SEARCH · PubMed Health

Results for “Class”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 829 records · Page 46Linked to original sources

PubMed2006

Mutational analysis of class A and class B penicillin-binding proteins in Streptococcus gordonii.

High-molecular-weight (HMW) penicillin-binding proteins (PBPs) are divided into class A and class B PBPs, which are bifunctional transpeptidases/transglycosylases and monofunctional transpeptidases, respectively. We determined the sequences for the HMW PBP genes of Streptococcus gordonii, a gingivo-dental commensal related to Streptococcus pneumoniae. Five HMW PBPs were identified, including three class A (PBPs 1A, 1B, and 2A) and two class B (PBPs 2B and 2X) PBPs, by homology with those of S. pneumoniae and by radiolabeling with [3H]penicillin. Single and double deletions of each of them were achieved by allelic replacement. All could be deleted, except for PBP 2X, which was essential. Morphological alterations occurred after deletion of PBP 1A (lozenge shape), PBP 2A (separation defect and chaining), and PBP 2B (aberrant septation and premature lysis) but not PBP 1B. The muropeptide cross-link patterns remained similar in all strains, indicating that cross-linkage for one missing PBP could be replaced by others. However, PBP 1A mutants presented shorter glycan chains (by 30%) and a relative decrease (25%) in one monomer stem peptide. Growth rate and viability under aeration, hyperosmolarity, and penicillin exposure were affected primarily in PBP 2B-deleted mutants. In contrast, chain-forming PBP 2A-deleted mutants withstood better aeration, probably because they formed clusters that impaired oxygen diffusion. Double deletion could be generated with any PBP combination and resulted in more-altered mutants. Thus, single deletion of four of the five HMW genes had a detectable effect on the bacterial morphology and/or physiology, and only PBP 1B seemed redundant a priori.

DNA Mutational Analysis↗

PubMed1990

Variation in expression of class 1 and class 5 outer membrane proteins during nasopharyngeal carriage of Neisseria meningitidis.

Accidental nasopharyngeal colonization of a laboratory worker by a human disease isolate of Neisseria meningitidis allowed us to examine the variation in expression of outer membrane components and the host humoral response over time. There were quantitative differences in class 1 outer membrane protein expression in nasopharyngeal isolates obtained at different times. Isolates also showed phase variation of all four class 5 outer membrane proteins produced by the colonizing strain. After colonization, we detected new host serum immunoglobulin G antibodies directed against class 1, class 5, and H.8 outer membrane proteins.

Bacterial Outer Membrane Proteins↗

PubMed1989

Combined anti-arrhythmic therapy with class 1 and class 3 drugs.

This study was designed to investigate the differences in efficacy between 3 different combinations of amiodarone and a class 1 anti-arrhythmic drug (one from each class). The purpose was to determine whether the known differing electrophysiological properties of class 1 drugs result in any particular one making a superior combination with the class 3 drug amiodarone. Eight patients were studied in a randomized single blind cross-over trial. Amiodarone and flecainide proved to be the superior combination producing a significantly greater reduction in mean ectopic counts/24 hours than the amiodarone/mexilitene combination (1,286 vs 3,243; P less than 0.05) or the amiodarone/disopyramide combination (3,795; P less than 0.05). All 3 combinations reduced mean ectopic counts from the baseline value (8,729), but this was only significant for amiodarone/flecainide (P less than 0.01) and amiodarone/mexilitene (P less than 0.05). In addition the amiodarone/flecainide combination produced a significant reduction in complex forms of arrhythmia with ventricular tachycardia abolished in all cases, which was not achieved by any other combination.

Adult↗

PubMed1994

Effects of heptanol, class Ic, and class III drugs on reentrant ventricular tachycardia. Importance of the excitable gap for the inducibility of double-wave reentry.

