Quantitative control of MHC class II expression by the transactivator CIITA

Activation of T lymphocytes is quantitatively controlled by the level of expression of MHC class II molecules. Both constitutive and inducible expression of MHC class II genes is regulated by the transactivator CIITA, which is itself tightly regulated. Since the level of MHC class II molecules expressed is a functionally essential parameter, it was of interest to explore whether MHC class II expression is quantitatively controlled by the level of the transactivator. This report shows that in a variety of experimental conditions one does indeed observe, in both mouse and man, a quantitative control of MHC class II expression by the level of CIITA. This relationship between the regulator gene, which behaves as a rate-limiting factor, and its target genes clarifies our understanding of the quantitative modulation of MHC class II expression, and thus of T lymphocyte activation.     

Promoter polymorphism rs3087456 in the MHC class II transactivator gene is not associated with susceptibility for selected autoimmune diseases in German patient groups

We analysed whether the single nucleotide polymorphism (SNP) rs3087456 in the promoter of the MHC class II transactivator (MHC2TA) gene is associated with manifestation of rheumatoid arthritis, multiple sclerosis, narcolepsy and Wegener granulomatosis. The recently reported association in a northern population of the MHC2TA variation with these autoimmune diseases is not evident in the German population.     

CIITA反义RNA抑制MHCII类分子表达

为探索利用CIITA (MHCclassIItransactivator)基因反义RNA抑制MHCII类分子表达的可能性 ,为CIITA的应用研究奠定基础。利用RT PCR扩增能与CIITAcDNA第 95至 5 0 0bp互补的片段 ,并构建成pcDNA3/CIITAa 重组质粒 ,脂质体转染法将其转入人HeLa/Raji细胞和猪PIEC/L2 3细胞 ,流式细胞术动态检测反义RNA对人 /猪MHCII类分子的抑制率和抑制程度。结果显示HeLa、Raji、PIEC和L2 3四种细胞MHCII类分子受抑制率分别为 4 6 7% ( 7/ 15 ) ,4 0 % ( 6 / 15 ) ,4 6 7% ( 7/ 15 )和33 3% ( 5 / 15 )。典型受抑克隆细胞MHCII类分子受抑程度高达 85 % ,反义RNA对MHCII类分子的抑制时间持续 35～ 5 0d。CIITA反义RNA能有效抑制人 /猪MHCII类分子的表达 ,它在自身免疫和移植免疫中有一定的应用前景     

Genetic influence of the nonclassical major histocompatibility complex class I molecule MICB in multiple sclerosis susceptibility

It has been widely reported that the major histocompatibility complex (MHC) class II region provides the main genetic contribution to multiple sclerosis (MS) susceptibility. However, recent studies have suggested that the MHC class I region may also contribute to the development of MS. In this study, we investigated the possible association of the human leukocyte antigen (HLA)-B, MHC class I chain-related gene B (MICB) and MHC class I chain-related gene A (MICA) genes, located in the MHC class I region, with MS susceptibility. For this purpose, we analyzed the distribution of HLA-DR, HLA-B, MICB and MICA alleles in 121 MS patients and 156 healthy controls. Neither HLA-B nor MICA alleles were found to be associated with MS susceptibility, and only the frequency of HLA-DRB1*01 allele was found to be increased in controls (31% vs 14%, P(c) = 0.011). However, MICB*004 allele frequency was significantly increased in MS patients (46.3% vs 23.3%, P(c) < 0.001, odds ratio = 2.82, 95% confidence interval = 1.68-4.73). Although, MICB*004 and HLA-DRB1*15 belong to the AH 7.1 ancestral haplotype, the association of MICB*004 to MS susceptibility was found to be independent of HLA-DRB1*15 in our population. This and previous studies clearly suggest that the MHC class I, in addition to class II, could be involved in MS susceptibility.     

