Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: 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)

Trypsin treatment of adherent human monocytes greatly reduced or eliminated the ability of these cells to support dengue virus replication. However, addition of dilute (nonneutralizing) antibody to the inoculum and the culture medium resulted in viral yields similar to those from monocytes not treated with trypsin. These results suggested that viral entry was facilitated by phagocytosis of immune complexes via Fc receptors on the monocytes. This concept was tested by (i) pretreating monocytes with aggregated gamma globulin, which resulted in a 40-fold reduction of viral yields after infection with dilute antibody-virus complexes and (ii) forming an immune complex with virus, antivirus F(ab')2 fragments, and rabbit anti-human Fab. Whereas F(ab')2 fragments alone would not enhance virus replication in trypsin-treated monocytes, the immune complex containing a rabbit Fc piece did increase the yield of dengue virus. These results suggest that dengue virus can infect a cultured monocyte in two ways: (i) through a viral receptor that is trypsin sensitive or (ii) through an Fc receptor that is not trypsin sensitive.
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PMID:Evidence for two mechanisms of dengue virus infection of adherent human monocytes: trypsin-sensitive virus receptors and trypsin-resistant immune complex receptors. 725 Nov 33

Monoclonal antibodies to sheep erythrocytes (SRBC) have proved useful in identifying two Fc receptors on mouse macrophages, one for IgG2a, and one for IgG1 and IgG2b. We have used monoclonal IgG3 anti-SRBC to identify a third Fc receptor on mouse macrophages which binds IgG3 uniquely. This receptor is present on primary resident and thioglycolate-induced peritoneal macrophages and on some macrophage cell lines. The binding of IgG3-coated SRBC is inhibited by aggregated byt not monomeric IgG3, and not by IgG1, IgG2a, and IgG2b aggregates. It is unaffected by treating the macrophages with trypsin or cytochalasin B and occurs at both 4 degrees and 37 degrees C. IgG3, like all other IgG subclasses, mediates phagocytosis. We have also generated a variant macrophage line which bears the receptors for IgG1 and IgG2b and for IgG2a, but not for IgG3.
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PMID:A new Fc receptor on mouse macrophages binding IgG3. 725 6

The plasma membrane Fc receptor for IgG2b on P388D1 cells, solubilized by detergent, was inactivated by incubation with phospholipase C. Soluble Fc receptor activity could be restored by the addition of liposomes of either phosphatidylethanolamine or phosphatidylinositol. The reconstituted Fc receptor was trypsin sensitive. These data indicate that Fc receptor binding of IgG2b results from the concerted action of membrane lipid and protein.
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PMID:The murine macrophage Fc receptor for IgG2b is lipid dependent. 739 68

Membrane proteins which selectively bind to the Fc portion of IgG were identified in the Nonidet P-40 extracts of radiolabeled thioglycollate- elicited mouse peritoneal macrophages. Affinity columns of various IgG preparations coupled to Sepharose 4B were used to absorb the Fc-binding proteins. Analysis of the acetic acid or sodium dodecyl sulfate (SDS) eluates from aggregated human IgG or antigen-complexed rabbit IgG columns revealed two Fc(gamma)/-specific proteins with apparent 67,000 and 52,000 mol wt. These proteins were not detected in acid or SDS eluates from F(ab')(2) columns or in eluates from IgG column, over which were passed lysates of Fc receptor-negative cells. With the use of affinity columns that contained aggregated mouse myeloma proteins of different IgG subclasses, we found that the 67,000-dahon protein selectively binds to IgG2a, whereas the 52,000-dalton protein binds to IgG1 and IgG2b. Neither protein was found in SDS eluates from IgG3 columns. Trypsin treatment of the macrophages before detergent lysis removed the 67,000-dalton protein, although it leaves intact the 52,000-dalton protein. These results provide structural confirmation for the existence of separate Fc receptors on mouse macrophages and indicate that the two Fc-binding proteins identified in this study represent all or part of the trypsin- sensitive Fc receptor which binds IgG2a and the trypsin-resistant Fc receptor which binds IgG2b and IgG1.
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PMID:Structural evidence for distinct IgG subclass-specific Fc receptors on mouse peritoneal macrophages. 743 Sep 49

