Neutrophil activation by surface bound IgG: pertussis toxin insensitive activation

Toxins-useful biochemical tools for leukocyte research

Leukocytes are a heterogeneous group of cells that display differences in anatomic localization, cell surface phenotype, and function. The different subtypes include e.g., granulocytes, monocytes, dendritic cells, T cells, B cells and NK cells. These different cell types represent the cellular component of innate and adaptive immunity. Using certain toxins such as pertussis toxin, cholera toxin or clostridium difficile toxin, the regulatory functions of Gα_i, Gαs and small GTPases of the Rho family in leukocytes have been reported. A summary of these reports is discussed in this review.

Quantification of the surface density of a fluorescent label with the optical microscope

Fluorescence microscopy can offer unique advantages for biomaterials characterization. Like spectroscopy or radioactivity, it can be used to quantify specific binding to surfaces, but it can also assess surface homogeneity at the micron scale or detect protein aggregation. To fully utilize the potential of this technique, there must be a way to calibrate the microscope in terms of the moles of a fluorophore per unit area. The method we propose involves the following steps: fluorescent labeling of erythrocytes and quantification of the label by flow cytometry; flattening of fluorescent erythrocytes for microscopic observation; imaging and digital analysis to relate the gray level intensities to the fluorophore density; and using this procedure to characterize a different, more easily obtainable, standard. The latter can be a 50% solution of Na fluorescein that yields a highly reproducible and uniform fluorescence. Concentrated fluorescein solution can also be used to correct images for the spatial nonuniformity of illumination and detection (shading correction). By applying this method to study the binding of IgG and fibrinogen to glass or amidated glass, we showed that protein adsorption to glass may result in protein aggregation that may affect the biological activity of the adsorbed protein.

A microscopic study of Fc gamma RIII-mediated respiratory burst in neutrophils

We investigated the relationship between the respiratory burst in neutrophils and the membrane distribution of the IgG receptor, Fc gamma RIII. Fc gamma RIII receptors were labeled with a fluoresceinated antibody that does not block binding of immune complexes. The respiratory burst was detected using covalently bound rosamine stain previously described for flow cytometric applications. This method allows visualization of intracellular oxidant production in fixed cells using attenuated illumination with a laser. Strong cytosolic oxidation of rosamine was observed only in those cells that displayed prominent receptor endocytosis upon interaction with insoluble immune complexes. Soluble immune complexes or insoluble complexes in the presence of cytochalasin B did not stimulate endocytosis of Fc gamma RIII and induced no rosamine oxidation. Extracellular superoxide production measured by the cytochrome c test did not correlate with intracellular rosamine oxidation: it was maximal in cytochalasin-treated cells and did not require any visible receptor rearrangement. Our results demonstrate the utility of the rosamine stain as an intracellular marker of the oxidative burst, support the role of Fc gamma RIII in neutrophil activation and emphasize the compartmental regulation of the oxidative burst.

Differential phosphorylation in normal and leukemic granulocytes in response to phorbol 12-myristate 13-acetate

Granulocytes from the peripheral blood of patients with chronic myeloid leukemia (CML) exhibit a number of functional defects. To explore the relationship of these aberrations to signal transduction, granulocytes from normal subjects and CML patients were labelled with 32Pi, stimulated with phorbol myristate acetate (PMA) and the phosphoproteins (Pps) in the unstimulated and stimulated cells analyzed by 2D-SDS-PAGE followed by autoradiography. Results show that there are six distinct reproducibly phosphorylated proteins referred to as Pp1-Pp6 identifiable in the basal patterns of the resting granulocytes. Amongst these, Pp1 and Pp5 are more intensely phosphorylated and Pp3 is very faint or absent in unstimulated CML cells, relative to the normal granulocytes. On stimulation of normal cells with PMA, Pp1, Pp3, Pp4 and Pp6 exhibit distinct patterns of phosphorylation-dephosphorylation. In the CML cells, however, Pp1 and Pp4 are unresponsive to PMA. We conclude that PKC-mediated functions involving Pp1, Pp3 and Pp4 are most probably defective in CML cells.

