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Biomedical subjects

H Bazin

Publications and source records attributed to H Bazin.

At least 19 recordsLinked to original sources
PubMed1992

Chemical synthesis of a biologically active natural tRNA with its minor bases.

The complete chemical synthesis of an E. coli tRNA(Ala) with its specific minor nucleosides, dihydrouridine, ribothymidine and pseudouridine, is reported. The method makes use of protected 2'-O-tertiobutyldimethylsilyl-ribonucleoside-3'-O-(2-cyanoethyl-N- ethyl-N- methyl)phosphoramidites. The exocyclic amino functions of the bases were protected by the phenoxyacetyl group for purines and acetyl for cytosine. The assembling has been performed on a silica support with coupling yield better than 98% within 2 min of condensation. Triethylamine tris-hydrofluoride allowed a clean and complete deprotection of the tBDMS groups. The synthetic tRNA(Ala) has been transcribed into cDNA by reverse transcriptase and sequenced. With E. coli alanyl-tRNA synthetase the alanyl acceptance activity and kcat/Km were 672 pmol/A260 and 6 x 10(4)M-1s-1, respectively.

Alanine-tRNA Ligase↗
PubMed1992

Antigen-pulsed dendritic cells can efficiently induce an antibody response in vivo.

The aim of this study was to develop an immunization procedure avoiding external adjuvant. Data are presented showing that syngeneic dendritic cells (DC), which have been pulsed in vitro with antigen, induce a strong antibody response in mice. By contrast, antigen (Ag)-pulsed low-density B cells, although equally able to induce interleukin 2 secretion by an Ag-specific T cell hybridoma in vitro, only weakly prime the mice in vivo. Moreover, we show that the injection of Ag-pulsed DC induces the synthesis of isotypes similar to the immunoglobulin classes detected after immunization with the same Ag in complete Freund's adjuvant. Importantly, high amounts of IgG2a antibodies are produced, suggesting that T helper type 1 cells are activated. Collectively, these data indicate that DC can initiate a primary humoral response and that they may be used as physiological adjuvant in vivo.

Animals↗
PubMed1992

The injection of deaggregated gamma globulins in adult mice induces antigen-specific unresponsiveness of T helper type 1 but not type 2 lymphocytes.

Injection of adult mice with high doses of monomeric human gamma globulins (dHGG) has been previously shown to produce a state of peripheral tolerance in both B and T cells. To gain insight into the mechanism of induction and maintenance of adult tolerance in this model, we have analyzed the pattern of lymphokines produced by control and tolerant animals in response to the tolerogen. The data presented indicate that HGG-specific, interleukin 2 (IL-2)- and interferon gamma (IFN-gamma)-producing T cells (thus referred to as T helper type 1 [Th1] cells) are rendered unresponsive after in vivo administration of soluble HGG. In contrast, antigenic stimulation of T cells isolated from tolerant adult mice leads to increased production of IL-4 in vitro. In vivo challenge of dHGG-treated adult animals with hapten-coupled HGG (p-azophenylarsonate [ARS]-HGG) induced a significant ARS-specific antibody response, suggesting that tolerance induction in this model does not completely abrogate tolerogen-specific Th activity in vivo. In agreement with the in vitro data, hapten-specific antibody response of tolerant animals is characterized by a selective deficiency in the IFN-gamma-dependent IgG2a subclass. Injection of immunogenic forms of HGG into tolerant animals also produced an IL-4-dependent increase in total serum IgE levels, indicative of an increased activity of HGG-specific Th2 cells in these animals. The finding that tolerance induction differentially affects Th subpopulations suggests that crossregulation among lymphocyte subsets may play a role in the induction and/or maintenance of acquired tolerance in adults.

Animals↗
PubMed1992

Modulation of oral tolerance to ovalbumin by cholera toxin and its B subunit.

