Myeloperoxidase modulates the phagocytic activity of polymorphonuclear neutrophil leukocytes. Studies with cells from a myeloperoxidase-deficient patient.

Patients lacking the primary granulae enzyme, myeloperoxidase (MPO), do not usually show any increased susceptibility to infection or altered inflammatory response, in contrast to several other biochemical defects in polymorphonuclear neutrophils. We have now evaluated the role of MPO on phagocyte function in a patient with complete MPO deficiency suffering from generalized pustular psoriasis. We found that the MPO-deficient neutrophils showed enhanced phagocytosis (greater than 200% of normal) of IgG- and C3b-opsonized yeast particles and prolonged N-formylmethionyl-leucyl-phenylaline-mediated stimulation of superoxide production. When purified human MPO was added to normal neutrophils during cell adhesion, their Fc- and C3b-mediated phagocytosis was reduced without affecting cell viability. 1 microgram/ml of MPO reduced the Fc and C3b phagocytosis to 47 and 65%, respectively, whereas 10 micrograms/ml reduced the activity to 20 and 54%. Both attachment and ingestion were reduced to a similar extent, indicating that MPO affected the receptor function per se. When MPO was added to the hyperactive MPO-deficient cells, phagocytosis was reduced more rapidly. Catalase, azide, and methionine eliminated the inhibitory effect, and catalase and methionine, in fact, enhanced the phagocytic activity of adherent neutrophils. These data indicate that, apart from being a potent antimicrobial system, the oxidizing activity of the MPO-H2O2-halide system may modulate the inflammatory response by impairing certain receptor-mediated recognition mechanisms of phagocytic cells, which otherwise could elicit inflammatory reactions and tissue injury.

Myeloperoxidase reduces the opsonizing activity of immunoglobulin G and complement component C3b.

The effect of myeloperoxidase, hydrogen peroxide (H2O2) and a halide (Cl) on the opsonizing molecules in immunoglobulin G (IgG) and complement factor C3b was assayed. At concentrations of the enzyme (1 microgram/ml) that can be found in the extracellular fluid during inflammation, the myeloperoxidase-H2O2-Cl system inhibited the opsonizing effect of IgG and C3b measured as phagocytic uptake and superoxide generation. The effect was related to the enzymatic peroxidative activity of the protein. The presence of albumin (10 mg/ml) reduced the effect of myeloperoxidase with 10-20%. Taurine, which in the presence of myeloperoxidase-H2O2-Cl forms hydrophilic chloramines, and D-penicillamine, which scavenges HOCl, neutralize the inhibitory effect of myeloperoxidase. This suggests that either hypochlorous acid or lipophilic chloramines may exert its effect by oxidizing free sulphydryl groups exposed on the opsonizing ligands. Since the myeloperoxidase-H2O2-halide system also affects chemotactic factors, leukotrienes, proteinases and membrane receptors, the system may in several ways affect the development of the inflammatory response.

Differences in intracellular pool and receptor-dependent mobilization of the adhesion-promoting glycoprotein Mac-1 between eosinophils and neutrophils.

Recruitment of cells to an inflammatory site is a process that is selectively regulated. At an inflammatory site caused by bacterial infection, predominantly neutrophil accumulation is observed. This is in contrast to allergic inflammation, where predominantly eosinophil accumulation occurs. Mac-1 is an inducible adhesion molecule for both neutrophils and eosinophils. We examined the mobilization of this receptor on neutrophils and eosinophils after exposure to factors related to bacterial infections and allergic inflammation. We found more pronounced mobilization of Mac-1 on neutrophils than eosinophils after exposure to N-formylmethionyl-leucyl-phenylalanine, lipopolysaccharides, and activated sera (C5a). There was no significant difference in Mac-1 expression after exposure to aggregated immunoglobulin G. Incubation with interleukin-5 (IL-5) caused a significant increase of Mac-1 expression on eosinophils but not on neutrophils. Neutrophils seem to respond to a greater extent than eosinophils to factors related to bacterial infections, whereas eosinophils respond better to IL-5 associated with allergic inflammation. We measured the total pool of Mac-1 to evaluate whether these differences could depend on the size of the intracellular pool. Eosinophils had a larger total pool of Mac-1 than neutrophils. This finding increases the difference between eosinophils and neutrophils when relating the mobilized pool to the total pool. Stimulation with receptor-independent stimuli such as phorbol myristate acetate and ionomycin induced more pronounced mobilization of Mac-1 on eosinophils, but no differences were obtained if the mobilized pool was related to their total pool. These results indicate that the difference in responsiveness depends on different receptor-mediated signaling, since receptor-independent stimulation resulted in relatively similar mobilization of the intracellular pool of Mac-1.

