Monoclonal antibody AHN-1 inhibits phagocytosis by human neutrophils

The granulocyte-specific monoclonal antibody, AHN-1, immunoprecipitates two major surface-iodinated proteins of 105,000 and 145,000 to 150,000 daltons from normal human neutrophils. In this study, the effect of AHN- 1 on a number of neutrophil functions was evaluated in vitro. Both complement- and antibody-mediated phagocytosis were inhibited when human neutrophils were pretreated with AHN-1 and opsonized bacteria were used as targets. The inhibition of phagocytosis was specific, in that lysosomal enzyme release and chemotaxis were not altered by treatment with AHN-1. AHN-1 did inhibit superoxide production by neutrophils in response to particulate stimuli, but not in response to the soluble stimulus, 12-O-tetradecanoylphorbol-13-acetate. The data indicate that one or both of these surface proteins may be important in the process of phagocytosis. AHN-1 should be useful in isolating and further characterizing the nature of these molecules.     

Interactions of phagocytes with the Lyme disease spirochete: role of the Fc receptor

The phagocytic capacity of murine and human mononuclear and polymorphonuclear phagocytes (including peripheral blood monocytes and neutrophils), rabbit and murine peritoneal exudate cells, and the murine macrophage cell line P388D1 against the Lyme disease spirochete was studied. All of these cells were capable of phagocytosing the spirochete; phagocytosis was measured by the uptake of radiolabeled spirochetes, the appearance of immunofluorescent bodies in phagocytic cells, and electron microscopy. Both opsonized and nonopsonized organisms were phagocytosed. The uptake of opsonized organisms by neutrophils was blocked by a monoclonal antibody specific for the Fc receptor and by immune complexes; these findings suggested that most phagocytosis is mediated by the Fc receptor. Similarly, the uptake of opsonized organisms by human monocytes was inhibited by human monomeric IgG1 and by immune complexes. These results illustrate the role of immune phagocytosis of spirochetes in host defense against Lyme disease.     

Surface glycoproteins of human white blood cells. Analysis by surface labeling.

We labeled surface glycoproteins of normal human blood platelets, granulocytes, monocytes, T and B lymphocytes, and null cells by the galactose oxidase-NaB3H4 and periodate-NaB3H4 labeling techniques. The labeled glycoproteins were observed by fluorography after separation by polyacrylamide slab gel electrophoresis. All major types of human leukocytes showed different and characteristic surface glycoprotein patterns. These patterns evidently also include common components.     

The Phagocytosis of Blood Leukocytes from Cystic Fibrosis Patients is not Impaired in General

Impaired phagocytosis of Pseudomonas aeruginosa was found in isolated monocytes of peripheral blood of cystic fibrosis patients, but not in their neutrophils, as reported some years ago. In the present study, we analysed the phagocytic capacity of peripheral blood neutrophils and monocytes of cystic fibrosis patients and of healthy controls. Phagocytosis was determined using a commercial phagocytosis “in whole blood” assay on the basis of fluorescence-labelled opsonized Escherichia coli bacteria and flow cytometry. Venous blood of cystic fibrosis patients and of healthy controls was collected and the phagocytosis assay was performed. No differences in the percentage of phagocytic cells or in the overall phagocytic capacity were found between samples of cystic fibrosis patients and healthy controls either in monocytes or in neutrophils. Thus, our results did not support the hypothesis of a generally reduced phagocytic ability in the peripheral blood immune cells of cystic fibrosis patients.

     