Oral administration to mice of ovalbumin (OVA), if given together with cholera toxin (CT) or its B subunit (CTB) prevented the hyporesponsiveness to OVA subsequently injected parenterally. Oral immunization with CT plus OVA or OVA plus CTB in fact primed the immune system, inducing a stronger response to a subsequent parenteral injection of OVA with complete Freund's adjuvant than in mice prefed only with OVA or with saline. Oral CT plus OVA also induced good serum IgG1 and IgA anti-OVA responses, with slightly (not significant) decreased IgG2a and IgG2b responses. Our in vivo findings agree well with earlier in vitro data from others, including CT inhibition of the Th1 CD4+ T cell subset and with CT effect on B cells (induction of LPS-stimulated IgM+ B cells to undergo increased switch differentiation to IgG1- and IgA-secreting cells).

Adjuvants, Immunologic↗
PubMed1992

Antibody mediated lysis of hapten-conjugated target cells by macrophages and by complement: the influence of IgG subclass, antibody and hapten density.

Lysis of 51Cr-labeled TNP-SRBC sensitised by rat IgG1 or IgG2a type antibodies by homologous, paraffin oil-elicited peritoneal macrophages (ADCC) or by homologous complement was studied. IgG2a was found to be markedly more efficient in mediating both ADCC and complement dependent lysis compared to IgG1. Inhibition of the ADCC pointed to the involvement of separate but partially overlapping interaction sites for the two isotypes. We suggest that FcRII type receptors play a favoured role in both IgG2a and IgG1 mediated ADCC. The threshold amount of bound antibody required for ADCC was lower than that sufficient for complement dependent lysis regardless on the subclass or on hapten density. The extent of lysis (both ways) was found to depend on hapten density using equal amounts of antibody. The results are interpreted as terms of the possible requirements for association of IgG molecules on the target cell surface.

Animals↗
PubMed1992

Interaction between rat peritoneal macrophages and sensitised erythrocytes: dependence on IgG subclass, antibody density and the degree of hapten conjugation.

The interaction between macrophages (M phi) and antibody sensitised target cells was studied by the use of rat peritoneal macrophages, TNP hapten conjugated sheep red blood cells (SRBC) and homologous antibodies of subclasses IgG1 and IgG2a. Under optimal conditions, the great majority of the M phi formed rosettes with IgG1-sensitised antibodies while a maximum of 50% was achieved when target cells were sensitised by IgG2a. Using a double rosette technique, the major part of rosette-forming cells was found to bind both of the isotypes. IgG1-mediated rosette formation was observed at very low degrees of sensitisation as opposed to IgG2a-mediated target cell binding. Not only the amount of bound antibody but also the degree of hapten conjugation (epitope density) appear to influence the ratio of rosette-forming cells. IgG1-mediated rosette formation was partially inhibited by monomeric IgG1 and more efficiently by soluble ovalbumin (OVA)-anti-OVA complexes involving IgG1-type antibodies, while IgG2a mediated rosette formation was inhibited by OVA-anti-OVA complexes containing IgG2a type antibodies, and less efficiently by complexes involving IgG1. No inhibition was found by monomeric IgG2a. Based on the present data, we propose that two types of receptors are involved in the interaction of M phi and target cells coated by IgG1 and/or IgG2a type antibodies. One requires a multiple antibody-receptor interaction, binding both subclasses at overlapping binding sites; the other is able to interact with IgG1 and does not depend on the multiplicity of interactions.

Animals↗
PubMed1992

IgG2b or IgE molecules can be co-expressed with those of the IgM and IgD isotypes of the membrane of normal rat B cells.

Expression of Ig isotypes other than IgD together with IgM on the membranes of single B cells has been reported in different experimental models. This paper describes the co-expression of IgG2b or IgE with IgM-IgD on the surface of single B cell subpopulations from normal rats. Their expression was demonstrated with anti-IgE or IgG2b monoclonal antibodies and their F(ab')2 fragments. After pronase digestion, the re-expression of these isotypes together with IgM-IgD was observed in vitro and was inhibited by cycloheximide. These observations imply that mechanisms other than class switching may participate in the expression of membrane isotypes in vivo. The role of these membrane isotypes is still to be established, but could be important as IgG2b molecules are found on a large B cell subpopulation.

