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Biomedical subjects

L Bracci

Publications and source records attributed to L Bracci.

At least 19 recordsLinked to original sources
PubMed2002

Endogenous morphine modulates acute thermonociception in mice.

The endogenous synthesis of morphine has been clearly demonstrated throughout the phylogenesis of the nervous system of mammals and lower animals. Endogenous morphine, serving as either a neurotransmitter or neurohormone, has been demonstrated in the nervous system of both vertebrates and invertebrates. As one of the effects of exogenous morphine is the modulation of pain perception, we investigated the effects that the depletion of endogenous morphine had on nociceptive transmission. The immunoneutralization of endogenous morphine from brain extracellular spaces was obtained through the intracerebroventricular administration of affinity purified anti-morphine IgG to mice, which then underwent the hot plate test. Endogenous morphine immunoneutralization decreased thermal response latency and attenuated the anti-nociceptive effect of the mu selective agonist DAMGO in hot plate test suggesting that endogenous morphine is involved in pain modulation.

Acute Disease↗
PubMed2001

A novel mimetic antigen eliciting protective antibody to Neisseria meningitidis.

Molecular mimetic Ags are of considerable interest as vaccine candidates. Yet there are few examples of mimetic Ags that elicit protective Ab against a pathogen, and the functional activity of anti-mimetic Abs has not been studied in detail. As part of the Neisseria meningitidis serogroup B genome sequencing project, a large number of novel proteins were identified. Herein, we provide evidence that genome-derived Ag 33 (GNA33), a lipoprotein with homology to Escherichia coli murein transglycosylase, elicits protective Ab to meningococci as a result of mimicking an epitope on loop 4 of porin A (PorA) in strains with serosubtype P1.2. Epitope mapping of a bactericidal anti-GNA33 mAb using overlapping peptides shows that the mAb recognizes peptides from GNA33 and PorA that share a QTP sequence that is necessary but not sufficient for binding. By flow cytometry, mouse antisera prepared against rGNA33 and the anti-GNA33 mAb bind as well as an anti-PorA P1.2 mAb to the surface of eight of nine N. meningitidis serogroup B strains tested with the P1.2 serosubtype. Anti-GNA33 Abs also are bactericidal for most P1.2 strains and, for susceptible strains, the activity of an anti-GNA33 mAb is similar to that of an anticapsular mAb but less active than an anti-P1.2 mAb. Anti-GNA Abs also confer passive protection against bacteremia in infant rats challenged with P1.2 strains. Thus, GNA33 represents one of the most effective immunogenic mimetics yet described. These results demonstrate that molecular mimetics have potential as meningococcal vaccine candidates.

Adult↗
PubMed2001

NMR studies of protein surface accessibility.

Characterization of protein surface accessibility represents a new frontier of structural biology. A surface accessibility investigation for two structurally well-defined proteins, tendamistat and bovine pancreatic trypsin inhibitor, is performed here by a combined analysis of water-protein Overhauser effects and paramagnetic perturbation profiles induced by the soluble spin-label 4-hydroxy-2,2,6,6-tetramethyl-piperidine-1-oxyl on NMR spectra. This approach seems to be reliable not only for distinguishing between buried and exposed residues but also for finding molecular locations where a network of more ordered waters covers the protein surface. From the presented set of data, an overall picture of the surface accessibility of the two proteins can be inferred. Detailed knowledge of protein accessibility can form the basis for successful design of mutants with increased activity and/or greater specificity.

Aprotinin↗
PubMed2001

Mimotopes of the nicotinic receptor binding site selected by a combinatorial peptide library.

Peptide libraries allow selecting new molecules, defined as mimotopes, which are able to mimic the structural and functional features of a native protein. This technology can be applied for the development of new reagents, which can interfere with the action of specific ligands on their target receptors. In the present study we used a combinatorial library approach to produce synthetic peptides mimicking the snake neurotoxin binding site of nicotinic receptors. On the basis of amino acid sequence comparison of different alpha-bungarotoxin binding receptors, we designed a 14 amino acid combinatorial synthetic peptide library with five invariant, four partially variant, and five totally variant positions. Peptides were synthesized using SPOT synthesis on cellulose membranes, and binding sequences were selected using biotinylated alpha-bungarotoxin. Each variant position was systematically identified, and all possible combinations of the best reacting amino acids in each variant position were tested. The best reactive sequences were identified, produced in soluble form, and tested in BIACORE to compare their kinetic constants. We identified several different peptides that can inhibit the binding of alpha-bungarotoxin to both muscle and neuronal nicotinic receptors. Peptide mimotopes have a toxin-binding affinity that is considerably higher than peptides reproducing native receptor sequences.

