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Biomedical subjects

G Benichou

Publications and source records attributed to G Benichou.

45 records · Page 3Linked to original sources
PubMed1989

T-cell chemiluminescence. A novel aspect of T-cell membrane activation studied with a Jurkat tumour cell line.

The binding of mitogenic lectins phytohaemagglutinin (PHA), concanavalin A (Con A) and/or of monoclonal antibodies to different receptors such as antigen receptor complex or CD2 on human T cells generates increases in the concentrations of inositol triphosphate (IP3) and cytoplasmic free calcium. This T lymphocyte requires the delivery of two signals; the first can be provided by specific monoclonal antibodies or by mitogenic lectins, and the second by a phorbol ester, phorbol myristate acetate (PMA). In other cells such as macrophages, the rise of intracellular calcium via the generation of IP3 and stimulation of protein kinase C can activate the phospholipase A2, a calcium-dependent enzyme. This enzyme initiates the release of reactive oxygen intermediates and metabolites of arachidonic acid. In order to know whether this other metabolic pathway can be generated in T cells, we tested the capacity of different T-cell lines and clones to produce superoxide anion after stimulation by the above-mentioned activating agents. In this paper, we demonstrate that treatment of the Jurkat human cell line with Con A, PHA, and PMA results in a significant release of reactive oxygen metabolites. Of the various T-cell lines and clones tested, only Jurkat exhibited an oxidative burst. Moreover, none of the antibodies tested (anti-CD3, anti-CD2, and anti-CD28) and known to activate T cells, and none of the immune complexes was able to mediate such an effect. The existence of an oxidative metabolism in at least one T-cell line suggests that T-cell activation may in some instances use another metabolic pathway.

Free Radicals↗
PubMed1988

Biochemical purification of various receptor molecules involved in human T lymphocyte activation. Separation of 9.3 antigen from the T cell receptor for antigen.

The now classical major histocompatibility complex (MHC)-restricted receptor for antigen on human T lymphocytes has been identified as a 90 kDa disulphide-linked heterodimer composed of two glycoproteins termed alpha and beta. More recently, another type of T cell receptor for antigen has been described, which seems to mediate killing of target cells without any obvious requirement for MHC recognition. This T cell receptor for antigen is also a heterodimer composed of gamma, delta chains non-covalently associated with the three mon morphic CD3 subunits. Another disulphide-linked dimer capable of triggering T lymphocytes has been defined recently by a monoclonal antibody: the anti-human 9.3 antigen. In order to generate monoclonal or polyclonal reagents against variable and constant regions of the T cell receptor chains and against new epitopes of the 9.3 antigen, we have developed a biochemical method of purification of T lymphocyte disulphide-linked dimers. Our method relies on two biochemical properties of the 9.3 surface molecule and the T cell receptor for antigen. (1) They are disulphide-linked dimers and thus can be separated from the vast majority of the cell surface molecules by two-dimensional (non-reduced versus reduced) sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). (2) T cell receptor chains are less hydrophobic than the 9.3 antigen, and thus can be isolated from it on reverse-phase high-performance liquid chromatography (HPLC) at a lower concentration of acetonitrile. Microsomal preparations from T cell clones and leukaemia lines were prepared by nitrocavitation and lysed in sodium deoxycholate. After concentration, this lysate was electrophoresed on SDS-PAGE in non-reducing conditions. The gel slice corresponding to the molecular weight of the T cell receptor was cut out and run in reducing conditions in the second dimension. The T cell receptor spots were easily located on the gel by autoradiography as the microsomal lysate had been mixed with iodinated glycoproteins. The T cell receptor was eluted from the gel with about 85% yield. At this stage, the T cell receptor preparations also contained the 9.3 antigen, another disulphide-linked dimer. The separation of this antigen from the T cell receptor chains had been achieved on reverse-phase HPLC. This procedure allows the purification and separation of two disulphide-linked dimers which are both involved in T cell activation. The obtention of antibodies against new epitopes of these important molecules would be extremely useful for analysing their role in T cell function and ontogeny.

Antigens, Differentiation, T-Lymphocyte↗
PubMed1988

[Influence of gamma irradiation on the chemiluminescence of alveolar macrophages in guinea pigs at rest or activated].

The capacity of Guinea Pig alveolar macrophages to produce oxygenated free radicals after in vitro gamma irradiation was studied. We observed an increase of resting cell chemiluminescence with 3 Gy, then an important decrease from 3 Gy to 30 Gy. Chemiluminescence of zymosan activated macrophages was reduced at 10 Gy and 30 Gy, while activation by IgG anti-MHC antigens was not affected by the same radiation doses. These results could be of great interest for the study pulmonary defense mechanisms after irradiation.