Animals↗
PubMed1992

Eradication of hantavirus infection among laboratory rats by application of caesarian section and a foster mother technique.

Hantavirus antibodies were demonstrated by the indirect immunofluorescent antibody assay, in the serum of inbred strains of laboratory rats, during the period 1973-1982, at the Unit of Experimental Immunology in the Catholic University of Louvain, Brussels, Belgium. LOU rats, as well as immunocytomas, which were requested by laboratories in the U.K. and The Netherlands, were supplied at a time when the infection was unknown and unsuspected in Europe. Hantavirus-infected laboratory rats were rendered free of virus through re-derivation by caesarian section and suckling by virus-free foster mothers. Immunocytomas were tested for the presence of hantaviruses by implantation into seronegative laboratory rats. The strain of hantavirus causing the laboratory infection was clearly different from the one circulating in free-living bankvoles in Belgium. The exchange of laboratory rats and rat tumours in relation to the potential risk of laboratory-acquired hantavirus infection, is discussed.

Animals↗
PubMed1992

Susceptibility and resistance to autoimmunity following neonatal injection of semi-allogeneic spleen cells in rats.

A model of neonatal allotolerance was developed in rats. Brown-Norway (BN) neonates injected with semi-allogeneic (BN x Lewis) F1 hybrid spleen cells express a long-lasting chimerism and exhibit polyclonal B cell activation demonstrated by hyperimmunoglobulinemia affecting mainly IgE and IgG1, anti-laminin and anti-DNA autoantibodies as well as glomerulonephritis and anti-hapten antibodies. These abnormalities are autoregulated although the chimerism persists. In contrast, Lewis (LEW) neonates injected with semi-allogeneic (BN x LEW) F1 hybrid spleen cells exhibit a very short-lasting chimerism and transient activation of B cells, as reflected by increased allo-class II antigen expression, but do not develop an autoimmune disease. The autoimmune syndrome observed in BN rats is similar to that reported in mice during host-versus-graft reaction. Similarities between the drug-induced models of autoimmunity and allogeneic reactions in BN rats are also striking. The susceptibility of BN rats and the resistance of LEW rats to these autoimmune diseases might respectively reflect the involvement of TH2-like or of TH1-like subsets.

Animals↗
PubMed1992

Experimental arthritis in rats induced by intra-articular injection of IgE aggregates: evidence for arthritogenic role of complexed IgE.

An experimental arthritis model in the rat was used to study the arthritogenic potential of complexed IgE. IgE aggregates were produced in vitro by cross linking monoclonal rat IgE by dimethyl suberimidate and were injected into the knee joints. Animals which had not been injected and animals injected with phosphate buffered saline served as controls. The concentration of histamine in tissues, diffusion into the joint of bovine serum albumin labelled with iodine-125 injected intravenously, and the histology of the joints were studied. There was a significant decrease in the concentration of histamine in synovial tissue 8 and 24 hours after the injection of the IgE aggregates. A decreased number of stainable mast cells were found 8, 24, and 48 hours after exposure. A moderate hyperplasia of the synovial lining layer was also noted. These results provide further evidence for the arthritogenic potential of complexed IgE, especially in the initiation of arthritis through activation of mast cells.

Animals↗
PubMed1992

CD23 expression in aged rats.

CD23 is considered as an activation marker. Its expression on lymphocytes was studied during aging by using 1- to 142-week-old rats. Before analysis, all animals were injected with monoclonal IgE, in order to detect their full expression of CD23 molecules on their lymphocyte surface membranes. In elderly rats, a decrease was observed in the percentages of CD23+ lymphocytes from mesenteric lymph nodes, spleen, Peyer's patches and peripheral blood. In addition, these lymphocytes expressed significantly fewer CD23 molecules per cell. Almost all CD23+ cells belonged to the B lineage and were bearing both IgM and IgD on their membranes. It is suggested that a decrease in the number of both IgM+IgD+CD23+ lymphocytes and CD23 molecules per cell may contribute to immune deficiency in the elderly.

