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PubMed1991

Molecular biology of murine MHC class II genes.

The murine class II genes are contained in the I region of the major histocompatibility complex (MHC). In the mouse, there are seven class II genes: A beta 3, A beta 2, A beta, E beta, E beta 2, A alpha, and E alpha. The A beta and A alpha genes code for the two polypeptide chains that form the I-A immune response molecule. The E beta and E alpha genes code for the two polypeptide chains that form the I-E immune response molecule. This review covers the genetic organization of the I region and the exon-intron structure of the class II genes. This review also discusses site-directed mutagenesis and exon shuffling studies and the effect of these changes on the function of Ia genes. Regulation of the cellular expression of Ia genes is discussed with emphasis on recent studies involving class II transgenic mice. Also, studies mapping recombination hotspots within the E alpha and E beta genes are reviewed.

Animals↗
PubMed1999

Absence of MHC class II gene expression in a patient with a single amino acid substitution in the class II transactivator protein CIITA.

We investigated the underlying genetic defect in an immunodeficient patient who presented with recurrent bacterial infections in his late twenties and demonstrated a transcriptional defect in major histocompatibility complex (MHC) class II regulation. Transient heterokaryon analysis implicated functional loss of CIITA, the MHC class II transactivator protein, and in support of this MHC class II antigen expression was restored by stable transfection with the wild-type molecule. A single amino acid substitution, phenylalanine to serine, in the COOH-terminal portion of the CIITA sequence correlated with reduced transcription of both classical (HLA-DP, -DQ, and -DR) and nonclassical (HLA-DM and -DO) class II genes. The long survival of the patient, although remarkable, was not associated with partial CIITA function as evidenced by residual MHC class II expression. These data define at high resolution a region of CIITA that is essential for function in both professional and nonprofessional antigen presenting cells and which could potentially constitute a target for therapeutic intervention by novel factors with a propensity to downregulate MHC class II antigen expression.

Adult↗
PubMed1996

Sequence analysis of a polymorphic Mhc class II gene in Pacific salmon.

Polymorphism of the nucleotide sequences encoding 149 amino acids of linked major histocompatibility complex (Mhc) class II B1 and B2 peptides, and of the intervening intron (548-773 base pairs), was examined within and among seven Pacific salmon (Oncorhynchus) species. Levels of nucleotide diversity were higher for the B1 sequence than for B2 or the intron in comparisons both within and between species. For the codons of the peptide binding region of the B1 sequence, the level of nonsynonymous nucleotide substitution (dN) exceeded the level of synonymous substitution (dS) by a factor of ten for within-species comparisons, and by a factor of four for between-species comparisons. The excess of dN indicates that balancing selection maintains diversity at this salmonid Mhc class II locus, as is common for Mhc loci in other vertebrates. Levels of nucleotide diversity for both the exon and intron sequences were greater among than within species, and there were numerous species-specific nucleotides present in both the coding and noncoding regions. Thus, neighbor-joining analysis of both the intron and exon regions provided phylogenies in which the sequences clustered strongly by species. There was little evidence of shared ancestral (trans-species) polymorphism in the exon phylogeny, and the intron phylogeny depicted standard relationships among the Pacific salmon species. The lack of shared allelic B1 lineages in these closely related species may result from severe bottlenecks that occurred during speciation or during the ice ages that glaciated the rim of the north Pacific Ocean approximately every 100000 years in the Pleistocene.

Amino Acid Sequence↗
PubMed2001

Toxoplasma gondii down-regulates MHC class II gene expression and antigen presentation by murine macrophages via interference with nuclear translocation of STAT1alpha.

