Insulin-IGF2 region on chromosome 11p encodes a gene implicated in HLA-DR4-dependent diabetes susceptibility

A class of alleles at the VNTR (variable number of tandem repeat) locus in the 5' region of the insulin gene (INS) on chromosome 11p is associated with increased risk of insulin-dependent diabetes mellitus (IDDM), but family studies have failed to demonstrate linkage. INS is thought to contribute to IDDM susceptibility but this view has been difficult to reconcile with the lack of linkage evidence. We thus investigated polymorphisms of INS and neighbouring loci in random diabetics, IDDM multiplex families and controls. HLA-DR4-positive diabetics showed an increased risk associated with common variants at polymorphic sites in a 19-kilobase segment spanned by the 5' INS VNTR and the third intron of the gene for insulin-like growth factor II (IGF2). As INS is the major candidate gene from this region, diabetic and control sequence were compared to identify all INS polymorphisms that could contribute to disease susceptibility. In multiplex families the IDDM-associated alleles were transmitted preferentially to HLA-DR4-positive diabetic offspring from heterozygous parents. The effect was strongest in paternal meioses, suggesting a possible role for maternal imprinting. Our results strongly support the existence of a gene or genes affecting HLA-DR4 IDDM susceptibility which is located in a 19-kilobase region of INS-IGF2. Our results also suggest new ways to map susceptibility loci in other common diseases.     

Linkage of a nasopharyngeal carcinoma susceptibility locus to the HLA region

The frequency of nasopharyngeal carcinoma is nearly 100-fold higher in southern Chinese than in most European populations. Earlier studies have suggested that an increased risk of nasopharyngeal carcinoma is associated with specific haplotypes in the HLA region: relative risks slightly over twofold were found for haplotypes A2, Bw46 and the antigen B17. We now report a linkage study based on affected sib pairs which suggests that a gene closely linked to the HLA locus confers a greatly increased risk of nasopharyngeal carcinoma. The maximum likelihood estimate is of a relative risk of approximately 21. The relationship between this suspected disease susceptibility gene (or genes) and known viral and environmental aetiological factors remains to be elucidated.     

Prevention of autoimmune insulitis by expression of I-E molecules in NOD mice

The NOD (non-obese diabetic) mouse spontaneously develops insulin-dependent diabetes mellitus (IDDM) characterized by autoimmune insulitis, involving lymphocytic infiltration around and into the islets followed by pancreatic beta (beta) cell destruction, similar to human IDDM. Genetic analysis in breeding studies between NOD and C57BL/6 mice has demonstrated that two recessive genes on independent chromosomes contribute to the development of insulitis. One of the two recessive diabetogenic genes was found to be linked to the major histocompatibility complex (MHC). This is of interest, because the NOD strain has a unique class II MHC: it does not express I-E molecules as no messenger RNA for the alpha-chain of I-E is visible in Northern blot analysis; I-A molecules are not detected with any available monoclonal antibodies or by allo-reactive or autoreactive T-cell clones, although their expression is demonstrated with a conventional antiserum to Ia antigens. To examine whether the unusual expression of class II MHC molecules may be responsible for the development of autoimmune insulitis, we attempted to express I-E molecules in NOD mice selectively, without introducing other genes on chromosome 17 by using I-E-expressing C57BL/6 (B6(E alpha d)) transgenic mice. We report here that the expression of I-E molecules in NOD mice can prevent the development of autoimmune insulitis.     

HLA-D region beta-chain DNA endonuclease fragments differ between HLA-DR identical healthy and insulin-dependent diabetic individuals

The human HLA-D histocompatibility region encodes class II antigens each of which consists of two polypeptide chains (alpha and beta) inserted in the plasma membrane. These molecules are implicated in the regulation of the immune response but several human diseases are also found to be associated with certain HLA-DR antigens. The occurrence of insulin-dependent (type I) diabetes (IDDM) is strongly associated with HLA-DR3 and/or 4 (ref. 5). The class II antigens, however, show a marked genetic polymorphism associated with the beta-chains which seem, from hybridization studies, to be encoded by several genes. We have therefore used the beta-chain cDNA probe, pDR-beta-1 (refs 8, 10) to test whether there are differences in hybridization pattern between DNA from healthy individuals and diabetic patients, after digestion with restriction endonucleases. Among the HLA-DR 4 and 3/4 individuals, the IDDM patients showed an increased frequency of a PstI 18 kilobase (kb) fragment. A BamHI 3.7 kb fragment, frequent among controls (30-40%), was rarely detected in the IDDM patients (0-2%). These differences may be related to susceptibility to develop the disease.     