Aging↗
PubMed1992

[Total chemical synthesis of natural transfer RNA].

New improvements in the chemical synthesis of oligoribonucleotides are reported and they are applied to the first total chemical synthesis of a natural RNA. This E. coli K12 alanine tRNA contains in its sequence dihydrouridine, ribothymidine and pseudo-uridine. The synthetic tRNA was fully sequenced and showed a 42% aminoacyl acceptance activity. When tRNA was used as a template, reverse transcriptase directed the incorporation of adenine opposite dihydrouridine, ribothymidine and pseudouridine.

Base Sequence↗
PubMed1991

[Treatment with Lo-Tact-1, a monoclonal antibody to the interleukin-2 receptor, in kidney transplantation].

From May to August 1989 15 cadaver-donor renal transplant recipients were treated for 14 days with LO-Tact-1 (10 mg i.v. per day) in combination with cyclosporin (8 mg/kg/day from day-1), low-dose steroids (1/2 mg/kg/day from day 1, then reduced to 0.25 mg/kg at day 26 and 10 mg/day at day 45), and azathioprine (1 mg/kg/day) started at day 45. LO-Tact-1 is a rat monoclonal antibody which is directed to the interleukin-2 receptor. The control group consisted of 20 patients receiving cyclosporin, high-dose steroids (2 mg/day at day 1) and a 14-day course of polyclonal horse antilymphocyte globulins (ALG). Seven patients experienced 9 rejections during the first 3 months post-transplant between day 10 and day 67 (mean 0.6 per patient), comparable to the incidence of rejections in the control group: 8 rejections in 7 patients (mean 0.4 per patient). All rejections were reversed by steroid boluses and ATG. To date, all study patients have functioning grafts, and at 1-year post-transplant, the mean blood creatinine level is 161.2 mumol/l. In the control group, one patient died of CMV infection, and 2 other grafts failed due to rejection. No adverse effect of antibody administration was observed, and hematological changes remained of minor importance. Viral infections were not observed, except one case of herpes simplex. Comparatively, clinical CMV infections occurred in 3 patients receiving ALG (15 percent). Our data suggest that a combination anti-IL-2 monoclonal antibody, cyclosporin and low-dose steroids can safely be administered to allograft recipients, avoid severe viral infections, and, in our early experience, is as potent as the powerful combination ALG, cyclosporin and high-doses steroids in preventing allograft rejection.

Adult↗
PubMed1991

Polyclonal activation of the murine immune system by an antibody to IgD. XI. Contribution of membrane IgD cross-linking to the generation of an in vivo polyclonal antibody response.

The injection of mice with a foreign, polyclonal antibody to IgD sequentially induces: 1) activation of B cells by cross-linking of their cell membrane (m) IgD; 2) B cell processing and presentation of the bound anti-IgD antibody to T cells; 3) activation of these T cells; and 4) T-dependent stimulation of B cell differentiation into IgG1 secreting cells. To determine whether the cross-linking of B cell membrane IgD and/or the resulting B cell activation that follows contribute to the generation of the polyclonal IgG1 response, we examined the abilities of three sets of anti-delta mAb or mAb fragments to stimulate polyclonal IgG1 production. Within each set mAb were matched for species and Ig isotypic determinants, but differed in avidity for IgD or in ability to cross-link IgD. In addition, experiments were performed to determine whether the anti-delta mAb had to be foreign to the immunized mouse to stimulate an IgG1 response. Results of these experiments indicate that: 1) recognition of the injected anti-delta antibody as foreign is required for the induction of a polyclonal IgG1 response; 2) the cross-linking of B cell membrane Ig, which directly activates B cells, can contribute considerably to the generation of in vivo IgG1 production; and 3) that even relatively weak cross-linking of membrane Ig by ligands that bind it with low avidity can make this contribution.

