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Biomedical subjects

S Muller

Publications and source records attributed to S Muller.

At least 289 records · Page 16Linked to original sources
PubMed1990

Fluorescence depolarization method in the study of dynamic properties of blood cells.

Fluorescence polarization is the most commonly used method to approach a property of cell membrane, the so-called "fluidity". Whether time resolved determinations may be of potential interest to get precise information on the behaviour of fluorescent probes incorporated into biological membranes, steady state measurements are still the most accessible for biologists. Steady-state anisotropy value may be considered as a semi-quantitative indication of the cohesion of the lipid chains. However, meaningful interpretation of the anisotropy values requires a careful sample preparation and a suitable use of fluorescent probes. This paper reviews the properties and uses of several hydrophobic membrane fluidity probes. In the case of intact cells, the potential interest of the association of fluorescence polarization with quenching fluorescence method in giving information on the "actual" membrane fluidity is outlined.

Diphenylhexatriene↗
PubMed1990

Analysis of factors affecting human hybridoma production.

Human hybridomas were produced by fusion of the GM 4672 cell line with lymphocytes from the peripheral blood, spleen, and bone marrow of patients with systemic lupus erythematosus. Lymphocytes were also obtained from normal human fetal liver of 12 weeks' gestation. The influence of anatomical source, fusion ratio, pre-stimulation with pokeweed mitogen, HLA match, and disease activity at the time of fusion was studied. Supernatants were screened for immunoglobulin secretion and binding to DNA, cardiolipin, poly(ADP-ribose), and histones by enzyme-linked immunoassay. A total of 28 fusions from 14 donors and 6 fusions with fetal lymphocytes were performed. The spleen was found to be the most efficient source of lymphocytes, with a fusion ratio of 1:1 resulting in a maximum yield of 27 clones/10(7) lymphocytes fused. HLA matching was a factor influencing the outcome with HLA A2 matching being the most important. Pre-stimulation with pokeweed mitogen did not improve the fusion frequency, and fusions using lymphocytes from patients with active disease were only marginally more successful. Over 95% of clones secreted immunoglobulin; autoreactivity was found against DNA, histones, cardiolipin, and poly(ADP-ribose). All hybrids with autoreactivity secreted IgM.

Antibodies, Monoclonal↗
PubMed1990

[Importance of membrane fluidity determination].

Translational motions of lipids and proteins and molecular motions within the lipid hydrocarbon chains of biological membranes can be approached by spectroscopic methods. The electron spin resonance (ESR) spectra of spin labels bound on proteins or grafted on fatty acids and incorporated into biological membranes undergo characteristic changes which may be resolved in terms of modifications of membrane environment. However, the method is still scarcely used in routine clinical studies. In contrast, fluorescence methods such as intermolecular excimers or fluorescence polarization might join the ranks of routine analyses. The labeling of lipid compartments with fluorescent probes and the study of their spectroscopic properties give informations on the cohesion of their immediate environment. Polyenic molecules (DPH and TMA-DPH) which are located in different lipid compartments characterize deep and superficial areas of cell membrane, respectively. A set of probes in which a 9-anthroyloxy group is attached to different positions of a long chain fatty acid provides a means of measuring a fluidity gradient into membrane bilayer. Thus, these fluorescence methods which are simple and rapid represent a semi-quantitative approach of the so called "membrane fluidity". Modifications in membrane fluidity can control the expression of proteins, receptors exposed on cell surface and alter functional properties of cells. Moreover, pathological processes can also be related to fluidity modifications. In particular, in hypertension and vascular diseases, a decrease in membrane fluidity has been shown in platelets and red cells. Nevertheless, further investigations combining biophysical, biochemical and immunological methods are needed to determine the exact relations between membrane fluidity, classical rheological properties and cell functions.

Biophysical Phenomena↗
PubMed1989

The effect of poly(ADP-ribosyl)ation on native and H1-depleted chromatin. A role of poly(ADP-ribosyl)ation on core nucleosome structure.