Quartz selectively down-regulates CR1 on activated human granulocytes.

We have investigated the interaction between quartz and granulocytes with respect to complement receptor expression. When N-formylmethionyl-leucyl-phenylalanine (fMLP)-stimulated leukocytes were exposed to quartz at 37 degrees C, CR1 was down-regulated but CR3 was not affected. This was a direct effect on granulocytes because it occurred in a similar fashion when mixed leukocyte suspensions and isolated granulocyte populations were used as targets for quartz. The observed down-regulation by quartz was not affected by the microfilament-disrupting agent cytochalasin B and the total detectable pool of CR1 was reduced after quartz exposure. When protease inhibitors, such as aprotinin or phenylmethanesulfonyl fluoride, were present during quartz exposure, the down-regulation of CR1 was less pronounced, but this was not the case not when protease inhibitors such as EDTA-Na2 and pepstatin were present. Exposure to quartz was not accompanied by a pronounced release of beta-glucuronidase (marker for the primary granules) or vitamin B12 binding protein (marker for the secondary granules). In contrast to quartz, exposure to alumina did not affect the expression of CR1 and CR3. The spontaneous mobilization of CR1 at 37 degrees C was reduced when quartz was present but the CR3 mobilization was unaffected. Our results indicate that quartz induces a granule protease-dependent selective shedding of CR1 but not CR3 despite a low degree of degranulation.

The stabilization of the C3b molecule in immune deposits by formalin.

Formalin-fixed tissue may be used as substrate for immunohistochemistry after enzymatic treatment with proteases. However, whether the antigenicity of C3b is restored is controversial owing to the protease sensitivity of the native molecule. The antigenicity and protease sensitivity of formalin-fixed and non-fixed C3b were tested by using C3b-opsonized yeast particles and the immunofluorescence technique. The results indicate that formalin, probably due to cross-linking, stabilizes C3b molecules and renders them less susceptible to protease treatment. Failures to detect C3b in immune deposits in fixed tissues may be due to factors other than protease treatment.

Detection of immune deposits in glomeruli: the masking effect on antigenicity of formalin in the presence of proteins.

Formalin is known to mask the antigenicity of immune deposits in glomeruli but not of surface immunoglobulins of isolated lymphocytes. We have shown in mice with experimental passive anti-GBM glomerulonephritis that formalin masks the antigenicity of GBM-bound immunoglobulins only if the tissue is fixed before sectioning. The presence of a high concentration of normal bovine serum during fixation of cryostat sections masks the antigenicity of immune deposits, whereas formalin alone has no obvious effect. The same results were obtained with human immunoglobulins (IgG, IgM and IgA) bound to tissue sections. Protease treatment with pepsin and trypsin restored the ability of the immunoglobulins to be stained. The masking effect seems to be due to extensive cross-linking of environmental proteins which prevents fluorescent conjugates reaching their antigens. Methods for detecting immunoglobulins in tissues must, therefore, take into consideration the influence of fixatives not only on epitopes but also on the environment in which the antigenic determinants are localised.

Differentiation between attached and ingested immune complexes by a fluorescence quenching cytofluorometric assay.

Immune complexes attached to and ingested by human polymorphonuclear (PMN) cells were quantified by cytofluorometry using a fluorescence quenching assay which permits differentiation between attachment and ingestion. The fluorescence intensity decreased after ingestion as a result of the low pH in the phagolysosomes. When extracellular pH was lowered a slight decrease in phagolysosomal pH was detected in macrophages but not in PMN. When measuring total fluorescence, interaction at pH 5.8 for PMN and at pH 4.4 for macrophages is recommended, since the intensity of extra- and intracellular fluorescence are equal under these conditions. Thirty different dyes were tested for dye exclusion and fluorescence quenching of FITC-conjugated yeast particles, and FITC-conjugated IgG. Because of the lysosomotropic effect of basic dyes, acid and direct dyes are preferable as quenching agents. We could not find physical or chemical properties of the dyes that correlated with their quenching effect. Heat aggregated IgG was used as an immune complex analogue in the development of the assay. Trypan blue (0.2 mg/ml) at pH 4.4 was found to be the best quenching agent of extracellular fluorescence when using ingested aggregated IgG. The technique offers a simple method of quantifying ingested protein aggregates and of studying heterogeneity in phagocyte populations.

