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 919 records · Page 51Linked to original sources

PubMed2002

Activated human T cells accomplish MHC class II expression through T cell-specific occupation of class II transactivator promoter III.

Activated human T cells express HLA-DR, HLA-DQ, and HLA-DP on their surface, but the regulation and functioning of MHC class II molecules in T lymphocytes are poorly understood. Because the MHC class II transactivator (CIITA) is essential for MHC class II expression, we have investigated transcriptional activation of CIITA in activated T cells. In this study, we show that in human activated CD4(+) T cells, CIITA promoter III (CIITA-PIII) drives the expression of CIITA. The in vivo genomic footprint analysis revealed activated T cell-specific occupation of CIITA-PIII. Subsequent EMSA analysis of several promoter regions showed differences in banding pattern among activated T cells, naive T cells, primary B cells, and Raji B cells. Activating response element (ARE)-1 is shown to interact with the acute myeloid leukemia 2 transcription factor in nuclear extracts derived from both T and B cells. Interestingly, the acute myeloid leukemia 3 transcription factor was bound in nuclear extracts of T cells only. The ARE-2 sequence is able to bind CREB/activating transcription factor family members in both T and B cells. In addition, a yet unidentified Ets family member was found to interact with site C in activated T cells, whereas in B cells site C was bound by PU.1 and Pip/IFN regulatory factor 4/IFN consensus sequence binding protein for activated T cells. In Jurkat T cells, both ARE-1 and ARE-2 are crucial for CIITA-PIII activity, similar to Raji B cells. The differential banding pattern in in vivo genomic footprinting and transcription factor binding at the ARE-1 and site C between T cells and B cells probably reflects differences in CIITA-PIII activation pathways employed by these cell types.

B-Lymphocytes↗

PubMed2003

IFN-gamma-induced MHC class II expression: transactivation of class II transactivator promoter IV by IFN regulatory factor-1 is regulated by protein kinase C-alpha.

Previous studies based on pharmacological evidence suggested a requirement for protein kinase C (PKC) activity in the regulation of IFN-gamma-induced MHC class II (MHC-II) expression. In the present study, we investigated the molecular mechanisms by which PKC-alpha modulates IFN-gamma-induced MHC-II expression in the mouse macrophage cell line RAW 264.7. Overexpression of a dominant-negative (DN) mutant of PKC-alpha inhibited the expression of IFN-gamma-induced MHC-II but had no effect on IFN-gamma-induced STAT1 nuclear translocation and DNA binding activity, as well as on the expression of inducible NO synthase, IFN consensus sequence binding protein, MHC class I, IFN regulatory factor (IRF)-1, and IFN-gamma-inducible protein-10. Further analysis showed that IFN-gamma-induced expression of the MHC class II transactivator (CIITA), a transcriptional coactivator essential for MHC-II expression, was inhibited in DN PKC-alpha-overexpressing cells. Studies with reporter constructs containing the promoter IV region of CIITA revealed that overexpression of a constitutively active mutant of PKC-alpha enhanced IRF-1, but not IRF-2, transcriptional activity. Furthermore, characterization of IRF-1 from both normal and DN PKC-alpha-overexpressing cells revealed differences in IRF-1 posttranslational modifications. Collectively, our data suggest a novel regulatory mechanism for IFN-gamma-induced MHC-II expression, whereby PKC regulates CIITA expression by selectively modulating the transcriptional activity of IRF-1.

Animals↗

PubMed2005

Interallelic class switch recombination contributes significantly to class switching in mouse B cells.

Except for the expression of IgM and IgD, DNA recombination is constantly needed for the expression of other Ig classes and subclasses. The predominant path of class switch recombination (CSR) is intrachromosomal, and the looping-out and deletion model has been abundantly documented. However, switch regions also occasionally constitute convenient substrates for interchromosomal recombination, since it is noticeably the case in a number of chromosomal translocations causing oncogene deregulation in the course of lymphoma and myeloma. Although asymmetric accessibility of Ig alleles should theoretically limit its occurrence, interallelic CSR was shown to occur at low levels during IgA switching in rabbit, where the definition of allotypes within both V and C regions helped identify interchromosomally derived Ig. Thus, we wished to evaluate precisely interallelic CSR frequency in mouse B cells, by using a system in which only one allele (of b allotype) could express a functional VDJ region, whereas only interallelic CSR could restore expression of an excluded (a allotype) allele. In our study, we show that interchromosomal recombination of V(H) and Cgamma or Calpha occurs in vivo in B cells at a frequency that makes a significant contribution to physiological class switching: trans-association of V(H) and C(H) genes accounted for 7% of all alpha mRNA, and this frequency was about twice higher for the gamma3 transcripts, despite the much shorter distance between the J(H) region and the Cgamma3 gene, thus confirming that this phenomenon corresponded to site-specific switching and not to random recombination between long homologous loci.

