Analysis of Fc gamma receptors on human peripheral blood leukocytes by flow microfluorometry. I. Receptor distributions on monocytes, T gamma cells and cells labeled with the 3Al anti-T cell monoclonal antibody

The role and therapeutic potential of monocytic cells in Alzheimer's disease

Alzheimer's disease (AD) is a dementing neurodegenerative disorder without a cure. The abnormal parenchymal accumulation of beta-amyloid (Abeta) is associated with inflammatory reactions involving microglia and astrocytes. Increased levels of Abeta and Abeta deposition in the brain are thought to cause neuronal dysfunction and underlie dementia. Microglia, the brain resident cells of monocytic origin, have a potential ability to phagocytose Abeta but they also react to Abeta by increased production of proinflammatory toxic agents. Microglia originate from hemangioblastic mesoderm during early embryonic stages and from bone marrow (BM)-derived monocytic cells that home the brain throughout the neonatal stage of development. Recent studies indicate that BM or blood-derived monocytes are recruited to the diseased AD brain, associate with the Abeta depositions, and are more efficient phagocytes of Abeta compared with resident microglia. The clearance of Abeta deposition by these cells has been recently under intensive investigation and can occur through several different mechanisms. Importantly, peripheral monocytic cells of patients with AD appear to be deficient in clearing Abeta. This review will summarize the findings on the role of blood-derived cells in AD and discuss their therapeutic potential for treating patients suffering from this devastating disease.

Surface expression and distribution of Fc receptor III (CD16 molecule) on human natural killer cells and polymorphonuclear neutrophils

Human natural killer cells and polymorphonuclear neutrophils constitutively express the low-affinity IgG Fc receptor (Fc gamma RIII, CD16 molecule). To investigate cell surface morphology, antigenic receptor density, and topographical distribution of Fc gamma RIII on the plasma membrane of natural killer cells and polymorphonuclear neutrophils, conventional scanning electron microscopy (SEM), flow cytometry, and immunoscanning electron microscopy were used. Fc gamma RIII was detected with an indirect immunogold labeling procedure, and receptors were visualized in the backscattered and secondary electron imaging mode of SEM. Natural killer cells showed a cell surface morphology compatible with lymphocytic differentiation characterized by microvilli and microridges. Polymorphonuclear neutrophils showed surface features characterized by ridges with folds and scattered short microvilli. Natural killer cells displayed a lower cell labeling density, whereas polymorphonuclear neutrophils showed a high level of expression of Fc gamma RIII on the plasma membrane by quantitative analysis with SEM in the backscattered electron imaging mode. Flow cytometry analysis confirmed these findings. Analysis of the topographical distribution of Fc gamma RIII antigenic receptor sites by SEM in the backscattered and secondary electron imaging modes showed that Fc gamma RIII on natural killer cells are randomly distributed, whereas Fc gamma RIII are located on ridges and folds of the plasma membrane of polymorphonuclear neutrophils. These observations suggest that natural killer cells and polymorphonuclear neutrophils differ in their levels of expression and topographic distribution of Fc gamma RIII on the plasma membrane. This different spatial distribution of Fc gamma RIII would provide morphological evidence of certain cellular functions mediated by natural killer cells and polymorphonuclear neutrophils.

A new photometric microassay for the quantitation of macrophage Fc receptor function. In vitro enzyme-containing immune complexes clearance (EIC) assay

A new photometric microassay for immune complex (IC) binding to macrophages was developed in a homologous system using glucose oxidase-anti-glucose oxidase complexes (GOAGO) as a model for IC clearance in vitro. Thioglycollate-elicited murine peritoneal cells were incubated with GOAGO solution and then cell-associated glucose oxidase activity was measured after the washing and solubilization of the cell membrane in a microtitre plate. GOAGO binding to macrophages was inhibited in the presence of either IgG or its Fc fragments in a dose-dependent manner, while yeast mannan or IgG Fab fragments had no effect. These results indicated that this binding occurred solely via the Fc receptors on the macrophages. The Fc receptors for GOAGO were eliminated by trypsin digestion of the cells. When the macrophages were cultured with LPS or TPA, GOAGO binding was enhanced compared to that of control, whereas carrageenan treatment suppressed GOAGO binding. The present results suggest that this assay may be of value in the measurement of IC clearance and for studying the expression of Fc receptors on macrophages.

