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Biomedical subjects

V Gheţie

Publications and source records attributed to V Gheţie.

At least 19 recordsLinked to original sources
PubMed2001

Expression of functionally active FcRn and the differentiated bidirectional transport of IgG in human placental endothelial cells.

The mechanism of selective transport of the immunoglobulins G from the placental stroma to the lumen of the fetal blood vessels has not been elucidated yet. It was postulated that the specific transport as well as the regulation of IgG level in the blood, involves the MHC class I related receptor FcRn for the Fc domain of IgG. We questioned whether human placental endothelial cells (HPEC) express FcRn and, if present, whether it is in a functionally active form. The experiments were performed on cultured HPEC and as positive control, human trophoblastic (JEG3) and mouse endothelial cells (SVEC) were used. Expression of FcRn, was demonstrated by indirect immunofluorescence and RT-PCR. The role of FcRn was assessed by quantifying the transcellular transport of [(125)I]-hIgG or [(125)I]-rF(ab')(2) fragments from the apical to basolateral surface, and in the reverse direction of HPEC grown on filters in a double chamber system. The intracellular pathway of FcRn or IgG was examined by electron microscopy using the proteins adsorbed to 5 nm and 20 nm colloidal gold particles, respectively. The results showed that: (a) FcRn is expressed by human placental endothelial cells, in a functionally active form; (b) transcytosis of IgG in HPEC is a time-dependent process that takes place preferentially from the basolateral to the apical compartment; and (c) both IgG and FcRn colocalize in an intracellular endocytic compartment, chloroquine sensitive. Together these data suggest that the regulation of IgG level by endothelial cells may result from interplay between salvaging, exocytosis, and transcytosis of the molecules. One can assume that IgG that does not bind to FcRn may be destined for destruction, and this would explain the mechanism by which IgG homeostasis is maintained.

Animals↗
PubMed1986

Modulation of IgG effector functions by a monovalent fragment of staphylococcal protein A.

The monovalent V-1 fragment of protein A (fSpA) with a mol. wt of 13,000 obtained from an u.v. mutant of Staphylococcus aureus Cowan I strain was proved to be able to modulate significantly some of the effector functions of IgG, such as complement fixation, catabolism, attachment to Fc receptors and antibody-dependent cell-mediated cytotoxicity. Moreover fSpA-like protein A obtained from the A676 strain is mitogenic and enhances NK activity of human peripheral lymphocytes. The efficiency of fSpA was found to be lower than that of protein A with regard to its ability to inhibit complement fixation, EA rosette formation and antibody-dependent cell-mediated cytotoxicity. Both protein A and fSpA had the same efficiency in activation of the complement system after reaction with human or guinea pig IgG, and in increasing the IgG catabolism. Unlike fSpA the monovalent B fragment of protein A (with mol. wt of 7000) was not able to inhibit EA rosette formation and antibody-dependent cell-mediated cytotoxicity. The results recommend fSpA, substituting for protein A, as a molecular probe for the investigation of IgG antibody and lymphocyte effector functions.

Animals↗
PubMed1985

Mutual inhibition of the binding of Clq and protein A to rabbit IgG immune complexes.

A complex of rabbit IgG antibody with horseradish peroxidase covalently linked to Sepharose 4B was used as an insoluble immune complex for studying the binding of complement factor C1q protein A from Staphylococcus aureus, and its IgG-binding fragments AB and B, to rabbit IgG. It was shown that protein A (mol. wt approx. 42,000) and fragments AB and B (mol. wts approx. 14,000 and 7000, respectively) inhibited the binding of C1q to insoluble immune complex at 4 degrees C. However, at 37 degrees C fragment B did not inhibit this binding. On the other hand, C1q, when bound to an insoluble immune complex, almost completely blocked the binding of protein A and fragment B at both temps. The higher affinity of C1q for its CH2-binding site than of fragment B for its CH2-binding site may explain the displacement of the latter from the CH2 domain. The mutual inhibition of the binding of C1q and protein A (and its smaller fragments) indicates that the binding sites for C1q and protein A are closely located in the CH2 domain.

Animals↗
PubMed1984

Preparation and some properties of dimeric rabbit IgG antibody.