BACKGROUND: Double-wave reentry (DWR) can be a mechanism for acceleration of ventricular tachycardia (VT) with a large excitable gap (EG). The purpose of this study was to determine the effects of heptanol, class Ic, and class III drugs on the inducibility of DWR. METHODS AND RESULTS: In 11 Langendorff-perfused rabbit hearts, a thin ring of anisotropic left ventricular epicardium was created by a cryoprocedure. VT with a revolution time of 180 +/- 26 milliseconds and an EG of 106 +/- 8 milliseconds was induced by incremental pacing. During control, entrainment with 10 stimuli at a 99 +/- 15-millisecond interval terminated VT in seven hearts. In four hearts VT was accelerated from 205 +/- 24 to 115 +/- 14 milliseconds by introduction of a second circulating wave in the ring. In the seven VTs that could not be accelerated, 0.5 mumol/L Org7797 (class Ic) and 1.0 mmol/L heptanol (uncoupling agent) prolonged the cycle length of VT by 32% and 37%, respectively. Because the refractory period (RP) only increased by 11%, the EG prolonged by 71% and the ratio between EG and RP was increased from 0.66 to 1.00. Under these conditions, DWR could be induced in all seven hearts. In the four VTs that could be accelerated during control, administration of the class III drug D-sotalol (35 mumol/L) only slightly slowed VT by 6%. Because the RP was prolonged by 15%, the ratio between the EG and the RP decreased from 0.76 to 0.63. Entrainment now failed to accelerate VT in two of four hearts, whereas in the two other hearts, double-wave reentry self-terminated within eight cycles. CONCLUSIONS: Drugs that increase the ratio of EG and RP enhance the susceptibility to acceleration of VT, whereas drugs that decrease this ratio prevent induction of sustained double-wave reentry.

Alcohols↗

PubMed1989

Generalization of student question asking from special class to regular class settings.

This study investigated the use of videotaped exemplars taken from a regular education mathematics class to teach generalization of question asking. Three mildly handicapped fourth-grade students who asked few questions in the regular education class served as subjects. Measures of the frequency of question asking and percentage of accuracy on assignments were obtained in the regular class. Treatment included showing the videotapes to the subjects, structuring opportunities for rehearsing question asking, and providing feedback. The results showed training procedures implemented in the learning resource room were effective in increasing the level of participants' question asking and in improving their scores on assignments in the regular mathematics class.

Behavior Therapy↗

PubMed2000

Opposite change with ischaemia in the antifibrillatory effects of class I and class IV antiarrhythmic drugs resulting from the alteration in ion transmembrane exchanges related to depolarization.

It is known that class I antiarrhythmic drugs lose their antifibrillatory activity with severe ischaemia, whereas class IV antiarrhythmic drugs acquire such activity. Tachycardia, which is also a depolarizing factor, has recently been shown to give rise to an alteration of ion transmembrane exchanges which is particularly marked in the case of calcium. This leads one to wonder if the change in antifibrillatory activity of antiarrhythmic drugs caused by ischaemia depends on the same process. The change in antifibrillatory activity was studied in normal conditions ranging to those of severe ischaemia with a class I antiarrhythmic drug, flecainide (1.00 mg x kg(-1) plus 0.04 mg x kg(-1)x min(-1), a sodium channel blocker, and a class IV antiarrhythmic drug, verapamil (50 microg x kg(-1) plus 2 microg x kg(-1) x min(-1)), a calcium channel blocker. The experiments were performed in anaesthetized, open-chest pigs. The resulting blockade of each of these channels was assessed at the end of ischaemic periods of increasing duration (30, 60, 120, 180, 300, and 420 s) by determining the ventricular fibrillation threshold (VFT). VFT was determined by means of trains of diastolic stimuli of 100 ms duration delivered by a subepicardial electrode introduced into the myocardium (heart rate 180 beats per min). Ischaemia was induced by completely occluding the left anterior descending coronary artery. The monophasic action potential was recorded concurrently for the measurement of ventricular conduction time (VCT). The monophasic action potential duration (MAPD) varied with membrane polarization of the fibres. The blockade of sodium channels by flecainide, which normally raises VFT (7.0 +/- 0.4 to 13.8 +/- 0.8 mA, p < 0.001) and lengthens VCT (28 +/- 3 to 44 +/- 5 ms, p < 0.001), lost its effects in the course of ischaemia. This resulted in decreased counteraction of the ischaemia-induced fall of VFT and decreased aggravation of the ischaemia-induced lengthening of VCT. The blockade of calcium channels, which normally does not alter VFT (between 7.2 +/- 0.6 and 8.4 +/- 0.7 mA, n.s.) or VCT (between 30 +/- 2 and 34 +/- 3 ms, n.s.), slowed the ischaemia-induced fall of VFT. VFT required more time to reach 0 mA, thus delaying the onset of fibrillation. Membrane depolarization itself was opposed as the shortening of MAPD and the lengthening of VCT were also delayed. Consequently there is a progressive decrease in the role played by sodium channels during ischaemia in the rhythmic systolic depolarization of the ventricular fibres. This reduces or suppresses the ability of sodium channel blockers to act on excitability or conduction, and increases the role of calcium channel blockers in attenuating ischaemia-induced disorders.