Downregulation of neutrophil CD43 by opsonized zymosan

CD43, a prevalent white blood cell molecule distinguished by its mucin- like surface region, has been proposed as a "functional barrier" that prevents or negatively regulates a variety of cell surface interactions. Implicit in this hypothesis is the expectation that CD43 will be altered or removed when white blood cells are activated. To investigate alterations of CD43 in a dramatic example of functional cell activation, suspension neutrophils were challenged with opsonized zymosan, a characterized stimulator of phagocytosis and respiratory burst oxidase. Flow cytometry showed decreased surface density of CD43 in opsonized zymosan-treated neutrophils, and immune precipitation showed decreased cellular CD43 content, indicating that opsonized zymosan downregulates CD43 by a proteolytic mechanism. Based on densitometry of immune precipitates, CD43 levels were decreased 42% +/- 6% in neutrophils treated for 10 minutes with opsonized zymosan and decreased 70% +/- 3% in neutrophils treated with phorbol 12-myristate 13-acetate (PMA). CD43 downregulation in response to opsonized zymosan, like PMA-induced CD43 downregulation, was insensitive to the serine protease inhibitor diisopropylfluorophosphate (DFP). In contrast, CD43 downregulation in response to opsonized zymosan or PMA was prevented by 4-(2-aminoethyl)-benzenesulfonylfluoride (AEBSF) and 3'4'- dichloroisocoumarin (3,4-DCI), both of which are characterized serine protease inhibitors. Activation of the neutrophil respiratory burst oxidase by opsonized zymosan or PMA was also insensitive to DFP and prevented by AEBSF and 3,4-DCI. These findings indicate a requirement for a proteolytic step in activation of the respiratory burst of intact suspension neutrophils by opsonized zymosan and PMA and suggest that CD43 cleavage may be a required proteolytic event.     

Phagocytosing neutrophils down-regulate the expression of chemokine receptors CXCR1 and CXCR2

CXC chemokines play a central role in regulation of neutrophil activation and chemotaxis. Because the chemotactic responses of neutrophils are impaired after phagocytosis, we explored the effect of phagocytic stimuli on the expression of interleukin-8 (IL-8) receptors, CXCR1 and CXCR2, in human neutrophils. After phagocytosis of opsonized yeast, the expression of CXCR1 and CXCR2 was substantially down-regulated and was accompanied by reduced Ca(++) responses to corresponding ligands, IL-8 and neutrophil-activating peptide-2 (NAP-2). The levels of CXCR1 and CXCR2 mRNA were constant during phagocytic stimulation of neutrophils. Confocal microscopy revealed that CXCR reduction was not via internalization. Metalloproteinase inhibitor, 1,10-phenantroline, prevented the reduction of CXCRs induced by phagocytosis, indicating that proteolytic degradation may be responsible for down-regulation. These observations suggest that down-regulation of CXCR expression may substantially reduce the responsiveness of phagocytosing neutrophils to CXC chemokines.     

Stimulation of the hexose monophosphate shunt independent of hydrogen peroxide and superoxide production in rabbit alveolar macrophages during phagocytosis.

Phagocytosis and oxidative metabolism of human polymorphonuclear leukocytes (PMN) and rabbit alveolar macrophages (AM) were studied. Human PMN ingested a mean of 12 polyvinyl toluene latex particles (2 micrometer in diameter) per cell. There was stimulation of O2- and H2O2 production, light emission, and activation of the hexose monophosphate shunt during phagocytosis by human PMN. Rabbit AM ingested 51 latex particles (2 micrometer in diameter) per cell. There was no stimulation of the production of O2- and H2O2 or light emission associated with phagocytosis by rabbit AM, while the hexose monophosphate shunt was activated. Similar metabolic changes were obtained in both cell types when opsonized zymosan was used as phagocytic particles. 1-14C-glucoseoxidation was stimulated by H2O2 and methylene blue in both resting human PMN and rabbit AM. It is concluded that activation of the hexose monophosphate shunt in rabbit AM during phagocytosis is independent of O2- and H2O2 production.     

Differential role of neutrophil Fcγ receptor IIIB (CD16) in phagocytosis,bacterial killing,and responses to immune complexes

Objective

To determine the roles played by the neutrophil Fcγ receptor type II (FcγRII) (CD32) and FcγRIIIb (CD16) in phagocytosis, bacterial killing, and activation by immune complexes (ICs) and to test the hypothesis that inhibition of pathologic effector neutrophil function is possible without compromising host defense.

Methods

Receptor function was probed by enzymic removal of FcγRIIIb from the cell surface and by use of Fab/F(ab‘)₂ fragments of monoclonal antibodies to block receptor‐ligand binding. Cells were challenged with (a) serum‐opsonized Staphylococcus aureus, (b) serum‐ and IgG‐opsonized latex particles, and (c) synthetic soluble and insoluble ICs to mimic bacterial and inflammatory stimuli.