Amino Acid Sequence↗
PubMed2001

Epitope focus, clonal composition and Th1 phenotype of the human CD4 response to the secretory mycobacterial antigen Ag85.

Lymphoproliferation of healthy donors was tested against mycobacterial antigens (PPD, Ag85, Ag85 peptides). All PPD responders recognized the secretory antigen Ag85 and the peptide specificity for Ag85B was defined. Peptide 91-108 was recognized by 85% of donors. In addition, all CD4 T cell lines generated from 12 donors against PPD or Ag85 responded to 91-108. When this peptide was used to generate T cell lines, the cells responded also to tuberculins from atypical mycobacterial species. Thus the cross-reactive peptide behaved as quasi-universal. The analysis of TCR-BV gene usage by cell lines showed that most Ag85-specific T cells correspond to 91-108-specific clonotypes. Intracytoplasmic staining of cell lines after phorbol myristate acetate stimulation resulted in dominance of interferon-gamma (IFN-gamma)-IL-4 double-positive cells, whereas antigen stimulation resulted in production of IFN-gamma only. The data show that peptide 91-108 is the major focus of the CD4 response to mycobacterial antigens in peripheral blood mononuclear cells and in T cell lines from PPD responders.

Acyltransferases↗
PubMed2001

Mimicking the nicotinic receptor binding site by a single chain Fv selected by competitive panning from a synthetic phage library.

We have developed a novel competitive method to select from a phage display library a single chain Fv which is able to mimic the alpha-bungarotoxin binding site of the muscle nicotinic receptor. The single chain Fv was selected from a large synthetic library using alpha-bungarotoxin-coated magnetic beads. Toxin-bound phages were then eluted by competition with affinity purified nicotinic receptor. Recognition of the toxin by the anti-alpha-bungarotoxin single chain Fv was very similar to that of the receptor, such as indicated by the epitope mapping of alpha-bungarotoxin through overlapping synthetic peptides. Moreover, several positively charged residues located in the toxin second loop and in the C-terminal region were found to be critical, to a similar extent, for toxin recognition by the single chain Fv and the receptor. However, although the anti-alpha-bungarotoxin single chain Fv seems to mimic the toxin binding site of the nicotinic receptor, it does not bind other nicotinic agonists or antagonists. Our results suggest that competitive selection of anti-ligand antibody phages can allow the production of receptor-mimicking molecules directly and exclusively targeted at one specific ligand. Since physiologically and pharmacologically different ligands can produce opposite effects on receptor functions, such selective ligand decoys can have important therapeutic applications.

Animals↗
PubMed2001

Probing the surface of a sweet protein: NMR study of MNEI with a paramagnetic probe.

The design of safe sweeteners is very important for people who are affected by diabetes, hyperlipemia, and caries and other diseases that are linked to the consumption of sugars. Sweet proteins, which are found in several tropical plants, are many times sweeter than sucrose on a molar basis. A good understanding of their structure-function relationship can complement traditional SAR studies on small molecular weight sweeteners and thus help in the design of safe sweeteners. However, there is virtually no sequence homology and very little structural similarity among known sweet proteins. Studies on mutants of monellin, the best characterized of sweet proteins, proved not decisive in the localization of the main interaction points of monellin with its receptor. Accordingly, we resorted to an unbiased approach to restrict the search of likely areas of interaction on the surface of a typical sweet protein. It has been recently shown that an accurate survey of the surface of proteins by appropriate paramagnetic probes may locate interaction points on protein surface. Here we report the survey of the surface of MNEI, a single chain monellin, by means of a paramagnetic probe, and a direct assessment of bound water based on an application of ePHOGSY, an NMR experiment that is ideally suited to detect interactions of small ligands to a protein. Detailed surface mapping reveals the presence, on the surface of MNEI, of interaction points that include residues previously predicted by ELISA tests and by mutagenesis.

Magnetic Resonance Spectroscopy↗
PubMed2000

Cyclophosphamide induces type I interferon and augments the number of CD44(hi) T lymphocytes in mice: implications for strategies of chemoimmunotherapy of cancer.

