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At least 253 records · Page 14Linked to original sources

PubMed1986

Sequential analysis of HLA-class II antigen expression in human renal allografts. Induction of tubular class II antigens and correlation with clinical parameters.

The expression of HLA-class II antigens was assessed in 142 biopsies from 29 recipients of cadaveric renal allografts who received either short-term cyclosporine (n = 12) or azathioprine and low-dose prednisolone (n = 17). Biopsies were obtained before transplantation, routinely at days 7, 21, 90, and 365 after transplantation, and at other times as clinically indicated. Cryostat sections were labeled with monoclonal antibodies using an indirect immunoperoxidase technique. In all biopsies HLA-class II antigens were expressed on glomeruli and intertubular structures. In pretransplant biopsies proximal tubules expressed class II antigens, whereas distal tubules were always negative. After transplantation three patterns of class II expression were recognized based on renal tubular class II staining: normal, focal increased, and generalized increased expression. Sequential biopsy analysis showed fluctuating levels of expression in individual patients, which correlated with cellular infiltration and was associated with allograft rejection. 71% of biopsies obtained at day 90 from patients on conventional therapy showed increased class II expression compared with only 9% of biopsies from patients on cyclosporine immunosuppression. All patients with normal class II antigen expression in day 90 biopsies had well-functioning grafts two years after transplantation, whereas 3 of 9 with increased class II antigen expression had failed. Furthermore, all grafts failing from irreversible rejection before 90 days showed marked increase of class II antigen expression. The increased class II antigen expression in renal allografts may be merely a marker of rejection or may have a role in the augmentation of the response, either in its induction or as a target for the effector arm of the reaction.

Azathioprine↗

PubMed1999

Differences in the roles of conserved glutamic acid residues in the active site of human class 3 and class 2 aldehyde dehydrogenases.

Although the three-dimensional structure of the dimeric class 3 rat aldehyde dehydrogenase has recently been published (Liu ZJ et al., 1997, Nature Struct Biol 4:317-326), few mechanistic studies have been conducted on this isoenzyme. We have characterized the enzymatic properties of recombinant class 3 human stomach aldehyde dehydrogenase, which is very similar in amino acid sequence to the class 3 rat aldehyde dehydrogenase. We have determined that the rate-limiting step for the human class 3 isozyme is hydride transfer rather than deacylation as observed for the human liver class 2 mitochondrial enzyme. No enhancement of NADH fluorescence was observed upon binding to the class 3 enzyme, while fluorescence enhancement of NADH has been previously observed upon binding to the class 2 isoenzyme. It was also observed that binding of the NAD cofactor inhibited the esterase activity of the class 3 enzyme while activating the esterase activity of the class 2 enzyme. Site-directed mutagenesis of two conserved glutamic acid residues (209 and 333) to glutamine residues indicated that, unlike in the class 2 enzyme, Glu333 served as the general base in the catalytic reaction and E209Q had only marginal effects on enzyme activity, thus confirming the proposed mechanism (Hempel J et al., 1999, Adv Exp Med Biol 436:53-59). Together, these data suggest that even though the subunit structures and active site residues of the isozymes are similar, the enzymes have very distinct properties besides their oligomeric state (dimer vs. tetramer) and substrate specificity.

Aldehyde Dehydrogenase↗

PubMed1998

Comparison of class II and class III activity of dl-sotalol in healthy volunteers.

Racemic sotalol has demonstrated anti-arrhythmic properties which include Class II (beta blockade) and Class III (potassium channel blockade) activity. The Class II activity is demonstrated primarily in l-sotalol, and Class III activity is almost equipotent in each isomer. Class II and Class III activity of dl-sotalol was investigated following repeated oral administration (80 mg b.i.d.) for 7 days. Class II activity was evaluated according to the low frequency spectral power obtained by fast Fourier analysis of the R-R interval variation. Class III activity was evaluated according to the change in the QTc interval of the surface electrocardiogram. The low frequency spectral power decreased after administration of the first dose on day 1 and this trend continued throughout the duration of the study. The QTc interval did not change with dl-sotalol administration. These findings may suggest that Class II activity is more potent than Class III activity.