Animals↗
PubMed1987

Interferon-gamma restores T lymphocyte proliferation of nonresponders to IgG1 anti-CD3 via the induction of Fc gamma 1 receptors on monocytes.

Human peripheral blood T lymphocytes are stimulated to grow and divide by some mouse anti-CD3 monoclonal antibodies. This polyclonal mitogenesis is dependent on both their immunoglobulin subclass and the presence of monocytes. The unresponsiveness of T lymphocytes from certain individuals to mouse IgG1 (or IgG2a) antibodies is due to a failure of their monocytes to bind these IgG isotypes. In this study, we have selected such nonresponder subjects to IgG1 anti-CD3 (UCHT 1) in order to study their monocytes. Two assays were used: IgG1 and IgG2 EA rosettes to evaluate their Fc receptor-binding capacity, and IgG-mediated monocyte chemiluminescence to test their receptor-related activation since mouse anti-T cell antibodies binding to lymphocytes trigger monocyte chemiluminescence via their Fc receptor. We have observed that in all nonresponder subjects the absence of IgG1 anti-CD3 monocyte chemiluminescence strictly correlates with the absence of IgG1 EA rosettes. Thus, the failure to respond to UCHT 1, in all nonresponders tested to date, is due to the absence of Fc gamma 1 receptors on their monocytes. Treatment of nonresponder monocytes by recombinant interferon-gamma was shown to restore T cell proliferation and monocyte chemiluminescence in nonresponders. This effect of interferon-gamma correlates with the appearance of Fc gamma 1 receptors on monocytes from these individuals. This work strongly suggests that nonresponder monocytes possess functional genes for Fc gamma 1 receptors which are not expressed normally at a detectable level but can be induced by interferon-gamma.

Antibodies, Monoclonal↗
PubMed1987

Transient suppression of the zymosan-induced chemiluminescence produced by bone marrow cells during a subcutaneous nonspecific inflammation in the mouse.

The oxidative metabolism of remote phagocytes has been studied during the course of an acute nonspecific inflammation in the mouse. The bone marrow cells (BMC) from mice bearing a polyacrylamide-microbead-induced granuloma (Biogels P4 and P100) show a transient striking decrease of their chemiluminescence (CL) response to opsonized zymosan. This decreased oxidative response occurs between the third and 72nd hr, with a minimum observed at the 24th hr. Bone marrow granulocytes are assessed to represent the main chemiluminescent BMC compartment, using complement-mediated cytotoxicity assays with a monoclonal antimouse granulocyte antibody. Biogel P4-treated mice, but not Biogel P100-treated ones, show at the 24th hr a significantly decreased percentage of segmented bone marrow granulocytes (-45%, P less than .001). The accurate mechanisms involved in this transient suppression of stimulus-induced CL produced by BMC remain to be elucidated.

Acrylic Resins↗
PubMed1987

Antibody bipolar bridging: isotype-dependent signals given to guinea pig alveolar macrophages by anti-MHC alloantibodies.

Antibody bipolar bridging of a cell membrane is the phenomenon by which an antibody specifically binds to the corresponding membrane antigen through its Fab and concomitantly to a membrane Fc receptor, through its Fc, thus forming a molecular bridge at the cell surface. This phenomenon, already described on mouse mast cells with anti-H-2 IgG1 antibodies and on guinea pig polymorphonuclear leukocytes with anti-GPLA IgG2 antibodies, presently is extended to and studied on guinea pig alveolar macrophages. These cell membranes present class I and class II MHC (GPLA) antigens as demonstrated by protein-A-sheep red blood cell rosetting and ELISA techniques. They also present Fc receptors for IgG2 and IgG1 as shown by an ELISA technique. IgG2 antibodies (but not their F(Ab')2) directed against corresponding class I or class II antigens induce a positive signal on alveolar macrophages, leading them to release H2O2 and superoxide anions as detected by a burst of chemiluminescence. This respiratory burst begins almost immediately, peaks at 4 to 11 min (depending on antibody concentrations), and decreases thereafter. There is a striking dose-effect curve. By contrast, IgG1 antibodies (but not there F(ab')2) induce a negative signal leading to a decrease of the background chemiluminescence. This type of mechanism appears potentially to be of importance in immune regulation.

Animals↗