In a previous study, we reported that a single injection of cyclophosphamide (CTX) in tumor-bearing mice resulted in tumor eradication when the animals were subsequently injected with tumor-sensitized lymphocytes. Notably, CTX acted by inducing bystander effects on T cells, and the response to the combined CTX/adoptive immunotherapy regimen was inhibited in mice treated with antibodies to mouse interferon (IFN)-alpha/beta. In the present study, we have investigated whether CTX induced the expression of type I IFN, and we have characterized the CTX effects on the phenotype of T cells in normal mice. CTX injection resulted in an accumulation of type I IFN messenger RNA in the spleen of inoculated mice, at 24 to 48 hours, that was associated with IFN detection in the majority of the animals. CTX also enhanced the expression of the Ly-6C on spleen lymphocytes. This enhancement was inhibited in mice treated with anti-type I IFN antibodies. Moreover, CTX induced a long-lasting increase in in vivo lymphocyte proliferation and in the percentage of CD44(hi)CD4(+) and CD44(hi)CD8(+ )T lymphocytes. These results demonstrate that CTX is an inducer of type I IFN in vivo and enhances the number of T cells exhibiting the CD44(hi) memory phenotype. Since type I IFN has been recently recognized as the important cytokine for the in vivo expansion and long-term survival of memory T cells, we suggest that induction of this cytokine may explain at least part of the immunomodulatory effects observed after CTX treatment. Finally, these findings provide a new rationale for combined treatments with CTX and adoptive immunotherapy in cancer patients. (Blood. 2000;95:2024-2030)

Animals↗
PubMed2000

Natural analogue peptides of an HIV-1 GP120 T-helper epitope antagonize response of GP120-specific human CD4 T-cell clones.

Neutralizing antibodies and specific cytotoxic T lymphocytes (CTL) may contribute to controlling viral spread, and ideally, to virus clearance in HIV infection. Both effector mechanisms depend on specific CD4 T-helper (Th) cells. Nevertheless, HIV hypervariability facilitates appearance of escape mutants for antibodies and for CTL responses. Here we also show that natural mutations (i.e., from sequences of different HIV strains) in an immunodominant Th epitope recognized by human CD4 clones specific for the envelope glycoprotein gp120 escape CD4 T-cell recognition. Furthermore, several natural analogue peptides exert an antagonistic function by inhibiting proliferative response of T cells specific to gp120 with a wild-type sequence. If similar events occur in vivo, they may represent an additional escape mechanism for HIV. In fact, antagonism for CD4 Th response may occur during superinfection with a different strain, or with the appearance of a variant carrying a mutated antagonistic sequence. In both cases, impaired Th cell function could lead to reduced immune control of HIV infection by interfering with CTL and antibody response.

Amino Acids↗
PubMed2000

Anti-ganglioside antibodies in a large cohort of European patients with systemic lupus erythematosus: clinical, serological, and HLA class II gene associations. European Concerted Action on the Immunogenetics of SLE.

OBJECTIVE: To assay anti-ganglioside antibodies (aGM1) in sera of a large cohort of European patients with systemic lupus erythematosus (SLE) to define the prevalence of these autoantibodies in SLE; to evaluate the association of aGM1 with clinical manifestations and other autoantibodies found in SLE; and to search for aGM1 association with HLA class II alleles. METHODS: Four hundred forty-eight patients with SLE were consecutively enrolled in 8 centers from 6 European countries. All sera were tested for antinuclear antibodies by immunofluorescence on HEp-2 cells as substrate, anti-dsDNA, aGM1, aCL, abeta2-glycoprotein I (abeta2-GPI) antibodies by ELISA, and antineutrophil cytoplasmic antibodies (ANCA) by immunofluorescence and by ELISA. Genomic typing for HLA class II loci was performed by polymerase chain reaction-sequence specific oligonucleotide probe method. Clinical assessment was done at the time of enrolment. RESULTS: We found 41.9% of patients with clinical signs of neuropsychiatric involvement; 15.5% of patients were positive for aGM1, 8% of the IgG isotype and 8.6% of the IgM isotype; aGM1-IgG were associated with neuropsychiatric manifestations (NPM) (RR = 3.7), with migraine (RR = 2.4), with OBS (RR = 7.3), and with peripheral neuropathy (RR = 8.5). aGM1-IgM were associated with NPM (RR = 4) and with depression (RR = 3.4). Furthermore, the genetic study showed that aGM1-IgG were associated with HLA-DQB1*0404 (RR = 7.2) while aGM1-IgM were associated with HLA-DQB1*0605 (RR = 33.3). No associations were found between aGM1 and anti-dsDNA, aCL, abeta2GP1, or ANCA. CONCLUSION: Our results show aGM1 can be found in patients with SLE. aGM1 may play a pathogenetic role for some NPM in this condition.

Adolescent↗
PubMed1999

Antigenicity and immunogenicity of the V3 domain of HIV type 1 glycoprotein 120 expressed on the surface of Streptococcus gordonii.