构建可抑制HLA-DR/DQ表达的MHC-Ⅱ类分子反式激活因子基因的突变体及其机制

目的：构建能抑制MHC—Ⅱ类分子表达的MHC—Ⅱ类分子反式激活因子(MHC class Ⅱ transactivator，CⅡTA)基因的突变体．并探讨其抑制MHC—Ⅱ类分子表达的机制。方法：用PCR、酶切及连接技术，构建不含起始密码子的pcDNA3mCⅡTA2，含起始密码子的pcDNA3mCⅡTA3以及含起始密码子及NLS(nuclear localization signal)的pcDNA3mCⅡTA4突变体。用脂质体转染法，将上述3种突变体及空载体pcDNA3转入Hela细胞和Raji细胞中。用流式细胞术和RT-PCR法，观察他们对Hela／Raji细胞HLA—DR／DQ分子的诱导性和组成性表达的影响。将mCⅡTA4转移到对四环素浓度依赖的质粒pU-HD10-3上，通过改变培养环境中四环素的浓度，调节外源CⅡTA突变体的表达量，观察突变体的表达量与MHC-Ⅱ类分子受抑率的关系。结果：细胞和基因水平证实，pcDNA3mCⅡTA3和pcDNA3mCⅡTA4对Hela／Raji细胞HLA-DR／DQ的表达均有明显的抑制作用；而pcDNA3mCⅡTA2和空载体pcD-NA3无此作用。MHC-Ⅱ类分子被抑制的程度与外源转入CⅡTA突变体(pUHD10-3mCⅡTA4)的量明显相关。结论：成功地构建pcDNA3mCⅡTA3和pcDNA3mCⅡTA4，并能抑制HLA-Ⅱ类分子的表达。初步证实CⅡTA突变体是通过与胞内的野生型CⅡTA竞争性结合反式激活蛋白，来抑制MHC-Ⅱ类分子的转录和表达。     

MHC II molecules in inflammatory diseases: interplay of qualities and quantities

It is generally accepted that MHC II molecules confer susceptibility to inflammatory diseases because of the different abilities they possess for binding and presenting peptides to T cells. A new study suggests that the level of MHC II gene expression is also a risk factor for such diseases. It shows that a polymorphism in the promoter of the MHC II transactivator (MHC2TA) gene (which encodes CIITA), leads to reduced MHC2TA expression, and hence reduced production of MHC II molecules. This predisposes to rheumatoid arthritis, multiple sclerosis and myocardial infarction.     

Tumor necrosis factor receptor II (TNFRII) exon 6 polymorphism in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a complex autoimmune disease that exhibits extensive clinical heterogeneity. Several studies have suggested a role for tumor necrosis factor alpha (TNFalpha) in SLE and recently, the locus encompassing the TNF receptor II (TNFRII), which is a mediator of TNF effect, was amongst the candidate loci suggested by genetic linkage studies of multi-case SLE families. Komata et al. reported an association between a polymorphism at position 196 (R allele) of TNFR II and SLE in Japanese patients. We have typed SLE patients from two different ethnic populations, Spanish and UK Caucasoids, for this polymorphism using a polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP)-based technique. No significant differences in allele or genotype frequencies were found between cases and matched controls in either population. The TNFRII 196R allele does not appear to be associated with SLE susceptibility in either Spanish or UK populations.     

Major histocompatibility complex class II and C4 alleles in Mexican Americans with systemic lupus erythematosus

Abstract: Few data exist on associations of class II and class III alleles of the major histocompatibility complex (MHC) and susceptibility to systemic lupus erythematosus (SLE) in Mexican Americans, a group of predominantly mixed Spanish and Native American ancestry. Therefore, MHC class II alleles (HLA-DRB1, DQA1, DQB1, DPA1 and DPB1 alleles) and C4 allotypes were determined in 52 Mexican American SLE patients and 105 ethnic-matched controls. HLA-DRB1*0301 and C4A*Q0 were each increased in the SLE patients, especially HLA-DRB1*0301 in those with anti-Ro/SSA autoantibodies. C4A*Q0 was associated with HLA-DRB1*0301 only in a minority of patients and controls. Anti-U1-RNP antibodies were significantly associated with the presence of HLA-DQB1*0302, and the risk for the production of anti-Ro antibodies was heightened by the presence of at least three (out of four possible) DQA1 chains possessing a glutamine at position 34 and/or DQB1 chains a leucine at position 26 of their outermost domains. Thus the HLA class II and C4 null allele associations that have been noted in other ethnic groups are also found in Mexican Americans, suggesting shared susceptibility factors across ethnic lines in predisposition to SLE.     

Hetero- and homozygosity of MHC class II gene products in systemic lupus erythematosus. The Members of the Deutsche Multizentrische SLE-Studie.

