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PubMed1986

Studies on human blood lymphocytes with iC3b (type 3) complement receptors. I. Granular, Fc-IgG receptor positive and negative subsets in healthy subjects and patients with systemic lupus erythematosus.

By using the OKM1 monoclonal antibody and the fluorescence-activated cell sorter to identify lymphocytes bearing iC3b (type 3) complement receptors, two principal populations of OKM1+ lymphocytes have been identified in human peripheral blood. One subset exhibited azurophilic granules and Fc receptors for IgG stained by Leu-11. The other population did not display FcR, but was enriched in cells reacting with OKT3 and OKT8 (low intensity). In healthy subjects, approximately 60% of CR3+ lymphocytes were granular FcR-bearing cells and only 18% co-expressed OKT3 determinants. In patients with systemic lupus erythematosus (SLE), CR3+ lymphocytes were predominantly FcR negative cells and 71% lacked granules. Only 33% reacted with Leu-11, but 50% co-expressed OKT3, 44% reacted with OKT8+, and 15% were OKT4+. We tested the hypothesis that agranular OKT3+ Leu-11- lymphocytes, such as those found in SLE patients, contained the precursors of natural killer (NK) cells. Leu-11+ cells were removed from normal lymphocytes by complement lysis, and the remaining cells were treated with recombinant IFN-alpha, IFN-gamma, or IL 2. These procedures were ineffective in generating typical NK effector cells. Our studies do not support the hypothesis that CR3+ Leu-11- lymphocytes are the precursors of granular Leu-11+ NK cells.

Antibodies, Monoclonal↗
PubMed1986

Interferon-gamma-dependent modulation of C3b receptors (CR1) on human peripheral blood monocytes.

Cell surface expression of the C3b receptor (CR1) was transiently down regulated on purified human monocytes exposed to purified recombinant human interferon-gamma(rIFN-gamma). Receptors were quantitated by using CR1-specific monoclonal antibody by radioimmunoassay or flow cytometry and by rosette analysis with the use of C3b-coated bovine erythrocytes. The reduction of CR1 was dependent on the dose of IFN-gamma used and the time of cellular exposure. Down-regulation was transient, with maximum loss occurring after 2 to 3 days of stimulation with IFN-gamma. However, after 6 days CR1 was re-expressed at the plasma membrane. This effect was observed with monocytes isolated by either centrifugal elutriation or adherence on fibronectin-coated dishes. IFN-gamma-dependent diminution of CR1 occurred concomitant with increased expression of Fc receptors and HLA-DQ antigen and unaltered expression of the C3bi receptor (CR3). The mechanism of CR1 loss from the monocyte cell surface was not due to internalization, because total cellular levels of CR1 (plasma membrane and intracellular pool) also decreased in response to IFN-gamma. These results indicate that IFN-gamma may be involved in regulating CR1 on mononuclear phagocyte surfaces.

Cell Line↗
PubMed1986

Phorbol esters cause sequential activation and deactivation of complement receptors on polymorphonuclear leukocytes.

Phorbol myristate acetate (PMA) exerts a biphasic effect on receptors for C3b and C3bi of human polymorphonuclear leukocytes (PMN). The addition of PMA for 10 min enhances the capacity of these receptors to promote binding and phagocytosis of C3b- and C3bi-coated erythrocytes. Upon additional incubation for 60 min, the capacity of these receptors to bind and ingest ligand-coated erythrocytes decreases to levels below those of resting cells. Although PMA does cause increased expression of cell surface C3b and C3bi receptors, the sequential rise and fall of receptor activity cannot be accounted for by alterations in the number of surface receptors. It appears, rather, that PMA causes qualitative changes in these receptors, first an increase in receptor activity (activation) and then a decrease in receptor activity (deactivation). In contrast with its effects on C3 receptors, PMA causes only a reduction in the capacity of Fc receptors to bind and ingest IgG-coated erythrocytes. Deactivation of Fc receptors also appears to involve a qualitative alteration in receptors, because the binding affinity of soluble immune complexes is sharply reduced upon stimulation of PMN with PMA. To explore the role of phosphorylation in the sequential activation and deactivation of phagocytosis-promoting receptors, we loaded PMN with thiophosphate (thioP). This compound is incorporated into cellular nucleotides and proteins, and the resultant (thio)phosphorylated proteins are resistant to phosphatases. thioP-loaded cells show enhanced receptor activity, suggesting that activation of receptors is mediated by a phosphorylation event. Cells loaded with thioP and treated with PMA for 70 min do not deactivate C3 or Fc receptors, suggesting that the deactivation is the result of a dephosphorylation event.