Alleles↗

PubMed2003

Efficient presentation of known HLA class II-restricted MAGE-A3 epitopes by dendritic cells electroporated with messenger RNA encoding an invariant chain with genetic exchange of class II-associated invariant chain peptide.

For the induction of an optimal immune response against cancer or infections not only CD8(+) CTLs but also CD4(+) T helper cells must be induced, in particular IFN-gamma-secreting type 1 T helper cells. Several strategies have been explored to target tumor-associated antigens to the HLA class II processing compartments. We engineered a genetic construct encoding an invariant chain (Ii) protein where the CLIP region has been replaced by sequences encoding HLA class II-restricted MAGE-A3 epitopes. Monocyte-derived dendritic cells (DCs) were electroporated with in vitro transcribed mRNA encoding a modified Ii protein containing the HLA-DP4-restricted MAGE-A3 epitope. The capacity of these electroporated DCs to stimulate a MAGE-A3-specific T-cell clone was compared at different stages of DC maturation with the T-cell stimulatory capacity of DCs pulsed with the synthetic peptide. After electroporation, the T-cell stimulatory capacity was shown to be high and long lasting, whereas the stimulatory capacity of peptide-pulsed DCs decreased rapidly. Upon coculture with epitope-specific T cells, electroporated immature DCs expressed enhanced levels of costimulatory molecules, HLA class II molecules, and CD83, suggesting the induction of maturation. The electroporated DCs can be frozen and thawed without losing their capability to stimulate the specific T-cell clone in vitro, and they are able to stimulate unprimed CD4(+) T cells specific to the HLA-DP4-restricted MAGE-A3 epitope in vitro. Similar results were obtained with a recombinant Ii containing the MAGE-A3 epitope presented in the context of HLA-DR13.

Amino Acid Sequence↗

PubMed1986

Monoclonal antibodies to sheep lymphocytes. I. Identification of MHC class II molecules on lymphoid tissue and changes in the level of class II expression on lymph-borne cells following antigen stimulation in vivo.

A rat monoclonal antibody is described that recognizes sheep MHC Class II antigen and appears to recognize a determinant that is non-polymorphic. This antibody precipitates polypeptides of apparent molecular weight 33,000 and 28,000/29,000 (under non-reducing conditions). The binding of this antibody was inhibited by an anti-human DP, DQ, DR beta-chain monoclonal (DA6.231) and its reactivity on murine cells suggests specificity for the I-E gene product. Using this antibody we have studied the distribution of Class II molecules in sheep and also the variations in Class II expression by cells in both peripheral and efferent lymph, produced as a result of in vivo antigen inoculation.

Animals↗

PubMed1989

Tolerance induction of allo-class II H-2 antigen-reactive L3T4+ helper T cells and prolonged survival of the corresponding class II H-2-disparate skin graft.

The present study investigates the effects of i.v. presensitization with class II H-2-disparate allogeneic cells on various L3T4+ T cell functions including the capability of rejecting the corresponding allogeneic skin graft. C57BL/6 (B6) mice were i.v. presensitized with class II H-2 disparate B6-C-H-2bm12 (bm12) spleen cells. Such presensitization did not affect the bm12-specific L3T4+ T cell-mediated proliferative and interleukin 2 (IL-2)-producing capacities. A single cell suspension of (B6 x bm12)F1 spleen cells was depleted of APC by two round-passages over Sephadex G-10 columns. This APC-depleted fraction of (B6 x bm12)F1 cells failed to stimulate B6 responding cells in mixed lymphocyte reactions (MLR). The addition of recombinant IL-1 to the MLR restored anti-bm12 MLR responses, indicating that APC-depleted (B6 x bm12)F1 cells bear bm12 alloantigens but are unable to stimulate B6 anti-bm12 L3T4+ T cells. A single i.v. administration of APC-depleted (B6 x bm12)F1 cells into B6 mice resulted in almost complete abrogation of the capacity of recipient B6 lymphoid cells to give anti-bm12 MLR and IL2 production. This suppression was bm12 alloantigen-specific and attributed to the elimination or functional impairment of anti-bm12 T cell clones rather than the induction of suppressor cells. The tolerance was also observed in graft-rejection responses. The strikingly prolonged survival of bm12 skin grafts was produced when grafts were implanted into B6 mice which had been presensitized with APC-depleted, but not with untreated (B6 x bm12)F1 spleen cells. These results indicate that allo-class II H-2 antigen-reactive L3T4+ T cells are rendered tolerant by i.v. presensitization with APC-depleted fraction of the corresponding allogeneic cells.