Prevention of insulin-dependent diabetes mellitus in non-obese diabetic mice by transgenes encoding modified I-A beta-chain or normal I-E alpha-chain

Insulin-dependent diabetes mellitus (IDDM) is a disease with an autoimmune aetiology. The inbred non-obese diabetic (NOD) mouse strain provides a good animal model of the human disease and genetic analysis suggests that, as in man, at least one of the several genes controlling the development of IDDM is linked to the major histocompatibility complex. The NOD mouse does not express I-E owing to a deletion in the promoter region of the I-E alpha-chain gene, and the sequence of NOD I-A beta-chain in the first external domain is unique with His 56 and Ser 57 replacing Pro and Asp, respectively, at these positions. There has been considerable interest in the role amino acid 57 might have in conferring susceptibility to autoimmune diseases, including IDDM. The presence of a charged residue (such as Asp) at this position might affect the conformation of the peptide binding groove. But it could be assumed that Pro 56 gives rise to a different conformation of I-A beta-chain than does His 56. We therefore constructed transgenic NOD mice in which the transgene encoded a modified A beta nod with Pro 56, and studied its effect on the development of IDDM in this mouse strain. Previous studies have suggested that NOD mice expressing I-E as a result of the introduction of an I-E alpha-chain (E alpha) transgene are protected from the development of insulitis and hence IDDM. To explore further the protective effect of this molecule we constructed a second class of transgenic NOD mouse carrying an E alpha d transgene. Both transgenes protected the mice from IDDM, but this was not associated with a complete deletion of any T cells expressing commonly used T-cell receptor V beta genes.     

Different amino acids at position 57 of the HLA-DQ beta chain associated with susceptibility and resistance to IgA deficiency

The human leukocyte antigens (HLA) are implicated in the genetic susceptibility to a large number of diseases. Some of the diseases associated with HLA class II are related to specific amino acids or epitopes of the domain of the HLA class II molecule that is distal to the membrane. In man, selective immunoglobulin A deficiency is the most common immunodeficiency, frequently resulting in recurrent sino-pulmonary infections and gastro-intestinal disorders. Associations have been described with HLA class I, and to a lesser extent with different class II alleles, which might indicate that they share some common feature. Here we study 95 IgA-D patients and find positive associations with three DR-DQ haplotypes and a strong negative association with a fourth haplotype. Comparison of the sequences of the polymorphic amino-terminal domain of the DQ beta chain showed that the three 'susceptibility' haplotypes all had a neutral alanine or valine at position 57. The 'protective' allele had the negatively charged aspartic acid at this position (Asp57). Codon 57 of the HLA-DQ beta chain has been implicated in the susceptibility to insulin-dependent diabetes mellitus. Our data suggest that the same amino acid position could possibly also influence susceptibility and resistance to selective immunoglobulin A deficiency.     

Prevention of diabetes in non-obese diabetic I-Ak transgenic mice

The non-obese diabetic (NOD) mouse develops insulin-dependent diabetes mellitus (IDDM) with mononuclear cell infiltration of the islets of Langerhans and selective destruction of the insulin-producing beta-cells, as in humans. Most infiltrating cells are T lymphocytes, and most of these carry the CD4 antigen. Adoptive transfer of T cells from diabetic NOD mice into irradiated NOD or athymic nude NOD mice induces diabetes. Susceptibility to IDDM in NOD mice is polygenic, with one gene linked to the major histocompatibility complex class II locus, which in NOD mice expresses a unique I-A molecule but no I-E. Speculation exists as to the role of the I-A molecule in the diabetes susceptibility of NOD mice, especially regarding the significance of specific unique residues. To examine the role of the NOD I-A molecule in IDDM pathogenesis, we made NOD/Lt mice transgenic for I-Ak by microinjecting I-Ak alpha- and beta-genes into fertilized NOD/Lt eggs. Insulitis was markedly reduced and diabetes prevented in NOD/Lt mice expressing I-Ak.     