Animals↗
PubMed1985

The effect of thrombin activated factor XIII, thrombin and plasmin on the chemiluminescence produced by human neutrophils stimulated by opsonized zymosan (Mannozym).

Coagulation factor XIII formed by thrombin activation from zymogen factor XIII decreases the chemiluminescence (CL) of human neutrophils stimulated by opsonized zymosan (Mannozym). At high concentrations, thrombin and plasmin also decreased the CL induced by opsonized zymosan. The inhibitory effect of all the three enzymes was due to their influence on the cell membrane receptors (C3b and Fe) and not to their direct effect on opsonized Mannozym. The potential clinical role of factor XIII, thrombin and plasma in the regulation of neutrophil functions is assumed.

Cells, Cultured↗
PubMed1986

[Comparative studies of Fc receptors for IgG on resting and activated mouse T lymphocytes using different methods].

Fc-receptors for IgG (Fc gamma R) on resting (i.e. freshly prepared) and mitogen (Con A) or alloantigen-activated mouse spleen T cells were compared using binding of different markers such as 125J-labelled immune complexes, 125J-labelled anti Fc gamma R monoclonal antibody, FITC-labelled aggr. IgG and sheep erythrocytes covered with specific antibody (EA rosetting). C3b receptors were detected by rosetting with sheep erythrocytes covered with antibody and complement (EAC rosetting). The electrophoretic mobility of the cells without or after binding of aggr. IgG was also tested. A number of differences between resting and activated T cells were found: After activation of T cells by mitogen or alloantigen, a proportion of Fc gamma R-positive cells increased two to four times. Fc gamma R number per Fc gamma R-positive cell seemed to be higher on activated then on resting cells. Fc gamma R-positive resting cells did not shed their Fc gamma R upon incubation at 4 degrees C followed by incubation at 37 degrees C, but Fc gamma R-positive activated cells shed a remarkable proportion of their Fc gamma R on the same conditions. Binding of aggr. IgG caused a decrease of electrophoretic mobility of activated but not resting cells. Fc gamma R-positive resting cells were also C3b receptor-positive, whereas Fc gamma R-positive activated cells had no detectable C3b receptors.

Animals↗
PubMed1986

Isolation, characterization and utilization of the fifth component (C5) of porcine complement.

The fifth component (C5) of porcine complement was isolated in immunochemically pure, homogeneous and native form. The isolated component was characterized, it has a molecular weight of 187,000 (under non-reducing conditions) and two non-identical chains of 112,000 and 76,000 under reducing conditions, respectively. The isolated C5 can be used for the detection of the C5b receptors on murine macrophages. Our findings are in good agreement with the results obtained using a rabbit and a human model, which suggests a high conservativeness of C5 during evolution. The described method of isolation of C5 from easily available porcine serum seems to be convenient for C5 receptors studies.

Animals↗
PubMed1986

Differential interaction of the C3b/C4b receptor and MHC class I with the cytoskeleton of human neutrophils.

As measured by fluorescence microscopy and radioligand binding, C3b/C4b receptors (CR1) became attached to the detergent-insoluble cytoskeleton of human neutrophils when receptors were cross-linked by affinity-purified polyclonal F(ab')2 anti-CR1, dimeric C3b, or Fab monoclonal anti-CR1 followed by F(ab')2 goat anti-mouse F(ab')2. CR1 on neutrophils bearing monovalent anti-CR1 was not attached to the cytoskeleton. In contrast, cross-linked CR1 on erythrocytes and cross-linked MHC Class I on neutrophils were not cytoskeleton associated. A possible role for filamentous actin (F-actin) in the binding of cross-linked CR1 to neutrophil cytoskeleton was suggested by three observations. When neutrophils were differentially extracted with either Low Salt-detergent buffer or High Salt-detergent buffer, stained with FITC-phalloidin, and examined by fluorescent flow cytometry, the residual cytoskeletons generated with the former buffer were shown to contain polymerized F-actin, whereas cytoskeletons generated with the latter buffer were found to be depleted of F-actin. In parallel experiments, High Salt-detergent buffer was also found to release cross-linked CR1 from neutrophils. Second, depolymerization of F-actin by DNAse I released half of the cytoskeletal-associated cross-linked CR1. Third, immunoadsorbed neutrophil CR1, but not MHC Class I or erythrocyte CR1, specifically bound soluble 125I-actin. In addition, Fc receptor and CR3, other phagocytic membrane proteins of neutrophils, specifically bound 125I-actin. These data demonstrate that CR1 cross-linked on neutrophils becomes associated with detergent-insoluble cytoskeleton and that this interaction is mediated either directly or indirectly by actin.