By reacting rabbit IgG with the fragment AB of protein A from S. aureus (mol. wt 14,000) an IgG dimer was formed with an approx. mol. wt of 320,000 and a molar composition of IgG2-AB1. A hybrid dimer with dual specificity consisting of IgG anti-sheep red blood cells/AB/IgG anti-bovine red blood cells was also obtained by reacting successively both rabbit antibodies with the AB fragment. The immunologic properties (affinity for antigen, complement activation and binding to Fc receptors) of the dimeric IgG were investigated in comparison with monomeric rabbit IgG and a tetrameric IgG obtained by reaction with protein A, (IgG2-protein A1)2.

Antibody Specificity↗
PubMed1983

Crosslinkage of antibodies to staphylococcal protein A matrices.

Crosslinkage of anti-human albumin (anti-HSA) with varying concentrations of glutaraldehyde to Staphylococcus aureus Cowan 1 (SpA-Staph) and to staphylococcal protein A-Sepharose (SpA-Sepharose) was tested. A concentration of 0.0075% glutaraldehyde was found efficient for an almost complete covalent binding of IgG to the matrices. The antibody activity of crosslinked anti-HSA SpA-Staph and anti-HSA SpA-Sepharose was more than 60 and 90% respectively compared with the corresponding noncrosslinked immunosorbents. Antigen was recovered with intact antigenic properties by elution with 3.5 M MgCl2.

Antibodies↗
PubMed1983

Effect of protein A and its fragment B on the catabolic and Fc receptor sites of IgG.

Radiolabeled protein A from Staphylococcus aureus (SpA) injected i.v. into mice and rabbits forms a soluble [(IgG)2-(SpA)1]2 complex (Mr = 684 000) which is identical in composition to that formed by SpA in vitro with an equivalent amount or an excess of IgG. A soluble rabbit IgG-SpA complex injected into a mice or rabbits dissociates completely in vivo and a new complex is formed with the IgG of the recipient animal. The half-life of SpA administered to a mouse or a rabbit is therefore the half-life of the IgG-SpA complex formed in vivo. In mice and rabbits the half-life of the complexes formed is 9 and 30 h, respectively, whereas the half-life of rabbit IgG in these animals is 106 and 153 h, respectively. Fragment B of SpA (fSpA) reacts with IgG of mouse and rabbit and forms an (IgG)1-(fSpA)1 complex. Complexes of identical composition are formed if fSpA is injected i.v. into mice and rabbits. The half-life of the complexes in mice and rabbits are much shorter than those of the corresponding free IgG in these animals (up to 15 times). This result suggests that the binding of fSpA to the CH2 and the CH3 domains of IgG alters the function of the site, which controls the catabolism of IgG and is located in the CH2 domain. By contrast, fSpA does not change the Fc receptor-binding site of IgG, indicating that the Fc receptor site and the catabolic site are unrelated to each other.

Animals↗
PubMed1983

Correlation between the triggering of proliferation and the potentiation of NK activity induced by protein A in human lymphocytes.

Various preparations of Staphylococci protein A (SpA) obtained either from strain Cowan-1 or strain A676 and two SpA low molecular fragments (AB and B) were tested for their mitogenic and NK-stimulating activity on human peripheral blood lymphocytes. Though all 4 preparations of SpA and both of its fragments were able to react with human IgG, apparently with both Fab and Fc sites of IgG, only the SpA preparations derived from A676 strain triggered the proliferation and potentiated the NK-activity of treated cells. The parallelism between the mitogenic and NK-stimulating activities of SpA suggests that both activities might be under the control of the same portion of the SpA molecule located in the non-immunoglobulin binding region of the molecule.

Amino Acid Sequence↗
PubMed1982

Specific cytotoxic activity of normal T-lymphocytes coated with multivalent hybrid antibody.

Mouse lymphoid cells treated with multivalent hybrid antibody consisting of rabbit IgG anti-T antibody and rabbit IgG anti-chicken red blood cell antibody formed rosettes and killed specifically chicken red blood cells. The attachment and killing of chicken red blood cells is due to multivalent hybrid antibody which is able to link with one antibody specificity (anti-T) the T-lymphocytes and with the other one the chicken red blood cell surface antigen(s). Some indirect results seem to suggest natural killer cells as a candidate for the multivalent hybrid antibody-induced cytolytic effects. Multivalent hybrid antibody can be a useful alternative to mitogen for assaying specifically the cytotoxic potential of various cell populations pre-existing in normal organisms and requiring only a link to the target cells to reveal their killing ability.