Results

Phosphatidylinositol‐phospholipase C treatment removed >97% of surface FcγRIIIb from neutrophils previously treated with tumor necrosis factor α to mobilize intracellular stores of receptor. This treatment profoundly inhibited activation of primed neutrophils by soluble ICs of the type found in diseased rheumatoid joints, but had no effect on phagocytosis and killing of serum‐opsonized S aureus.

Conclusion

FcγRIIIb plays a major role in the secretion of toxic products in response to ICs, but little or no role in the phagocytosis and killing of serum‐opsonized bacteria. The selective suppression of effector neutrophil function is therefore possible. FcγRIIIb, or its intracellular signaling pathway, is a potential therapeutic target in inflammatory diseases such as rheumatoid arthritis, because disruption of its function should decrease inflammatory tissue damage, but not jeopardize host protection against infection.

     

Immune thrombocytopenia and Fc receptor-mediated phagocyte function

Summary The response to intravenous immunoglobulin treatment (IVIG) is thought, in part, to be due to blockade of Fc receptor for IgG in the mononuclear phagocyte system (MPS). We have studied this by measuring splenic clearance of heat-damaged and IgG antibody-coated red cells in immune thrombocytopenic patients receiving IVIG. Clearance of heat-damaged red blood cells (HDRBC) labelled with technetium 99MM was measured in eight patients before and after a 5-day infusion of IVIG. In six of the eight there was an enhanced clearance of HDRBC post IVIG. Clearance studies were performed in eight rhesus-D-positive patients using autologous red cells coated with anti-D and labelled with^99MTc. The time taken for the radioactivity at 3 min to fall to 50% (T 1/2) was calculated. The (T 1/2) increased in seven of the eight patients from a mean of 78.5 min to 137.1 min, a prolongation of 74.6%. In addition, we have examined the effect of IVIG on Fc-mediated phagocytosis by neutrophils. Platelet phagocytosis by patients' neutrophils was measured using opsonized autologous platelets in nine patients. There was a marked reduction in platelet phagocytosis as measured by formazan production in all patients at day 4–5 when compared with the preinfusion value, and in half of these this reduction was still evident at further studies, 1 week after the end of the infusion period. The platelet count rose in parallel with the fall in platelet phagocytic ability of the neutrophils, reaching a peak at 7 days post infusion, and fell with the recovery of phagocytic function in weeks 2 and 3. These findings suggest that IVIG has a marked effect on Fc-mediated phagocytosis.     

Monocytes and granulocytes in rheumatoid arthritis (RA): phagocytic activity and superoxide anion production

Summary It is suggested by many tests that phagocytic cells were implied in inflammation which occurred during rheumatoid arthritis (RA). Further, three subject populations were selected for this study: — Rheumatoid arthritis patients diagnosed according to American Rheumatism Association criteria (ARA mean=6) and treated with gold compounds. — Control subjects treated with the same non-steroidal anti-inflammatory drug (NSAID), diclofenac (75 mg per day). — Normal subjects without disease or treatment. Blood granulocytes and monocytes were separately tested for ingestion of three different particle species (opsonized zymosan, immunoglobulin G sheep red cells, glutaraldehyde-treated sheep red cells) and stimulation of Superoxide anion production by these particles. All phagocytic cells in RA patients have normal phagocytic response and Superoxide anion production. Autologous serum does not inhibit the activity of these cells. In addition the NSAID (diclofenac) does not act upon phagocytosis and oxidative burst of control cells.     

Two-dimensional analysis of metabolically and cell surface radiolabeled proteins of some human lymphoid and myeloid leukemia cell lines. I. 35S-methionine labeled, lactoperoxidase radioiodinated and 3H-reductively methylated proteins

Cell surface and cytoplasmic polypeptides of some human hemopoietic cell lines were radiolabeled by three different techniques: 35S-methionine metabolic radiolabeling, lactoperoxidase catalyzed radioiodination and reductive methylation with formaldehyde and tritiated sodium borohydride. Two-dimensional patterns of 35S-methionine labeled proteins revealed more than 500 separated protein spots with essentially similar general aspects of all examined cell lines, sharing major polypeptides such as those with electrophoretic mobilities of major cytoskeletal proteins. 125I-lactoperoxidase radio-iodinated cell surface protein patterns contained about 30 separated protein macromolecules with some marked differences between lymphoid versus myeloid lines and also between individual cell lines. Two-dimensional patterns of tritiated membrane polypeptides consisted of approximately 200 separated protein spots, some prominent of them appeared with electrophoretic mobilities of major cytoskeletal proteins being common to both 35S-methionine and reductive methylation patterns. Two-dimensional patterns of 35S-methionine labeled and cell surface radioiodinated proteins immunoprecipitated by monoclonal antibodies Bra30 and HL39, recognizing MHC class II antigens, appeared as bimolecular complex of larger acidic and smaller basic chains structurally corresponding to the expected two-dimensional patterns of MHC class II antigens.     

