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B Bellon

Publications and source records attributed to B Bellon.

At least 37 records · Page 2Linked to original sources
PubMed1995

Mechanism of allergic cross-reactions. V. High incidence of unanticipated cross-stimulation by natural allergens of rat basophilic leukemia cells sensitized with monoclonal IgE antibodies.

The incidence of cross-stimulations by natural allergens was investigated using RBL-2H3 cells sensitized with five different mouse monoclonal anti-DNP IgEs and four mercury-induced rat monoclonal IgEs. Cells sensitized with 3 of the 5 monoclonal anti-DNP IgEs (clones SPE-7, SRT-1, LB4) responded by serotonin release upon stimulation by natural allergens such as Dermatophagoides pteronyssinus, horse dander and mugwort extracts. Serotonin release could be inhibited by monovalent DNP-lysine, indicating the involvement of DNP-binding sites of IgEs. Two of the clones (LO-DNP-30 and LA2) were negative on all tests with allergens. All but one (Hg32) of the mercury-induced rat IgE monoclonal antibodies tested positive with DNP-BSA, and with at least one of the six allergen extracts. IgE clone Hg12 mediated serotonin release with 5 of the 6 allergens tested.

Allergens↗
PubMed1994

Monoclonal antibodies to human pancreatic procolipase: production and characterization by competitive binding studies.

Hybridomas secreting monoclonal antibodies (MAbs) specific for human pancreatic colipase were established and 11 clones were selected by using a dot immunobinding assay. Characterization of the MAbs was carried out by using direct and competitive epitope mapping methods, including ELISA and inactivation of colipase-dependent pancreatic lipase. Monoclonal antibodies showed four distinct patterns of reactivity. Monoclonal antibody 5.30 (group I) inhibited colipase-dependent lipase activity. The dissociation constant of the inactive antibody-antigen complex was 10(-9) M. Monoclonal antibodies 48.30, 66.24, and 153.23 (group II) had no effect on activity although they bound competitively with MAb 5.30 to antigen as shown by their capacity to displace MAb 5.30 from the antibody-antigen complex and by ELISA additivity test. Dissociation constants calculated from the displacement curves were 0.9 10(-9) M, 0.6 10(-9) M, and 2 10(-9) M, respectively. Noninhibitory MAbs 13.29, 16.25, and 33.30 bound competitively with MAbs of group II but not with MAb 5.30 (group I). Monoclonal antibodies of group IV (MAbs 17.6, 18.1, 37.39, and 169.29) had no effect on activity and did not react with immobilized antigen. None of the MAbs reacted in ELISA with reduced and carboxymethylated human procolipase, indicating that epitopes involved conformationally dependent determinants on protein antigen. Anti-human colipase MAbs showed no cross-reactivity with porcine or equine procolipases. Monoclonal antibodies described here appear to be useful tools for studying surface hydrophobic domain of colipase and/or interaction between colipase and lipase in its active conformation (open lid).

Animals↗
PubMed1993

[Cytokines and immune response].

This review paper briefly describes the principal cytokines involved in immune response, and in particular their role in some of its key-steps: antigen presentation; activation, proliferation and differentiation of CD4+ T cell subsets; antibody response by B cells; manifestations of hypersensitivity. The role played by cytokines in cytotoxic T cell (CTL) differentiation and in T cell-mediated suppression phenomena is also discussed. It seems that the auxiliary CD4+ memory cells secrete either IL-2 and interferon gamma (Th1) or IL-4 and IL-5 (Th2). It has recently been suggested that cytotoxic/suppressor CD8+ cells can also be divided into cells that secrete interferon gamma and no IL-4 (CTL) and cells that secrete IL-4 and IL-5 (suppressor T cells). The reciprocal regulatory effects of these cell populations through these interleukins is also discussed.

Animals↗
PubMed1993

TH2 activated cells prevent experimental autoimmune uveoretinitis, a TH1-dependent autoimmune disease.