Mechanisms of biomaterial-induced superoxide release by neutrophils

Biomaterial-centered infection is an important cause of the failure of prosthetic implants and organs. Because neutrophils mediate host defense against infection, the effect of biomaterials on neutrophil superoxide release and the mechanism of that effect were investigated using three materials commonly employed in surgical practice. The graft materials were expanded polytetrafluorethylene (PTFE), polyurethane and woven dacron. Polystyrene, a commonly used laboratory support vessel, was also studied. Both polystyrene and polyurethane were activating, but serum inhibitable, whereas PTFE was nonactivating, and woven dacron was not activating unless serum was present. The signaling mechanisms used by these materials demonstrated time and material dependency. Pertussis toxin inhibition of G protein-dependent activation had little or no effect on biomaterial induced activation, whereas FMLP-induced activation of the same biomaterial-associated cells was inhibited. Protein kinase C inhibition with staurosporine greatly inhibited polystyrene-induced activation, but had only a partial effect with polyurethane and even less effect with the activation associated with serum-treated woven dacron. These studies demonstrated that biomaterial contact-induced neutrophil activation differed from that described for cells in suspension, and showed that activation mechanisms on one material cannot be extrapolated to mechanisms on other materials.

Stimulation of the intracellular killing of Staphylococcus aureus by human monocytes mediated by Fc gamma receptors I and II

Previous studies have shown that intracellular killing of bacteria by monocytes is stimulated by interaction between IgG and Fc gamma receptors (Fc gamma R) in the membrane of these cells. In the present study anti-Fc gamma R monoclonal antibodies (mAb) were used to investigate the relative contributions of the various classes of Fc gamma R to the intracellular killing of Staphylococcus aureus by human monocytes and the biochemical pathways involved. Anti-Fc gamma RI or anti-Fc gamma RII mAb, but not anti-Fc gamma RIII mAb, efficiently stimulated the intracellular killing of bacteria by monocytes. Cross-linking Fc gamma RI or Fc gamma RII, but not Fc gamma RIII, on monocytes with mouse anti-Fc gamma R mAb followed by bridging with F(ab')2 fragments of goat anti-mouse IgG enhanced this process. Since the NADPH oxidase inhibitor diphenyleneiodonium blocked the Fc gamma R-mediated intracellular killing of S. aureus, oxygen-dependent bactericidal mechanisms are most probably involved. Cross-linking Fc gamma RI or Fc gamma RII but not binding of the mAb to the Fc gamma R on monocytes activated phospholipase C, as demonstrated by the increase in the intracellular concentration of inositol-(1,4,5)-triphosphate. The enhanced intracellular killing stimulated by cross-linking Fc gamma R on monocytes was completely blocked by U-73122, an inhibitor of phospholipase C-dependent processes. Protein kinase C activity, but not the rise in the cytosolic free Ca++ concentration or pertussis toxin-sensitive G proteins, is essential for the Fc gamma R-mediated intracellular killing of bacteria by monocytes. Together, these results demonstrate that cross-linking Fc gamma RI or Fc gamma RII is equally effective in stimulating the intracellular killing of bacteria by monocytes and that this stimulation is a phospholipase C-dependent process.

Tyrosine phosphorylation and its possible role in superoxide production by human neutrophils stimulated with FMLP and IgG

Superoxide production by human neutrophils stimulated with FMLP and soluble aggregated human IgG were inhibited in a dose dependent manner by two kinds of tyrosine kinase inhibitors, erbstatin and genistein. Superoxide production stimulated with surface bound IgG, however, was scarcely inhibited by either inhibitor. Protein tyrosine phosphorylation studies with immunoblotting revealed specific tyrosine phosphorylation of a 40 Kd protein by soluble aggregated and surface bound IgG, and that of a 39 Kd protein, as well as the 40 Kd protein, by FMLP. These were all inhibited by the tyrosine kinase inhibitors. These data suggest that superoxide production induced by FMLP and soluble aggregated IgG are, at least in part, tyrosine kinase dependent, but the tyrosine kinases and/or substrates of tyrosine kinases involved may be different. In addition, tyrosine kinase independent pathways are also suggested to be involved in superoxide production by stimulation with surface bound IgG.