Vitronectin (S protein) augments the functional activity of monocyte receptors for IgG and complement C3b

An arginine-glycine-aspartic acid sequence (RGD in the single letter code for amino acids) is present in the cell attachment site of both vitronectin and fibronectin. Inasmuch as fibronectin and synthetic peptides containing RGD enhance ingestion of opsonized particles by monocytes, we investigated the effects of vitronectin on phagocytosis by monocytes of sheep erythrocytes bearing IgG (EA) or complement C3b (EC3b). Peripheral blood monocytes were isolated by countercurrent elutriation and allowed to adhere to slides that had been coated with either vitronectin or fibronectin. Next, EA or EC3b were incubated with the adherent monocytes, and phagocytosis was subsequently quantified. Vitronectin caused the same dose dependent increase in phagocytosis as fibronectin. The augmentation of phagocytosis of EA induced by vitronectin could be inhibited by the F(ab')2 fragments of anti-vitronectin IgG but not by preimmune F(ab')2. The maximum phagocytosis of EA induced by vitronectin could not be enhanced by the addition of fibronectin, suggesting that vitronectin and fibronectin act on the same population of monocytes and that the two proteins stimulate the same mechanism through which the enhanced phagocytosis is mediated. Fibronectin and vitronectin caused a tenfold increase in the attachment of EC3b to monocytes, but phagocytosis was augmented minimally. These studies demonstrate that vitronectin modulates interactions between monocytes and opsonized particles.     

Fcgamma receptor-mediated immune phagocytosis depends on the class of FcgammaR and on the immunoglobulin-coated target cell

BACKGROUND AND OBJECTIVES: Three human Fcgamma receptors (FcgammaR) are known to mediate immune phagocytosis. A variety of different phagocytic assays have been described, but their comparability is complicated by the use of different effector cells and different antibody-coated target cells. The aim of this study was to determine the influence of these variable components on the FcgammaR-mediated phagocytosis. MATERIALS AND METHODS: We sensitized human red blood cells (RBC) with polyclonal human anti-D (huaD), or with human monoclonal anti-D of the isotypes IgG1 (huIgG1) or IgG3 (huIgG3). Sheep RBC coated with rabbit immunoglobulin (RBC-RAS) were also used. Monocytes or polymorphonuclear neutrophils (PMN) were incubated with different FcgammaR-specific antibodies or their F(ab')2 fragments to determine the contribution of the different FcgammaRs on these effector cells in the phagocytic process of different antibody-coated target cells. RESULTS: huaD-RBC and huIgG1-RBC were preferentially ingested via the FcgammaRI on monocytes and, to a minor extent, also by the FcgammaRII. PMN ingested these target cells only after induction of the FcgammaRI by interferon-gamma (IFN-gamma). huIgG3-RBC extensively formed rosettes with monocytes but were seldom ingested. RAS-RBC phagocytosis was induced primarily via the FcgammaRI on monocytes and was mediated by the FcgammaRII on PMN. CONCLUSION: When performing phagocytosis assays with different effector and target cells, one has to take into account that phagocytosis is mediated by different FcgammaR, making comparability of these assays more difficult.     

Subcellular localization of H2O2 production in human neutrophils stimulated with particles and an effect of cytochalasin-B on the cells