Actins↗
PubMed1987

Activation of mouse peritoneal macrophages by lysophospholipids and ether derivatives of neutral lipids and phospholipids.

Cellular damage and inflammatory processes cause activation of phospholipase A in plasma membranes resulting in the production of various lysophospholipids. Treatment of mice with L-alpha-lysophosphatidylcholine, a decomposition product of phosphatidylcholine, greatly stimulates mouse peritoneal macrophages to ingest target cells via the Fc receptors. Similarly, treatment of mice with L-alpha-lysophosphatidylethanolamine and L-alpha-lysophosphatidyl-L-serine resulted in an enhanced ingestion activity of macrophages. Cancer cell membranes contain alkyl ether derivatives of phospholipids and neutral lipids. Inflamed cancer cells release decomposition products of alkyl ether phospholipids and neutral lipids, alkyl-lysophospholipids and alkylglycerols, respectively. Administration of alkyl ether analogues of lysophospholipids into mice were able to induce stimulation of macrophages for ingestion with Fc receptor preference. Two synthetic alkylglycerols, dodecylglycerol and tridecylglycerol, were tested. Dodecylglycerol induced an efficient stimulation of macrophages for Fc-mediated ingestion whereas tridecylglycerol induced a minimal level of activation. Therefore, in vivo effect of dodecylglycerol on macrophage stimulation is similar to that of lysophospholipids and their alkyl analogues. These in vivo stimulations of macrophages for Fc receptor-mediated ingestion activity were reproduced in in vitro activation of macrophages by treatment of peritoneal cells with the alkyl lipid derivatives. Among these compounds, dodecylglycerol was found to be the most potent agent for macrophage stimulation. Since macrophages are antigen-presenting cells, the degradation products of cancer cell membrane lipids may have immune potentiating capacity.

Animals↗
PubMed1986

Cellular composition of lymph in experimental lymphedema.

Lymph cell populations were characterized immunologically in dogs with chronic post-surgical lymphedema. There was a 10- to 30-fold increase in lymph total cell count as compared with normal (control) dogs. Morphologically, these were predominantly small lymphocytes with approximately 4-6% monocytes and veiled cells. In contrast, lymph from normal dogs contained 33% granulocytes and 27% monocytes. The Fc-R+ and C3b-R+ mononuclear nonadherent cells were less represented in lymph in chronic stasis than in normals. A high autotransformation rate of lymph cells and marked responsiveness to PHA and Con A were also observed. In chronic lymphedema K-cell and NK-cell cytotoxicity were lower than in normal lymph. Interruption or retardation of the lymphocyte recirculation pathway with lymph stasis may alter regulation of immune responsiveness in lymphedematous tissue.

Animals↗
PubMed1986

Fc and C3b receptor expression of phagocytes in poorly controlled diabetic patients.

Attachment, an energy-independent step, of sensitized sheep erythrocytes EA and EAC to Fc and C3b receptors, respectively, on granulocytes and monocytes from poorly controlled diabetic patients was investigated. The results show similar percentages of EA and EAC rosette-forming cells for normal and diabetic human neutrophils. The expression of Fc receptors on normal and diabetic monocytes were also similar in that the former contained 74.5 +/- 9.3% and the latter contained 66.0 +/- 9.4% rosette-forming cells. However, a significantly lower percentage (48.3 +/- 15.2%) of EAC rosette positive cells was found in diabetic monocytes as compared to that (68.1 +/- 8.2%) found in normal controls (p less than 0.001). Incubation of diabetic monocytes with insulin or serum obtained from normal individuals one hour prior to assay corrected the impaired expression of C3b receptors in diabetic monocytes. In addition, we also found that diabetic serum itself is noxious to C3b receptor expression by normal human monocytes and that high concentrations of glucose play no apparent role in the regulation of the receptor function.

Adult↗
PubMed1987

Increased adhesion to fibronectin and Mo-1 expression by diabetic monocytes.