Detection of immune deposits in glomeruli: a comparative study of paraffin-embedded, enzyme-treated sections and cryostat sections as substrates in immunofluorescence.

Paraffin-embedded tissue can be used as substrate for immunohistochemistry after enzymatic treatment with proteases. The sensitivity of immunofluorescence on enzyme-treated paraffin sections and on unfixed cryostat sections is compared in this study. Pepsin was more efficient by weight than trypsin in restoring the antigenicity of immune deposits. Increased fluorescence intensity was obtained up to a pepsin concentration of 0.4%. Intensity was further increased when pepsin treated sections were treated with trypsin. Immune deposits were detected in enzyme treated, paraffin sections of kidneys of mice injected with anti-GBM diluted 1/200 or less and in cryostat sections of mice injected with anti-GBM diluted 1/400 or less. This small decrease in sensitivity is considered trivial compared with the advantage gained by the excellent preservation of the tissue.

A quantitative microassay for leukocyte chemotaxis, using a microscopic slide system with complement-activating yeast particles as gradient source.

A simple quantitative microassay was developed for studying polymorphonuclear leukocyte (PMNL) chemotaxis under conditions where the number of available cells is a limiting factor, e.g., pustules, neutropenia, small children and cerebrospinal fluid. PMNL suspensions are placed on glass slides to which fluorescein-labeled yeast particles have been fixed. After adherence, normal human serum is added to the slides. Owing to complement activation, a chemotactic gradient which attracts the adherent PMNL is formed around the yeast particles. The number of PMNL-associated yeast particles in the presence of normal serum is scored, and compared with cells migrating in the presence of inactivated serum or in the absence of serum. A locomotory index is calculated as the number of yeast particles associated with PMNL divided by the total number of yeast particles.

Quenching of intracellular autofluorescence in alveolar macrophages permits analysis of fluorochrome labelled surface antigens by flow cytofluorometry.

We report a new technique in which the autofluorescence of alveolar macrophages from smokers is quenched by crystal violet. This technique permits immunostaining of surface antigens of these cells and enables the stained cells to be analysed by flow cytofluorometry. The variable solubility of crystal violet makes it important to characterize the crystal violet solution by its quenching properties and not rely on the assumed concentration of dissolved dye. High concentrations of crystal violet lowered the number of cells and gave a decreased amount of surface antigen (CD11b). However, a lower concentration of crystal violet could be used if the cells were fixed with paraformaldehyde (4%) and the membranes were permeabilized with n-octyl-beta-D-glucopyranoside (0.6%). Using a phagocytic model with FITC-conjugated particles we were able to show that this treatment gave an efficient permeabilization of phagolysosomal membranes.

A new membrane permeabilization method for the detection of intracellular antigens by flow cytometry.

This article describes a new cell membrane permeabilization method for the detection of intracellular antigens by immunofluorescence staining and flow cytometry. The number of cells remained unaltered and no cell aggregation or loss of intracellular antigenicity was observed after this permeabilization treatment. A mixed leukocyte population from human peripheral blood was used in this study and the leukocytes were fixed and permeabilized, which permitted monoclonal anti-vimentin antibodies to reach intracellular antigens. The stabilization of cell membranes and preservation of intracellular antigenicity was achieved with paraformaldehyde fixation. This pretreatment prevents cell destruction and subsequent treatment with the detergent n-octyl-beta-D-glucopyranoside results in permeabilization of the cell membrane. The procedure does not alter the expression of cell surface antigens, which is of importance if phenotypic characterization of intracellularly stained cells is to be undertaken. Furthermore, this simple, rapid and reproducible technique makes it possible to detect and distinguish between different human peripheral blood leukocytes without prior purification steps. The leukocyte subpopulations remain well-separated and easily detectable by flow cytometry.

Altered expression of CD11b/CD18 and CD62L on human monocytes after cell preparation procedures.