The ultrastructural localization of H2O2 production in suspended polymorphonuclear leukocytes (PMN) stimulated with particles was studied using CeCl3 technique. PMN stimulated with opsonized zymosan or polystylene latex with or without IgG were incubated in 0.1 M Tris- maleate buffer with 1 mM CeCl3 and 10 mM aminotriazole. Cells were then fixed and embedded in a resin for electron microscopy. The reaction product of cerium perhydroxide was observed on the phagosomal membranes and on the areas of the plasma membrane engulfing the particles. Catalase or ferricytochrome-c decreased the deposits. p-Benzoquinone (O2- scavenger) inhibited the formation of the deposits, but KCN or NaN3 enhanced it. Pretreatment with p-diazobenzenesulfonic acid inhibited the reaction. In some PMN pretreated with cytochalasin-B, cellular aggregation was observed. The H2O2 production in these cells were observed on the membrane adherent to the particles and on the contact surface of the membrane of adjoining PMN. The plasma membrane was damaged and the electron-dense product was diffused into the cytoplasm. These results clearly show that H2O2 production is initiated at the area of the plasma membrane adherent to the particles and that H2O2 is released before the completion of phagocytosis.     

Nramp1 equips macrophages for efficient iron recycling

OBJECTIVE: Natural resistance-associated macrophage protein 1 (Nramp1) is a divalent metal transporter expressed exclusively in phagocytic cells, such as macrophages and neutrophils. As macrophages are responsible for the engulfment and clearance of senescent red blood cells (RBC), we hypothesize that Nramp1 may participate in the recycling of iron acquired through phagocytosis. MATERIALS AND METHODS: To test this hypothesis, we examined the contribution of Nramp1 expression to iron metabolism in macrophages loaded with iron via either hemin or opsonized RBC. RESULTS: Western blot analysis indicated that Nramp1 protein levels increased with hemin, opsonized erythrocytes, or erythropoietin treatment. The pool of chelatable iron was also found to transiently increase following iron-loading with hemin or opsonized RBCs, with a greater increase observed in macrophages expressing Nramp1. Overexpression of Nramp1 was also found to result in a greater cellular release of (59)Fe following phagocytosis of (59)Fe-labeled reticulocytes. Expression of Nramp1 was associated with a twofold increase in heme oxygenase-1 (HO-1) levels in macrophages undergoing erythrophagocytosis. Nramp1-expressing macrophages were also found to phagocytose nearly twice as many RBC than their Nramp1-deficient counterparts. CONCLUSION: The rapid and strong induction of Nramp1 during erythrophagocytosis, combined with its positive effects on (59)Fe-release, HO-1 induction and phagocytic ability, suggest that Nramp1 has a role in the recycling of hemoglobin-derived iron by macrophages.     

Platelet-derived growth factor stimulates phagocytosis and blocks agonist-induced activation of the neutrophil oxidative burst: a possible cellular mechanism to protect against oxygen radical damage.

The effect of platelet-derived growth factor (PDGF) on agonist-induced activation of the superoxide-generating oxidative burst in human neutrophils was tested. PDGF had no effect on the resting level of superoxide generation but inhibited both the rate and the extent of fMet-Leu-Phe-stimulated superoxide production in a dose-dependent manner. The concentration required to inhibit the response by 50% was 95 +/- 26 pM (n = 10). PDGF also blocked activation by other receptor-mediated agonists such as the complement protein C5a and opsonized zymosan, but not by phorbol myristate acetate or arachidonate, both of which may act at postreceptor sites. The growth factor, however, had no effect on the binding of fMet-Leu-Phe to its receptor. PDGF in concentrations that blocked the oxidative burst stimulated phagocytosis of opsonized latex particles. Thus, PDGF functions as a heterologous "down-regulator" of receptor-mediated activation of the neutrophil oxidative burst and an activator of phagocytosis. A model for a feedback regulatory loop between platelets and neutrophils is proposed.     

Enhancing Effect of Levamisole on the Phagocytic Activity of Human Neutrophil Polymorphonuclear Leucocytes in vitro

The effect of levamisole on the phagocytic activity of normal human polymorphonuclear neutrophil leucocytes has been studied in vitro. In concentrations comparable with the serum levels obtained in treatment with levamisole perorally, the engulfment of heat-killed yeast cells is moderately but significantly increased. It is shown that levamisole can only stimulate phagocytosis of adequately opsonized particles. The action of the drug is still unknown but appears to be directly linked to the phagocytic cell.     

Is there an effect of immunoglobulins and G-CSF on neutrophil phagocytic activity in preterm infants?

