely affect phagocyte antibacterial function was considered. Thus, we studied the effects of multiple antibiotics and adenosine, a known modulator of the PMN respiratory burst response, on neutrophil antibacterial function. At nontoxic concentrations, these drugs had no effect on degranulation in stimulated PMN. Adenosine was a potent inhibitor of formyl-methionyl-leucyl-phenylalanine (FMPL)-stimulated superoxide and hydrogen peroxide generation in PMN but produced less inhibition of microbial particle-induced respiratory burst activity. Three of the tested antibiotics, all of which reach high concentrations in phagocytic cells, had a marked modulatory effect on the PMN respiratory burst. Clindamycin, which enters phagocytes by the cell membrane adenosine (nucleoside) transport system, had only a modest effect on FMLP-mediated superoxide production but inhibited the microbial particle-induced response by approximately 50%. Roxithromycin and trimethoprim were efficient inhibitors of PMN superoxide generation stimulated by FMLP and concanavalin A (also inhibited by erythromycin) but had less effect on zymosan-mediated respiratory burst activity. Antibiotics which entered phagocytes less readily had no effect on the respiratory burst response in PMN. These results, as well as those of experiments with inhibitors of cell membrane nucleoside receptors, indicated that the antibiotic effect is mediated through intraphagocytic pathways. The possibility that antibiotic-associated inhibition of the PMN respiratory burst response might alter leukocyte antimicrobial and inflammatory function deserves further evaluation.

Ammonia as a potential mediator of adult human periodontal infection: inhibition of neutrophil function

Neutrophils (polymorphonuclear leucocytes) are the principal cell of the host defence system. Consequently, if periodontal pathogen-derived substances in the gingival crevice significantly inhibit their function, they could shift the bacterial-host balance in favour of the bacteria. The hypothesis that ammonia can inhibit neutrophil function was tested. Ammonia was specifically selected because periodontal pathogens produce substantial amounts of ammonia. The findings indicated that ammonia can inhibit neutrophil phagocytosis, degranulation and oxygen metabolism. Ammonia decreased the total number of phagocytosing polymorphonuclear neutrophils (66% of control) and also decreased degranulation (61% of control). Ammonia decreased oxygen metabolism of both resting and stimulated neutrophils (33 and 42% of control, respectively). These observations support the hypothesis that ammonia can inhibit the function of polymorphonuclear leukocytes. They suggest that the presence of ammonia in the gingival crevice may increase the risk of development of periodontal disease.

Effects of ammonia on human neutrophil N-formyl chemotactic peptide receptor-ligand interaction and cytoskeletal association

Ammonia is a bacterial metabolite which is commonly used to alter cytoplasmic and lysosomal pH of eukaryotic cells. Here we examine its effect on external N-formyl peptide receptors of human neutrophils. Ammonia does not affect the number of N-formyl peptide receptors on the cell surface, nor the association of the ligand-receptor complex with the cytoskeleton. However, ammonia causes a marked decrease in the affinity of the chemotactic peptide receptor for its ligand. The Kd of untreated cell for the chemotactic peptide was 0.65 +/- 0.06 nM, whereas that of ammonia treated cells was 1.02 +/- 0.10 nM (Mean +/- SEM, N = 6). These results suggest that ammonia can affect external as well as internal cellular components. Since ammonia is used to alter lysosomal and cytoplasmic pH, and is a metabolite of common bacterial pathogens, these results bear directly on its use in cell biology and on its potential as a virulence factor.

Antibiotics and human monocyte function. II. Phagocytosis and oxidative metabolism

The influence of thirteen commonly used antibacterial drugs on the phagocytic and oxidative burst responsiveness of human blood monocytes in vitro was investigated. Cefotaxime and rifampicin produced a significant inhibition of monocyte oxidative metabolism at therapeutic concentrations with increasing inhibition at higher concentrations. The effect of rifampicin was irreversible, which may reflect intracellular accumulation of the drug. Tetracycline, clindamycin, chloramphenicol and tobramycin at high concentrations produced a significant inhibition of monocyte superoxide anion release after stimulation, whereas normal therapeutic concentrations produced insignificant inhibition. Benzylpenicillin, ampicillin, fusidic acid, metronidazole, ofloxacin, sulfamethoxazole and trimethoprim did not alter monocyte oxidative metabolism in vitro. Phagocytosis of yeast cells was significantly suppressed by high concentrations of tobramycin, but otherwise unaffected by the drugs mentioned. These observations suggest that cefotaxime and rifampicin may interfere with blood monocyte oxidative metabolism in vivo, whereas it can be expected that at normal dosage it is unlikely that the other drugs will affect monocyte phagocytosis and oxidative burst activity.