The obligate intracellular protozoan parasite Toxoplasma gondii is able to establish persistent infections within human and animal hosts. We have shown recently that T. gondii down-regulates IFN-gamma-induced MHC class II expression in murine bone marrow-derived macrophages (BMM4). As shown in this study, the capacity of IFN-gamma-activated murine BMMphi to present ovalbumin to CD4+ T cell hybridomas was dose-dependently inhibited by T. gondii. IFN-gamma-induced up-regulation of H2-Aa, H2-Ab, H2-Eb, H2-Ma, H2-Mb, H2-Oa and invariant chain transcripts was prominently down-regulated by T. gondii. Furthermore, mRNA levels of class II transactivator and interferon-regulatory factor-1 were significantly diminished. Electromobility shift assays demonstrated a decrease in the binding activity of nuclear extracts to the IFN-gamma-activated site after infection with T. gondii, indicating parasitic interference with IFN-gamma-induced signaling. However, neither the expression of the IFN-gammaR nor the IFN-gamma-induced tyrosine phosphorylation of IFN-gammaR alpha chain and signal transducer and activator of transcription (STAT) 1alpha was diminished by T. gondii. IFN-gamma-induced nuclear translocation of STAT1alpha was nevertheless inhibited after infection as demonstrated by immunofluorescence microscopy and subcellular fractionation analyses. In conclusion, this novel mechanism of microbial interference with MHC class II gene expression may contribute to intracellular survival and establishment of persistent infection with T. gondii.

Active Transport, Cell Nucleus↗
PubMed1992

Induction of MHC class II gene products in rat intestinal epithelium during graft-versus-host disease and effects on the immune function of the epithelium.

The induction of major histocompatibility complex (MHC) class II expression in the epithelium of the small intestine of the rat during graft-versus-host disease (GVHD) and the effect of this process on the capacity of isolated epithelial cells to present antigen has been investigated. By immunohistology, increased class II (I-A) was noted in lamina propria cells and villus epithelium and de novo expression in crypt epithelium by Day 7 after transfer of parental spleen cells into irradiated hybrid rats. This increased expression reached a maximum by Day 9 or 10. The kinetics of induction of I-E products paralleled those of I-A in villus epithelium, but I-E was not seen in crypt epithelium. Direct radioimmunoassay of class II in isolated villus and crypt epithelial cells revealed a minor peak of class II, particularly in villus cells, very soon after cell transfer which waned and then increased to a second peak at Days 7-9. Assay of presentation of ovalbumin by isolated enterocytes to primed T cells at the peak of class II induction showed that increased class II expression by villus cells mediated enhanced antigen-presenting activity, whereas increases in crypt cell class II did not enable these cells to present ovalbumin.

Animals↗
PubMed2006

Effect of interferon alpha on MHC class II gene expression in ex vivo human islet tissue.

Type 1 diabetes (T1D) is caused by autoimmune destruction of the insulin-producing beta-cells of the islets of Langerhans. One still open question is where naive islet-reactive T cells encounter antigens and become stimulated. In this report we have re-examined the expression of MHC class II (MHCII) genes in human islets to further explore the possibility that non-professional antigen presenting cells (APCs) within islets contribute to autoimmunity. Since development of T1D has been linked to viral infections, we also studied ex-vivo MHCII expression in response to interferon-alpha (IFNalpha) in islet tissue and in different APCs. The findings are: first, MHCII genes expression in human islets is linked with the expression of the class II transactivator isoform transcribed from the promoter IV, similar to that described in non-professional APCs. Second, there is IFNalpha-mediated lineage-specific regulation of MHCII genes expression, seen as a decrease in the accumulation of MHCII transcripts in pancreatic islets opposite to an increase in dendritic cells and B-lymphoblastoid cell lines. Third, there is allele-specific regulation of the HLA-DQA1 gene by IFNalpha in islet tissue. These findings may begin to explain the molecular events that create favorable conditions for organ-specific autoimmunity and explain the incomplete penetrance of T1D susceptibility alleles.

Alleles↗
PubMed1999

Analysis of the defect in IFN-gamma induction of MHC class II genes in G1B cells: identification of a novel and functionally critical leucine-rich motif (62-LYLYLQL-68) in the regulatory factor X 5 transcription factor.