Five different V3 domains of HIV-1 gp120 were expressed on the surface of the gram-positive bacterium Streptococcus gordonii, a model live vector for vaccine delivery. Sera of HIV-1-infected individuals and human monoclonal antibodies specifically recognized the gp120 sequences on the bacterial surface. Recombinant V3 from the reference HIV-1 strain MN was also shown to retain a conformation that allowed reaction with a conformation-specific monoclonal antibody. A V3-specific serum antibody response was detected in mice immunized both by subcutaneous injection and by vaginal colonization. V3-specific IgG2a antibodies, suggestive of a Th1 response, were found in the sera of mice colonized by recombinant bacteria.

Amino Acid Sequence↗
PubMed1999

Antagonistic activity of HIV-1 T helper peptides flanked by an unrelated carrier protein.

Antagonism is the ability of a modified antigenic peptide (altered peptide ligand, APL) to prevent CD4 T cell activation by the original peptide. Here we show that antagonistic activity can be conferred to peptides of HIV envelope glycoprotein gp120 and reverse transcriptase p66 by adding flanking polypeptide sequences at the C or at the N terminus by genetic engineering, rather than by introducing substitutions by synthesis. The glutathione S-transferase (GST)-peptide system has been used to produce molecules that display the peptide at the appropriate end of the GST carrier. When the gp120 peptide 191-205 (pep24) was expressed at the C terminus of GST (GST-24), antigenicity of specific human CD4 T cells was maintained. In contrast, when the peptide was expressed at the N terminus of GST (24-GST), antigenicity was abolished and antagonistic activity was introduced. Similar results were obtained with a p66-derived peptide at the C terminus of the GST carrier. Antagonism was (1) specific; proliferation of a CD4 T cell line from the same donor responding to the envelope glycoprotein of another retrovirus, HTLV-1, was not affected; (2) reversible; proliferative response was rescued in T cells exposed to antigen-presenting cells (APC) pulsed with the antagonist; (3) dominant; T cells cultured with APC pulsed with the agonist and with APC pulsed with the antagonist did not proliferate. The carrier could be cleaved by proteolysis while the antagonistic activity was preserved. Thus a minimal sequence that confers antagonistic activity can be engineered or synthesized with peptides to antagonize undesired CD4 responses as an alternative to the use of APL.

Amino Acid Sequence↗
PubMed1999

Functional expression in bacteria and plants of an scFv antibody fragment against tospoviruses.

BACKGROUND: Recombinant antibodies expressed in plants ('plantibodies'), directed against crucial antigens and addressed to the right cell compartment, may be able to protect against viral diseases. Moreover, antibody fragments produced in bacteria or plants may provide low cost reagents for immunodiagnosis. OBJECTIVES: In an attempt to develop genetic immunisation against tomato spotted wilt tospovirus (TSWV), we engineered an scFv fragment starting from a monoclonal antibody (mAb) able to recognise an epitope of the glycoprotein G1 conserved among a large number of tospoviruses. After establishing functional expression in bacteria, we aimed to drive expression of this molecule in the secretory pathway of plants. STUDY DESIGN: An antibody phage display expression system was used to isolate the correct VH and VL binding regions from the hybridoma secreting the original mAb. To assess functional expression in plant, we first used an epichromosomal expression vector derived from potato virus X (PVX). In this vector the scFv gene was cloned to produce a cytosolic or a secretory protein. For secretion, the signal sequence derived from the polygalacturonase-inhibiting protein (PGIP) of Phaseolus vulgaris was used. Subsequently, the gene encoding the secretory scFv, was used to transform Nicotiana benthamiana plants. RESULTS: High expression levels of fully active molecule were obtained in Escherichia coli. The engineered molecule retained the binding specificity and dissociation rate constant (k(off)) of the cognate monoclonal antibody. Both PVX-infected and transformed plants expressed fully functional scFv molecules in the secretory pathway. CONCLUSION: This engineered scFv may be valuable for inexpensive diagnosis, for studying the role of the glycoproteins in virus transmission and, possibly, for a 'plantibody'-mediated resistance to tospoviruses.

Amino Acid Sequence↗
PubMed1998

11Beta-hydroxysteroid dehydrogenase expression in first trimester human trophoblasts.