Properties of guinea pig peritoneal macrophage Fc receptor for IgG are described. It was found that the receptor was binding both monomeric and aggregated rabbit IgG. The values of apparent affinity constants were 2.6 +/- 0.6 x 10(8) M-1 and 3.84 +/- x 10(8) m-1 for IgG monomers and aggregates, respectively. The number of monomeric IgG molecules bound was calculated to be 3.3 +/- 0.2 x 10(5) per cell and of aggregated IgG 3.95 +/- 0.12 x 10(5) per cell. When the homologous system: guinea pig IgG2 and guinea pig macrophages was investigated, the affinity constant found was 1.66 +/- 0.45 x 10(8) M-1 and 2.6 +/- 0.24 x 10(5) molecules of IgG were bound per cell. Both, rabbit IgG and, guinea pig IgG2, interacted wih the same receptor binding sites on macrophages. Treatment of macrophages with 2-mercaptoethanol, formaldehyde, and iodoacetamide was without any effect on the IgG binding properties of cells. Periodate, trypsin, pronase, phospholipase C considerably diminished the number of IgG molecules bound to macrophages. Treatment of macrophages with neuraminidase increased the number of IgG molecules bound per cell. The results obtained suggests that both sugar and protein components are important for the IgG binding activity of guinea pig peritoneal macrophages. Studies on the effect of pH, ionic strength, and temperature on the interaction of macrophages with IgG showed that electrostatic interactions are important for binding of IgG to the macrophage Fc receptor.
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PMID:Studies on properties of guinea pig peritoneal macrophage Fc receptor. 744 40

Flaviviruses, when complexed with antibody at subneutralizing concentrations, show enhanced replication in human and simian peripheral blood leukocytes (ref. 1, and J.S.M.P. and J.S.P., unpublished observations) and in P388 D1 and other macrophage cell lines. A comparable phenomenon has been demonstrated with alphaviruses and Bunyaviruses in P388 D1 cells, (J.S.M.P. and J.S.P., unpublished observations) but cells lacking macrophage characteristics fail to show antibody-dependent enhancement (ADE) of viral replication. It has been suggested that the macrophage Fc receptor (FcR) provides an efficient route of entry of virus through the attachment of non-neutralized virus-antibody complexes and that for those viruses that escape destruction by the phagocyte, antibody results in a paradoxical increase in virus replication. West Nile virus (WNV) replication in the P388 D1 macrophage cell line provides a reproducible model system for studying ADE of viral replication. Mouse macrophages have two FcRs-FcRI, which is trypsin-sensitive and binds IgG2a, and FcRII, which is trypsin-resistant and binds IgG2b and IgG1 complexes. The FcR has been purified using rat anti-mouse FcR monoclonal antibody which blocks FcRII. We show here that anti-FcRIgG and its Fab fragment block ADE of virus replication by anti-WNV monoclonal antibodies.
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PMID:Monoclonal anti-Fc receptor IgG blocks antibody enhancement of viral replication in macrophages. 745 20

Murine monoclonal antibodies (mAb) of IgM and IgG subclasses that do not bind to canine cells have been used to detect the expression of Fc receptors on canine peripheral blood mononuclear cells and the cell line MAXEY-DH82. Murine Ig of IgG2a and IgG3 isotypes bound specifically to canine peripheral blood monocytes and to MAXEY-DH82, whereas Ig of IgG1, IgG2b, and IgM did not. No other cell types, including resting and activated peripheral blood lymphocytes, expressed this canine Fc receptor (cFcR) specific for murine IgG2a and IgG3. MAXEY-DH82 was used to characterize this Fc gamma 2a/gamma 3 receptor. Binding of murine IgG2a and IgG3 is trypsin sensitive and partially suppressed by phosphatidyl inositol-phospholipase C (PI-PLC) treatment, indicating that this cFc gamma 2a/gamma 3 receptor is a lipid-anchored protein. Preincubation of MAXEY-DH82 with canine sera or canine IgG prevented the binding of murine gamma 2a/gamma 3 Ig, demonstrating that this receptor is a cFc receptor for canine IgG. The cFc gamma R expressed on canine monocytes and on MAXEY-DH82 is probably the analog of the murine and human Fc gamma RI. The specific expression of this analog by canine cells could be used in identifying and purifying canine monocytes.
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PMID:Canine monocytes express a receptor specific for murine Fc gamma 2a and Fc gamma 3 immunoglobulins. 838 14