MHC class II deficiency found in bare lymphocyte syndrome patients results from the absence or dysfunction of MHC class II transcriptional regulators, such as regulatory factor X (RFX) and class II transactivator (CIITA). Understanding the roles of these factors has been greatly facilitated by the study of genetic defects in cell lines of bare lymphocyte syndrome patients, as well as in cell lines that have been generated by chemical mutagenesis in vitro. The latter group includes MHC class II-deficient lines that are no longer responsive to induction by IFN-gamma. Here, we show that the defect in G1B, one such cell line, is attributed to the lack of functional RFX5, the largest subunit of RFX. The RFX5 gene isolated from G1B cells contains two separate single-base pair mutations. One alteration does not exhibit a phenotype, whereas a leucine-to-histidine mutation eliminates DNA-binding and transactivating functions. This mutation lies outside of previously defined functional domains of RFX5 but within an unusual, leucine-rich region (62-LYLYLQL-68). To further investigate the significance of the leucine-rich region, we targeted all neighboring leucine residues for mutagenesis. These mutants were also unable to transactivate a MHC class II reporter gene, confirming that these leucine residues play an essential role in RFX activity and characterize a novel leucine-rich motif.

Amino Acid Motifs↗
PubMed2003

Histone deacetylation, but not hypermethylation, modifies class II transactivator and MHC class II gene expression in squamous cell carcinomas.

In this study, we first categorized nine squamous cell carcinoma (SCC) cell lines into two groups in terms of the expression of HLA-DR, -DP, and -DQ molecules. Subsequently, the expression of class II transactivator (CIITA) was studied in these cell lines, because it is widely accepted that the expression of MHC class II molecules is regulated by different types of CIITA transcripts that are initiated by distinct promoters. The majority of the SCC cell lines (six of nine) expressed HLA-DR molecules and CIITA promoter IV (pIV) transcripts in the presence of IFN-gamma. In contrast, three of the nine SCC cell lines were completely negative for class II molecules and all types of CIITA, suggesting epigenetic changes in the promoter region in these cells. Previously, methylation of CIITA pIV was reported to silence CIITA gene expression. We extensively studied the methylation status of CIITA pIV using a panel of 22 SCC cell lines. Remarkably, none of the SCC cell lines demonstrated hypermethylation at the site. In contrast, treatment with a histone deacetylation inhibitor in combination with IFN-gamma clearly restored the expression of the CIITA type IV gene in the HLA-DR-negative SCC cell lines, and the acetylation status of histone H3 examined by chromatin immunoprecipitation analysis was closely associated with the gene expression. Moreover, stable transfection of the CIITA gene into an HLA-DR-negative cell line restored constitutive expression of MHC class II molecules. Therefore, histone deacetylation, but not hypermethylation, modifies CIITA DNA and class II gene expression in SCC.

Acetylation↗
PubMed1987

Distinct mechanisms regulate MHC class II gene expression in B cells and macrophages.

In a previous series of studies, we had shown that the constitutive Ia expression in an immunoselected Ia-human B cell variant, RJ 2.2.5, could be restored by somatic cell hybridization with mouse B cells. These experiments allowed us to show the existence of a transacting activator factor(s) operating across species barriers and encoded by the aIr-1 locus located on mouse chromosome 16. The aim of the present study was to investigate whether the B cell constitutive Ia expression and the inducible Ia expression, as seen in macrophages treated with IFN-gamma, are controlled by similar intracellular factors. To this purpose, we constructed an interspecies somatic cell hybrid between the human Ia-RJ 2.2.5 B cells and the mouse Ia-P388 D1 macrophage cells. These murine cells transiently express Ia antigens when incubated with IFN-gamma. Our results show that RJ 2.2.5 X P388 D1 cell hybrids do not express either human or mouse class II gene products. Treatment with human recombinant IFN-gamma did not modify the MHC phenotype of either the hybrid cells or the human parental cells. On the other hand, treatment of the hybrid cells with murine recombinant IFN-gamma resulted in de novo expression of mouse Ia mRNA and corresponding cell surface antigens without, however, reinduction of the human class II-positive phenotype. Furthermore, treatment with the mouse lymphokine significantly increased the levels of human HLA class I mRNA and corresponding cell surface antigens in the hybrid cells, further reinforcing the notion of the existence of non-species-specific secondary mediators generated after receptor-ligand interaction in the IFN-gamma system. Together, these results indicate that in macrophages, the intracellular events taking place after binding of IFN-gamma with its own receptor and leading to the expression of a class II-positive phenotype do not operate via an activation of the aIr-1 locus and/or its products. Thus, at least in our experimental system, we can firmly establish a first, relevant distinction between constitutive and inducible class II gene expression. This difference, dictated by the specific differentiation program of each cell type, may be relevant for the understanding of the function of class II gene products.