Mercuric chloride (HgCl2) injections protect (Lewis x Brown-Norway) F1 (F1) rats against experimental autoimmune uveoretinitis (EAU) induced by immunization with the retinal S antigen (S-Ag); in contrast HgCl2-injected F1 rats develop EAU following transfer of lymph node (LN) cells from rats immunized with S-Ag alone. In the present study we demonstrate that the ability of LN cells from rats protected against EAU to transfer the disease into naive F1 rats was considerably reduced. These LN cells neither produced interleukin (IL)-2 nor (interferon (IFN)-gamma but exhibited mRNA for IL-4. In contrast, LN cells from diseased rats easily transferred EAU into naive F1 rats, produced significant IL-2 and IFN-gamma levels but barely exhibited mRNA for IL-4. Furthermore protected rats predominantly produced IgG1 anti-S-Ag antibodies, while diseased rats produced IgG2b anti-S-Ag antibodies and the increase in expression of MHC class II molecules on B cells was higher in protected rats than in diseased rats. These data suggest that (1) to exert a protective effect, HgCl2 must act at an early stage of differentiation of precursors of S-Ag specific T cells, and (2) this effect is related to the preferential activation of TH2 cells to the detriment of uveitogenic TH1 cells. Finally, these results indicate that activation of TH2 cells protect from a TH1-dependent autoimmune disease.

Animals↗
PubMed1993

Human immunoglobulin preparations for intravenous use prevent experimental autoimmune uveoretinitis.

We have evaluated the effect of human Igs for intravenous use (IVIg) on the onset and development of experimental autoimmune uveoretinitis (EAU), a T cell-dependent autoimmune disease induced in rats by a single immunization with retinal S-antigen (S-Ag). Five consecutive daily infusions of IVIg, starting on the same day as S-Ag immunization, protected (Lewis x Brown-Norway) F1 rats against EAU. The prevention of EAU was IVIg-specific, i.e. mediated by pooled human IgG from multiple donors, since neither infusions of BSA nor infusions of pooled Ig from only two healthy individuals were effective. Treatment with IVIg decreased lymphocyte proliferative and antibody responses to S-Ag and the proliferative response to concanavalin A. Lack of proliferation was not dependent upon generation of suppressor cells. Lymph node (LN) cells from IVIg-treated and S-Ag-immunized animals neither proliferated nor secreted IL-2 in response to S-Ag but proliferated when co-cultured with LN cells from rats immunized with S-Ag. Our findings are compatible with an induction of a state of functional inactivation/anergy of T lymphocytes by infusions of IVIg. This functional inactivation may be due to the presence in IVIg of antibodies that bind both in vivo and in vitro to rat lymphocytes. Results from the present study suggest a novel mechanism by which IVIg may be beneficial in human autoimmune diseases.

Animals↗
PubMed1993

Anti-interleukin-2 receptor monoclonal antibody therapy supports a role for Th1-like cells in HgCl2-induced autoimmunity in rats.

Brown-Norway (BN) rats injected with HgCl2 develop an autoimmune disease characterized by a T-dependent polyclonal B-cell activation. Increase in major histocompatibility complex class II molecule expression on B cells concomitant with enhancement of serum IgE concentration supports the involvement of the T helper 2 (Th2)-like subset in the induction of the disease. The mercury disease is autoregulated and does not develop in Lewis (LEW) rats. Considering the reciprocal regulation, well defined in mice, between the Th1 and Th2 subsets, we addressed the role of the Th1-like subset in this disease. Brown-Norway and LEW rats injected with HgCl2 were treated with NDS61, a mouse anti-rat-IL-2R MoAb that blocks mainly Th1 cells. Data reported herein show that: (1) HgCl2 treatment does not modify either the percentage of IL-2R+ cells or IL-2R expression in both BN and LEW rats; (2) treatment of BN rats with NDS61 MoAb does not modify the induction phase of the mercury disease but delays in part the regulation phase; (3) such a treatment leads to some immune abnormalities in LEW rats; (4) HgCl2 markedly potentiates the anti-mouse Ig antibody response in BN rats which probably limits the effect of this treatment. This study supports a role for the Th1-like subset in HgCl2-induced autoimmunity in the rat.

Animals↗
PubMed1992

Separation and characterization of the precursor and activated forms of porcine and human pancreatic colipase by reversed-phase liquid chromatography.