As excessive monocyte adhesion to blood vessel wall could produce endothelial cell injury, we undertook comparative studies on the monocyte adhesiveness in insulin-dependent diabetics with vascular complications (n = 26) and healthy, normal subjects (n = 36). In the diabetic group, the extent of monocyte adhesion on fibronectin- and autologous plasma-coated surfaces was significantly increased compared with that in the control group (p less than 0.01 on both types of surfaces). Monocytes adhesion to the plasma-coated surface, but not to the fibronectin-coated surface, could be inhibited by monoclonal anti-Mo-1 antibody in a dose-dependent manner. For diabetic monocyte adhesion, a higher amount of anti-Mo-1 antibody was required to produce a similar extent of inhibition as observed with control monocytes. This indication of increased Mo-1 expression on diabetic monocytes was further confirmed by analyzing the fluorescence intensity of monocytes labeled with the antibody anti-Mo-1. The results of the present study suggest that diabetic monocytes have increased adhesiveness as the result of increased expression of fibronectin and Mo-1 receptors.

Antibodies, Monoclonal↗
PubMed1987

Studies on human blood lymphocytes with iC3b (type 3) complement receptors. II. Characterization of subsets which regulate pokeweed mitogen-induced lymphocyte proliferation and immunoglobulin synthesis.

Human blood lymphocytes that express Type 3 complement receptors (CR3) can be divided into a major subset with high density Fc receptors for IgG (FcR) identified with the monoclonal antibody Leu 11 and two minor subsets which display either CD8 (Leu 2) or CD4 (Leu 3) markers. We isolated CR3+ lymphocyte subsets and examined them for regulatory effects on pokeweed mitogen (PWM) stimulated cells. The FCR CR3+ cell suppressed PWM-induced proliferation and Ig production. Pretreatment of these lymphocytes with immune complexes was required to suppress proliferation, but not IgG production. The CR3+ Leu 2+ FCR- subset also had suppressive activity, but this effect was not observed unless the CR3+ Leu 3+ enriched subset was removed. In fact, the CR3+ Leu 3+ enriched subset enhanced IgG synthesis. Brief exposure of CR3+ lymphocytes to recombinant interleukin 2, recombinant alpha-interferon, but not gamma-interferon, markedly enhanced the inhibitory effect. Time course studies and a comparison of inhibition of Ig synthesis with natural killer cell activity suggested that CR3+ lymphocytes act shortly after lymphocytes are exposed to PWM and that Ig production was regulated by suppression rather than cytotoxicity. These CR3+ lymphocyte subsets may have broad antigen non-specific effects on immunoglobulin synthesis.

Antigen-Antibody Complex↗
PubMed1987

Studies on human blood lymphocytes with iC3b (type 3) complement receptors: III. Abnormalities in patients with active systemic lupus erythematosus.

Lymphocytes displaying iC3b (Type 3) complement receptors (CR3) were quantified by flow cytometry in patients with systemic lupus erythematosus. The percentages and absolute numbers were compared to age and sex matched controls. Total CR3+ lymphocytes identified by the monoclonal antibodies OKM1 or Leu 15 were significantly decreased in patients with symptomatic arthritis, serositis or vasculitis and those with lupus nephritis, whereas values for CR3+ lymphocytes in patients with inactive disease were similar to normal donors. The phenotype of CR3+ lymphocytes was markedly different in patients with active SLE. In normals granular lymphocytes bearing Fc receptors for IgG (L cells) comprised two-thirds of CR3+ lymphocytes. However, in SLE this subset was reduced to 20% and there was a corresponding increase in CR3+ lymphocytes co-expressing the T3 marker. Percentages of CR3 T4+ but not CR3+ T8+ lymphocytes were significantly increased in SLE. Although patients with active disease were lymphopenic, absolute numbers of CR3+ lymphocytes co-expressing T cell markers were similar to normal controls. Since L cells are non-specific suppressors of Ig production, the reduction of this subset along with the increase in CR3 T4+ cells could contribute to unregulated antibody production characteristic of SLE.

Adult↗
PubMed1987

Functional role of the alpha-chain of complement receptor type 3 in human eosinophil-dependent antibody-mediated cytotoxicity against schistosomes.