Animals↗

PubMed1987

Class II genes of the human major histocompatibility complex. The DO beta gene is a divergent member of the class II beta gene family.

A novel class II beta chain gene is described. This gene, tentatively called DO beta, displays considerably less polymorphism than beta genes of the DP, DQ, and DR loci. The nucleotide sequence of the DO beta gene is strikingly similar to that of the previously identified murine A beta 2 gene. The DO beta gene displays the same exon/intron organization as other beta genes although the fifth exon and the translated portion of the sixth exon are longer than in other genes. A striking feature of the amino acid sequence deduced from the DO beta gene sequence is the pronounced hydrophobicity of the NH2-terminal region. This feature distinguishes the putative DO beta chain from other class II beta chains and raises the possibility that DO beta chains may interact with an alpha chain that is structurally different from those of the DP, DQ, and DR loci. It further suggests that the putative DO molecule may have a function different from those of other class II antigens.

Base Sequence↗

PubMed1983

A comparison of the neonatal tolerance-inducing capacities of H-2 class I and class II antigens.

We have investigated the abilities of murine major histocompatibility complex-encoded antigens to induce in vitro hyporeactivity of T lymphocytes when these antigens are injected neonatally. Class I molecules, presented on F1 donor cells having an H-2 K or D region difference from recipients, can readily induce tolerogen-specific cytotoxic T cell hyporeactivity; as few as 1 X 10(6) neonatally injected donor cells suffice. In contrast, class II molecules, presented on F1 donor cells having an H-2 I region difference from recipients, can induce tolerogen-specific helper T cell hyporeactivity only when at least 1 X 10(7) neonatally injected donor cells are used, and then only in some of these recipients. Results from another in vitro assay system, taken in conjunction with these data, indicate that the molecular class of the tolerizing disparity, rather than the effector function of the responding cell type assayed, may be the most important factor in controlling the ease with which neonatally induced alloantigen tolerance can be achieved. In each type of tolerance described here, the hyporeactivity seen is antigen specific, in its induction and its expression; the implications of this fact for considerations of possible mechanisms of tolerance maintenance are discussed.

Aging↗

PubMed1997

Prominence of beta 2-microglobulin, class I heavy chain conformation, and tapasin in the interactions of class I heavy chain with calreticulin and the transporter associated with antigen processing.

Newly synthesized class I heavy (H) chain/beta 2m heterodimers awaiting peptides in the endoplasmic reticulum are associated with the transporter associated with Ag processing (TAP). We present evidence here that calreticulin, but not calnexin, displays steady state association with class I/TAP complexes. To separate the ability of beta 2m to bind with TAP and calreticulin from that of H chain, we studied human cell lines that lack expression of beta 2m or H chain. Little if any H chain was detected in association with TAP and calreticulin in the beta 2m- cell line Daudi. By contrast, high levels of beta 2m are found with TAP and calreticulin in the H chain-deficient cell line LCL 721.221, even after preclearance of the trace amount of class IB protein expressed by this cell line. Thus, beta 2m appears to bind TAP in the absence of H chain, providing an elegant mechanism to retain beta 2m in the endoplasmic reticulum at the site of peptide loading. To investigate whether other molecules participate in the binding of beta 2m and H chain to TAP and calreticulin, we analyzed the deletion mutant cell line LCL 721.220, which lacks tapasin. In 721.220, TAP and calreticulin are not associated with each other. Also, in these cells, H chain/beta 2m are not associated with TAP, but H chain and a low level of beta 2m are associated with calreticulin. These results suggest that tapasin is an obligatory mediator of the assemblage of calreticulin/H chain/beta 2m with TAP.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1998

Class II transactivator-independent endothelial cell MHC class II gene activation induced by lymphocyte adhesion.