Animals↗
PubMed1980

Multivalent hybrid antibody with double specificity as a tool for locating cell surface antigens by electron microscopy.

Multivalent hybrid antibody complexes with dual specificity were prepared by combining rabbit antibody with anti-mouse immunoglobulin (mIg) and anti-peroxidase (HRP) specificity using protein A of Staphylococcus aureus. The presence of two antibody molecules with anti-mIg and anti-HRP specificity in a single molecule of hybrid complex was demonstrated by their abilities to produce hemagglutination with both HRP-coated and mIg-coated sheep red cells, to give a reaction of complete identity with mIg and HRP and to allow mIg bearing lymphocytes to form rosettes with HRP-coated sheep red blood cells. Electron microscopy of mouse lymphocytes and thymocytes (previously coated with mIg anti-Thy-1 antibody) treated with hybrid antibody complex and HRP showed strong and specific staining of the cell membrane of both cell types. The hybrid antibody complex containing anti-HRP antibody is a valuable reagent for determining various antigenic markers on cell membranes by electron microscopy.

Animals↗
PubMed1979

IgG-binding sites on macrophage cell membrane. I. Identification of two distinct Fc receptors on mouse peritoneal macrophages.

Evidence is presented concerning the existence on mouse peritoneal macrophages of two separate and distinct Fc receptors, one for cytophilic monomeric IgG (mIgG) and the other for polymeric IgG. The latter Fc receptor recognizes both heat-aggregated IgG and antigen-complexed IgG. The major findings of our studies are: (a) the different susceptibility of the two Fc receptor types by pronase, trypsin or phospholipase C; (b) the independent modulation of these two binding sites on the cell membrane; (c) the inability of mIgG to inhibit the binding of particulate antigen-complexed IgG ligand; (d) the ability of mIgG molecules which are devoid of the cytophilic property to attach to the macrophage surface upon their polymerization induced by heating or antigen. The results are discussed in terms of "cytophilic" and "opsonic" Fc receptor types which may provide different functional abilities for normal macrophages.

Animals↗
PubMed1979

IgG-binding sites on macrophage cell membrane. II. Mobility of Fc receptors induced by the interaction with their corresponding IgG ligands.

Mouse peritoneal macrophages were charged with IgG molecules in monomeric (mIgG), heat-aggregated (agIgG) or antigen-complexed (acIgG) form. Upon exposure to 37 degrees C, all bound IgG ligand types are redistributed on the cell surface due to the mobilization of their corresponding Fc receptor (FcR). The major findings regarding the fate of FcR on macrophages bearing IgG ligands are as follows: (a) the FcR involved in the binding of cytophilic molecules has a slow movement on the cell membrane and forms patches but never caps, while the opsonic type of FcR is rapidly capped; (b) the mobility of IgG-binding sites was temperature-dependent and was affected differently by sodium azide; this metabolic inhibitor enhances the disappearance of mIgG from the cell surface but decreases the capping and the disappearance of polymeric ligands; (c) both FcR types are probably ingested when complexed with specific ligand, and consequently, the rebinding of homologous IgG molecules is reduced, the clearing induced by agIgG or acIgG binding being much more extensive; and (d) cells cleared of their opsonic types of FcR are able to regenerate the receptor molecules with 8 h of incubation at 37 degrees C.

Animals↗
PubMed1979

Red cell-linked antibody assay for detection of antigenic markers on cell surfaces.

A direct method for demonstrating antigenic markers on cell surface has been developed which makes use of the ability of bovine red blood cells coated with protein A of Staphylococcus aureus (ES) to binding IgG antibody without agglutinating. Red cell-linked rabbit IgG antibody reagents (ESA) were prepared in this way, and Ig-, IgM- and Thy-1-bearing mouse spleen and peripheral blood lymphocytes were identified by a rosette assay.

Animals↗