Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.4.21.4 (trypsin)
 42,187 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Mouse peritoneal macrophages possess distinct Fc receptors (FcR) for binding the various murine IgG isotypes. FcRI binds monomeric IgG gamma 2a, but not monomeric IgG gamma 2b or IgG gamma 1 with high affinity at 4 degrees C and is sensitive to trypsin degradation. We have assessed the functional consequences of the cytophilic binding at 4 degrees C of monomeric IgG gamma 2a to FcRI of mouse peritoneal macrophages using newly developed photometric microassays for quantification of binding, phagocytosis, and antibody dependent cellular cytotoxicity (ADCC) of post-opsonized sheep red blood cell (SRBC) targets. Dose-dependent binding specificity of monomeric IgG gamma 2a, but not IgG gamma 2b or IgG gamma 1 to FcRI of oil-elicited mouse peritoneal macrophages at 4 degrees C for 2 h was confirmed to display typical saturation kinetics both by the photometric assay and by a cellular enzyme-linked immunosorbent assay (CELISA). Binding of monomeric IgG gamma 2a to macrophage FcRI promoted highly efficient phagocytosis of opsonized SRBC in that most cells that were bound were also rapidly internalized by the phagocytic process during a 1 h incubation at 37 degrees C. Upregulation of FcRI-dependent binding and phagocytosis occurred during 24-48 h in vitro culture of macrophages as shown both by the photometric assays and CELISA. Trypsin treatment of macrophages abrogated FcRI-dependent binding and phagocytosis by monomeric IgG gamma 2a, but had little effect on FcRII-dependent functions. Cytophilic binding of monomeric IgG gamma 2a to FcRI failed to trigger ADCC activation. Thus functional characterization of macrophage FcRI-dependent effector functions confirmed the fidelity of binding specificity of monomeric IgG gamma 2a to a trypsin degradable receptor which mediates highly efficient phagocytosis but fails to initiate the signal for ADCC activation. It appears that passively bound immune monomeric IgG gamma 2a could provide an efficient mechanism by macrophages in vivo for FcRI-dependent immune clearance of soluble or particulate cellular antigens without elicitation of potentially harmful cytolytic factors associated with ADCC activation.
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PMID:Photometric assays for FcRI-dependent binding, phagocytosis, and antibody-dependent cellular cytotoxicity mediated by monomeric IgG gamma 2a in murine peritoneal macrophages. 297 39

The culture supernatants of unstimulated T cells (TCS) from asthmatic patients with elevated serum IgE were tested for IgE-binding factors (IgE-BFs) displaying the IgE-potentiating activity. The IgE-BFs were detected by their ability to inhibit the rosetting of RPMI 8866 cells with ox erythrocytes coupled with mouse monoclonal antibody (E-Mab) specific to Fc receptors for IgE (Fc epsilon R). TCS showing the rosette-inhibiting activity significantly enhanced the spontaneous IgE synthesis by B cells of allergic individuals. Interestingly, rosette-inhibiting factors could be removed by absorption with IgE-Sepharose from which they were subsequently eluated with acid buffer, indicating that the rosette inhibition was indeed mediated by IgE-BFs. In addition, such IgE-BFs had affinity for concanavalin A and lost their IgE-potentiating activity after treatment with trypsin and neuraminidase. In contrast, T cells treated with tunicamycin released IgE-suppressing factors capable of inhibiting the IgE-potentiating activity of TCS derived from untreated T cells. On the other hand, the culture supernatants from subpopulations depleted of Fc epsilon R+ T cells but not of Fc gamma R+ T cells contained neither rosette-inhibiting factors nor IgE-potentiating factors, suggesting that IgE-BFs were released by in vivo pre-activated Fc epsilon R+ T cells. With regard to circulating Fc epsilon R+ T cells determined by E-Mab, they were significantly higher in asthmatic patients with elevated serum IgE (0.77 +/- 0.15%) than in normal subjects (0.17 +/- 0.07%) in spite of a very small proportion of T cells bearing Fc epsilon R.
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PMID:Modulation of IgE synthesis by IgE-binding factors released by T cells of asthmatic patients with elevated serum IgE. 349 27

The mononuclear phagocyte system (MPS) plays an important role in the removal of both particulate and soluble immunogenic material from the circulation. E.IgG adhere to mononuclear phagocytes if the Fc portion of the IgG can interact with the phagocytes' Fc receptors. Simultaneous sensitization with IgG and C3b enhances the effectiveness of binding and ingestion. If soluble material cannot adhere to the surface of macrophages, it will be endocytosed in vitro via fluid-phase pinocytosis at the concentration that is present in the medium. If the material adheres to the cell's surface via its chemical properties or via specific receptors, it will be selectively concentrated at the cell's surface and endocytosed by an adsorptive pinocytosis. Ingestion of IC via Fc gamma R and C3b depends on the ability of the antibodies to interact with Fc gamma R and their capacity to activate the complement system. IC-bound C3b enhances the adsorptive pinocytosis of IC. Soluble AIgG are also pinocytosed more efficiently when C3b is bound to AIgG. The degree of endocytosis varies with the level of C3b sensitization. The highly effective C3b-mediated pinocytosis can be abolished by treating the macrophages with trypsin to inactivate C3bR. This observation illustrates that C3-mediated pinocytosis can replace Fc-mediated pinocytosis in unstimulated macrophages. Soluble IC and AIgG are removed from the circulation mainly by hepatic Kupffer cells. It seems that the size, the Ag/Ab ratio, the capacity of the IC to bind C1, activate C1, and allow deposition of C3b together with the degree of phagocyte activation determine the degree of binding and subsequent degradation of soluble IC.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Activation of complement by soluble IgG aggregates and their subsequent interaction with macrophages. 357 Mar 61