Activation of immunocompetent cells in the peritoneum of patients treated with CAPD

Chemiluminescence and flow cytometry, employing a number of monoclonal antibodies, was used to investigate activation of immunocompetent cells in the blood and peritoneum of patients treated with CAPD. Increased expression of HLA-DR and RFD7, both markers of macrophage maturation, was observed on peritoneal macrophages, 78% and 33.5% cells positive, when compared to blood monocytes, which were 46% and 5.3%, respectively (P less than 0.001). Macrophage chemiluminescent response to opsonized zymosan was greater than that of circulating blood monocytes in CAPD patients, whereas the inverse was true for normal controls. Enhanced expression of IL-2 receptor and surface IgG by peritoneal macrophages were 24.9% and 65.3% cells positive compared with monocytes, 5.7% and 12.3% (P less than 0.01), and also suggests their activation. There was a marked increase in the HLA-DR expression by peritoneal lymphocytes from CAPD patients (32% cells positive) compared with those from CAPD blood (13.8%), normal blood (11.3%) and normal peritoneal fluid (14.5%), P less than 0.001. This was partially accounted for by increased numbers of B cells (18%) and activated T cells bearing HLA-DR. TFR and IL-2 receptor expression by CAPD peritoneal lymphocytes was similar to that of blood lymphocytes, implying the lack of an organized immune response within the peritoneum. Taken together, these results suggest that peritoneal macrophages from CAPD treated patients have features of maturation and activation, while changes in the lymphocyte populations are compatable with the actions of IL-1, indicating activity of the cellular immune system within the peritoneum.

Induced proteins in human peripheral mononuclear cells over a range of clinically tolerable doses of interferon-gamma

This study assessed biologic response modification at three different dose levels (0.15, 1.5, and 15 mg/m2) of interferon-gamma (IFN-gamma) administered by intravenous bolus three times weekly. A final total of 24 patients were evaluable. Dose-limiting toxicity occurred at the highest dose level (15 mg/m2) and included fatigue, leukopenia, and hepatotoxicity. Evaluation of biologic response modification included assessment of 2',5'-oligoadenylate (2-5A) synthetase activity in peripheral mononuclear cells, measurement of serum beta 2-microglobulin and expression of beta 2-microglobulin on monocytes, measurement of monocyte HLA Class II expression (HLA-DR, HLA-DQ), and measurement of hydrogen peroxide generation by monocytes 24 h after the first and fourth IFN-gamma treatments. Significant increases (p less than 0.05) from baseline were seen at 24 h with all parameters except H2O2 generation. Except for enhancement of HLA-DR, even the lowest dose (0.15 mg/m2) augmented synthesis of 2-5A synthetase and HLA proteins. A dose-response effect was noted for changes in serum and monocyte beta 2-microglobulin levels but not for 2-5A synthetase levels or HLA Class II antigen expression on monocytes. After 4 doses administered over 9 days, most parameters remained increased when compared to pretreatment, but were not further enhanced when compared with levels attained after the first dose. The results of this study document the efficacy of IFN-gamma for biological activation over a wide dose range and are consistent with the postulate that immunoregulatory effects of biological therapeutics can be obtained in man at doses substantially less than those that are maximally tolerated. Further documentation of biologic response parameters by IFN-gamma at low doses will be necessary to determine the importance of biologic activation in relation to antitumor activity.

Interferon-gamma (IFN-gamma) as in vitro enhancing factor of peritoneal macrophage defective bactericidal activity during continuous ambulatory peritoneal dialysis (CAPD)

Interferon-gamma (IFN-gamma) can be considered a primary factor required in vitro and in vivo for inducing endocellular lysis of microorganisms by peritoneal macrophages (PM luminal diameter), an essential activity in continuous ambulatory peritoneal dialysis (CAPD) patients that prevents bacterial peritonitis. In 22 uremic patients treated with CAPD we analyzed: (1) the amount of IFN-gamma released by elicited peritoneal lymphocytes (PL); (2) oxidative metabolism and microbicidal activity by elicited PM luminal diameter; (3) immunoglobulin G (IgG) Fc-receptor expression on PM luminal diameter membrane; (4) the effect on PM luminal diameter hydrogen peroxide (H2O2) generation, bactericidal activity, and IgG Fc-receptor expression exerted in vitro by human recombinant IFN-gamma (rIFN-gamma). Results demonstrate that IFN-gamma release by elicited PL is lower in some CAPD patients with high peritonitis incidence (HPI) than in healthy donors or in CAPD patients with low peritonitis incidence (LPI). Simultaneously, PM luminal diameter from CAPD patients with HPI are characterized by a decreased ability to generate oxygen metabolites, to kill bacteria, and by a lack in IgG Fc-receptor expression; these defects were completely cured after being treated with rIFN-gamma. These results show that the IFN-gamma treatment in vitro could strengthen PM luminal diameter phagocytosis, oxygen metabolite generation, and bacterial killing in CAPD patients with HPI, and suggest that IFN-gamma may be considered a possible therapy in vivo for these patients.

