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Biomedical subjects

G Moţa

Publications and source records attributed to G Moţa.

16 recordsLinked to original sources
PubMed1989

Experimental model for testing the efficiency of immunotoxins administered in vivo: evaluation of two ricin A-chain--multivalent antibody immunotoxins.

Two immunotoxins, the ricin A chain-multivalent hybrid antibody (750 kDa) and the complex A chain-staphylococcal protein A-rabbit IgG antibody (370 kDa), were prepared. A simple method was elaborated to test the immunotoxins' efficiency in selectively killing target cells in tumor-bearing mice. The target cell (murine EL4 leukemia) was coated with a xenogenic molecule by a method conserving its ability to proliferate and kill the inoculated animals. When the challenged animals were treated with these immunotoxins, which were specific for the antigenic molecule coating the tumor cells, survival time was lengthened compared with that of untreated animals, corresponding to a proportion of over 90% cells killed. This demonstrates the efficiency of the immunotoxins and the validity of the method elaborated.

Animals↗
PubMed1988

The Fc receptor for IgA expression and affinity on lymphocytes and macrophages.

The interaction between the Fc receptor for IgA (FcR alpha) and human secretory IgA (sIgA) was studied in a heterologous system by using rabbit alveolar macrophages or splenic lymphocytes. The capacity of FcR alpha-bearing cells to interact with the ligand via the Fc region was demonstrated. The proportion of FcR alpha-bearing lymphocytes and macrophages was found to be 11 and 17%, respectively. The cell-bound radiolabelled ligand showed a release half-time of 70 min for lymphocytes and 45 min for macrophages. The equilibrium constant (K) and the maximum number of ligand molecules bound per cell (n) in mean values was 5.2 +/- 0.05 X 10(8) M-1 and 3.3 +/- 0.15 X 10(5) molecules per cell, respectively. Increased percentages of FcR alpha-bearing cells and of ligand density per cell were obtained after stimulation by lung inflammation. A significant increase of the K value was recorded with macrophages from rabbits with lung acute inflammation (mean value 7.3 +/- 0.21 + 10(8) M-1) while the increase with lymphocytes was not significant. The calculation method of K and n is discussed.

Animals↗
PubMed1988

In vivo follow-up of the cytotoxic effect of protein A--ricin toxin conjugate, on antibody-coated target cells.

Antibodies of the IgG class, specifically interacted with H-2 antigens of murine leukemia EL4 cells, were used to bind the ricin toxin covalently linked to protein A of Staphylococcus aureus. The toxin thus complexed, introduced in the cytoplasm by endocytosis, was able to kill the leukemic cells inoculated in animals. The interaction of immunotoxin with the leukemic cells was performed in vitro using one, two or three treatments and the cytotoxic effect on the target cells was followed up in vivo. The time interval between immunotoxin treatments was indicated by the membrane turn-over study of EL4 cells coated with specific antibodies in their monomeric form, complexed by protein A or interacted with protein A--ricin toxin conjugate. A proportion of 99.8% cells killed was obtained after three treatments.

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

The inhibition capacity of concanavalin A on monomeric and polymeric hemolytic antibodies.

The ability of concanavalin A (Con A) to inhibit the complement consumption by sheep erythrocytes coated with IgG, (IgG2-SpA1)2 complex and IgM anti-Forssman antibodies was studied. The (IgG2-SpA1)2 anti-Forssman antibody complex showed an increased hemolytic activity compared to uncomplexed IgG antibody. Con A in the presence of the (IgG2-SpA1)2 complex or the IgM antibody exhibited a high inhibitory capacity. An inhibitory capacity of Con A on IgG antibody hemolytic activity was also proved but at a Con A:IgG antibody concn ratio about 10 times higher than that for the Con A-IgM antibody system. A time dependence of Con A inhibitory capacity was determined, thus explaining the variable behaviour of the IgG antibody in the inhibition experiments. Radioactivity experiments demonstrated that only half of the Con A interacted with the (IgG2-SpA1)2 complex compared to the amount of Con A which interacted with IgG uncomplexed antibody.

Animals↗
PubMed1984

Binding of immune complexes to IgA-sepharose 4B.