We have investigated the effect of different cell preparation procedures on the surface expression of CD11b/CD18 and CD62L on human monocytes. Both EDTA and heparin anticoagulated blood were used as sources for leukocytes. The monocytes were analysed by flow cytometry in a mixed leukocyte suspensions obtained after ammonium chloride mediated lysis and in mononuclear cell suspension prepared by density gradient centrifugation (Ficoll-Paque) performed both at 4 degrees C and at 20 degrees C. Monocytes from heparinized blood had a higher expression of CD11b/CD18 and a more pronounced inter-individual variation than monocytes from EDTA blood. Monocytes isolated by Ficoll-Paque had a higher degree of ex vivo activation by means of altered expression of CD11b/CD18 and CD62L compared to monocytes prepared by ammonium chloride mediated lysis. This was more pronounced when the isolation procedure was performed at 20 degrees C. Our findings indicate that monocytes prepared by ammonium chloride mediated lysis of EDTA blood and with the cell handling temperature kept at 4 degrees C are exposed to the smallest ex vivo modulation by means of receptor alteration. An awareness of ex vivo modulation by different cell preparation procedures is of importance especially when comparing the expression of functional receptors on leukocytes of disparate origin.

The use of fluorescence quenching in flow cytofluorometry to measure the attachment and ingestion phases in phagocytosis in peripheral blood without prior cell separation.

Flow cytofluorimetry identifies and quantifies cell markers of different leukocyte subpopulations by combining cytofluorimetry with the differences in the light scattering properties of the leukocytes in mixed populations. In the phagocytic assay, reported in this paper, the experimental conditions were selected in such a way that it was possible to analyse the phagocytic function of granulocytes in peripheral blood without time-consuming cell separation. The percentage of phagocytosing granulocytes was not dependent on the concentration of granulocytes at the selected incubation time and particle (yeast-C3b) concentration. Furthermore, it was possible to adapt a previously described fluorescence quenching technique (FQ method) to differentiate between attachment and ingestion. Crystal violet, originally used in the FQ method, could not be used in this assay due to its lysomotropic effect. Trypan blue at a concentration of 0.25 mg/ml or higher at pH 4.5 showed a plateau effect in fluorescence quenching indicating an effect on attached but not ingested particles. This assay offers a simple technique to screen the functional properties of phagocytic cells in peripheral blood.

Improved cell depletion in a panning technique using covalent binding of immunoglobulins to surface modified polystyrene dishes.

A method for the chemical modification of plastic surfaces permits covalent binding of proteins and we have used this method in the development of an efficient panning technique. Thus, human peripheral T lymphocytes coated with mouse monoclonal antibodies directed against the CD4 marker may be selectively and reproducibly removed from a lymphocyte population by a short incubation in modified plastic dishes coated with rabbit anti-mouse IgG antibody. Due to the higher protein binding capacity of the dishes the use of the IgG fraction of the coating antibody was sufficient for optimal and reproducible results. In contrast, control dishes with passively adsorbed antibody required an affinity-purified fraction and even then were less efficient.

Enumeration of IFN-gamma-producing cells by flow cytometry. Comparison with fluorescence microscopy.

A new intracytoplasmic immunofluorescence staining to detect and quantify human interferon-gamma (IFN-gamma)-producing cells by means of flow cytometry is described. Mononuclear leukocytes, stimulated in vitro to produce IFN-gamma, were fixed and made permeable to antibodies by sequential exposure to paraformaldehyde and the detergent n-octyl-glucoside. Cytoplasmic IFN-gamma was demonstrated by indirect immunofluorescence using IFN-gamma-specific mouse monoclonal antibodies. The staining exhibited a very characteristic morphology and was localized in the Golgi apparatus. An excellent agreement between the enumeration of cytoplasmic IFN-gamma-positive cells by immunofluorescence microscopy and flow cytometry was noted. However, the latter has the advantage of a standardized control, is less labor consuming and is observer independent.

Complement activation according to the alternate pathway by glass and plastic surfaces and its role in neutrophil adhesion.

C3-deposition, generated by complement activation according to the alternate pathway, was detected on borosilicate glass slides and polystyrene Petri dishes. The C3-depositions grew peripherally until the entire surface was covered. The deposits were also visualized with scanning electron microscopy and could not be washed away with low-pH (3.5) or high-pH (9.6) buffers. No consumption of complement function was detected indicating a phenomenon restricted to the glass and plastic surfaces. The C3-deposits could mediate an adherence of human neutrophils.

In vitro effects of ethanol on polymorphonuclear leukocyte membrane receptor expression and mobility.