Characterization of MHC class II A genes in Hainan Eld’s deer (Cervus eldi hainanus)

The major histocompatibility complex(MHC) genes play pivotal roles in the immune system of vertebrates against antigens.They are also significant indicators of genetic structure,and are vital to species-level population viability analyses and disease risk assessments.In this study,two DRA and two DQA sequences were isolated from Hainan Eld’s deer(Cervus eldi hainanus) using rapid amplification of cDNA ends(RACE) and single-strand conformation polymorphism-heteroduplex(SSCP-HD) analysis.Nucleotide sequence analysis revealed large differences between the two DQA sequences,especially in their exon 2 regions,but only minimal differences between the variants of the DRA gene.Comparison of the predicted amino acid sequences of the Ceel-MHC class Ⅱ A variants with those from six other species revealed that these molecules share high homology among ruminants.A phylogenetic tree of four class Ⅱ A sequences from Hainan Eld’s deer and the other species placed the newly identified DQA and DRA genes on two distinct branches(100%-supportively),and further divided the two DQA sequences into 98%-supportive DQA1 and 99%-supportive DQA2 clusters,respectively.Therefore,this study identified monomorphic Ceel-DQA1 and Ceel-DQA2 genes,and one dimorphic Ceel-DRA gene from Hainan Eld’s deer.     

中国人重症肌无力的遗传易感性研究

重症肌无力与ＨＬＡⅡ类基因关联性在不同人种和民族中具有不同遗传易感性。为探讨中国人重症肌无力（ＭＧ）与ＨＬＡ－ＤＱ分子关联性，采用聚合酶链式反应—限制性片段长度多态性（ＰＣＲ－ＲＦＬＰ）方法，分析了５０例中国正常人及４９例重症肌无力患者的ＨＬＡ－ＤＱＡ１和－ＤＱＢ１座位的基因型。结果：共检出正常人ＤＱＡ１等位基因８种，ＤＱＢ１等位基因１０种，重症肌无力患者ＤＱＡ１等位基因８种，ＤＱＢ１等位基因９种。结果分析表明ＤＱＡ１＊０５０１与ＭＧ成负相关，ＤＱＢ１＊０３０２与ＭＧ成正相关。从基因水平首次用ＰＣＲ－ＲＦＬＰ方法得出中国人重症肌无力ＤＱ分子的易感基因型。     

Localization of type 1 diabetes susceptibility to the MHC class I genes HLA-B and HLA-A

The major histocompatibility complex (MHC) on chromosome 6 is associated with susceptibility to more common diseases than any other region of the human genome, including almost all disorders classified as autoimmune. In type 1 diabetes the major genetic susceptibility determinants have been mapped to the MHC class II genes HLA-DQB1 and HLA-DRB1 (refs 1-3), but these genes cannot completely explain the association between type 1 diabetes and the MHC region. Owing to the region's extreme gene density, the multiplicity of disease-associated alleles, strong associations between alleles, limited genotyping capability, and inadequate statistical approaches and sample sizes, which, and how many, loci within the MHC determine susceptibility remains unclear. Here, in several large type 1 diabetes data sets, we analyse a combined total of 1,729 polymorphisms, and apply statistical methods-recursive partitioning and regression-to pinpoint disease susceptibility to the MHC class I genes HLA-B and HLA-A (risk ratios >1.5; P(combined) = 2.01 x 10(-19) and 2.35 x 10(-13), respectively) in addition to the established associations of the MHC class II genes. Other loci with smaller and/or rarer effects might also be involved, but to find these, future searches must take into account both the HLA class II and class I genes and use even larger samples. Taken together with previous studies, we conclude that MHC-class-I-mediated events, principally involving HLA-B*39, contribute to the aetiology of type 1 diabetes.     

New class II-like genes in the murine MHC

Major histocompatibility complex (MHC) class I molecules present endogenous antigens to CD8+ (cytotoxic) T cells. MHC class II molecules present primarily exogenously derived antigens to CD4+ T cells. Three new genes (Ma, Mb1 and Mb2) located between the Pb and Ob genes of the murine MHC have properties indicating that they are members of the MHC class II gene family, but they are the most divergent class II members so far identified and are almost as closely related in sequence to class I genes as they are to the known class II genes.     