NK cells induce MHC class II molecules on the surface of allogeneic endothelial cells in an adhesion-dependent, IFN-gamma-independent manner. Here, we demonstrate that NK cells induce HLA-DR on the surface of a mutant cell line that is defective in IFN-gamma-induced MHC class II expression. RNA analysis in these cells and in a cell line that is defective in class II transactivator (CIITA) demonstrates that NK cell-induced HLA-DR alpha mRNA expression is also CIITA-independent. The Janus kinase-1-deficient cell line U4A expresses HLA-DR alpha mRNA in response to NK cell activation, and HLA-DR alpha promoter constructs transfected into these cells are induced by NK cells but not IFN-gamma. These data indicate that the IFN-gamma-independent component of the target cell HLA-DR expression induced by lymphocyte adhesion uses a signaling pathway that is distinct from the IFN-gamma-dependent mechanism and also suggest that CIITA is not required.

Adult↗

PubMed2003

In vitro expression of major histocompatibility class I and class II antigens by conditionally immortalized murine neural stem cells.

The expression of major histocompatibility complex (MHC) antigens on the surface of cells is intimately linked to in vivo graft survival. It has been previously shown that the conditionally immortalized temperature-sensitive Maudsley hippocampal clone 36 (MHP36) neural stem cells show good long-term graft survival and do not elicit an acute immunological response following transplantation. Here we report that MHP36 cells express both MHC class I and class II antigens when grown in culture under proliferative conditions (33 degrees C), whereas cells with a differentiated morphology in the non-proliferative (37-39 degrees C) condition express low to undetectable levels of either MHC molecules. However, morphologically undifferentiated cells persisting under non-proliferating conditions continued to express both MHC antigens. The downregulation of MHC antigens upon differentiation following cell transplantation could therefore contribute to the graft survival of MHP36 cells.

Animals↗

PubMed2000

Analysis of the phenotypic distribution of HLA class I and class II in atopic and non-atopic asthma patients.

In several studies the HLA system has been implicated in the development of asthma, but the importance of the associations between HLA genes and asthma remains unclear. The aim of this study was to determine the HLA class I and II phenotypic frequencies in a population of asthmatics, and to analyse the relationship between these phenotypes and any type of asthma. We typed HLA class I and II antigens in a series of 189 asthmatic individuals (102 atopic and 87 non-atopic), and in a control population of 150 unrelated healthy Caucasoid donors. When the HLA phenotypic frequencies were compared, no statistical differences were found. Therefore, no definitive HLA association could be established with atopic or non-atopic asthma in the studied population. Abbreviations AA, atopic asthma; FEV1, forced expiratory volume in 1 s; NAA, non-atopic asthma; PCR, polymerase chain reaction; SSOP, sequence-specific oligonucleotide probes; SPT, skin prick test.

Asthma↗

PubMed1989

A versatile and potentially general approach to the targeting of specific cell types by retroviruses: application to the infection of human cells by means of major histocompatibility complex class I and class II antigens by mouse ecotropic murine leukemia virus-derived viruses.

A technique for delivering genes carried by recombinant retroviruses into specific cell types could have numerous applications in oncology, developmental biology, and gene therapy. As a first step toward this remote goal we designed a procedure allowing in vitro cell targeting by retroviruses. Biotinylated antibodies against the viral envelope protein on one side, and against specific cell membrane markers on the other side, were bridged by streptavidin and used to link the virus to the host. The method was successfully used to infect human cells with ecotropic murine retroviruses by means of major histocompatibility complex class I and class II antigens and appears easily adaptable to other cell membrane markers. Moreover, the sequential protocol we designed, although allowing infection of human cells, requires less stringent safety constraints than would handling of amphotropic virus stocks.

Animals↗

PubMed1993

Mice lacking major histocompatibility complex class I and class II molecules.

Mice lacking major histocompatibility complex (MHC) antigens were generated by mating beta 2-microglobulin-deficient, and therefore class I-deficient, animals with MHC class II-deficient animals. When housed under sterile conditions, the resulting MHC-deficient mice appear healthy, survive for many months, and breed successfully. Phenotypically, MHC-deficient mice are depleted of CD4+ and CD8+ T cells in peripheral lymphoid organs due to a lack of appropriate restricting elements. In contrast, the B-cell compartment of these animals appears intact, and MHC-deficient mice can mount specific antibody responses when challenged with a T-independent antigen. Spleen cells from MHC-deficient animals are poor stimulators and responders in a mixed lymphocyte reaction. Despite their relatively weak cellular immune responses in vitro, MHC-deficient mice reject allogeneic skin grafts with little delay, and grafts from MHC-deficient animals are rapidly rejected by normal allogeneic recipients. Taken together, these results emphasize the plasticity of the immune system and suggest that MHC-deficient mice may be useful for examining compensatory mechanisms in severely immunocompromised animals.