Differential phosphorylation--cause for defective internalization of aggregated IgG by chronic myeloid leukemic granulocytes?

Granulocytes from the peripheral blood of patients with chronic myeloid leukemia (CML) are known to exhibit a defect in internalization of aggregated IgG relative to normal cells. As this aberration may arise due to defective transmembrane signalling, this study was undertaken to analyze alterations, if any, in protein phosphorylation between the two cell types. Normal and CML granulocytes were labeled with 32P-sodium orthophosphate and then stimulated with aggregated IgG. The phosphoproteins in the unstimulated and stimulated cells were analyzed by 2D-SDS-PAGE followed by autoradiography. The results show that there are five distinctly identifiable, reproducibly phosphorylated proteins referred to as Pp1-Pp5. In the unstimulated normal cells, Pp1 is less phosphorylated than Pp3, while in CML cells, Pp1 is more intense than Pp3. On stimulation of normal cells, with aggregated IgG, intensity of Pp1 increases while that of Pp3 decreases. In CML cells this response is reversed. We conclude that one of the causes for the defective internalization of IgG by CML granulocytes may probably be the observed differences in the phosphorylation of the proteins under study.

The effect of serine and thiol protease inhibitors on the chemiluminescence of human neutrophils in investigations in vitro

We have studied an indirect role of serine and thiol proteases in the activation of human neutrophils in vitro. Stimulation was evaluated using a chemiluminescence (CL) generation system. Receptor-dependent and receptor-independent stimuli were studied, e.g. opsonized zymosan, formyl-methionyl-leucyl-phenylalanine, platelet activating factor, phorbol myristate acetate, and calcium ionophore A23187. The serine protease inhibitors TPCK and TLCK, and thiol protease inhibitor PHMB, diminished the CL with different potencies and in a dose-dependent manner after treatment of cells with the various stimuli. Non-specific serine protease inhibitor, PMSF, and trypsin substrate TAME, showed a low inhibitory potency with respect to CL generation. Synthetic substrates for chymotrypsin (BTEE, ATEE) significantly inhibited CL with the various stimuli used with some differences in susceptibility to their inhibition. Specific chymotrypsin inhibitors diminished both the resting and activator-induced CL. We suggest that cell-bound chymotrypsin-like protease(s) is involved in the activation of signal transduction in human neutrophils after both receptor-dependent and receptor-independent stimulation.

Pertussis toxin partially inhibits phagocytosis of immunoglobulin G-opsonized Staphylococcus aureus by human granulocytes but does not affect intracellular killing

The aim of the present study was to determine whether pertussis toxin (PT)-sensitive GTP-binding proteins (G proteins) are involved in the signal transduction pathway(s) used for phagocytosis and intracellular killing of bacteria by human granulocytes. Treatment of granulocytes with PT resulted in decreased phagocytosis of immunoglobulin G (IgG)-opsonized Staphylococcus aureus but did not affect subsequent intracellular killing of these bacteria. PT also caused a decrease in the extracellular release of superoxide anion (O2-) and hydrogen peroxide (H2O2) by granulocytes in response to S. aureus opsonized by IgG. However, neither the phagocytosis nor the intracellular killing of S. aureus opsonized by fresh serum was affected by PT, and the release of O2- was partially inhibited. The release of O2- in response to serum-treated zymosan, opsonized mainly by complement components, was also only partially inhibited by PT. It is therefore possible that PT inhibits responses mediated through complement receptors to a lesser extent than those mediated via Fc gamma receptors. The results of this study indicate that PT-sensitive G proteins are involved in the signal transduction pathways that mediate the phagocytosis of IgG-opsonized bacteria and the accompanying respiratory burst.