Action Potentials↗

PubMedDate not supplied

Composite matrix for large, non-wedgeable Class III or Class IV preparations with gingival or subgingival margins.

Dentists sometimes are required to place a matrix to restore large Class III or Class IV preparations that have gingival or subgingival margins or are prepared in rotated or malposed teeth. In these situations, dentists sometimes cannot place a wedge between the prepared tooth and a neighboring tooth because the wedge cannot engage enough interproximal tooth structure to firmly anchor both itself and a matrix strip. This article presents a technique for placing a matrix around such large, non-wedgeable Class III or Class IV preparations.

Composite Resins↗

PubMed1991

Class I and class II HLA antigens in a homogeneous Argentinian population with Whipple's disease: lack of association with HLA-B 27.

The prevalence of class I and class II HLA antigen was analyzed in 14 patients (12 males, two females) with Whipple's disease, diagnosed an average of 9.7 yr (range 6 months to 25 yr) before the typing. They were compared with 174 healthy control subjects of the same geographic area in Argentina. Class I antigens (locus A, B, C) were studied by lymphocytotoxic test, and class II antigens (locus DR, DQ) were detected by the double immunofluorescence technique. HLA-B27 was positive in one patient (7.7%) and in 4% of the control population. No significant association was found with the antigens tested. We observed no difference in the clinical picture or in the frequency of arthralgias, compared with those reported in the literature. Our data suggest that there is no conclusive proof of an association between HLA-B27 and Whipple's disease.

Aged↗

PubMed1986

Human class II antigens. Implication of carbohydrate in the determinants recognized by several antihuman class II monoclonal antibodies.

Several monoclonal antibodies (McAbs) to human class II antigens are described; three of these recognize monomorphic epitopes, and two are polymorphic. The biochemical nature of the reactive epitopes was investigated by determining the binding ability of the McAbs to protease- or glycosidase-treated antigen preparations. Both of the polymorphic McAbs recognized protein-defined epitopes. However, for one of the antibodies F5C9, carbohydrate residues were also implicated. The extent of carbohydrate involvement varied with class II antigens of different DR specificity, suggesting that the proximity of the F5C9 epitope to carbohydrate side chains can vary. One of the three monomorphic McAbs recognized a protein-defined epitope, while the other two antibodies detected epitopes in which carbohydrates were involved. These results indicate that both protein and carbohydrate residues of the human class II antigens can influence the epitopes recognized by murine McAbs. This could explain some of the apparent complexities of the anti-human class II McAbs.

Antibodies, Monoclonal↗

PubMed1985

Delineation of three subsets of class I human T antigens (HTA) on Molt-4 cells: serologic and regulatory relationship to HLA class I antigens.

Three subsets of class I human T antigens (HTA) were serologically identified on the surface of the Molt-4 T lymphoma cell line. The HTA 1 subset is defined by NAI/34, D47, or 10H3.9 cross-reactive m.Ab. and by BL6 m.Ab. The HTA 2 and HTA 3 subsets are defined by M241 and 4A7.6 m.Ab., respectively. We obtained no evidence of any additional HTA subset. The different HTA antigens share only few epitopes with human leukocyte antigens (HLA-A, -B, and -C). Interestingly, these epitopes all belong to the same cluster defined on HLA class I molecules, but differ from one HTA subset to another. These results would therefore suggest that HTA and HLA class I antigens display a limited structural homology, but have a conserved epitopic area whose detailed structure differs for each HTA subset. Furthermore, the cell surface expression of each HTA class I molecule type is differently enhanced by natural interferon (IFN)-alpha or -gamma. This result additionally supports the serologic delineation of HTA subsets, and suggests that the corresponding genes in Molt-4 cells, are subjected to distinct regulations.

Animals↗

PubMedDate not supplied

Class definition and mixture class definition by means of construction of convex hull boundaries: application to analysis for animal fat adulteration.

A visual classification technique based on the construction of convex hull boundaries in combination with a principal component analysis is described. This combined technique was evaluated in the situation in which a distinction has to be made between 2 pure animal fat classes and the corresponding mixture class. In the first instance, a principal component analysis is carried out to ensure the 2-dimensional and thus visual aspect of the technique. Convex hulls are then constructed in the 2-dimensional principal component plane to delimit the boundaries of the different classes to be defined. The effectiveness of the constructed hull boundaries in the definition of class-membership was investigated by means of the classification of different simulated test samples. The results show that, at least for the tested applications, the technique is valid, although some false positive classifications occur. The detection of outliers especially seemed to pose problems. Therefore, some propositions are made of how to refine the developed hull technique to enhance the classification results.