Animals↗
PubMed1988

Molecular characterization and genetic mapping of class I and class II MHC genes of the domestic cat.

The major histocompatibility complex (MHC) of the domestic cat has been poorly characterized to date, primarily because of numerous difficulties in the preparation of allotypic sera. We present here a comparative analysis of class I and class II genes in domestic cat populations using molecular probes of the MHC from man and mouse. The cat possesses a minimum of 20 class I loci and 5 class II genes per haploid genome. Class I genes of the domestic cat expressed limited restriction fragment length polymorphism. The average percent difference of the size of DNA fragments between individual cats was 9.0%, a value five times lower than the value for mice, but comparable to the human DNA polymorphism level. Class I and class II genes were both genetically mapped to feline chromosome B2 using a panel of rodent x cat somatic cell hybrids. Since feline chromosome B2 is syntenically homologous to human chromosome 6 and mouse chromosome 17, these results affirm the linkage conservation of the MHC-containing linkage group in the three mammalian orders.

Animals↗
PubMed1995

Class II MHC gene expression in microglia. Regulation by the cytokines IFN-gamma, TNF-alpha, and TGF-beta.

The molecular mechanism(s) by which three cytokines (IFN-gamma, TNF-alpha, TGF-beta) affect class II MHC gene expression in primary rat microglia was examined. IFN-gamma is a potent inducer of the class II gene, and this induction is unaffected by treatment with either TNF-alpha or TGF-beta. Transient transfection of primary rat microglia with an HLA-DRA promoter linked to the chloramphenicol acetyltransferase reporter gene (DRA-CAT) demonstrated that IFN-gamma acts at the transcriptional level to induce class II MHC gene expression, and that TNF-alpha and TGF-beta have no influence on IFN-gamma-induced promoter activity. Experiments using a series of DRA substitution mutants that individually affect the W, X1, X2, or Y elements, as well as a double mutation in both X1 and X2, indicate that all four of these elements are required for responsiveness of the DRA promoter to IFN-gamma. The effect of IFN-gamma and TNF-alpha on DNA binding proteins by microglia was examined. A constitutive complex with specificity for the X2 box was detected in extracts from unstimulated microglia. IFN-gamma treatment changed this complex to migrate with slower mobility, and TNF-alpha had no effect on either the constitutive or IFN-gamma-induced complexes. These studies provide information on the molecular regulation of the class II MHC gene in microglia, a cell type critically involved in immune regulation within the central nervous system.

Animals↗
PubMed1995

TGF-beta suppression of IFN-gamma-induced class II MHC gene expression does not involve inhibition of phosphorylation of JAK1, JAK2, or signal transducers and activators of transcription, or modification of IFN-gamma enhanced factor X expression.