Adrenergic beta-Antagonists↗

PubMed1995

Different roles of class I and class II Clostridium histolyticum collagenase in rat pancreatic islet isolation.

Crude Clostridium histolyticum collagenase was purified by gel filtration and fractionated by anion exchange chromatography into class I with high collagen digestion activity (CDA) and low FALGPA (2-furanacryloyl-L-leucylglycyl-L-prolyl-L-alanine) hydrolysis activity (FHA), class II with low CDA and high FHA, and a fraction called class I/II with intermediate activities. The roles of these collagenase classes in rat pancreatic islet isolation were investigated. Dissociations were carried out with 360 mg of pancreatic tissue in 10 ml of buffer containing 10% (wt/vol) albumin to suppress endogenous proteolytic activity, 100 U of C. histolyticum neutral protease, and one or two purified collagenase(s). For purified nonfractionated (PNF) collagenase, 2.6 mg of enzyme containing 2.4 U CDA and 38.0 U FHA was used, and for the separate classes, comparable amounts of activity were added. PNF collagenase dissociated the tissue completely in 32 min and yielded 5.0 +/- 0.4 microliters islet tissue/g pancreas. Class I collagenase alone dissociated pancreatic tissue extremely slowly and incompletely; only a few islets were released (0.7 +/- 0.2 microliters/g pancreas). Class II collagenase alone dissociated the tissue adequately in 50 min, and a high islet yield of 5.7 +/- 0.6 microliters/g was obtained. With class I/II, a similar dissociation time (47 min) and islet yield (5.5 +/- 0.3 microliters/g) were obtained. Combining class I and class II collagenase resulted in a more rapid dissociation (32 min) and a higher islet yield (7.1 +/- 0.8 microliters/g) than that obtained with PNF collagenase (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗

PubMed1990

Fracture strength of Class I versus Class II restored premolars tested at the marginal ridge. I. Standard preparations.

Two groups of maxillary premolars with Class I cavities were prepared with one marginal ridge thickness to a width of 1.0 mm. One group was restored with amalgam and the other group with composite resin. Two groups of Class II cavities also were prepared and restored with amalgam and composite resin. The teeth in the four treatment groups were subjected to a centric load at the marginal ridge until fracture occurred. A two-factor analysis of variance revealed a statistically significant difference between the class of preparation (Class I preparations were weaker than were Class II preparations) but differences in strength between restorative materials (composite resin versus amalgam) and the interaction effect (class of preparation x restorative materials) were not found to be statistically significant (alpha = .05). A Newman-Keuls sequential range test found no statistically significant differences in strength between groups (alpha = .05). Fracture patterns were observed under scanning electron microscope. Fractures extended into the enamel and into the material in the Class I composite resin, Class I amalgam, and Class II composite resin restorations. Fractures extended only into the material in Class II amalgam restorations.

Bicuspid↗

PubMed1985

HLA class-I and class-II antigen expression by human leukemic K562 cells and by Burkitt-K562 hybrids: modulation by differentiation inducers and interferon.

K562 cells, which could be regarded as pluripotent hematopoietic progenitors, are usually considered as HLA class-I and class-II-negative cells. We show here that differentiation induction (with either sodium butyrate, 12-O-tetradecanoyl-phorbol-13-acetate, or teleocidin) or recombinant alpha- or gamma-interferon (IFN) treatment resulted in the augmentation of HLA class-I antigen expression. This augmentation of HLA class-I antigens was also observed in the Burkitt X K562 hybrid cells PUTKO and DUTKO (the latter coming from two presumably HLA-A, B-negative parents). HLA class-I genes are thus functional in K562 cells. In this system, alpha- and gamma-IFN had no clear differentiating capacity, since they were not able to modulate the expression of various hematopoietic markers, as chemical differentiation inducers did. On the other hand, neither differentiation induction nor interferon treatment could induce HLA class-II antigen expression on K562 cells. These molecules could be very faintly induced in PUTKO and DUTKO hybrids, in contrast with strong HLA class-II expression on the B parental lines. Whether these results are due to "lineage infidelity" in K562 cells or whether K562 cells represent the proliferation of HLA class-I-positive class-II-negative hematopoietic cells, with active suppression of HLA class-II antigen expression, is discussed.