Animals↗

PubMed1988

Lack of HLA class I and class II antigens on human preimplantation embryos.

The expression of HLA Ag on polyploid early human embryonic stages, obtained in an in vitro fertilization and embryo transfer program, was investigated by indirect immunofluorescence tests using a panel of mAb. Neither HLA class I Ag, beta 2-microglobulin, nor HLA class II molecules could be detected on blastomers. The zona pellucida also lacked these Ag, but granulosa cells expressed HLA class I Ag, beta 2-microglobulin, and HLA class II Ag. These results make it likely that the absence of HLA Ag is one of the mechanisms involved in protecting the implanting embryo from rejection by the immunocompetent mother.

Antibodies, Monoclonal↗

PubMed1983

Domain structures of cell surface glycopeptides encoded by class I and class II beta genes of the major histocompatibility complex.

Published sequence data of MHC genes, cDNAs and MHC products were analyzed for their sequence homologies. Alignment statistics revealed that class I gene products consist of four mutually homologous domains, and that class II beta gene products is composed of three mutually homologous domains. Not only extracellular domains but also newly discovered C-terminal shorter domains of class I and class II beta gene products were found to have evolved from a one-domain-long beta 2-microglobulin-like protein by repeated exon duplications and splittings.

Animals↗

PubMed1994

Characterization of peptide binding to the murine MHC class I H-2Kk molecule. Sequencing of the bound peptides and direct binding of synthetic peptides to isolated class I molecules.

Peptides that are bound by the murine class I MHC molecule H-2Kk have been isolated and sequenced. The initial step in the fractionation was affinity column isolation of the peptide-class I complex from either RDM-4 or x5563 tumor cell lines. Acid denaturation of the complex followed by HPLC fractionation of the peptides allowed us to sequence individual peptides, as well as pools of peptides. To date, a total of 10 sequences have been characterized, and all were 8 mers. The sequences were variable except for glutamic acid in the second position (P2) and isoleucine in the eighth (P8), which were highly conserved. To further study peptide binding to H-2Kk, a competitive binding assay consisting of the immobilized histocompatibility protein and a biotinylated self-peptide for signal generation was developed. A complete set of single-alanine variants for this one self-peptide was tested in the assay, demonstrating that substitution at P2 and P8 markedly decreased the affinity for the class I molecule; alanine at position 3 had an intermediate effect on binding. A comparison of the identified self-peptides for binding to H-2Kk showed that they differed in affinity by more than one order of magnitude. Influenza virus nucleoprotein peptide, SDY EGR LI, associated with the plate-bound class I molecule, and the resulting MHC-peptide complex could trigger TNF release by influenza-primed CTLs. This result demonstrated the functional activity of the plate-bound H-2Kk-peptide complex.

Amino Acid Sequence↗

PubMed1993

Molecular basis of the alcohol dehydrogenase-negative deer mouse. Evidence for deletion of the gene for class I enzyme and identification of a possible new enzyme class.

The molecular basis of the alcohol dehydrogenase (ADH)-negative deer mouse (Peromyscus maniculatus) has been investigated. Several classes of mammalian ADHs have been recognized based upon biochemical and structural properties. ADH cDNA clones identified by hybridization to a mouse class I ADH cDNA clone were obtained from a deer mouse ADH-positive liver cDNA library. This cDNA has been identified as being a class I sequence and represents the deer mouse Adh-1 gene. An additional cDNA sequence identified in both the ADH-positive and -negative deer mouse cDNA libraries was identified by weak cross-hybridization to the mouse cDNA. This cDNA encodes an amino acid sequence representing a new class of mammalian ADH, and the deer mouse gene for this ADH is named Adh-2. ADH-negative deer mice do not produce mRNA, that is detected by the Adh-1 cDNA probe. However, both stocks of deer mice produce high levels of Adh-2 mRNA in liver. Southern analysis using an essentially full-length Adh-1 cDNA probe has shown that the Adh-1 gene is deleted in the ADH-negative mice. Biochemical analysis of enzyme activity suggests at least three ADH polypeptides are expressed in different tissues and have somewhat different substrate specificities, as in the mouse.