Animals↗

PubMed1987

Human MHC class III genes, BF and C4. Polymorphism, complotypes and HLA class I and II associations in the Lombardy population (Italy).

The polymorphisms of the fourth component of human serum complement and factor B (BF) (controlled by class III MHC genes) was investigated in a panel of 250 unrelated individuals from the Lombardy population, previously HLA typed (A, B, C, DR, DQ antigens) and in 25 families. Nine different alleles at the C4A and eight at the C4B loci were detected. At both loci, alleles without a gene product (i.e. "null alleles") were observed with high frequency: 8.2% for C4A "nulL" and 10% C4B "null". As expected from allele frequencies the most common haplotype was C4A*3, C4B*1 (52%). The most common BF alleles, BF*S and BF*F had a frequency of 77.7% and 17.7% respectively, while the gene frequencies of SO.7 and F1 were 2.9 and 0.9% respectively. The association of complotypes and HLA haplotypes was analysed in 50 chromosomes. The most common combination, defined by class I, II and III alleles was B35-S31-DR5 (11%) followed by B16(38)-S31-DR5 with a frequency of 6.5%. Two duplications at the C4B locus were detected. A new variant (C4A*X) strikingly faster than that of the C4A*6 product was identified in two related individuals (aunt and nephew). The practical advantages of complotype determination in disease association studies and in healthy population is discussed.

Alleles↗

PubMed1988

Allele and locus-specific differences in cell surface expression and the association of HLA class I heavy chain with beta 2-microglobulin: differential effects of inhibition of glycosylation on class I subunit association.

The assembly of HLA class I antigens, and the contribution of the single N-linked glycan to this process were examined. We observed a requirement for N-linked glycosylation in the proper assembly and surface expression of HLA-B locus products in particular, although considerable variation was seen within the allelic series of the HLA-A and B loci. We conclude that the single N-linked glycan can contribute in a major way to that conformation of the heavy (H) chain which is competent to associate with the light chain beta 2-microglobulin, and that the presence, rather than the type, of carbohydrate chain is important in this respect. The association of human class I H chains with beta 2-microglobulin shows biphasic kinetics, where an initially rapid phase is followed by a prolonged period during which no further association can be measured. It appears that HLA-C H chains are initially synthesized in amounts similar to HLA-A and B H chains, but associate inefficiently with beta 2-microglobulin, resulting in low expression of HLA-C at the cell surface. The individual stages of assembly and maturation of class I antigens including the transfer from Golgi to cell surface were found to display characteristic allelic variation.

1-Deoxynojirimycin↗

PubMed1993

Structure determination and refinement of human alpha class glutathione transferase A1-1, and a comparison with the Mu and Pi class enzymes.

The crystal structure of human alpha class glutathione transferase A1-1 has been determined and refined to a resolution of 2.6 A. There are two copies of the dimeric enzyme in the asymmetric unit. Each monomer is built from two domains. A bound inhibitor, S-benzyl-glutathione, is primarily associated with one of these domains via a network of hydrogen bonds and salt-links. In particular, the sulphur atom of the inhibitor forms a hydrogen bond to the hydroxyl group of Tyr9 and the guanido group of Arg15. The benzyl group of the inhibitor is completely buried in a hydrophobic pocket. The structure shows an overall similarity to the mu and pi class enzymes particularly in the glutathione-binding domain". The main difference concerns the extended C terminus of the alpha class enzyme which forms an extra alpha-helix that blocks one entrance to the active site and makes up part of the substrate binding site.

Amino Acid Sequence↗

PubMed1991

Nucleotide sequence of a new class A beta-lactamase gene from the chromosome of Yersinia enterocolitica: implications for the evolution of class A beta-lactamases.

The nucleotide sequence has been determined of a 1400 bp fragment from the chromosome of Yersinia enterocolitica containing the gene for beta-lactamase I. An ORF of 882 bp was identified, which could code for a polypeptide of 294 amino acids, closely related to other beta-lactamases of molecular class A. Amino acids 1-30 could constitute a signal peptide. The mature protein would be 264 amino acids long with a calculated pI of 6.2. Alignment of the amino acid sequence of the class A beta-lactamases suggested the existence of two subgroups in the same class, and this is discussed in the context of the evolution of the enzymes.

Amino Acid Sequence↗