Lysosomotropic amines modulate neutrophil calcium homeostasis

Lysosomotropic amines can raise the acidic internal pH of the neutrophil lysosome and inhibit neutrophil function. Because pH and calcium regulation are intimately connected in various types of excitable cells, we studied the effects of several lysosomotropic weak bases on neutrophil calcium homeostasis. Base-treated cells had normal to minimally elevated resting cytosol free calcium, but weak bases produced significant release of calcium from organelles when this release was directly measured in permeabilized cells, even after depletion of inositol-triphosphate-sensitive stores. Collapse of transmembrane pH gradients with monensin similarly released organelle calcium. The initial cytosol calcium response to f-met-leu-phe was enhanced by some of the lysosomotropic amines but the calcium rise was more transient in base-treated cells than in control samples. These findings suggest that existence of an acidic intracellular compartment, such as the lysosome, is important to normal calcium homeostasis in the neutrophil and that pH sensitivity and inositol triphosphate sensitivity may define two pools of releasable organelle calcium. The effect of pH perturbation on calcium homeostasis may partially account for the inhibition of neutrophil function by lysosomotropic amines.

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.

Small increases in pH decrease uptake of Escherichia coli by human neutrophils in vitro

Increases in pH from 7.4 to 7.8 decreased the ability of human neutrophils in serum to ingest and kill Escherichia coli ATCC 29552 in vitro. In contrast, similar increases in pH did not decrease the bactericidal activity of neutrophils in serum against Staphylococcus aureus 502A. Increases in pH did not alter opsonization of E. coli by serum or the growth of E. coli but rather appeared to alter neutrophil uptake of bacteria by a direct effect on the neutrophil.

The cellular regulation of vesicle exocytosis by Entamoeba histolytica

We studied the cellular regulation of vesicle exocytosis by Entamoeba histolytica utilizing release of endocytosed 125iodine (125I) labeled tyrosine conjugated dextran; 125I-dextran entered the acid pH vesicles of the amebae and was not degraded during these studies. Exocytosis was temperature dependent with 74%, 36%, 4%, and 0% of 125I-dextran released after 120 min at 37 degrees C, 31 degrees C, 25 degrees C, and 4 degrees C, respectively (P less than 0.01 for each). Exocytosis at 37 degrees C was inhibited by cytochalasin D (10 micrograms/ml), EDTA (10 mM), or the putative intracellular calcium antagonist TMB-8 (250 microM) (P less than 0.01 for each at greater than or equal to 60 min). Calcium ionophore A23187 (1 microM) enhanced exocytosis at 5 and 15 min (P less than 0.01). Elevation of vesicle pH with NH4Cl (10 mM) had no effect on release of 125I-dextran; phorbol myristate acetate (10(-6) M) increased exocytosis by 46% at 30 min (P less than 0.01). Centrifugation of amebae with target Chinese hamster ovary cells resulted in decreased 125I-dextran release into the cell supernatant after 30 and 60 min at 37 degrees C (by 40% and 42%, respectively, P less than 0.01); release of 125I-dextran returned to control values with addition of 1.0 g% galactose or GalNac but not with mannose or N-acetyl-D-glucosamine. Amebic phagocytosis of serum-exposed latex beads had no effect on release of dextran by amebae (n = 16). Exocytosis of acid pH vesicles by E. histolytica is temperature-, microfilament-, and calcium-dependent, and stimulated by phorbol esters.