A method for the determination and removal of circulating immune complexes in pathological sera was developed using human secretory or dimeric myeloma IgA covalently bound to Sepharose 4B. IgA-Sepharose 4B was able to selectively bind heat or antigen-aggregated human IgG (circulating immune complexes) but not monomeric IgG. The absorbent was also able to remove a very high proportion (95%) of circulating immune complexes from pathological sera as determined by a turbidimetric technique. An immunoradiometric assay for the direct measurement of circulating immune complexes is described. The assay uses IgA-Sepharose 4B as an absorbent (for the binding of IgG immune complexes from sera) and 125I-rabbit anti-IgG antibody (for the quantitation of IgG immune complexes bound to IgA-Sepharose 4B). The mean value obtained for pathological sera (27.1 +/- 0.9) was significantly higher than that of normal sera (4.8 +/- 0.5).

Antigen-Antibody Complex↗
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

Selective binding of heat- and antigen-aggregated IgG to Blue-Sepharose. Radioimmunoassay of circulating immune complexes.

In an attempt to find a direct method for the determination of circulating immune complexes in pathological sera we studied the ability of Cibacron Blue 3GA covalently bound to Sepharose 4B to bind heat- or antigen-aggregated human IgG. Blue-Sepharose was found to bind significant amounts of aggregated IgG (about 1.5 mg/ml packed gel) but very low amounts of monomeric IgG (about 0.1 mg/ml gel). The ability of Blue-Sepharose to bind immune complexes was tested on human pathological sera containing variable amounts of circulating immune complexes. Using both a turbidimetric measurement and Barkas' method we found that Blue-Sepharose is able to remove a very high percent of circulating immune complexes (greater than 80%) from sera. Considering the above observations a new method is described for the direct determination of circulating immune complexes using Blue-Sepharose as serum adsorbent and either 125I-labeled protein A or 125I-labeled rabbit IgG anti-human IgG to demonstrate the binding of immune complexes.

Animals↗
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

Immunogenicity and effector functions of glutaraldehyde-treated rabbit and mouse immunoglobulin G.

Rabbit and mouse IgG treated with glutaraldehyde (GA) were immunogenic in homologous species. Glutaraldehyde treatment induced in the IgG molecule two types of antigenic determinants. One of them was found on the monomeric fraction of GA-treated rabbit IgG (haptenic determinant) and the other on the polymeric fraction (structural determinant). The haptenic determinants were found also on monoaldehyde-treated rabbit IgG and GA-treated Fab and Fc fragments. It was demonstrated that rabbit and mouse antibodies are specific for GA-treated IgG and have species specificity. While GA treatment did not alter the antigen binding capacity of rabbit IgG antibody, its effector functions (except protein A binding) were much affected. Thus it was found that GA treatment enhances IgG ability to react with rheumatoid factor, reduces drastically its capacity to activate the complement system, abolishes the cytophilic properties of IgG and accelerates its catabolic rate. The possible blocking effect of GA on the amino acid residues (mainly Lys) situated in or very close to the effector sites of the IgG molecule is suggested.

Agglutination↗
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↗
PubMedDate not supplied

IgA monoclonal and polyclonal proteins as regulatory factors of the NK cytotoxic activity.

The presence of receptors for IgA (IgAR) on natural killer (NK) cells was only indirectly suggested yet. To elucidate the presence of IgAR on NK cells and its possible role in modulation of the NK activity, was initiated a preliminary study carried out in a homologous system, using human non adherent lymphocytes (NAL) and human seric or secretory IgA. A proportion of over 20% NK cells (CD16+ CD56+) was determined by flow-cytometry in the NAL-cells population. Dose-dependent IgA-binding to NAL cells was determined, showing a limitation of the IgA+ NAL proportion for a cell population of 32% and a ligand concentration of 4 mg/ml/10(7) cells. The binding parameters of the IgA/IgAR system, calculated by Scatchard procedure, revealed values of the affinity constant (K) and of the maximum number of ligand molecules bound/cell (n) depending on the aggregation degree of the ligands: K-values of 1.0 and 0.4 x 10(7) M-1 for dimeric and respectively, monomeric IgA, and n-values of 0.8 and 1.7 molecules/cell, respectively. A proportion of 3% IgA molecules endowed with cytophilic property was also calculated. The turnover rate of secretory IgA (sIgA) on the NAL cells surface showed values of the ligand half time (T 1/2) of 1 h. The effect of polyclonal IgA, (sIgA and normal seric IgA) and of monoclonal IgA myeloma (monomeric and dimeric IgA) on the NK cytotoxicity target K562 cell line was of inhibition, depended on the ligand doses and varied with the IgA type. The possible relevance of immunoglobulins A and of the activity of natural killer cells in processing of some mechanisms of the antiviral protection was discussed.

Cytotoxicity, Immunologic↗