Burkitt Lymphoma↗

PubMed1995

Cloned rat cardiac titin class I and class II motifs. Expression, purification, characterization, and interaction with F-actin.

Titin (connectin) is a giant protein that forms a single-molecule elastic filament extending from the M-line to the Z-line in the striated muscle sarcomere. The sequence of titin consists mainly of repeats of two types of approximately 100-amino acid motifs (class I and class II that show homology to the fibronectin type III and immunoglobulin-C2 domains, respectively). To investigate the functions of the two classes of titin motifs as the basic units of this large sarcomere organizer molecule, titin cDNA segments encoding single class I or class II or linked class I-II motifs were cloned by polymerase chain reaction from a rat cardiac cDNA library into the T7 RNA polymerase-based pAED4 vector to express non-fusion titin fragments in Escherichia coli. High level expression of the three titin fragments was achieved, and effective rapid purification procedures were developed. The purified titin fragments were verified by their amino acid composition, apparent molecular mass, and charge. Antibodies raised against the genetically expressed titin motifs specifically recognized intact rat cardiac and skeletal muscle titins in Western blotting and immunofluorescence microscopy, confirming the authenticity of the cloned fragments. High beta-sheet contents of these titin motifs indicate a folding state very similar to that of intact native titin. Solid-phase protein-binding assays demonstrated that a single class I motif was able to bind both myosin and F-actin. In comparison, a single class II motif had weaker binding to only F-actin but the fragment containing linked class I and class II motifs showed significantly stronger interactions with both myosin and F-actin. The binding of titin motifs to myosin supports the proposed association of A-band titin with the thick filament, and the novel titin-F-actin interaction was confirmed by F-actin cosedimentation assays, suggesting that titin may also be involved in the structure and/or function of the thin filament.

Actins↗

PubMed1993

In vivo dimeric association of class I MHC heavy chains. Possible relationship to class I MHC heavy chain-beta 2-microglobulin dissociation.

Class I MHC molecules have been thought to occur in vivo both as class I MHC heavy chain-beta 2-m heterodimers, which are or are not associated with antigenic peptide, and as free class I MHC heavy chains. Class I MHC molecules are now found also to occur in another type of structure: a heavy chain-heavy chain dimer. Biochemical studies show that heavy chain dimers are disulfide-linked via a conserved cytoplasmic domain cysteine. H-2Ld, H-2Db, and H-2Dd class I dimers fail to react with certain alpha 1 and alpha 2 domain-specific antibodies. Furthermore, although beta 2-m-specific antibodies coprecipitate class I MHC heavy chains, they do not coprecipitate class I MHC heavy chain dimers. Pulse-chase studies show that heavy chain dimer formation occurs at different points in the biosynthesis of class I MHC molecules in beta 2-m+ and beta 2-m- cells: in beta 2-m+ cells, heavy chain dimers form after the class I molecules have traversed the medial Golgi cisternae, whereas in beta 2-m- cells they form immediately. Culturing of beta 2-m+ cells with exogenous beta 2-m prevents the formation of H-2Ld/Db heavy chain dimers. We conclude that dimer formation occurs as a consequence of loss or unavailability of beta 2-m. Class I MHC heavy chain dimerization may provide a mechanism for removal of immunologically dysfunctional molecules.

Amino Acid Sequence↗

PubMed1991

Cytosolic targeting of hen egg lysozyme gives rise to a short-lived protein presented by class I but not class II major histocompatibility complex molecules.