Summary The percentage of neutrophils phagocytosing group B streptococci (GBS)in vitro was determined in ten healthy preterm infants (<32 weeks of gestation) and adult controls by using an acridine orange fluorescence whole blood assay. When GBS were opsonized with adult serum, no difference in phagocytic activity was found between both groups after 10 and 30 min (preterms: 40% and 68%, adults: 32% and 56%, respectively). Phagocytosis rates in preterm infants decreased significantly to 6% and 18% (at 10 and 30 min) when pool serum of preterm infants was used instead. Supplementation of the preterm serum with either intravenous immunoglobulin or IgM-enriched immunoglobulin did not change the results significantly. The addition of granulocyte colony-stimulating factor (G-CSF) accelerated phagocytosis significantly after 10 min, but did not increase the overall phagocytic activity after 30 min in either group. Hence the potential benefits of intravenous immunoglobulins and G-CSF in neonatal sepsis may not be attributable to an immediate increase in and direct effect on neutrophil phagocytic activity.     

Aclacinomycin, an anti-leukemic anthracycline, impairs human neutrophil functions.

The effects of aclacinomycin, an anti-leukemic anthracycline, on human neutrophil functions were investigated. The release of superoxide (O2-) in neutrophils stimulated by opsonized zymosan, myristate, or phorbol myristate acetate was inhibited by aclacinomycin in a dose- and time-dependent manner. The phagocytosis of yeast particles and oil droplets, and membrane potential changes stimulated by phorbol myristate acetate were also inhibited by aclacinomycin. On the other hand, the O2(-)-producing enzyme (NADPH oxidase) in the particulate fraction prepared from myristate-stimulated neutrophils was not affected by aclacinomycin. When high concentrations of aclacinomycin (10-100 micrograms/ml) were employed, significant inhibition of O2- release, phagocytosis, and membrane potential changes was observed within 5 min. Phagocytic activity was also inhibited when neutrophils were preincubated for 13 h at 37 degrees C with a low concentration (40 ng/ml) of aclacinomycin, which could be obtained by intravenous administration of 20 mg aclacinomycin. Myristate-induced O2- release was not impaired by cytosine arabinoside (2-800 micrograms/ml), vincristine (0.1-100 micrograms/ml), adriamycin (25-100 micrograms/ml), or daunomycin (5-75 micrograms/ml) when the cells were preincubated with these drugs for 5 min at 37 degrees C. These findings suggest that aclacinomycin inhibits the respiratory burst by impairing the activating system of NADPH oxidase and phagocytic activity.     

Cell surface alterations of avian sarcoma virus B77- and 3,4-benzo(a)pyrene-transformed rat fibroblasts. I. Cell surface proteins characterized by two-dimensional electrophoresis

Plasma membrane proteins of avian sarcoma virus B77-, 3,4-benzo(a)pyrene- and spontaneously transformed rat fibroblasts were metabolically- and cell surface radiolabeled and analyzed by electrophoresis under denaturing conditions (SDS-PAGE) or by two-dimensional electrophoresis. Most extensive series of protein alterations on transformed cells was detected by two-dimensional electrophoresis of cell surface proteins radiolabeled by lactoperoxidase catalyzed radioiodination: a fibronectin-like 220k protein with two isoelectric forms (pI 5.9 and 6.2-6.6), a 180k protein of pI 6.2-6.6 and two proteins of 48k and 50k with pI approximately 5.4-all decreased on examined transformed cells. In addition to these proteins, a series of proteins more markedly detectable on transformed cells was found: a 110-120k (pI 5.6) protein found particularly on 3,4-benzo(a)pyrene- and spontaneously transformed cells, a series of proteins in the region of molecular weights 46-54k with pI 5.5-6.0, two proteins of 35k (pI 6.2 and 6.4) and two further, basic proteins of 38k (pI approximately 7.2 and 7.8). Some of these changes were visualized also by further techniques for radiolabeling of proteins, i.e. reductive methylation of cell surface proteins, metaboling radiolabeling by 3H-leucine followed by plasma membrane isolation, as well as by protein staining after two-dimensional electrophoresis of isolated plasma membrane proteins. A 70k and a 120k radioiodinated proteins were immunoprecipitated from all transformed cells and, to a markedly lesser extent from untransformed fibroblasts by the immune serum against rat type-C endogenous virus. A similar 70k protein was immunoprecipitated from avian sarcoma virus B77-transformed cells also by the antiserum against Friend murine leukemia virus envelope glycoprotein gp70.