The participation of complement receptor type 3 (CR3) in antibody-dependent effector function of human eosinophils against parasites was studied by using monoclonal antibodies directed against various surface molecules. Both adherence and cytotoxicity of hypodense eosinophils to IgE-coated schistosomula of Schistosoma mansoni were strongly inhibited by anti-CR3 antibodies (OKM1 or Mo1). The specificity of the inhibitory effect for the alpha-chain of CR3 was shown by the lack of inhibition of anti-beta-chain or anti-LFA1 alpha-chain monoclonal antibodies, although these antigens were expressed on human eosinophils. These results associated to previous works on IgE receptors demonstrate that both receptor for Fc fragments of IgE and CR3 are essential in IgE-dependent cytotoxicity of human eosinophils. Flow microfluorometry analysis revealed that hypodense eosinophils were more intensively stained by OKM1 antibodies than the normodense populations. In the case of IgG-mediated cytotoxicity by normodense eosinophils, only the enhancement of cytotoxicity due to monokine activation was inhibited by anti-CR3 alpha-chain antibodies. These findings suggest an increased expression of CR3 on eosinophils after activation either in vivo or in vitro. The participation of CR3 in IgE-mediated cytotoxicity against schistosomes was also required in the case of blood monocytes but not for platelet-mediated killing, which does not require prior adherence. The biologic role of CR3 is therefore extended to effector mechanisms involving eosinophils and two different isotypes of antibodies and possibly implied in immunity against schistosomes.

Antibodies, Monoclonal↗
PubMed1988

The elevated natural killer sensitivity of targets carrying surface-attached C3 fragments require the availability of the iC3b receptor (CR3) on the effectors.

Human serum-treated Raji and Daudi cells were shown to bind C3 fragments on their surface as a consequence of their capacity to activate C via the alternative pathway. C3 molecules were detectable on the cell surfaces up to 24 h after serum exposure. The C3 fragment-coated cells showed increased sensitivity to spontaneous lymphocyte-mediated cytotoxicity. The effector lymphocytes involved in the enhanced cytotoxicity were NK cells with low buoyant density, carrying both CR3 and FcR. Blocking of the FcR and CR3 with F(ab)2 fragments from Leu-11c or Leu-15 mAb, respectively, did not influence the lysis of targets that did not carry C3 fragments. In contrast, the accessibility of CR3 on the effector lymphocytes was essential for the C3 fragment-mediated enhancement of cytotoxicity. In addition to the Leu-15 antibody, N-acetyl-D-Glucosamine, a compound known to block iC3b binding to CR3, also abrogated the C3 fragment-imposed effect. Our previous experiments showed that the C3 fragments bind to acceptor sites on target cells. The present experiments show that the C3 fragments fixed onto the target bind to CR3 on effector cells. These data substantiate the hypothesis that the bivalent C3 fragments, which are fixed on the targets, promote their interaction with lytic lymphocytes by bridging the two cells.

Binding Sites↗
PubMed1988

Shedding and synthesis de novo of Fc and C3b receptors by cultured guinea-pig macrophages.

Resident macrophages freshly obtained from the peritoneal cavity of guinea-pigs were demonstrated to form a higher percentage of Fc and C3b rosettes than elicited macrophages when low concentrations of IgG and IgM-C3b were used to sensitize ox red blood cells (ORBC) in rosette assays. Culture of the total resident and elicited macrophages for 6 h at 37 degrees C resulted in a decrease of Fc and C3b rosette-forming cells, the loss of Fc receptor-bearing cells by resident macrophages only being apparent when using a sub-optimal concentration of sensitizing IgG. After 24 h incubation the percentages of Fc and C3b rosettes returned to their initial values. In contrast, there was no decline in the percentage of Fc and C3b rosettes formed by the adherent population of resident and elicited macrophages cultured for 6 h. However, extending the incubation of the adherent macrophage to 24 h produced an increase of Fc receptor-positive cells and a dramatic decrease of C3b receptor-positive cells. Culture supernatants of the total macrophage population that had been incubated for 6 h inhibited Fc and C3b rosette formation by freshly obtained elicited macrophages. These results, together with the demonstration that treatment of the total macrophage population with cycloheximide led to an inhibition of Fc and C3b receptor expression after 24 h culture, suggest that the Fc and C3b receptors of guinea-pig macrophages are shed and synthesized de novo during short-term culture. This system could be applied to the study in vitro of soluble immunoregulatory mediators on macrophage functions which are dependent on the expression of Fc and C3b receptors.

Animals↗