A way to study the role of intracellular trafficking of an antigen in its presentation to T cells is to target the antigen to various cell compartments of the antigen-presenting cells (APC) and compare the nature of the complexes associating major histocompatibility complex (MHC) molecules and antigenic peptides, expressed on the cell surface. MHC class I+ and MHC class II+ mouse L fibroblasts secreting hen egg lysozyme (HELs cells) or expressing HEL in their cytosol (HELc cells) were obtained after transfection with HEL cDNA and signal sequence-deleted HEL cDNA, respectively. HEL was evidenced in both HELs- and HELc-transfected cells and the former type of transfectant secreted a large amount of HEL. However, HEL produced in the cytosol exhibited a short half-life of less than 5 min. HEL-derived peptides could not be shown biochemically either in HELc- nor in HELs-transfected cells. We then studied the capacity of these cells to present HEL to HEL-specific class I- and class II-restricted T cells. Both cell types could be recognized by the HEL-specific MHC class I-restricted CTL clones. In contrast, MHC class II-HEL peptide complexes, recognized by HEL-specific helper T cell hybridomas, could be detected on MHC class II+ HELs- but not HELc-transfected cells. In vivo experiments showed, however, that HELc-transfected cells could provide host APC with HELc-derived peptides able to associate with MHC class II molecules. This was inferred from the capacity of MHC class II-HELc-transfected cells, unable by themselves to elicit any anti-HEL antibody response, to prime syngeneic and allogeneic mice against HEL. The priming was revealed by the induction of an antibody response after a boost with an amount of HEL unable itself to elicit an antibody response.

Amino Acid Sequence↗

PubMed1995

Major histocompatibility complex class I-restricted CD8+ T cells and class II-restricted CD4+ T cells, respectively, mediate and regulate contact sensitivity to dinitrofluorobenzene.

Contact sensitivity (CS) is a form of delayed-type hypersensitivity to haptens applied epicutaneously and is thought to be mediated, like classical delayed-type hypersensitivity responses, by CD4+ T helper-1 cells. The aim of this study was to identify the effector T cells involved in CS. We studied CS to the strongly sensitizing hapten dinitrofluorobenzene (DNFB) in mice rendered deficient by homologous recombination in either major histocompatibility complex (MHC) class I, MHC class II, or both, and which exhibited deficiencies in, respectively, CD8+, CD4+, or both, T cells. MHC class I single-deficient and MHC class I/class II double-deficient mice, both of which have a drastic reduction in the number of CD8+ T cells, were unable to mount a CS response to DNFB. In contrast, both MHC class II-deficient mice and normal mice treated with an anti-CD4 monoclonal antibody (mAb) developed exaggerated and persistent responses relative to heterozygous control littermates. Furthermore, anti-CD8 mAb depletion of class II-deficient mice totally abolished their ability to mount an inflammatory response to DNFB. Removal of residual CD4+ T cells in class II-deficient mice by anti-CD4 mAb treatment did not diminish the intensity of CS. These data clearly demonstrate that class I-restricted CD8+ T cells are sufficient for the induction of CS to DNFB, and further support the idea that MHC class II-restricted CD4+ T cells down-regulate this inflammatory response.

Animals↗

PubMed1993

Uncoordinate induction and differential regulation of HLA class-I and class-II expression by gamma-interferon in differentiating human neuroblastoma cells.

Recombinant gamma-interferon (IFN-gamma) has recently been shown to be one of the most effective inducers of neuroblastoma (NB) cell differentiation. Since increasing evidence indicates that expression of MHC class-I and class-II antigens by tumour cells is important for immunorecognition and cell targeting, we tested whether induction of NB cell differentiation by IFN-gamma is followed by expression of HLA class-I and class-II molecules. LAN-5 human NB cell line completely lacks HLA class-I antigens. Their expression was induced in a dose-dependent manner by IFN-gamma. HLA class-II molecules are also absent on LAN-5 cells, but only DP antigens were dose-dependently induced by IFN-gamma, while DR and DQ molecules were unaffected by the treatment. To confirm and extend the immunological data to all the class-II molecules, we performed Northern blot analysis, observing that DP alpha mRNA was induced in a dose- and time-dependent manner. DO beta and DZ alpha genes were also induced peaking after 3 days of IFN-gamma treatment. DR beta and DQ beta genes, which were not induced by IFN-gamma, gave a normal pattern of enzyme restriction by Southern blot. To get an insight into the regulation of HLA class-II gene expression in the neuronal model, we measured the decline of the steady-state HLA class-II mRNA. DO beta mRNA rapidly returned to baseline level after removing IFN-gamma, while the decay rates of DP alpha and DZ alpha mRNA were very slow. This might indicate different regulation at the post-transcriptional level for DO beta mRNA with respect to DP alpha and DZ alpha mRNA. To strengthen these findings we evaluated the half-lives of the mRNA after IFN-gamma induction by means of actinomycin D treatment. HLA-DO beta mRNA had a shorter half-life, while DZ alpha and DP alpha had a longer decay rate. Finally, we report that treatment of LAN-5 cells with cycloheximide did not alter the rate of transcription of the HLA-DP alpha gene, suggesting that no protein factor(s) is/are needed to maintain DP alpha gene expression.