CR1-receptor recycling in phorbol ester-activated polymorphonuclear leucocytes

Complement-receptor type 1, CR1, which recognizes the C3b cleavage fragment of C3, is present on the membranes of human phagocytic cells, but does not mediate phagocytosis or undergo internalization unless activated by one of a variety of stimuli. Among these stimuli low doses of phorbol esters have been shown to induce a consistently increased expression of CR1, despite apparently continuous receptor internalization. We have studied the fate of internalized receptor-ligand complexes in neutrophils activated with low concentrations of phorbol dibutyrate. In our studies, we followed CR1 with either 125I-C3b, the physiologic ligand, or with 125I-Fab fragments of a monoclonal anti-CR1 antibody. We observed rapid internalization of CR1-C3b complexes by PMN treated with 10 ng/ml (1.98 x 10(-8)M) PDBu, consistent in rate and extent with previously reported results using monoclonal antibodies. The fate of the internalized ligand was studied after elution of cell-surface C3b at 0 degrees. Intracellular ligand was externalized in a time- and temperature-dependent fashion, reaching a plateau at 10-15 min. Released C3b was totally TCA precipitable and structurally unaltered, as determined by SDS-PAGE, suggesting that recycling occurs via a prelysosomal predegradative compartment. Loading the cells with chloroquine did not affect this process. A monoclonal anti-CR1 Fab probe behaved in exactly the same manner, suggesting that the recycling of intact ligand-receptor complexes takes place. The possible physiological consequences of this finding are discussed.

Lysosomotropic behavior of adrenergic antagonists in interactions with human neutrophils

Autonomic neurohormones affect the secretory activity of neutrophils by modulating release of lysosomal enzymes in response to immunologic stimuli. Autonomic agents are also weak bases which might modify cell function by accumulating in the acidic interior of the lysosome, in addition to their receptor-mediated activity. We examined the association of the beta-adrenergic antagonist [3H]dihydroalprenolol with human neutrophils and lysosome and membrane fractions derived from neutrophils, and the subcellular distribution of the photoaffinity-labeled beta-adrenergic ligand [3H]azidobenzylcarazolol after incubation with intact cells. Isolated neutrophil lysosomes accumulated significantly more [3H]dihydroalprenolol than isolated membrane preparations. Decreasing the transmembrane pH gradient markedly reduced [3H]dihydroalprenolol accumulation by intact cells or lysosomes but not by membranes. Since [3H]dihydroalprenolol accumulated by intact cells remained rapidly exchangeable, the photoaffinity ligand [3H]azidobenzylcarazolol was used to assess ligand distribution after association with whole cells. After cell disruption, 18.5 +/- 1.3% of this ligand appeared in the lysosome fraction as compared to 2.2 +/- 0.6% in the membrane fraction. The secretagogue phorbol myristate acetate caused release of the ligand as well as lysosomal enzymes from cells. These findings suggest that there is significant pH-dependent lysosomal accumulation of beta-antagonists. This lysosomotropic interaction may be important both as it affects the sequestration and redistribution of the drugs, and as it might in some circumstances affect host defense functions of the neutrophil.

Protein kinase C inhibition by sphingoid long-chain bases: effects on secretion in human neutrophils

Sphingoid long-chain bases (sphinganine and sphingosine) have recently been shown to inhibit protein kinase C both in vitro [Y. Hannun et al. (1986) J. Biol. Chem. 261, 12604-12609] and in intact human neutrophils, in which they block activation of the superoxide-generating respiratory burst [E. Wilson et al. (1986) J. Biol. Chem. 261, 12616-12623]. In the present study we have used sphingosine to investigate the pathways for agonist-induced secretion of neutrophil granule contents. Induction of secretion of the specific granule component lactoferrin by a variety of agonists [phorbol 12-myristate-13-acetate (PMA), formyl-methionyl-leucyl-phenylalanine (fMLP), and calcium ionophore A23187] was completely inhibited by sphingosine with an ED50 of 6 to 10 microM. PMA-induced secretion of lysozyme (present in both the azurophilic and specific granules) was completely blocked with an ED50 of 10 microM, whereas fMLP-induced secretion was only about 50% inhibited. Secretion of the azurophilic granule proteins beta-glucuronidase and myeloperoxidase was activated by fMLP and A23187, but not by PMA, and was not affected by sphingosine. The use of A23187 in the presence of sphingosine allowed differentiation between calcium activation of protein kinase C-dependent versus-independent pathways. The effect of sphingosine was not mediated by neutralizing intracellular acidic compartments, since treatment of neutrophils with inhibitory concentrations of sphingosine did not significantly alter the uptake of labeled methylamine. We conclude that at least two mechanisms participate in the regulation of specific and azurophilic granule secretion, respectively: a protein kinase C-dependent pathway and a calcium-dependent pathway which does not involve protein kinase C.