Eosinophils of human colonic mucosa: C3b and Fc gamma receptor expression and phagocytic capabilities

Because little is known about eosinophils of the human intestine, we measured their C3b and Fc gamma receptor expression and phagocytic activity in mucosal suspensions from colon resections for large bowel neoplasms. Enzymatically dissociated suspensions were enriched for eosinophils by countercurrent centrifugation. C3b and Fc gamma receptors were measured by immunofluorescent assays with flow cytometry. Phagocytosis of Escherichia coli ON2 was determined by an in vitro microscopic method. Suspensions of normal tissue from neoplasm resections yielded 1.8 X 10(6) eosinophils/g mucosa, and these cells were more numerous than either macrophages or neutrophils. Fivefold enrichment was achieved by countercurrent centrifugation, and 75% of these cells expressed C3b receptors and 90% expressed Fc gamma receptors. Sixty-seven percent of mucosal eosinophils were phagocytic for E. coli ON2 and ingested a mean of 4.7 bacteria per cell. Eosinophils accounted for more overall phagocytic activity than either neutrophils or macrophages.

Immunoelectron microscopic identification of human NK cells by FITC-conjugated anti-Leu-11a and biotinylated anti-Leu-7 antibodies

Human natural killer (NK) cells have been reported to express various surface antigens. The majority and the most functionally potent NK cells are Leu-11a (NKP-15) positive cells. Only a small number of functional NK cells express Leu-7 (HNK-1) antigen. In the present study, we have established techniques for immunoelectron microscopic identification of NK cells by mouse monoclonal FITC-conjugated anti-Leu-11a and biotinylated anti-Leu-7 antibodies. Ficoll-Hypaque-isolated peripheral blood lymphocytes (PBL) were reacted with the specific antibodies before or after fixation in a 1% glutaraldehyde/1% paraformaldehyde fixative. Prefixation labeling of viable cells with the antibodies was carried out at 4 degrees C or 37 degrees C. Cells prelabeled with anti-Leu-11a antibody were reacted with secondary antibodies either before or after fixation. Anti-Leu-7 antibody was stained directly via an avidin-biotin-peroxidase (ABC) system, anti-Leu-11a antibody was stained indirectly by the ABC immunoperoxidase procedure via a biotinylated anti-mouse IgG secondary antibody or by a 10 nm or 40 nm colloidal gold-labeled anti-mouse IgG antibody. Results indicate that Leu-7 antigen could be localized by incubation with the specific antibody either before or after 20 min fixation; however, Leu-11a antigen was totally abrogated following the same fixation procedure. The Leu-11a antigen was well stained by the methods of prefixation labeling of cells with anti-Leu-11a antibody and incubation with a biotinylated secondary antibody and the ABC system after fixation. With respect to colloidal gold labeling, better results were obtained when cells were reacted with the gold-labeled antibodies immediately after incubation with anti-Leu-11a antibody but before fixation. Ultrastructurally both Leu-7 positive (+) and Leu-11a positive (+) cells shared common ultrastructural features associated with large granular lymphocytes. Using the above described techniques, we found approximately 2-5% Leu-7+ and 9-15% Leu-11a+ cells in the PBL of healthy donors. The overall results suggest that Leu-11a antigen is more sensitive to glutaraldehyde/paraformaldehyde fixation than Leu-7, since it can be localized only by prefixation labeling procedures; the ABC immunoperoxidase procedure is an ideal technique for labeling NK cells for light and electron microscopic enumeration; the immunogold method provides an adequate technique for labeling NK cells which are designated for ultracytochemical studies.

Regulation of K562 cell transferrin receptors by exogenous iron

Single-cell analysis of K562 human erythroleukemia cells by flow cytometry was used to demonstrate the specific role of iron in regulating transferrin receptors (TfRs) and to establish that TfR expression does not necessarily correlate with growth rate. Exogenous iron concentration in culture was manipulated by supplementing the medium with sera having different iron concentrations over the range 0.6 to 5.4 micrograms/ml, by the addition of iron in the form of FeCl3, iron-saturated serum, or diferric transferrin, and by the addition of the iron chelator Desferal (desferrioxamine). TfR expression was negatively correlated with exogenous iron content: any treatment that reduced exogenous iron supply by at least 15% resulted in as much as a 1.8-fold increase in external receptors, detected as binding by both transferrin and monoclonal anti-TfR antibodies, and a 1.5-fold increase in the pool of internal receptors, as detected by anti-TfR antibody binding. None of these treatments altered growth rate, total cellular protein content, protein synthetic rate, cell cycle distribution or cell size. The rapid (12 hr) and reversible induction of internal and external receptors by Desferal was inhibited by cycloheximide and therefore may have resulted from de novo synthesis and not just mobilization of internal receptor pool to the cell surface. The correlation between growth rate and TfR expression previously observed in these and other cells must be secondary to cellular mechanisms that maintain intracellular iron pools by regulating synthesis, recycling, and cell surface expression of TfRs.