Blotting, Northern↗

PubMed1988

A molecular map of the chicken major histocompatibility complex: the class II beta genes are closely linked to the class I genes and the nucleolar organizer.

We have cloned in a cosmid vector four DNA clusters covering 320 kb of the chicken MHC (B complex), including five class II (B-L) beta genes defining two related isotypic families. Additional B complex genes have been revealed using tissue-specific cDNA probes. A cosmid fragment has been used to isolate a cDNA for a class I (B-F) transcript. This transcript, that is by far the most divergent known member of the class I gene family, hybridized to six B-F genes present in the cosmids. One of the clusters was shown to contain two rRNA transcriptional units from the nucleolar organizer region (NOR), marking the telomeric boundary of the B complex. None of the other B complex genes hybridizes to, or has the transcriptional characteristics of mammalian MHC class II alpha or class III genes. The map we have obtained shows that the B complex does not contain well defined class I and class II regions since B-F and B-L beta genes are closely associated with unrelated genes. Moreover, class II beta genes are very closely linked to class I genes in two clusters, and to the NOR in a third one.

Amino Acid Sequence↗

PubMed2000

Pseudomonas exotoxin-mediated delivery of exogenous antigens to MHC class I and class II processing pathways.

Peptides associated with class II MHC molecules are normally derived from exogenous proteins, whereas class I MHC molecules normally associate with peptides from endogenous proteins. We have studied the ability of Pseudomonas exotoxin A (PE) fusion proteins to deliver exogenously added antigen for presentation by both MHC class I and class II molecules. A MHC class II-restricted antigen was fused to PE; this molecule was processed in a manner typical for class II-associated antigens. However, a MHC class I-restricted peptide fused to PE was processed by a mechanism independent of proteasomes. Furthermore, we also found that the PE fusion protein was much more stable in normal human plasma than the corresponding synthetic peptide. We believe that effective delivery of an antigen to both the MHC class I and class II pathways, in addition to the increased resistance to proteolysis in plasma, will be important for immunization.

ADP Ribose Transferases↗

PubMed1995

Analysis of the structure of naturally processed peptides bound by class I and class II major histocompatibility complex molecules.

Antigen-specific T-cell responses require antigenic peptides presented on the cell surface by the major histocompatibility complex (MHC) molecules. The structural characteristics of these peptides are being defined. It is now known that the majority of peptides that associate with MHC Class I are 8-10 residues long, with allotype-specific binding motifs containing up to three anchor positions. This is consistent with the presence of six pockets and the close-ended structure of the MHC Class I peptide binding groove. In contrast to peptides associated with MHC Class I, those associated with MHC Class II are 10-34 residues in length and are commonly presented in nested sets with extensions or truncations at the N- or C-terminal ends. Binding motifs for MHC Class II appear to contain up to four anchor positions, with more loosely defined amino acid preferences. The expression of histocompatibility proteins in cells that do not load peptides but fold them correctly has permitted the X-ray analysis of the three-dimensional structure of Class I and Class II complexes with single defined peptides. The differences in length between the Class I and Class II sequences can be ascribed to small structural differences between the two binding sites and the positioning of key residues, that make hydrogen bonds to the bound peptides. Recent advances in mass spectrometry are making possible the analysis and sequencing of subpicomolar quantities of MHC-bound peptides and the estimation of the size of the total population of peptides. The sequence information derived from this technique, in conjunction with X-ray crystallographic analysis of MHC complexes involving single, defined peptides, may provide a new approach towards the development of useful reagents for therapeutic intervention.

Alleles↗

PubMed2005

Genomic sequence analysis of the 238-kb swine segment with a cluster of TRIM and olfactory receptor genes located, but with no class I genes, at the distal end of the SLA class I region.