Circulating immune complexes were present in half of 31 patients with sarcoidosis and raised levels were associated with low numbers of T suppressor cells (T gamma- and Fc gamma-receptor-positive lymphocytes). Incubation of T cells with trypsin restored the percentage of T gamma cells to within or above the normal range. Incubation of normal lymphocytes with sarcoid immune complexes significantly reduced the number of detectable T gamma cells. Preincubation of normal lymphocytes with circulating immune complexes significantly reduced their blastogenic response to concanavalin A. These studies suggest an interaction between immune complexes and T suppressor cells in sarcoidosis and emphasise the importance of immune complexes in modulating the immune response.
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PMID:Interaction of immune complexes and T suppressor cells in sarcoidosis. 621 75

To clarify the co-expression phenomenon of T-cell Fc receptors (FcR) specific for different isotypes on the clonal level, a murine hybridoma clone T2D4 was studied. T2D4 cells originally reported to bear FcR for IgG (Fc gamma R) and to release a Fc gamma R-related T-cell factor binding to IgG (immunoglobulin binding factor; IBF) proved to have also the receptor for IgA. The binding of IgA was detected by rosette formation with trinitrophenylated ox red blood cells (TNP-ORBC) after preincubation of T2D4 cells with MOPC 315 IgA having anti-TNP activity, or directly with TNP-ORBC sensitized with MOPC 315 IgA. While the binding of MOPC 315 IgA was competed for by IgA but not by IgG2A nor IgG2B, IgA failed to inhibit the rosette formation of the cells with ORBC sensitized with rabbit IgG antibody (EA ox gamma), proving that T2D4 cells express FcR specific for IgA (Fc alpha R) in addition to Fc gamma R. Co-expression of both receptors on the same cell surface was demonstrated by a double rosette technique using TNP-quail red blood cells (TNP-QRBC) and EAox gamma. Fc alpha R activity of the cells was completely abrogated by 15 min. incubation with 0.1 mg/ml trypsin, whereas Fc gamma R was resistant even to 1 mg/ml trypsin. The expression of Fc alpha R was augmented (up-regulation) by IgA at the concentration above 300 micrograms/ml and inhibited (down-regulation) by 1000 u./ml of murine beta-interferon (beta-IFN). Conversely, the expression of Fc gamma R was down-regulated by IgA and up-regulated by alpha-IFN. Thus, Fc gamma R and Fc alpha R are co-expressed and reciprocally regulated on these cell lines. The possible co-production of IBF and the Fc alpha R-related binding factor specific for IgA is discussed.
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PMID:T-cell hybridoma co-expressing Fc receptors for different isotypes. I. Reciprocal regulation of Fc alpha R and Fc gamma R expression by IgA and interferon. 621 65

C3b acceptors (C3bAs) of human peripheral blood mononuclear cells (PBMC) reacting with the labile binding site of nascent C3b(C3bx) have been investigated by the immune adherence (IA) test. In non-cellular systems some conventional chemical groups (OH-, NH-2) have been reported to be the target of the covalent binding of C3bx. Thus it should be assumed that every cell can fix C3bx via its labile binding site and C3bAs are barely saturable. Contrary to this expectation, however, normal human PBMC were found to be heterogeneous from this point of view, as 57 +/- 4% of B cells and 21 +/- 2% of Null cells possess C3bAs while T cells do not. C3bAs of human PBMC are saturable and trypsin-sensitive structures. The covalent nature of the C3bx-C3bA interaction has also been proved. Studying the effect of acceptor-bound C3b on the function of other cell-surface structures, the inhibition of the Fc gamma receptor function and the abolishment of the enhancement of pokeweed mitogen-stimulated blastogenesis by immune complexes were found.
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PMID:C3b acceptors on human peripheral blood mononuclear cells; characterization and functional role. 622 65

Intact rheumatoid factor (RF)-active IgM dissociated soluble antigen-antibody complexes formed in the antigen excess zone, whereas trypsin-digested protein had less effect. The dissociation mechanism involved an interaction between the RF IgM and the Fc gamma of antibodies in the complexes. RF-active IgM had no demonstrable effect on antigen-antibody complexes when the antigen or the antibody had been immobilized. This was true irrespective of whether the experiments were performed in the antigen or in the antibody excess zone and despite binding between RF IgM and the immobilized proteins.
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PMID:Dissociation of soluble antigen-antibody complexes by rheumatoid factor IgM. 622 91