TGF-beta is a widely expressed immunoregulatory protein that exerts a diverse range of effects on many types of cells. One of the effects of TGF-beta is the inhibition of both constitutive and cytokine-inducible class II MHC gene expression. In this study, we demonstrate that TGF-beta inhibits expression of class II MHC surface protein, mRNA, and promoter activity in primary astrocytes, and that this inhibition is both dose and time dependent. TGF-beta does not act to inhibit IFN-gamma-induced gene expression in a global fashion, as induction of ICAM-1 and IRF-1 gene expression by IFN-gamma is unaffected by treatment with TGF-beta. Furthermore, TGF-beta does not affect events that are involved in IFN-gamma-induced intracellular signaling such as tyrosine phosphorylation of JAK1, JAK2, and STAT1 alpha, nor does it affect IFN-gamma induction of the class II X2 box binding protein IFN-gamma enhanced factor X. We speculate that TGF-beta may be exerting its effects by modulating the expression or function of constitutively expressed factors responsible for regulation of class II MHC gene expression in astrocytes.

Animals↗
PubMed1987

The expression of class II MHC gene products by fallopian tube epithelium in pregnancy and throughout the menstrual cycle.

The expression of HLA class II antigens by human fallopian tube epithelium was investigated in ectopic tubal pregnancy, in normal early and full-term intrauterine pregnancy, and during the menstrual cycle. Monoclonal antibodies directed against non-polymorphic (DA6.231, CR3/43, B7/21) and polymorphic (DA6.147, DA6.164, anti-leu-10) determinants of the HLA-D locus were used in a standard indirect immunoperoxidase method on fresh cryostat sections of fallopian tube. In ectopic pregnancy the tube epithelium showed uniform, intense reactivity for DR, DP and DQ. A similar reaction pattern was observed in normal first-trimester pregnancy. At term, most epithelial cells were DR-, DP- and DQ-positive, but a few were DP- and DQ-negative. In fallopian tubes from non-pregnant individuals, a variable number of epithelial cells labelled for DR alpha and DR beta but there was essentially no reactivity for DP or DQ. These results suggest differential regulation of class II MHC gene expression by tube epithelial cells, possibly mediated by hormones and/or a trophoblast product.

Antibodies, Monoclonal↗
PubMed2002

MHC class II genes in European wolves: a comparison with dogs.

The genome of the grey wolf, one of the most widely distributed land mammal species, has been subjected to both stochastic factors, including biogeographical subdivision and population fragmentation, and strong selection during the domestication of the dog. To explore the effects of drift and selection on the partitioning of MHC variation in the diversification of species, we present nine DQA, 10 DQB, and 17 DRB1 sequences of the second exon for European wolves and compare them with sequences of North American wolves and dogs. The relatively large number of class II alleles present in both European and North American wolves attests to their large historical population sizes, yet there are few alleles shared between these regions at DQB and DRB1. Similarly, the dog has an extensive array of class II MHC alleles, a consequence of a genetically diverse origin, but allelic overlap with wolves only at DQA. Although we might expect a progression from shared alleles to shared allelic lineages during differentiation, the partitioning of diversity between wolves and dogs at DQB and DRB1 differs from that at DQA. Furthermore, an extensive region of nucleotide sequence shared between DRB1 and DQB alleles and a shared motif suggests intergenic recombination may have contributed to MHC diversity in the Canidae.

Amino Acid Substitution↗
PubMed1988

Expression of class II MHC gene products by macrophages in human uteroplacental tissue.

The expression of class II MHC determinants by fetal and maternal macrophages in human uteroplacental tissues was examined with monoclonal antibodies directed against HLA-DR, DP and DQ antigens. Maternal macrophages in early and full-term pregnancy decidua were HLA-DR positive, and a substantial proportion also expressed DP and DQ antigens. Fetal macrophages in chorionic villous stroma in first-trimester pregnancy were rarely HLA-DR positive, and DQ and DP antigens were never expressed. In term placental tissues, groups of villous stromal macrophages were HLA-DR positive, as were fetal macrophages within amniotic mesenchyme. In contrast, DP and DQ antigens were detected on a small minority of fetal macrophages in term placental tissues. DP and DQ antigens were not detected in the absence of DR antigens.