Trophoblast cells, dispersed by trypsin digestion of human term placental villi and purified on Percoll gradient, were maintained in serum-containing medium as monolayer cultures up to 7 days. The initially mononucleated cells, probably cytotrophoblasts, differentiated in culture within 90 h to multinucleated syncytiotrophoblast-like cells. The enigmatic binding of human immunoglobulin G (hIgG) to these cells was studied and compared to the well-known binding of hIgG to cultured human monocytes. Binding of hIgG to cultured trophoblasts at 4 degreesC reached steady state by 0.5-1 h, increased about two- to threefold after 90 h in culture and was linear throughout all concentrations tested (0.00067-132 microM). Fc fragments and even F(ab')2 fragments were found to bind to a similar extent to trophoblasts as the complete hIgG molecules. In contrast, in experiments with cultured monocytes, saturation of hIgG binding could be demonstrated. The binding of complete hIgG molecules and of Fc fragments to monocytes was similar whereas binding of F(ab')2 fragments to monocytes was significantly lower. Our results suggest that, despite morphological and at least partially functional differentiation of trophoblast cells in primary culture, no measurable amounts of functional Fc receptor for monomeric hIgG was expressed.
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PMID:Binding of human IgG and F(ab')2 and Fc fragments to cultured trophoblast cells from human term placenta. 977 Mar 57

Nitric oxide is an important mediator that participates in reduction-oxidation (redox) mechanisms and in cellular signal transduction pathways. Two types of post-translational modifications are induced by nitric oxide: S-nitrosylation of cysteine residues and nitration of tyrosine residues. Two-dimensional gel electrophoresis-based Western blotting was used to detect, and liquid chromatography (LC)-tandem mass spectrometry (MS/MS) to determine the amino acid sequence of, several different nitrated proteins in the human pituitary. Proteins from several 2D gel spots, which corresponded to the strongly positive anti-nitrotyrosine Western blot spots, were subjected to in-gel trypsin-digestion and LC-MS/MS analysis. MS/MS, SEQUEST analysis, and de novo sequencing were used to determine the nitration site of each nitrated peptide. A total of four different nitrated peptides were characterized and were matched to four different proteins: synaptosomal-associated protein, actin, immunoglobulin alpha Fc receptor, and cGMP-dependent protein kinase 2. Those nitrotyrosyl-proteins participate in neurotransmission, cellular immunity, and cellular structure and mobility.
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PMID:The human pituitary nitroproteome: detection of nitrotyrosyl-proteins with two-dimensional Western blotting, and amino acid sequence determination with mass spectrometry. 1555 51

How human cytomegalovirus (CMV) reaches the fetus across the placenta is unknown. The major viral cause of congenital disease, CMV infects the uterine-placental interface with varied outcomes depending on the strength of maternal humoral immunity and gestational age. Covering the surface of villi that float in blood, syncytiotrophoblasts express the neonatal Fc receptor (FcRn) that transports IgG for passive immunity. Immunohistochemical analysis of early-gestation biopsy specimens showed an unusual pattern of CMV replication proteins in underlying villus cytotrophoblasts, whereas syncytiotrophoblasts were spared. Found in placentas with low to moderate CMV-neutralizing antibody titers, this pattern suggested virion transcytosis across the surface. In contrast, syncytiotrophoblasts from placentas with high neutralizing titers contained viral DNA and caveolin-1-positive vesicles in which IgG and CMV glycoprotein B co-localized. In villus explants, IgG-virion transcytosis and macrophage uptake were blocked with trypsin-treatment and soluble protein A. Quantitative analysis in polarized epithelial cells showed that FcRn-mediated transcytosis was blocked by the Fc fragment of IgG, but not F(ab')(2). Our results suggest that CMV virions could disseminate to the placenta by co-opting the receptor-mediated transport pathway for IgG. These findings could explain the efficacy of hyperimmune IgG for treatment of primary CMV infection during gestation and support vaccination.
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PMID:Maternal antibodies enhance or prevent cytomegalovirus infection in the placenta by neonatal Fc receptor-mediated transcytosis. 1656 96


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