The MPS plays an important role in the removal of both particulate and soluble immunogenic material from the circulation. E.IgG adhere to mononuclear phagocytes if the Fc portion of the IgG can interact with the phagocyte's Fc receptors (Fc gamma R). Simultaneous sensitization with IgG and C3b via complement activation enhances the effectiveness of binding and ingestion. E.IgM adhere mainly via C3b to C3b receptors (C3bR) of macrophages. Unstimulated macrophages do not ingest E.C3b. Stimulated macrophages, on the other hand, can ingest E.C3b. If soluble material cannot adhere to the surface of macrophages, it will be endocytosed in vitro via fluid-phase pinocytosis at the concentration that is present in the medium. If the material adheres to the cell's surface via its chemical properties or via specific receptors, it will be selectively concentrated at the cell's surface and endocytosed by adsorptive pinocytosis. Ingestion of IC via Fc gamma R and C3b depends on the ability of the antibodies to interact with Fc gamma R and their capacity to activate the complement system. IC-bound C3b enhances the adsorptive pinocytosis of IC. Soluble AIgG are also pinocytosed more effectively when C3b is bound to AIgG. The degree of endocytosis varies with the level of C3b sensitization. The highly effective C3b-mediated pinocytosis can be abolished by treating with trypsin to inactivate C3bR. This observation illustrates that C3b-mediated pinocytosis can replace Fc-mediated pinocytosis in unstimulated macrophages. When macrophages are stimulated in vivo, Fc-mediated pinocytosis increases significantly. Under these conditions, the binding of C3b no longer stimulates; instead, it sterically interferes with Fc-Fc gamma R interaction. In vivo, E.IgG are removed mainly by splenic macrophages. C4-deficient guinea pigs clear E.IgG less effectively than guinea pigs with an intact complement system. On the other hand, soluble IC and AIgG are removed from the circulation mainly by hepatic Kupffer cells. Complement depletion does not seem to influence the clearance rates of these soluble IC or AIgG. The different results obtained in vitro and in vivo and the finding that different effector organs are responsible for the removal of sensitized erythrocytes and soluble Ic in vivo, suggest that more reliable techniques have to be developed to measure IC clearance in patients with a supposedly deficient or saturated MPS.
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PMID:Factors influencing the endocytosis of immune complexes. 623 77

The existence of a molecule responsible for the induction of Fc receptor (FcR) on bone marrow cells (FcR inducer, FcRI) is demonstrated in conditioned media from the macrophage-like cell line WR19M.1 activated by bacterial lipopolysaccharides. The molecular weight obtained from molecular sieving chromatography in gel and density gradient sedimentation is found to be 18,500 daltons and 16,000 daltons, respectively, with an isoelectric pH of 7.4. The factor is found to be thermolabile and trypsin sensitive. The macrophage and granulocyte inducer (MGI), also known as colony-stimulating factor (CSF) or colony-stimulating activity (CSA), is identified from the same source and found to have a molecular weight and an isoelectric pH different from FcRI. The fractions that contained the MGI did not induce FcR on bone marrow cells, while the fractions rich in FcRI did not induce colony formation.
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PMID:Evidence of the existence of a factor that induces Fc receptors on bone marrow cells. 705 77

To determine the biochemical basis for the two distinct IgG subclass binding specificities on mouse macrophage-like cell lines, Fc-binding proteins were isolated from P388D1 and J774 cells by affinity chromatography using immobilized IgG. Similar IgG subclass-specific Fc gamma-binding proteins were identified on both cell lines. The Fc-binding proteins were characterized by their IgG subclass binding specificity, size, charge, and trypsin sensitivity. Using immobilized IgG1, a protein was isolated with an average m.w. of 65,000 and a pI range of pH 4.7 to 5.8. This protein could also be isolated, although in reduced amounts, with immobilized IgG2b. Two proteins with average m.w. of 70,000 and 60,000 and a pI range of 3.8 to 4.7 were isolated with immobilized IgG2a. The 60-kd protein appeared to be derived from the 70-kd protein. The IgG1/IgG2b Fc-binding proteins were resistant to trypsin, whereas the IgG2a Fc-binding proteins were sensitive to trypsin. In IgG-binding studies with the isolated proteins, the IgG2a Fc-binding proteins continued to exhibit restricted binding specificity for the IgG2a subclass; however, the IgG1/IgG2b Fc-binding proteins showed a broader specificity and would rebind to IgG1, IgG2a, and IgG2b. The IgG-binding properties and trypsin sensitivity of these Fc-binding proteins were similar to the properties of the IgG binding sites on the intact cells. These data indicate that the IgG subclass-specific binding sites on macrophage-like cell lines are due to the presence of distinct protein molecules on the cell surface.
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PMID:Fc receptors of mouse cell lines. I. Distinct proteins mediate the IgG subclass-specific Fc binding activities of macrophages. 706 50


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