The hampered inflammation and host defense seen in alcoholics may be due to impairment of functional responses of neutrophil polymorphonuclear leukocytes (PMN). We have shown that ethanol inhibits the oxidative metabolism of PMN induced by surface receptor dependent stimuli, such as N-formyl-methionyl-leucyl-phenylalanine (fMLP) and opsonized zymosan. Because the unresponsiveness might be due to reduced numbers of surface receptors, we assessed the expression of CR1, Fc-gamma, and fMLP receptors as well as membrane fluidity after treatment of PMN with ethanol in vitro. Ethanol impaired the induced expression of CR1 and fMLP receptors to 71% and 51% of control, respectively, but did not affect the resting level of CR1 nor Fc-gamma receptor expression. Furthermore, the mobility of cell membrane glycoconjugates was increased by ethanol. However, phagocytosis, a functional response dependent on membrane rheology, was unaffected. Because the results indicated an effect of ethanol on mobilization of receptors from intracellular stores, we assessed lactoferrin release, which was reduced to 59%. Thus, ethanol appeared to hamper the upregulation of PMN surface receptors or functional subsets of those stored in granules. Ethanol also increased the mobility of the cell membrane. These reactions were accompanied by reductions in the functional responses mediated by either class of receptors.

Smoking cessation rapidly reduces cell recovery in bronchoalveolar lavage fluid, while alveolar macrophage fluorescence remains high.

Bronchoalveolar lavage (BAL) was performed in smokers (22.6 +/- 7.8 pack-years) before (n = 18) and 1 (n = 14), 3 (n = 13), 6 (n = 11), 9 (n = 9), and 15 (n = 8) months after smoking cessation. The recovery of the BAL fluid increased after smoking cessation (p less than 0.05). The total number of cells and the cell concentration were significantly lower already at one month (p less than 0.05 and p less than 0.01, respectively), and this decline was more pronounced at the following lavages. By using flow cytofluorometry, alveolar macrophage (AM) fluorescence was quantified, since it is known that AMs lavaged from smokers have an increased fluorescence, due to interaction with fluorescent substances in the inhaled smoke. Not until six months after smoking cessation was a significant (p less than 0.05) decrease in AMs fluorescence noted. At 15 months, the fluorescence was still increased, with great individual variations, compared with AMs from nonsmokers. The decline in fluorescence of AMs after smoking cessation was negatively correlated to the previous cigarette consumption. The absence of new, low fluorescent cells in the BAL fluid, despite a slow, but significant decrease in the fluorescence intensity of the whole cell population, suggests that the fluorescent material is redistributed from older AMs to newly recruited cells. These substances can thus remain in the alveolar space for a longer time than the estimated life span of the AMs.

Intracellular and surface distribution of CD9 in human eosinophils.

Expression of CD9 is a feature of both eosinophils and platelets. We have investigated the CD9 expression on resting and activated eosinophils with regard to possibly interacting platelets. Mixed leukocytes were obtained from the platelet-containing (PC) and platelet-depleted (PD) peripheral blood of healthy donors. A cell membrane permeabilization technique, the FOG method, enabled us to detect the eosinophils as a separate population and permitted flow cytometric analysis of both surface and intracellular antigens. Monoclonal antibodies against CD61 were used to identify platelets. The CD9/CD61 ratio indicated that CD9 on resting eosinophils originates mainly from eosinophils and not from adhered platelets. No difference in CD9 expression was obtained between resting eosinophils in PC and PD blood. However, the expression of CD9 was decreased (p < 0.05) on eosinophils in PMA-activated PD blood but increased (p = 0.001) in PC blood, probably due to interacting platelets since CD61 increased simultaneously. In addition, we were able to detect an intracellularly stored pool of CD9 in eosinophils which decreased after activation with PMA. Together these results indicate a translocation of intracellularly stored CD9 to the cell membrane upon activation, probably followed by a subsequent shedding.

Increased expression of adhesion proteins (MAC-1) and altered metabolic response in human leukocytes exposed to surfactant in vitro.

In this study the modulatory effects of a well-defined surfactant preparation on blood leukocytes were investigated. The expression of the cell surface receptor MAC-1 was analyzed by flow cytofluorometry, and the metabolic response was measured by a chemiluminescence technique. An increase (p less than 0.05) in the MAC-1 receptor expression was observed in the granulocytes but not in the monocytes. There was a decrease in the metabolic response of the leukocytes after stimulation with phorbol myristate acetate (PMA) and a delay (p less than 0.01 for both) in the peak activity. Formyl-methionyl-leucyl-phenylalanine (fMLP) caused an increased peak (p less than 0.01). Thus, the surfactant preparation had a modulatory effect on blood leukocytes with regard to the expression of the cell surface receptor MAC-1 and the metabolic response.