Alcohol Dehydrogenase↗

PubMed1996

Supramolecular complexes of MHC class I, MHC class II, CD20, and tetraspan molecules (CD53, CD81, and CD82) at the surface of a B cell line JY.

The results of previous biochemical studies indicated that a fraction of MHC class II proteins is associated with four proteins of the tetraspan family, CD37, CD53, CD81, and CD82, and possibly with other membrane components, at the surface of JY B lymphoma cells. In the present communication we used a biophysical technique, namely the flow cytometric energy transfer method, to demonstrate the proximity of these molecules at the surface of the cells. Significant energy transfer (and, therefore, proximity within the 2-10 nm range) was observed between fluorescently labeled mAbs to DR, DQ, and the tetraspan molecules CD53, CD81, and CD82. Moreover, two other B cell surface molecules, CD20 and MHC class I, were found to be close to each other and to MHC class II and the tetraspan proteins, based on the observed high energy transfer efficiencies between the relevant fluorescently labeled mAbs. The character of simultaneous energy transfer from CD20, CD53, CD81, and CD82 to DR suggests that all these molecules are in a single complex with the DR molecules (or a complex of several DR molecules) rather than that each of them is separately associated with different DR molecules. Based on these data and previous biochemical results, a model is proposed predicting that the B cell membrane contains multicomponent supramolecular complexes consisting of at least two MHC class I and at least one DR, DQ, CD20, CD53, CD81, and CD82 molecules. Closer analysis of the energy transfer efficiencies makes it possible to suggest mutual orientations of the components within the complex. Participation of other molecules, not examined in this study (CD19 and CD37), in these supramolecular structures cannot be ruled out. These large assemblies of multiple B cell surface molecules may play a role in signaling through MHC molecules and in Ag presentation to T cells.

Antibodies, Monoclonal↗

PubMed1998

MHC class II-associated invariant chain peptide replacement by T cell epitopes: engineered invariant chain as a vehicle for directed and enhanced MHC class II antigen processing and presentation.

Proteolysis of the invariant chain (li) leads to the generation of abundant MHC class II-associated invariant chain peptides (CLIP), which bind in the MHC class II binding groove via supermotifs in a manner similar to that of antigenic peptides. We have engineered an li vector with the capacity to express any antigenic peptide of interest instead of CLIP, for T cell stimulation. When peripheral blood mononuclear cells (PBMC) were pulsed with li hybrids encoding T cell epitopes of tetanus toxin or acetylcholine receptor, stimulation of T cells was dramatically enhanced compared to stimulation after priming with either the native or recombinant proteins. Site-specific insertion of antigenic sequences into the CLIP region promoted enhanced antigenicity of li hybrids which were shown to be processed intracellularly in a chloroquine-sensitive compartment. Naturally processed T helper epitopes were visualized directly on the surface of PBMC and identified as analogs of CLIP associated with MHC class II molecules. This novel li vector provides a flexible and efficient system for the delivery of defined peptide epitopes to T cells which might be useful in the development of specific vaccines and in the study of intracellular processing.

Amino Acid Sequence↗

PubMed1997

Nonionic triblock copolymers facilitate delivery of exogenous proteins into the MHC class I and class II processing pathways.

Nonionic triblock copolymers are relatively nontoxic adjuvants that induce high-titer, long-lasting antibody responses. We have previously shown that these adjuvants also induce cell-mediated immunity including lymphokine production by CD4(+) T cells and cytolytic responses by CD8(+) T cells. These copolymers are thought to modulate hydrophobic adhesive interactions between antigens (Ag) and lymphoid cells. We sought to test the hypothesis that copolymers facilitate uptake of exogenous Ag by antigen-presenting cells (APC) using an in vitro model system. Our data show that nonionic triblock copolymers enhanced presentation of soluble ovalbumin (OVA) to the major histocompatibility complex (MHC) class II-restricted CD4(+) T cells and MHC class I-restricted CD8(+) T cells, respectively. Presentation of OVA via the class I pathway was enhanced by copolymers in both phagocytic and nonphagocytic APC. However, copolymers did not enhance binding of peptides to the MHC molecules on APC, presentation of endogenously synthesized Ag, or presentation of exogenous Ag delivered by electroporation. These results provide additional evidence that these nonionic triblock copolymers can serve as powerful adjuvants for augmenting both humoral and cell-mediated immunity to protein Ag.

Adjuvants, Immunologic↗