The effect of poly(ADP-ribosyl)ation on native and H1-depleted chromatin was analyzed by gel electrophoresis, electron microscopy, and velocity sedimentation. In parallel, the interaction of automodified poly(ADP-ribose) polymerase with native and H1-depleted chromatin was analyzed. In H1-depleted chromatin histone H2B becomes the major poly(ADP-ribose) histone acceptor protein, whereas in native chromatin histone H1 was the major histone acceptor. Poly(ADP-ribosyl)ation of H1-depleted chromatin prevented the recondensation of polynucleosomes reconstituted with exogenous histone H1. This is probably due to the presence of modified poly(ADP-ribose) polymerase and hyper(ADP-ribosyl)ated histone H2B. Indeed, about 40% of the modified enzyme remained associated with H1-depleted chromatin, while less than 1% of the modified enzyme was bound to native chromatin. The influence of poly(ADP-ribosyl)ation on the chromatin conformation was also studied at the level of nucleosome in using monoclonal and polyclonal antibodies specific for individual histones and synthetic peptides of histones. In native chromatin incubated in the presence of Mg2+ there was a drop in the accessibility of histone epitopes to monoclonal and polyclonal antibodies whereas upon poly(ADP-ribosyl)ation their accessibility was found to remain even in the presence of Mg2+. In poly(ADP-ribosyl)ated H1-depleted chromatin an increased accessibility of some histone tails to antibodies was observed.

Animals↗
PubMed1989

A branched, synthetic octapeptide of ubiquitinated histone H2A as target of autoantibodies.

Two peptides of eight (T2) and 10 (T1) residues corresponding to the branched moiety of ubiquitinated histone H2A have been synthesized and used for raising specific antibodies in rabbits. Antisera to peptide T1 reacted in ELISA with T1 and with H2A but not with ubiquitin; antisera to peptide T2 reacted with T2 but not with H2A or ubiquitin. When tested in immunoblotting, both peptide antisera reacted with ubiquitinated H2A but not with unconjugated H2A or with ubiquitin. Sera from patients with systemic lupus erythematosus (SLE) were shown previously to react with ubiquitin in ELISA and immunoblotting. When tested for their ability to react in ELISA with synthetic peptides T1 and T2, 96% of the SLE sera (diluted 1:500) that recognized ubiquitin also reacted with peptide T2. Of the SLE sera that did not react with ubiquitin, only 13% possessed antibodies able to bind peptide T2. Antibodies from seven SLE sera, purified on a T2-immunoadsorbent column, were also able to react either with H2A, and in three cases also with ubiquitin.

Amino Acids↗
PubMed1989

Inhibition of T cell response with peptides is influenced by both peptide-binding specificity of major histocompatibility complex molecules and susceptibility of T cells to blocking.

Synthetic peptides corresponding to sequences 46-62 and 51-62 of mouse lysozyme and 46-61 of hen egg-white lysozyme (HEL) were used as competitors in a variety of T cell responses. The competitors, according to their binding specificity for major histocompatibility complex (MHC) were expected to inhibit T cell responses restricted to I-Ak, but not those restricted to I-Ad, I-Ek molecules. In competition experiments with T cell hybridomas, the poor binder I-Ed molecule required 10- to 15-fold higher competitor concentrations than the good binder I-Ak molecule to achieve 50% inhibition of antigen presentation. Similarly, the nonresponder state of H-2d mice to HEL peptide 46-61 could be overcome by increasing the immunizing dose, and proliferative T cell responses to different antigens in association with a variety of class II MHC molecules could be blocked by the mouse lysozyme and HEL peptides. Thus, the capability of some and failure of other MHC molecules to bind certain peptides appeared quantitative, rather than of an all or none nature, in these experimental systems. The susceptibility of uncloned T cell lines to peptide competitors was found to decrease with time. Lines maintained by repeated restimulation with antigen and APC, but without exogenous interleukin 2, acquired resistance within weeks. In contrast, T cell clones retained their susceptibility to peptide competitors over a long period of time. The latter data raise the possibility that a competition between ubiquitous (self) peptides and foreign antigen may result in the selection of T cells that have high avidity for the activating antigen-MHC complex, and are thus relatively resistant to competition at the level of antigen presentation.

Amino Acid Sequence↗
PubMed1989

Why peptides? Their possible role in the evolution of MHC-restricted T-cell recognition.

The peptide-presenting function of major histocompatibility complex (MHC) molecules permits pathogenic microorganisms to evade the host's immune system in two different ways: first, by escape of pathogen-derived antigenic peptides from presentation, and second, by molecular mimicry, that is resemblance between MHC-bound self and foreign peptides. These two mechanisms could have served as selective pressures in the evolution of the MHC. In this article, Zoltan Nagy and colleagues propose that escape from presentation selects for one or a few MHC molecules with the capacity to bind a broad range of different peptides. In contrast, molecular mimicry is considered to be the driving force for MHC diversification, that is it increases the number (polymorphism) and selectivity of peptide-binding sites.

Animals↗
PubMed1989

Immunocytochemical localization of histones H2B, H3 and H4 in pronuclei and four-cell stages of porcine embryos. Preliminary results.