Chorionic Villi↗
PubMed1999

MHC class II gene associations with autoantibodies to U1A and SmD1 proteins.

Autoantibodies against U small nuclear ribonucleoproteins (snRNP) are frequently present in the serum of patients with systemic rheumatic diseases, and have been reported to be associated with HLA-DR and -DQ genes. To better define the role of HLA genes in the production of such antibodies, we studied immunogenetic associations with autoantibodies reacting with U1 RNP, U1A and SmD1 proteins, and synthetic peptides containing immunodominant linear epitopes of these proteins. Only two out of the 15 overlapping peptides of U1A (i.e. peptides 35-58 and 257-282) and three of 11 peptides of SmD1 (i.e. peptides 1-20, 44-67 and 97-119) were significantly recognized by patients' sera selected on the basis of their antibody positivity with RNP in immunodiffusion. The distribution of DRB1, DQB1 and DPB1 alleles among the anti-RNP antibody-positive patients (n = 28) and healthy control subjects was similar. Antibodies against U1A (tested in Western immunoblotting with HeLa cell extracts) were positively associated to DRB1*06 allele; antibodies reacting with SmD1 peptide 44-67 were negatively associated to DRB1*02 and DQB1*0602 alleles. No association was found between DPB1 alleles and antibodies reacting with U1A and SmD1 antigens. This first study reporting an association between autoantibodies reacting with U1A and SmD1 proteins (and peptides of these proteins), and immunogenetic markers suggest that the production of antibody subsets directed against different components (or regions of these proteins) bound to the same snRNP particle is associated with distinct MHC class II alleles.

Alleles↗
PubMedDate not supplied

Functional expression of a transfected murine class II MHC gene.

The activation of T helper lymphocytes involves the recognition of class II major histocompatibility complex antigens, which are dimeric glycoproteins (of subunit composition A alpha A beta or E alpha E beta) expressed on the surfaces of macrophages and B lymphocytes. One approach to understanding the relationship between the structure of these antigens and their functions in the immune response is to clone the genes that encode them, to obtain functional expression of the cloned genes transfected into an appropriate cell line, and then to see how those functions are affected in variant genes generated in vitro. We report here the expression in Iad-bearing B cells of an Ak beta gene, which confers on the transfected cells the capacity for both allostimulation and antigen-dependent activation of an I-Ak-restricted T-cell clone.

Animals↗
PubMed1994

Ectopic expression of gamma interferon in the eyes of transgenic mice induces ocular pathology and MHC class II gene expression.

PURPOSE: To direct the expression of gamma IFN to the eyes of transgenic mice as a means of investigating the possible role of this lymphokine in ocular pathogenesis. METHODS: Transgenic mouse strains were generated by injection of a DNA fragment containing the murine alpha A-crystallin promoter fused to the coding sequence of murine gamma IFN gene. PCR and RT-PCR were used to screen for the presence of the transgene and mRNA analyses, respectively. Methacrylate-embedded eye sections were analyzed for morphology and cryosections for immunoperoxidase antibody staining. RESULTS: The most notable effects of gamma IFN in these transgenic mice include cataract, microphthalmia, blepharophimosis, microphakia, impairment of lens fiber formation, arrest of retinal differentiation, serous retinal detachment with presence of macrophages in the subretinal space, persistent hyperplastic primary vitreous, and corneal vascularization. MHC class II mRNA levels were significantly increased in the transgenic eyes and MHC class II proteins were expressed in their cornea, iris, ciliary body, choroid, lens and RPE. CONCLUSIONS: Ectopic expression of gamma IFN in the lens affected the growth of the whole eye, resulting in microphthalmia and microphakia. The author's data suggest that alpha ACry-gamma IFN transgenic mouse ocular cells express functional gamma IFN receptors and that interaction of gamma IFN with its receptor induced biochemical and morphologic changes in the transgenic eyes. These mice provide an animal model for the study of the linkage between aberrant MHC expression and predisposition to autoimmune diseases.

Animals↗