Animals↗
PubMed1991

Complement enhances the clearance of large-sized soluble IgA aggregates in rats.

In the present study the involvement of the complement system (C) in the clearance of soluble IgA aggregates in the rat was studied. Monoclonal monomeric IgA (mIgA) antibody (which does not activate C) or aggregated polymeric IgA (aIgA; which activates C) were administered intravenously to phosphate-buffered saline-treated and complement-depleted [Cobra venom factor (CVF)-treated] rats and assessed for clearance from the circulation. In control rats, mIgA was cleared in a biphasic fashion with a first half-life (T1/2) of 29.5 +/- 14.2 min and a second T1/2 of 230 +/- 176 min. No differences were observed in clearance of mIgA in CVF-treated rats as compared to PBS-treated rats. In PBS-treated rats, aIgA with a size between 20 S and 150 S disappeared very rapidly from the circulation with a first T1/2 of 1.1 +/- 0.4 min and a second T1/2 of 23.2 +/- 11.3 min. In CVF-treated rats the clearance of aIgA was significantly delayed as compared to that in control rats, namely with a first T1/2 of 7.3 +/- 2.6 min and a second T1/2 of 64.2 +/- 19.4 min. Immunohistochemical studies of the liver (which is the main site of clearance of aIgA) revealed that Kupffer cells (KC) are mainly responsible for the uptake of aIgA. Furthermore, in PBS-treated rats aIgA deposition was accompanied by C3 deposition in the KC. In CVF-treated rats, the percentage of KC containing aIgA was significantly lower during the first 16 min after aIgA administration as compared to PBS treated rats. In addition no detectable C3 was found in KC of CVF-treated rats. These results indicate that KC play an important role in the clearance of large molecular weight IgA in rats and that C facilitates the clearance of these complexes from the circulation.

Animals↗
PubMed1991

Transcriptional deregulation of myc in IgH/myc 6;7 translocation carrying rat immunocytomas.

We have previously shown that the reciprocal translocation t(6;7) associated with the spontaneous immunocytoma of the Louvain rat (RIC) leads to the juxtaposition of myc to the IgH cluster. In 10 of 14 tumors investigated the breakpoints on the myc carrying chromosome were clustered in a 1.5 kb region 5' of the intact gene, proximal to the myc promoters. In this paper we describe the effect of the translocation on myc transcription in the RIC system. Run-on analysis showed transcriptional attenuation in the normal rat myc gene, similar to the situation in mice and humans. The attenuation was almost completely abrogated in the three immunocytomas studied. Sequence analysis of two tumors failed to reveal any structural changes within exon 1, as found by others in Burkitt's lymphoma. We also show that the transcriptional initiation of myc mRNA is changed in the RICs. In an established line of rat fibroblasts (Rat-2), the more distal myc promoter (P2) is the preferred site of initiation. In RIC, however, only 30% of transcripts were initiated from P2. We found that 40% of the transcripts were initiated from P1 and 30% from a novel promoter, designated P1a, located between P1 and P2.

Animals↗
PubMed1991

Synovial inflammation induced by a local allergic reaction.

A rat model has been developed to examine the possible role of homocytotropic antibodies in initiating or exacerbating synovial inflammation. The technique, passive synovial anaphylaxis, involves passively sensitizing rat knee joints with specific IgE, then challenging intravenously with the corresponding antigen while monitoring for signs of inflammation. Swelling of the sensitized joints reached maximum 2 h after the challenge, then gradually decreased to prechallenge levels by 24 h. Radioisotopic joint scans detected a passive synovial anaphylaxis induced increase in local blood flow and exudation within the joints. The degree of swelling correlated directly with the amount of antigen specific IgE in the sensitizing serum, and individual joints remained sensitized for up to 36 days after the IgE injection.

Animals↗