Identification and mapping to chromosome 1 of a susceptibility locus for periinsulitis in non-obese diabetic mice

Insulin-dependent diabetes mellitus (IDDM) is a polygenic disease caused by autoimmune destruction of insulin-producing beta cells in the islets of Langerhans. Its onset is preceded by a long and variable period in which lymphoid cells infiltrate the pancreas but first remain outside the islets (peri-insulitis) before invading them (insulitis). Among susceptibility loci, only the major histocompatibility complex (MHC) has been clearly assigned. Genetic study of the nonobese diabetic (NOD) mouse model for insulin-dependent diabetes mellitus has revealed genetic linkage of insulitis and of early onset diabetes with two non-MHC loci mapping to chromosome 3 and 11 respectively. Here we report a close association of periinsulitis with a third non-MHC locus mapping to chromosome 1. Successive stages in the progression of diabetic disease thus appear to be controlled by distinct genes or sets of genes.     

HLA-DQ beta gene contributes to susceptibility and resistance to insulin-dependent diabetes mellitus

Over half of the inherited predisposition to insulin-dependent diabetes mellitus maps to the region of chromosome 6 that contains the highly polymorphic HLA class II genes which determine immune responsiveness. Analysis of DNA sequences from diabetics indicates that alleles of HLA-DQ beta determine both disease susceptibility and resistance, and that the structure of the DQ molecule, in particular residue 57 of the beta-chain, specifies the autoimmune response against the insulin-producing islet cells.     

Structural and serological similarity of MHC-linked LMP and proteasome (multicatalytic proteinase) complexes

Major histocompatibility complex (MHC) class I molecules associate with peptides derived from endogenously synthesized antigens. Cytotoxic T-lymphocytes can thus scan class I molecules and bound peptide on the surface of cells for foreign antigenic determinants. Recent evidence demonstrates that the products of trans-acting, non-class I genes in the class II region of the MHC are required in the class I antigen-processing pathway. There are genes (called HAM1 and HAM2 in the mouse) in this region that encode proteins postulated to be involved in the transport of peptide fragments into the endoplasmic reticulum for association with newly synthesized class I molecules. But, the mechanism by which such peptide fragments are produced remains a mystery. At least two genes encoding subunits of the low-molecular mass polypeptide (LMP) complex are tightly linked to the HAM1 and HAM2 genes. We show that the LMP complex is closely related to the proteasome (multicatalytic proteinase complex), an intracellular protein complex that has multiple proteolytic activities. We speculate that the LMP complex may have a role in MHC class I antigen processing, and therefore that the MHC contains a cluster of genes required for distinct functions in the antigen processing pathway.     

Evidence against Ha-ras-1 involvement in sporadic and familial melanoma

It was recently reported that different rare alleles at the Ha-ras-1 locus occurred at a significantly higher combined frequency in cancer patients than in an unaffected population. In particular, melanoma patients were reported to have a significantly higher frequency of such alleles. We have examined the frequency of rare Ha-ras-1 alleles in a large number of cases of sporadic melanoma. Our results indicate that the distribution of rare alleles in this population does not differ from that found in normal populations. Also, to test the hypothesis that a hereditary predisposition to melanoma could be inherited via an allele at the Ha-ras-1 locus, we examined the transmission of the segment of the short arm of chromosome 11 (11p) carrying the Ha-ras-1 locus in a number of families previously shown to exhibit a hereditary predisposition to melanoma and its precursor lesion, the dysplastic nevus syndrome (DNS). Our genetic linkage results thus obtained strongly exclude the association of a predisposition to melanoma or the precursor lesion with the inheritance of the Ha-ras-1 locus or the segment of chromosome 11 on which it is located. These results imply that hereditary predisposition to melanoma is associated with genes other than the Ha-ras-1 locus, contradicting the original suggestion of Krontiris et al., made on the basis of either an inadequate sample size or other misleading experimental factors.     

Restored expression of major histocompatibility class I molecules by gene transfer of a putative peptide transporter

Cytotoxic T lymphocytes recognize antigen-derived peptides bound to major histocompatibility complex (MHC) class I molecules with which they assemble in the endoplasmic reticulum or in an undefined subcompartment. There is genetic evidence that the peptides that are products of cytosolic protein degradation are transported into this compartment by a peptide supply factor (PSF), encoded in the MHC class II region. Like the corresponding genes RING4, HAM1 and mtp1, PSF is related to the multidrug-resistance family of transporters and may be a peptide pump, as translocation of peptides across membranes must occur independently of the secretory pathway. There is, however, no functional evidence for this role so far. Here we report gene transfer experiments showing that expression of PSF complementary DNA in the human lymphoblastoid cell line mutant 721.134 restores normal levels of surface HLA-A2 and -B5. No similar effect was observed in 721.174 mutant cells, in which a homozygous deletion includes PSF among several other closely linked genes. At least one of these genes may therefore also be required for PSF function.     