In this preliminary work, using pig embryos ultrastructural immunocytochemistry with polyclonal antibodies against purified histones was used to demonstrate both their localization and the time of their appearance in pronuclei, from 15 h after ovulation (pronuclear stage) to 48 h postinsemination (4-cell stage). In pronuclei, the histones H2B, H3, and H4 were located in the heterochromatin as soon as it appeared. Usually, one of the pronuclei seemed to be more heavily labelled. The chromatin facing the zone of pronuclear contact formed a bowl-shaped region in each pronucleus heavily labelled for these histones. The so-called pseudo-nucleoli were present in both pronuclei and contained H2B. In 4-cell stages, the labelling intensities of heterochromatin for H2B, H3 and H4 were equal in all the nuclei. H2B was still evident in the pseudo-nucleoli, but in a lower quantity than before. The condensed chromatin located either under the nuclear envelope or surrounding the pseudo-nucleoli was heavily labelled for H2B, H3 and H4.

Animals↗
PubMed1989

Serological abnormalities, including common idiotype PR4, in families with rheumatoid arthritis.

A broad range of autoreactivity among a group of 12 French patients with rheumatoid arthritis (RA) and 58 of their healthy first degree relatives has been identified. Over 15% of the patients were found to have antibodies to ssDNA, histone H1, H2A, and H2bB. Among the relatives, IgG and IgM rheumatoid factor and antibodies to ssDNA, H2A, and H4 were present in more than 10%. Even more remarkable, a common anti-DNA antibody idiotype designated PR4, known to be present in 70% of patients with systemic lupus erythematosus (SLE), was found in approximately 30% of both patients with RA and their healthy relatives. This is quite different from its lack of increased expression in relatives of patients with SLE and suggests that in the family members of those with RA a particular combination of environmental influence on germline gene expression is responsible.

Antibodies, Anti-Idiotypic↗
PubMed1989

Significance of venous and lymphatic invasion in malignant polyps of the colon and rectum.

Three hundred and sixty seven neoplastic colorectal polyps removed at endoscopy of which 34 were complicated by invasive carcinoma, were reviewed clinically and histologically to assess the prevalence and clinical significance of venous and or lymphatic invasion. Traditional stains for histological assessment were supplemented by immunohistochemical methods. Venous and or lymphatic invasion was present in six cases (17.6%), with a statistically significant association with recurrent carcinoma or Dukes's C carcinoma in polyps otherwise regarded as completely excised. The presence or absence of venous and or lymphatic invasion in malignant polyps should be documented as if present, further treatment is indicated. A combination of haematoxylin and eosin and elastic-van Gieson stains will usually identify the presence of vascular invasion. Where a discrepancy arises, however, additional immunohistochemical stains may be of value.

Colon↗
PubMed1989

Reactivity of autoantibodies in systemic lupus erythematosus with synthetic core histone peptides.

The specificity of autoantibodies present in the serum of 151 patients with systemic lupus erythematosus (SLE) was investigated by ELISA using as antigen individual histones as well as 17 different core histone synthetic peptides. Many of the sera reacted with four terminal peptides (residues 1-21 and 130-135 of H3, 1-29 of H4 and 1-25 of H2B) while fewer reacted with internal peptides (residues 65-85 of H2A and 40-55 of H3). Of the 151 SLE sera, 88% reacted with one or more of the six core histone peptides whereas only 57% reacted with one or more of the complete core histone molecules. Antibodies to mononucleosomes from chicken erythrocytes were also prepared in rabbits. The rabbit antisera were tested by ELISA using as antigen chromatin subunits, native and denatured DNA, individual histones and 23 natural and synthetic peptides of histones. The antinucleosome antibodies were found to recognize the same peptide fragments as those recognized by the SLE sera.

Animals↗
PubMed1989

Ultrastructural distribution of histones within Ehrlich tumor cell nucleoli: a cytochemical and immunocytochemical study.

We investigated the ultrastructural distribution of histones within Ehrlich tumor cell nucleoli by means of three cytochemical methods and by a Lowicryl post-embedding immunogold labeling procedure involving anti-histone (H2B, H3, H4) antisera as well as antibodies to synthetic peptides of histones. With the two technical approaches, labeling was particularly concentrated over the perinucleolar chromatin and over its intranucleolar invaginations which penetrate the nucleolar body and come in close contact with the fibrillar centers. Furthermore, the high-resolution immunocytochemical technique revealed the presence of a small amount of the three histones in the fibrillar centers, preferentially located towards their peripheral regions. In addition, colocalization of DNA at all the histone-positive sites could be visualized after double immunogold staining using a monoclonal anti-DNA antibody and the anti-histone antisera. These results appear to indicate that all the DNA detected within the nucleolus was associated with histones. This finding suggests that the ribosomal DNA, including transcriptionally active genes, is bound to histones.