This study evaluated the levels and the enzymatic characteristics of 11beta-hydroxysteroid dehydrogenase activity (11beta-HSD) of chorionic villi isolated from first trimester human placenta. The results demonstrated a predominant expression of the NAD-dependent dehydrogenase isoform (11beta-HSD2) over the NADP-dependent oxoreductase (11beta-HSD1). Thus, in tissue homogenates exogenous NAD increased the conversion of corticosterone to 11-dehydrocorticosterone of about 14-fold while NADP was ineffective. There was no conversion of 11-dehydrocorticosterone to corticosterone either with NADH or NADPH demonstrating the lack of reductase activity. In keeping with these results, RT-PCR analysis indicated a mRNA for 11beta-HSD2 in villous tissue while 11beta-HSD1 mRNA levels were undetectable. In addition, immunohistochemical staining localized the 11beta-HSD2 protein to syncytiotrophoblasts and cell columns of the chorionic villi. These results suggest roles for the trophoblast-associated 11beta-HSD2 oxidative activity in modulating the exposure of the embryo to active glucocorticoids in the early gestation and in regulating trophoblasts invasion of the uterine wall.

11-beta-Hydroxysteroid Dehydrogenases↗
PubMed1997

Molecular mimicry between the rabies virus glycoprotein and human immunodeficiency virus-1 GP120: cross-reacting antibodies induced by rabies vaccination.

The 160-170 sequence of human immunodeficiency virus (HIV)-1 gp120 mimics a nicotinic receptor-binding motif of rabies virus glycoprotein and snake neurotoxins. This sequence has been proposed to be involved in the binding of HIV-1 gp120 to the acetylcholine binding sites of nicotinic receptors. By using biomolecular interaction analysis (BIA) technology we have found that HIV-1 gp120 can bind to detergent-extracted nicotinic receptor from fetal calf muscle. The binding is inhibited by nicotine and by a synthetic peptide reproducing the gp120 160-170 sequence. The molecular mimicry between gp120 and rabies virus glycoprotein is confirmed by cross-reacting antibodies. We have found that vaccination against rabies can induce the production of anti-HIV-1 gp120 antibodies in humans. The cross-reacting antibodies are directed to the gp120 sequence involved in the mimicry with the rabies virus glycoprotein. The cross-reactivity between the rabies virus and HIV-1 has important implications in transfusion medicine. Moreover, the presence of cross-reacting antibodies between the nicotinic receptor binding site of rabies virus glycoprotein and a fragment of HIV-1 gp120 strengthens the hypothesis about the possible role of nicotinic receptors as potential receptors for HIV-1 in the central nervous system.

Antibodies, Viral↗
PubMed1996

Antigenicity of HIV-derived T helper determinants in the context of carrier recombinant proteins: effect on T helper cell repertoire selection.

T helper (Th) epitopes can be included in a recombinant protein with B and CTL epitopes to create more effective immunogens. To determine whether the antigenicity of HIV Th epitopes is preserved in this altered molecular context, human Th clones specific for peptides of HIV gp120 and reverse transcriptase p66 were challenged with recombinant proteins carrying the antigenic epitopes in different sites. We found that a given epitope was recognized by a specific T cell clone only when it was inserted in a particular position of the carrier. However, the permissive position was not the same for all epitopes. Enzymatic excision from a nonpermissive context or insertion of a polyserine spacer between the epitope and the carrier restored antigenicity. Nevertheless, antigenicity was not abolished in a synthetic peptide encompassing the epitope and the neighboring residues from the nonpermissive location. These data suggest that, in this case, the primary sequence of the chimeric protein flanking the HIV peptide is not responsible for loss of antigenicity. Furthermore, constructs carrying the epitope in a given position were recognized by peptide-specific Th clones raised from some individuals, but not from others. We show that this is due neither to individual modes of processing nor to the use of distinct major histocompatibility complex MHC class II restriction elements, but rather that it is related to the fine specificity of the clones. To study the effect of epitope context on selection of T cell repertoire in a naive individual, T cell lines were generated in vitro by stimulation with different peptide constructs. This resulted in the induction of diverse clonotypes defined by the pattern of recognition of different constructs, by T cell receptor V beta gene usage and by fine epitope mapping.

AIDS Vaccines↗
PubMed1993

Characterization of immunoreactive octapeptides of human-cytomegalovirus gp58.

We have mapped continuous epitopes, for positions 591-673 of the human cytomegalovirus 58-kDa glycoprotein using overlapping synthetic peptides and human sera. This region contains a fragment previously described as including the dominant site for induction of human-cytomegalovirus antibodies. Since the selected sequence is highly conserved among herpes viruses, we have considered the possible presence of antigenic cross-reactivity, particularly with the Epstein-Barr virus. Several peptides in the studied region were antigenic and two main continuous epitopes have been identified. Serological cross-reactions observed with Epstein-Barr virus are discussed, focusing on the possible implications of structural features and sequence similarity between human-cytomegalovirus and Epstein-Barr-virus glycoproteins.

Amino Acid Sequence↗