Correlation between a DNA restriction fragment length polymorphism and C4A6 protein

The fourth component of complement (C4) in man, is coded for by two separate but closely linked loci (C4A and C4B) within the major histocompatibility region (MHC), on the short arm of chromosome 6. Like class I and II loci of this region, the C4 genes are highly polymorphic with more than 30 alleles, including null alleles, assigned to the two loci. This extensive polymorphism, based mainly on electrophoretic mobility, provides a useful marker for studies of disease susceptibility. Several disorders, including systemic lupus erythematosus and type I diabetes, show associations with C4 phenotypes. We have used the technique of Southern with a C4 specific probe to examine the genomic DNA of individuals typed for C4 by protein electrophoresis. We have identified 10.7 and 3.8 kilobase (kb) BglII restriction fragments in each of 9 unrelated individuals with a C4A6 allele, and in none of 22 unrelated individuals in whom this allele was not expressed. This clear correlation of restriction fragment length polymorphism with C4 phenotype provides a precise basis for analysis of C4 polymorphism. It is likely to be of value in clinical investigations of autoimmune disease.     

The chicken B locus is a minimal essential major histocompatibility complex.

Here we report the sequence of the region that determines rapid allograft rejection in chickens, the chicken major histocompatibility complex (MHC). This 92-kilobase region of the B locus contains only 19 genes, making the chicken MHC roughly 20-fold smaller than the human MHC. Virtually all the genes have counterparts in the human MHC, defining a minimal essential set of MHC genes conserved over 200 million years of divergence between birds and mammals. They are organized differently, with the class III region genes located outside the class II and class I region genes. The absence of proteasome genes is unexpected and might explain unusual peptide-binding specificities of chicken class I molecules. The presence of putative natural killer receptor gene(s) is unprecedented and might explain the importance of the B locus in the response to the herpes virus responsible for Marek's diseases. The small size and simplicity of the chicken MHC allows co-evolution of genes as haplotypes over considerable periods of time, and makes it possible to study the striking MHC-determined pathogen-specific disease resistance at the molecular level.     

HLA DQ位点多样性模拟分析及其PCR—RFLP分型

选择２７个识别序列为４ｎｔ的限制性内切酶,通过计算机对最新获得的１９个ＤＱＡ１和３５个ＤＱＢ１等位基因第２外显子中的一段序列进行模拟酶切分析,根据酶切格局数目及各格局所代表的等位基因数的均衡性,确定酶的优先次序,在此基础上进行ＰＣＲ－ＲＦＬＰ模拟分析,确定最佳的酶组合。结果表明,分别采用４个和６个酶的组合,可有效鉴定ＤＱＡ１和ＤＱＢ１等位基因。同时通过比较分析ＤＱＢ１各等位基因核苷酶位点的变异系数     

Polymorphism of human Ia antigens generated by reciprocal intergenic exchange between two DR beta loci

Class II molecules encoded by the human major histocompatibility complex (MHC) are involved in regulating T-cell response to antigens. The mechanisms for generating polymorphism in products of the MHC have been studied extensively for both the murine H-2 and the human HLA complex. Such studies indicate that point mutations plus selection have a major role in the generation of polymorphisms of class I and class II MHC genes. However, a non-reciprocal gene conversion mechanism has been proposed to explain several examples of clustered sequence variation in MHC genes. In all these examples, the proposed gene conversion event is unidirectional; that is, one of the two interacting genes acts as sequence donor and the other as sequence recipient. No examples of potential reciprocal genetic exchange (as occurs in the fungal system), in which the two interacting genes act as both donor and recipient of gene fragments, have been found in the MHC system or in other multigene families of higher organisms. We sequenced two different HLA-DR beta complementary DNAs from each of two different cells all expressing the same serologically defined determinant (DR2) but different T-cell-recognized (Dw) specificities (Dw12 and MN2). Sequence comparisons of these four cDNA clones (and two DR beta amino-acid sequences from the DR2-Dw2 subtype) suggest that new coding sequences for DR beta molecules in the DR2 haplotypes are potentially generated by reciprocal intergenic exchange.