Inhibition of 5-lipoxygenase product formation and polymorphonuclear cell degranulation by tenidap sodium in patients with rheumatoid arthritis

We studied the effect of tenidap sodium, a new antiinflammatory/antirheumatic drug (120 mg/day for 7 days), on eicosanoid production and neutrophil degranulation in patients with rheumatoid arthritis. Endogenous prostaglandin E2 levels and ex vivo production of leukotriene B4 (LTB4) were measured in synovial fluid samples obtained at baseline and 1 week later. We measured peripheral blood polymorphonuclear cell (PMN) degranulation following surface-bound IgG stimulation, a possible 5-lipoxygenase product-mediated event, by determining lactoferrin and elastase release into the culture fluid. We found decreased levels of endogenous prostaglandin E2 as measured by radioimmunoassay, and decreased ex vivo production of LTB4 by PMN as measured by high performance liquid chromatography, in synovial fluid samples from patients who took tenidap. Release of the granule proteins lactoferrin and elastase was decreased in PMN obtained from patients receiving tenidap, as well as in the PMN incubated in vitro with tenidap. Improvement in clinical measures paralleled the biochemical changes. The unique 5-lipoxygenase inhibitory property of tenidap, as measured by LTB4 production and degranulation, suggests that it may have clinical activity which differentiates it from nonsteroidal antiinflammatory drugs.

Tenidap, in contrast to several available nonsteroidal antiinflammatory drugs, potently inhibits the release of activated neutrophil collagenase

Neutrophils contain a collagenase that is stored in a latent form within the specific granule. With cellular activation, the latent enzyme is activated in association with the production of a variety of oxidants, including hypochlorous acid. We evaluated 4 nonsteroidal antiinflammatory drugs (NSAIDs) currently on the market and the new antiinflammatory/antirheumatic drug tenidap for their effects on the release of activated collagenase. In contrast to the 4 NSAIDs, tenidap profoundly inhibited the release of activated collagenase. This inhibition was predominantly due to interference with activation of the latent enzyme, rather than interference with enzyme release. The inhibition of collagenase activation was associated with a profound reduction in myeloperoxidase activity and in hypochlorous acid production. These observations demonstrate that tenidap has properties that set it apart from conventional NSAIDs and suggest that it may be a particularly useful agent in the treatment of inflammatory rheumatic disorders.

Lysis of fibrillar collagen by neutrophils in synovial fluid. A role for surface-bound immunoglobulins

Synovial fluids (SF) contain inhibitors capable of neutralizing the activity of proteases secreted by inflammatory cells and fibroblasts. To further define a potential role for SF polymorphonuclear neutrophils (PMN) in mediating joint destruction, peripheral blood PMN were suspended in SF and incubated with reconstituted collagen fibrils. Incubation of PMN-SF mixtures with collagen fibrils precoated with monomeric IgG resulted in significant lysis of the underlying fibrils relative to that seen with uncoated fibrils. Augmented fibril lysis by PMN-SF mixtures in which the PMN were activated with fluid-phase ligands such as phorbol myristate acetate or heat-aggregated IgG was not seen. Lysis of IgG-coated fibrils by PMN-SF was inhibited in the presence of EDTA or sodium azide. PMN-mediated resorption of fibrillar collagen occurred despite the presence of protease inhibitors in the SF at a concentration capable of neutralizing human neutrophil collagenase. These results suggest that the focal release and activation of human neutrophil collagenase during PMN stimulation by tissue-bound immunoglobulins may mediate the resorption of joint tissue collagens in rheumatoid arthritis, even in the presence of protease inhibitors.

Human immunoglobulin G potentiates superoxide production induced by chemotactic peptides and causes degranulation in isolated human neutrophils

Neutrophils are major cellular mediators of host defense and inflammation. They can be activated to produce superoxide and to release the contents of their granules to the extracellular space. We observed that monomeric human immunoglobulin G (IgG) sensitizes these cells to the chemotactic peptide N-formylmethionylleucylphenylalanine (fMLP). In cells submaximally stimulated by fMLP this enhancement was especially prominent. With saturating fMLP concentrations, the rate of O2- production was still about twice that in the control. No synergy with other activators (phorbol myristate acetate, concanavalin A) was observed. Binding of fMLP to the cells was decreased by IgG, resembling the effect of cytochalasin B. IgG did not induce O2- production on its own, but it stimulated degranulation of the neutrophils.