Reversed-phase liquid chromatography was used as an alternative method for the characterization of the precursor and activated forms of porcine and human pancreatic colipase. Using a Beckman Ultrasphere column with an increasing acetonitrile gradient in 0.1% trifluoroacetic acid, it was possible to obtain well-resolved separation of the precursor form of colipase (procolipase) from its trypsin-activated derivative. This protocol was used (1) to study the activation of porcine procolipase by trypsin or thrombin in vitro, (2) to assess the homogeneity of porcine colipase preparations used in tridimensional structure studies and in combination with immunoaffinity chromatography, (3) to identify the form of colipase present in samples of human pancreatic juice.

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

The yemanuclein-alpha: a new Drosophila DNA binding protein specific for the oocyte nucleus.

The Drosophila yG 4.5 gene (now called yemanuclein-alpha gene), which maps at 98F, is a member of the yema gene cluster isolated in a search for differentially expressed maternal genes. The yemanuclein-alpha transcript (formerly yT 4.5) is specifically expressed in the female germ cells at early oogenic stages and displays a graded distribution along the antero-posterior axis of the oocyte. These provocative features are reminiscent of that of K10, bicoid and Bicaudal-D gene transcripts and lead us to hypothesize that the yemanuclein-alpha gene plays a key role in egg organization. We show in the present work that the yemanuclein-alpha is a nuclear protein highly specific for the oocyte nucleus. The sequence analysis of the 5696 bp EcoRI fragment containing the yemanuclein-alpha gene, and of 5 overlapping cDNAs, reveals a 3006 nucleotides long open reading frame (ORF) flanked by long untranslated 5' and 3' sequences. This ORF predicts a 109,215 kDa protein which is basic (pHi: 8.57), and serine rich (12.08%). It contains a 40 amino acid acidic domain in the first third of the protein with a potential alpha-helix organization; this domain has some similarity with the nucleolin acidic domain. Parts of the yemanuclein-alpha sequence are likely to form secondary structures known to interact with DNA. We demonstrate the DNA binding activity of the yemanuclein-alpha by affinity chromatography experiments. Our data indicate that the yemanuclein-alpha shares some of the features which are characteristic of genuine transcriptional activators.

Amino Acid Sequence↗
PubMed1992

Adoptive transfer of experimental autoimmune uveoretinitis in HgCl2 injected rats.

We previously demonstrated that mercuric chloride (HgCl2) injected-(Lewis x Brown-Norway) F1 rats are protected against experimental autoimmune uveoretinitis (EAU) induced by active immunization with the retinal S-antigen (S-Ag). To better understand the mechanisms of the protection promoted by HgCl2, we studied the effect of HgCl2-induced autoimmune disease on transferred EAU. We demonstrate herein that HgCl2 has no effect on adoptively transferred EAU. Therefore, the HgCl2-induced autoimmune disease does not affect effector S-Ag specific T cells activated in vitro but acts at an earlier stage.

Animals↗
PubMed1991

Antigen specificity of anticolipase monoclonal antibodies: characterization of colipase-Fab complexes using gel filtration high-performance liquid chromatography.

The epitope specificity of eight mouse monoclonal antiporcine procolipase antibodies (MAbs) was characterized on the basis of their competitive binding with antigen. Binary and ternary Fab-colipase complexes formed between antibody and porcine procolipase or its trypsin activated derivative were identified using gel filtration HPLC. The eight MAbs were divided in two groups that recognized overlapping epitopes located in distinct antigenic regions on procolipase. The gel filtration HPLC technique allowed to characterize two MAbs which did not react with solid-phase coupled antigen. Three MAbs formed Fab-antigen complexes with procolipase and not with activated colipase which suggests that epitopes recognized by these MAbs involve residues of the N-terminal pentapeptide of procolipase.

Animals↗
PubMed1991

Antigen specificity and cross-species reactivity of a monoclonal antibody (mAb 72.11) against porcine pancreatic procolipase.

We have studied the antigen specificity and cross-reactivity of a monoclonal antibody (mAb 72.11) of subclass IgG1, raised against the precursor form of porcine colipase (procolipase), whose epitope lies near the amino terminal region of the polypeptide. mAb 72.11 cross-reacts with native porcine, equine and human procolipase, as shown by immuno-inactivation and ELISA titration studies carried out on pure proteins, pancreatic tissue homogenate or pancreatic juice. The epitope site recognized by mAb 72.11 was further characterized by studying antibody binding to denatured procolipase. Reduced carboxymethylated procolipase reacted with mAb 72.11 in ELISA. Heat inactivated or reduced carboxymethylated porcine procolipase displaced antigen from the complex formed between antibody and native procolipase. The lack of sensitivity of epitope recognized by mAb 72.11 on procolipase to heat denaturation or reduction of the disulfide bridges is indicative that antigen specificity of mAb 72.11 is not dependent on the conformation of the antigenic site. Cross-reactivity of mAb 72.11 with procolipase from the three species demonstrates that substitution of amino acid at positions 1 and 3 causes no loss of antigenicity. Finally, mAb 72.11 was coupled to sepharose to isolate human procolipase from human pancreatic juice and to separate the precursor form from activated colipase non-adsorbed on the column.