An analysis of HLA class II antigens in 356 white patients with systemic lupus erythematosus (SLE) showed that all HLA-DR and -DQ homozygous and heterozygous combinations appear with frequencies expected from the observed gene frequencies. HLA-DR2 and HLA-DR3 gene frequencies were both increased in SLE, as were the odds ratios of all DR2 and DR3 hetero- and homozygous combinations. HLA-DR2/C4AQ0 heterozygotes were also not increased over expected values. Therefore, gene complementation at MHC loci does not contribute to susceptibility to SLE, but rather one or two MHC allele(s) in linkage with HLA-DR2 and HLA-DR3.     

CIITA M1-RNA抑制HeLa细胞表面MHC II类抗原的表达

探讨MHC II类转录激活因子(CIITA)的M1-RNA对细胞表面MHC II类分子表达的抑制。M1-RNA是核糖核酸酶P的催化活性单位,设计并克隆针对CIITA第452、629位点的M1-RNA(分别为M1-452-GS、M1-629-GS)及其相应的CIITA靶基因,分别插入pUC19、pGEM-7zf(+)载体,进行细胞外切割活性筛选。将细胞外切割作用明显的M1-629-GS亚克隆入psNAV载体(psNAV-M1-629-GS,pA629)并稳定转染HeLa细胞株,流式细胞术检测经典的MHC II类抗原(HLA-DR、-DP、-DQ)的表达,RT-PCR检测CIITA的mRNA水平。在重组人γ干扰素诱导下,pA629阳性HeLa细胞株表面HLA-DR、-DP抗原表达分别降低了83.03%及89.91%;同时CIITA的mRNA含量明显减少(P<0.05)。CIITA的M1-RNA抑制了自身mRNA含量,从而阻止其调控的MHC II类分子的表达,为移植物抗宿主病的研究提供了一种新方法。     

Influenza A virus abrogates IFN-gamma response in respiratory epithelial cells by disruption of the Jak/Stat pathway

The innate immunity to viral infections induces a potent antiviral response mediated by interferons (IFN). Although IFN-gamma is detected during the acute stages of illness in the upper respiratory tract secretions and in the serum of influenza A virus-infected individuals, control of influenza A virus is not dependent upon IFN-gamma as evidenced by studies using anti-IFN-gamma Ab and IFN-gamma(-/-) mice. Thus, we hypothesized that IFN-gamma is not critical in host survival because influenza A virus has mechanisms to evade the antiviral activity of IFN-gamma. To test this, A549 cells, an epithelial cell line derived from lung adenocarcinoma, were infected with influenza virus strain A/Aichi/2/68 (H3N2) (Aichi) and/or stimulated with IFN-gamma to detect IFN-gamma-stimulated MHC class II expression. Influenza A virus infection inhibited IFN-gamma-induced up-regulation of HLA-DRalpha mRNA and the IFN-gamma induction of class II transactivator (CIITA), an obligate mediator of MHC class II expression. Nuclear translocation of Stat1alpha upon IFN-gamma stimulation was significantly inhibited in influenza A virus-infected cells and this was associated with a decrease in Tyr701 and Ser727 phosphorylation of Stat1alpha. Thus, influenza A virus subverts antiviral host defense mediated by IFN-gamma through effects on the intracellular signaling pathways.     

The antagonism of interferon-gamma (IFN-gamma) by heparin: examination of the blockade of class II MHC antigen and heat shock protein-70 expression

IFN-gamma is a pleiotropic cytokine that is primarily involved in the regulation of immune cell activation and the development of tissue inflammation. It is capable of activating a range of non-immune cells, including those of the vascular endothelium. These cells respond by increasing the expression of intracellular and cell-surface molecules such as class II MHC antigens and adhesion molecules that, together, increase the tendency for interaction with immune cells. It is known that IFN-gamma can bind cell surface and extracellular heparan sulphate. Furthermore, soluble heparin can inhibit the function of this cytokine, presumably by competitive displacement from the cell surface, resulting in the failure of normal receptor signal transduction. In this study it is shown that heparin can prevent normal induction of the class II transactivator and heat shock cognate protein-70 in an IFN-gamma-treated endothelial cell line. Both of these molecules are dependent on the activation of intracytoplasmic STAT-1, which is the most receptor proximal component of their respective induction pathways. This provides further evidence for the blockade by heparin of ligand activation of the specific IFN-gamma receptor.