Studies on the binding of C3b-coated microspheres to human neutrophils

A method is described for the quantitation of C3b receptors on human neutrophils using a mixture of C3b-coated fluorescent and C3b-coated non-fluorescent microspheres. The method measures the "sterically available' C3b receptors on the cells, for example, the receptors available to opsonized bacteria. The use of mixtures of fluorescent and non-fluorescent microspheres resulted in lowered fluorescence intensities of the microsphere-coated neutrophils that were well within the fluorescence limitations of fluorescence activated cell analyzers or sorters used in the assay procedure. These mixtures also allowed the distribution of the C3b-coated microspheres around the neutrophils to be easily visualized in the fluorescence microscope. The binding of the C3b-coated microspheres to the neutrophils was shown to be receptor mediated by typical saturable binding kinetics, by complete inhibition by fluid phase C3b, but not by other proteins and by nearly complete inhibition by anti-C3b receptor antibody. Several parameters that could affect the binding of C3b-coated microspheres to neutrophils were studied; these included time and temperature of incubation of the microspheres with the cells, the diameter of the microspheres, the C3b content of the C3b-coated microspheres, the presence of metal ions, azide, EDTA, protein (BSA, IgG), soybean trypsin inhibitor in the buffers, and the method of isolation of the neutrophils. The C3b-coated microspheres were evenly distributed around the neutrophils in almost all of the cases; however, the neutrophils used in these studies were not activated and were not phagocytosing. The method is extremely reproducible and sensitive in detecting small changes in number of C3b receptors on cells.

Fc receptor--more answers, more questions

Fc receptors, belonging to the most important surface structures of a number of cells participating in the immune processes, have been intensely studied during the past decade. The present review summarizes the contemporary knowledge of the specificity and heterogeneity of Fc receptors and of factors influencing their expression, and includes some views on their function. In addition, it mentions their relationship to other cell surface structures, expression of Fc receptors during ontogeny of the organism and in certain diseases. Finally, data concerning the isolation and biochemical characterization of the Fc receptor molecule are presented.

Recombinant immune interferon increases immunoglobulin G Fc receptors on cultured human mononuclear phagocytes

Although recent studies suggest that interferons can increase the number of IgG Fc receptor (FcR gamma) sites on mouse macrophages, direct assessment of similar effects on human mononuclear phagocytes is lacking. We therefore measured the specific binding of 125I- and fluorescein-labeled IgG1 to human monocytes and leukemic cell lines after culture in vitro with highly purified human interferons. We report that natural and recombinant human gamma-interferon causes a dramatic (nearly 10-fold) increase in the number of FcR gamma on normal human monocytes and on the human cell lines HL-60 and U-937. Alpha and beta-interferons cause a modest but significant increase in these receptors. This report demonstrates that gamma-interferon acts directly on human mononuclear phagocytes to increase FcR gamma sites, it identifies a qualitative difference in the physiologic actions of human type I and type II interferons, and it suggests that HL-60 and U-937 cells will be important models for further study of the molecular mechanisms of interferon action. The results reported here could also be the basis for a bioassay to assess the pharmacokinetics and variability of gamma-interferon action on monocytes of individual patients during treatment in vitro and in vivo.

Texas Red, a hydrophilic, red-emitting fluorophore for use with fluorescein in dual parameter flow microfluorometric and fluorescence microscopic studies

The sulfonylchloride derivative of the red-emitting fluorophore, sulforhodamine 101, has been synthesized in order to provide a reagent for coupling to amino groups on proteins and other compounds, and it is now commercially available under the name 'Texas Red'. Texas Red conjugates of antibodies and other proteins have been prepared in high protein yields; these conjugates retained their biological activities and were strongly fluorescent. The excitation and emission spectra of Texas Red conjugates are widely separated from those of molecules labeled with fluorescein isothiocyanate. Texas Red is therefore an excellent reagent for use in single or dual label flow microfluorometric and fluorescent microscopic studies.