Continuous genomic sequence has been previously determined for the swine leukocyte antigen (SLA) class I region from the TNF gene cluster at the border between the major histocompatibility complex (MHC) class III and class I regions to the UBD gene at the telomeric end of the classical class I gene cluster (SLA-1 to SLA-5, SLA-9, SLA-11). To complete the genomic sequence of the entire SLA class I genomic region, we have analyzed the genomic sequences of two BAC clones carrying a continuous 237,633-bp-long segment spanning from the TRIM15 gene to the UBD gene located on the telomeric side of the classical SLA class I gene cluster. Fifteen non-class I genes, including the zinc finger and the tripartite motif (TRIM) ring-finger-related family genes and olfactory receptor genes, were identified in the 238-kilobase (kb) segment, and their location in the segment was similar to their apparent human homologs. In contrast, a human segment (alpha block) spanning about 375 kb from the gene ETF1P1 and from the HLA-J to HLA-F genes was absent from the 238-kb swine segment. We conclude that the gene organization of the MHC non-class I genes located in the telomeric side of the classical SLA class I gene cluster is remarkably similar between the swine and the human segments, although the swine lacks a 375-kb segment corresponding to the human alpha block.

Amino Acids↗

PubMed2000

Class I and class II MHC bind self peptide sets that are strikingly different in their evolutionary characteristics.

Comparison of peptides eluted from human class I and class II major histocompatibility complex (MHC) molecules and the proteins from which they are derived (source proteins) revealed that class I MHC bind peptides derived from proteins that are highly conserved, hydrophilic, and universally expressed, while the peptides themselves are hydrophobic and even more conserved than their source proteins. In contrast, source proteins for class II-bound peptides were not significantly more conserved than a random sample of proteins. Class II-bound peptides were generally more conserved than their source proteins but were significantly less conserved than class I-bound peptides. The characteristics of class I-bound peptides can probably be explained by the selectivity of processing and transport of peptides for binding by class I, while the relative lack of selectivity of peptide binding for class II may explain the high incidence of autoimmune diseases associated with alleles of these molecules.

Alleles↗

PubMed2006

HPV16E7 mediates HADC chromatin repression and downregulation of MHC class I genes in HPV16 tumorigenic cells through interaction with an MHC class I promoter.

Downregulation of the expression of major histocompatibility complex class I antigens on the surface of high-risk HPVs-transformed cells may contribute to their high tumorigenic potential, which enables them to escape immune recognition by cytotoxic T lymphocytes. In this study, we show that the viral E7 oncoprotein mediates transcriptional downregulation of the major histocompatibility complex (MHC) class I genes by targeting the class I promoter in HPV16 containing CaSki tumor cells. Using the chromatin immunoprecipitation assay, we demonstrated that HPV16E7 and specific HADCs, including HADC1, HADC2, and HADC8, are physically associated with the class I promoter and the histone of the class I promoter was deacetylated. Knocking down of HPV16E7 expression with the E7-specific small interfering RNA induced the release of HPV17E7 as well as HDAC1 and HDAC2 from the class I promoter. Furthermore, HPV16E7 siRNA resulted in a dramatic increase in histone acetylation. Importantly, MHC class I antigen expression was up-regulated on the surface of cells transfected with the E7 siRNA, but not on that of untransfected cells. Taken together, our results demonstrate that the HPV16E7 protein is associated with the MHC class I promoter and mediates MHC class I downregulation by repressing chromatin activation.

Cell Line, Tumor↗

PubMed1997

Induction of MHC class I expression by the MHC class II transactivator CIITA.

Major histocompatibility complex (MHC) class I-deficient cell lines were used to demonstrate that the MHC class II transactivator (CIITA) can induce surface expression of MHC class I molecules. CIITA induces the promoter of MHC class I heavy chain genes. The site alpha DNA element is the target for CIITA-induced transactivation of class I. In addition, interferon-gamma (IFNgamma)-induced MHC class I expression also requires an intact site alpha. The G3A cell line, which is defective in CIITA induction, does not induce MHC class I antigen and promoter in response to IFNgamma. Trans-dominant-negative forms of CIITA reduce class I MHC promoter function and surface antigen expression. Collectively, these data argue that CIITA has a role in class I MHC gene induction.

Breast Neoplasms↗