Animals↗
PubMed1989

Phagocytosis and membrane fluidity: application to the evaluation of opsonizing properties of fibronectin.

The uptake of particles by phagocytic cells involves an increase in the membrane fluidity determined by steady-state fluorescence polarization. Binding and endocytosis of target particles is in vivo enhanced by humoral factors called opsonins. In this work, fluorescence polarization was used to detect in vitro the opsonic activity of a plasma protein: fibronectin. The assay is based on the analysis of membrane fluidity variations following the uptake of gelatinized latex beads by phagocytic cells in the presence or in the absence of fibronectin. Using TMA-DPH as fluorescent probe, it was observed that the increase in membrane fluidity was enhanced in presence of fibronectin and depended upon the enhanced in presence of fibronectin and depended upon the opsonic activity was related to the integrity of the molecule. Using this method, the opsonic activity of various plasmas could be also determined.

Cell Line↗
PubMed1989

[Cell cycle analysis of hybridoma cultures: study by cytofluorimetry].

An hybridoma cell line cultivated in flasks has been used as a model to study the loss of cell viability in high density cell cultures. Cell cycle analysis by cytofluorimetry has shown that a new hypochromosomic cell population appeared as soon as the viability began to decrease. However there is no evidence that this new population is constituted of dead cells.

Animals↗
PubMed1988

In vivo competition between self peptides and foreign antigens in T-cell activation.

Cytotoxic and helper T lymphocytes recognize foreign antigen in the form of short peptides associated with class I and class II major histocompatibility complex (MHC) molecules, respectively. A recent study of the three-dimensional structure of a class I MHC molecule revealed a cleft formed by the amino-terminal half of the protein, which could serve as the binding site for these peptides. Because an individual possesses only a limited set of different MHC molecules, each molecule of this set must have the ability to bind a large number of different peptides in order to ensure full immunocompetence. Thus, it can be anticipated that peptides with unrelated sequences compete for binding to the same MHC molecule, and, indeed, this has been shown to occur in vitro. We therefore decided to see whether such competition could also regulate the cell responses in vivo. We have found that a synthetic peptide corresponding to residues 46-62 of mouse lysozyme, although not immunogenic itself, effectively inhibits the priming for T-cell responses when injected into mice together with foreign protein or peptide antigens. The inhibition observed strictly correlates with the capacity of the competitor to bind to the particular MHC molecule presenting the foreign antigen, and its extent depends on the molar ratio between antigen and competitor.

Animals↗
PubMed1988

The double reactivity of a human monoclonal rheumatoid factor to IgG and histones is related to distinct binding sites.

The structural basis of the double reactivity of a human monoclonal rheumatoid factor (RF) with both human IgG and histones H1 and H3 was investigated by means of competitive inhibition experiments. The monoclonal RF binding to solid-phase histones was inhibited by increasing concentrations of heat-aggregated IgG. However, increasing concentrations of purified histones were almost unable to reduce the RF binding to solid-phase IgG. Inhibition of antigen binding with two murine monoclonal anti-idiotopes reacting with distinct idiotopes on the monoclonal RF indicated that the fixation to the different antigens was mediated by distinct binding sites. This result was confirmed by showing the selective sensitivity to mild acid treatment of the histone binding site but not of the IgG binding site. This report provides a structural basis for the existence of polyfunctional combining regions on a human autoantibody.

Antibodies, Monoclonal↗
PubMed1988

Po, MBP, histone, and DNA levels in sciatic nerve. Postnatal accumulation studies in normal and trembler mice.

We studied the quantitative changes in proteins (total, Po, MBP, and histones) and DNA from sciatic nerves of normal and Trembler mice during postnatal development. Polyacrylamide gel electrophoresis and immunoblotting procedures allowed an accurate characterization of Po, MBP, and histones, as well as the comparison of their respective amounts from d 2 to d 120 after birth. It was found that 1. The immunoblotting procedure ascertains the presence of Po in the sciatic nerve of Trembler. In the 2-d-old mice, Po is detected in essentially similar amounts in Trembler and normal PNS, whereas its level in adult mutant sciatic nerves is never greater than 20% of the control. The sharp increase in Po levels observed during the third week in the normal nerves is not observed in those of the mutant; 2. MBP species are at most 4% of the control in the 10- to 12-d-old Trembler mice, whereas they were not detectable in adult nerves. The distribution of the different MBP species is the same in both mutant and control mice; 3. In normal mice, Po and MBP accumulate at similar rates, but the 14 kDa MBP accumulates faster than the 18.5 kDa MBP; and 4. Histone and DNA contents decrease 3- to 5-fold in normal nerves, whereas they remain constant, or increase slightly, in the mutant.

Animals↗