Evidence for the involvement of an acidic compartment in the processing of myeloperoxidase in human promyelocytic leukemia HL-60 cells

The observation that myeloperoxidase precursor and larger intermediate (Mr 91,000 and 81,000, respectively) were extracted in the presence of detergent from isolated granule fractions of human promyelocytic leukemia HL-60 cells under mildly acidic conditions was investigated. In contrast, under conditions of neutral pH, only the Mr 74,000 intermediate and mature species were extracted. Extraction of the Mr 91,000 and 81,000 forms was also enhanced in the presence of EDTA. Kinetic studies of the processing of the different myeloperoxidase species confirmed the intermediate nature of the Mr 81,000 and 74,000 forms. Support for a role of an acidic intracellular compartment was obtained through evidence that the acid-extractable precursor and intermediates accumulated in HL-60 cells which had been treated with 1 microM monensin. Under these conditions, the production of mature heavy (Mr 63,000) and light (Mr 13,500) subunits of myeloperoxidase was consistently inhibited by greater than 40% over a 16-h period. The effects of monensin on processing of myeloperoxidase were completely reversed if monensin was removed during this 16-h period. These data support the idea that an acidic compartment may be involved in the transport of myeloperoxidase precursors to azurophil granules and/or their processing to a smaller intermediate form (Mr 74,000) of the enzyme.

Acid intracellular vesicles and the cytolysis of mammalian target cells by Entamoeba histolytica trophozoites

Entamoeba histolytica kills mammalian target cells in a multi-step sequential process with separate adherence, cytolytic, and phagocytic events. In the studies reported here, we used fluorescein isothiocyanate linked to dextran to label the endocytic vesicles of the HM1 strain of E. histolytica and measure vesicle pH (5.1 +/- 0.2 by spectrofluorimetry). Concentrations of NH4Cl (1.0-10.0 mM) sufficient to increase vesicle pH to greater than or equal to 5.7 inhibited amebic killing of target Chinese hamster ovary (CHO) cells as assayed by trypan blue staining, by the release of 3H-thymidine previously incorporated into CHO cell monolayers, and by the release of 111indium oxine from radiolabeled CHO cells. Similar effects were also observed with two other weak bases, primaquine and chloroquine (both 50 microM). In contrast, NH4Cl (10 mM) did not affect either the adherence or phagocytic events, as measured by amebic adherence to CHO cells at 4 degrees C and by the binding and ingestion of 3H-leucine-labeled bacteria. In the presence of NH4Cl and the carbohydrate ligand asialofetuin, there was no evidence of intracellular trapping of the amebic galactose-inhibitable lectin; inhibition of adherence by cycloheximide (10 micrograms/ml for 3 h) suggested rapid turnover of the surface lectin. Prolonged exposure to NH4Cl for 48 h (which had no effect on amebic protein synthesis) or shorter exposure to cycloheximide (10 micrograms for 3 h) produced persistent inhibition of cytolysis. These results indicate that an uninterrupted acid pH in intracellular endocytic vesicles is necessary for the cytolysis of target cells by E. histolytica trophozoites.

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.

A quantitative fluorescent method for measurement of bacterial adherence and phagocytosis

We have developed a new two-color fluorescent method for the quantitative measurement of adherence and ingestion of Streptococcus pneumoniae by human monocytes. The method employs a fluorescent naphthalimide, Lucifer Yellow VS, that has been covalently linked to the bacterial cell wall. Bacteria were opsonized and allowed to adhere to monocytes. Lucifer Yellow did not alter the bacterial interaction with complement in serum or with the phagocytic cell. The ability of monocytes to ingest the adherent bacteria was tested under a variety of conditions. Rabbit antibody to Lucifer Yellow derivatized with Texas Red was used to detect monocyte-bound, but uningested bacteria. Dual laser flow cytometry simultaneously quantitated the total number of monocyte-associated S. pneumoniae and the number that remained surface adherent. This method allows separate analysis of the opsonins and receptors involved in bacterial adherence to phagocytes and in the ingestion process.