Activation of superoxide formation and lysozyme release in human neutrophils by the synthetic lipopeptide Pam3Cys-Ser-(Lys)4. Involvement of guanine-nucleotide-binding proteins and synergism with chemotactic peptides

Upon exposure to the bacterial chemotactic peptide fMet-Leu-Phe, human neutrophils release lysozyme and generate superoxide anions (O2.-). The synthetic lipoamino acid N-palmitoyl-S-[2,3-bis(palmitoyloxy)-(2RS)-propyl]-(R)-cysteine (Pam3Cys), which is derived from the N-terminus of bacterial lipoprotein, when attached to Ser-(Lys)4 [giving Pam3Cys-Ser-(Lys)4], activated O2.- formation and lysozyme release in human neutrophils with an effectiveness amounting to about 15% of that of fMet-Leu-Phe. Palmitic acid, muramyl dipeptide, lipopolysaccharide and the lipopeptides Pam3Cys-Ala-Gly, Pam3Cys-Ser-Gly, Pam3Cys-Ser, Pam3Cys-OMe and Pam3Cys-OH did not activate O2.- formation. Pertussis toxin, which ADP-ribosylates guanine-nucleotide-binding proteins (G-proteins) and functionally uncouples formyl peptide receptors from G-proteins, prevented activation of O2.- formation by fMet-Leu-Phe and inhibited Pam3Cys-Ser-(Lys)4-induced O2.- formation by 85%. Lipopeptide-induced exocytosis was pertussis-toxin-insensitive. O2.- formation induced by Pam3Cys-Ser-(Lys)4 and fMet-Leu-Phe was enhanced by cytochalasin B, by a phorbol ester and by a diacylglycerol kinase inhibitor. Addition of activators of adenylate cyclase and removal of extracellular Ca2+ inhibited O2.- formation by fMet-Leu-Phe and Pam3Cys-Ser-(Lys)4 to different extents. Pam3Cys-Ser-(Lys)4 synergistically enhanced fMet-Leu-Phe-induced O2.- formation and primed neutrophils to respond to the chemotactic peptide at non-stimulatory concentrations. Our data suggest the following. (1) Pam3Cys-Ser-(Lys)4 activates neutrophils through G-proteins, involving pertussis-toxin-sensitive and -insensitive processes. (2) The signal transduction pathways activated by fMet-Leu-Phe and Pam3Cys-Ser-(Lys)4 are similar but not identical. (3) In inflammatory processes, bacterial lipoproteins and chemotactic peptides may interact synergistically to activate O2.- formation, leading to enhanced bactericidal activity.

Ligand-dependent release of active neutrophil collagenase

The amount of active neutrophil (PMN) collagenase released extracellularly is dependent on the PMN-activating ligand. Neutrophils stimulated with soluble ligands, including FMLP, platelet-activating factor, or heat-aggregated IgG, released very little active collagenase, in contrast to cells stimulated with opsonized zymosan or surface-bound IgG. However, opsonized zymosan and surface-bound IgG did not differ appreciably from soluble ligands in effecting PMN production of superoxide, release of the specific granule component lactoferrin, or total (latent plus active) collagenase release, which suggests that there is more efficient collagenase activation during PMN stimulation with surface-bound ligands. These results suggest a role for surface (cartilage)-bound IgG in the release and activation of human neutrophil collagenase in the joints of patients with rheumatoid arthritis.

Neutrophil activation by surface bound IgG is via a pertussis toxin insensitive G protein

Pre-treatment of neutrophils with either pertussis or cholera toxins does not inhibit neutrophil activation by surface bound IgG. In contrast, pretreatment with the phorbol ester, phorbol myristate acetate, results in a dose dependent inhibition of degranulation by surface bound IgG. This inhibition is similar to that seen with soluble ligands where it is thought to be due to interference with the interaction of an activated guanine nucleotide binding protein with phospholipase C (J. Biol. Chem.,262,6121,1987). More directly, GTP binding and GTPase activity are enhanced when human neutrophil membranes are incubated in wells containing surface bound IgG. Neither of these G protein functions were inhibited when membranes were prepared in the presence of pertussis toxin, suggesting that neutrophil activation by surface bound IgG proceeds by a mechanism that involves a pertussis toxin insensitive G protein.