Amino Acid Sequence↗
PubMed1991

Increased expression of class II major histocompatibility complex molecules on B cells in rats susceptible or resistant to HgCl2-induced autoimmunity.

Administration of HgCl2 to the susceptible Brown-Norway (BN) rats induces an autoimmune disease characterized by a T-dependent polyclonal activation of B cells responsible for a dramatic increase in serum IgE concentration. The resistant Lewis (LEW) rats injected with HgCl2 do not exhibit such autoimmune manifestations. We show here that, upon HgCl2 injections, major histocompatibility complex (MHC) class II molecule expression is increased very early in lymph nodes and spleen B cells from both strains. So far, it is the earliest marker (day 3) of the effect of HgCl2 on the immune system. In both strains this enhancement is transient, but regulatory mechanisms are much more efficient in the resistant LEW strain than in the susceptible BN strain. In addition, we observed that MHC class II molecule expression on B cells differs according to the organ and the rat strain tested. All these findings are discussed in an attempt to underline the role of MHC class II molecule expression in the occurrence of mercury-induced autoimmunity.

Animals↗
PubMed1991

Beneficial effect of human therapeutic intravenous immunoglobulins (IVIg) in mercuric-chloride-induced autoimmune disease of Brown-Norway rats.

Administration of HgCl2 to the susceptible Brown-Norway (BN) strain of rats induces an autoimmune disease characterized by polyclonal B cell activation, increased serum levels of IgE and the occurrence of anti-glomerular basement membrane antibody-mediated glomerulonephritis. We have observed that the simultaneous administration to BN rats of normal human polyspecific immunoglobulins for therapeutic use (IVIg) with HgCl2 significantly decreased the occurrence and severity of proteinuria, and reduced serum IgE levels in diseased animals. Hypergammaglobulinaemia was potentiated in animals receiving HgCl2 and IVIg, compared with animals receiving HgCl2 alone. In vitro experiments indicated that F(ab')2 fragments from IVIg inhibited the binding to laminin of pathogenic anti-laminin antibodies from diseased rats, as did antibodies from the resistant Lewis strain of rats but not antibodies from susceptible BN rats. These observations suggest that IVIg may interfere with the immune regulatory mechanisms involved in mercury-induced autoimmune disease in an analogous fashion to the ability of IVIg to suppress the expression of certain pathological autoimmune responses in humans.

Animals↗
PubMed1991

Conformational prediction studies on pancreatic colipase.

Comparison of the primary structures of pancreatic colipases from man, pig, horse and rat shows a high degree of homology between proteins. Fifty-two out of the 95 residues of the polypeptide are identical. All colipases contain 10 half-cystines which are located at invariant positions. The secondary structure of colipases has been predicted from the sequence using the statistical method of Chou and Fasman and the method of Gibrat, Garnier and Robson based on information theory. Predictions indicate that colipases have a low content of alpha-helix and beta-strand structure. The two segments at positions 7-10 and 56-59, assumed to be part of the lipid binding domain, have predicted beta-sheet conformation and should be in close spatial vicinity to each other in the proteins. Four beta-turns are predicted in all colipases at positions 3-6, 46-49, 61-64, and 81-84. They might contribute, with the five disulfide bridges, to a tight packing of the protein molecule. Surface residues and major sequential antigenic determinants of mammalian colipases have been predicted using methods based either on hydrophilicity/hydropathy scales or amino acid mutability. From these studies, it appears that colipases exhibit large conformational homologies. In the absence of data on the tertiary structure of colipase, predictive methods, together with physico-chemical and immunological studies, provide valuable information on the conformation of the protein in relation to the topology of residues involved in the functional and antigenic sites.

Amino Acid Sequence↗