Crystal structure of an NK cell immunoglobulin-like receptor in complex with its class I MHC ligand

Target cell lysis is regulated by natural killer (NK) cell receptors that recognize class I MHC molecules. Here we report the crystal structure of the human immunoglobulin-like NK cell receptor KIR2DL2 in complex with its class I ligand HLA-Cw3 and peptide. KIR binds in a nearly orthogonal orientation across the alpha1 and alpha2 helices of Cw3 and directly contacts positions 7 and 8 of the peptide. No significant conformational changes in KIR occur on complex formation. The receptor footprint on HLA overlaps with but is distinct from that of the T-cell receptor. Charge complementarity dominates the KIR/HLA interface and mutations that disrupt interface salt bridges substantially diminish binding. Most contacts in the complex are between KIR and conserved HLA-C residues, but a hydrogen bond between Lys 44 of KIR2DL2 and Asn 80 of Cw3 confers the allotype specificity. KIR contact requires position 8 of the peptide to be a residue smaller than valine. A second KIR/HLA interface produced an ordered receptor-ligand aggregation in the crystal which may resemble receptor clustering during immune synapse formation.     

Immune self-reactivity triggered by drug-modified HLA-peptide repertoire

Human leukocyte antigens (HLAs) are highly polymorphic proteins that initiate immunity by presenting pathogen-derived peptides to T?cells. HLA polymorphisms mostly map to the antigen-binding cleft, thereby diversifying the repertoire of self-derived and pathogen-derived peptide antigens selected by different HLA allotypes. A growing number of immunologically based drug reactions, including abacavir hypersensitivity syndrome (AHS) and carbamazepine-induced Stevens-Johnson syndrome (SJS), are associated with specific HLA alleles. However, little is known about the underlying mechanisms of these associations, including AHS, a prototypical HLA-associated drug reaction occurring exclusively in individuals with the common histocompatibility allele HLA-B*57:01, and with a relative risk of more than 1,000 (refs?6, 7). We show that unmodified abacavir binds non-covalently to HLA-B*57:01, lying across the bottom of the antigen-binding cleft and reaching into the F-pocket, where a carboxy-terminal tryptophan typically anchors peptides bound to HLA-B*57:01. Abacavir binds with exquisite specificity to HLA-B*57:01, changing the shape and chemistry of the antigen-binding cleft, thereby altering the repertoire of endogenous peptides that can bind HLA-B*57:01. In this way, abacavir guides the selection of new endogenous peptides, inducing a marked alteration in 'immunological self'. The resultant peptide-centric 'altered self' activates abacavir-specific T-cells, thereby driving polyclonal CD8 T-cell activation and a systemic reaction manifesting as AHS. We also show that carbamazepine, a widely used anti-epileptic drug associated with hypersensitivity reactions in HLA-B*15:02 individuals, binds to this allotype, producing alterations in the repertoire of presented self peptides. Our findings simultaneously highlight the importance of HLA polymorphism in the evolution of pharmacogenomics and provide a general mechanism for some of the growing number of HLA-linked hypersensitivities that involve small-molecule drugs.     

中国人HLA-G1的cDNA克隆、序列分析、表达和蛋白质空间结构预测

从中国人外周血单个核细胞、胎盘组织和肝癌组织等样品中克隆了包含完整HLA-G1读框的cDNA;与国外同行获得的该基因及其蛋白质序列比较分析表明,该基因虽然有着细微的种族特异性,但高度保守;并获得了它的截断型重组蛋白,根据蛋白一级结构和同源比较方法,模建了它及其与特异性受体KIR2DL4形成复合体的空间结构模拟,预测了它们之间相互作用的特征.     

HLA-B*6701 as a subtype performing post-selected marking gene for cervical cancer

A method of sequence-based typing (SBT) has been adopted to assort types of exons 2 and 3, which have the most polymorphism, of HLA-B locus of the Tujia nation group in Hubei province. The correlation among the HLA-B alleles, human papillomavirus (HPV) infection and cervical cancer risk has also been investigated. Under the condition of resident location and age, race unified, 100 specimens of cancer patients were sampled as a case group, of which 86 were HPV positive and were screened for HLA-B alleles; while 187 specimens were taken from healthy people, of which 92 were HPV negative as a control group. The result shows that by comparing the above mentioned 86 HPV positive cervical cancer group and 92 HPV negative normal group, it was concluded that HLA-B*6701 was only found in the cervical cancer group (p < 0.034), which shows that HLA-B*6701 can be used as an important candidate biological marking gene for generation of cervical cancer in Wufeng county of Hubei province.     

Cell lines producing human T-cell lymphoma virus show altered HLA expression

Human T-cell leukaemia/lymphoma virus (HTLV) can be identified in fresh and cultured T-lymphocytes from patients with adult T-cell malignancies. HLA typing of the peripheral blood lymphocytes and cultured cell lines from the patient from which the virus was originally isolated suggested the expression of additional HLA-A and -B locus antigens on the HTLV positive cultured T-cells that were not present on the EBV transformed B-cell line or on the peripheral blood lymphocytes. Peripheral blood lymphocytes (PBLs) and T-cell lines established from patients and cord blood lymphocytes, infected with virus by co-culture with T-cell lines, were typed for HLA antigens with alloantisera and in addition tested for reactivity with a monoclonal antibody (4D12) which recognizes a polymorphic HLA class-I antigen. In all HTLV positive cells, with demonstrable provirus replication, altered HLA alloantigen expression was observed. This may be explained by the observations reported in the accompanying paper which shows homology between the envelope gene region of HTLV and the region of an HLA-B locus gene which codes for the extracellular portion of a class I histocompatibility antigen.     

Dominant influence of HLA-B in mediating the potential co-evolution of HIV and HLA

The extreme polymorphism in the human leukocyte antigen (HLA) class I region of the human genome is suggested to provide an advantage in pathogen defence mediated by CD8+ T cells. HLA class I molecules present pathogen-derived peptides on the surface of infected cells for recognition by CD8+ T cells. However, the relative contributions of HLA-A and -B alleles have not been evaluated. We performed a comprehensive analysis of the class I restricted CD8+ T-cell responses against human immunodeficiency virus (HIV-1), immune control of which is dependent upon virus-specific CD8+ T-cell activity. In 375 HIV-1-infected study subjects from southern Africa, a significantly greater number of CD8+ T-cell responses are HLA-B-restricted, compared to HLA-A (2.5-fold; P = 0.0033). Here we show that variation in viral set-point, in absolute CD4 count and, by inference, in rate of disease progression in the cohort, is strongly associated with particular HLA-B but not HLA-A allele expression (P < 0.0001 and P = 0.91, respectively). Moreover, substantially greater selection pressure is imposed on HIV-1 by HLA-B alleles than by HLA-A (4.4-fold, P = 0.0003). These data indicate that the principal focus of HIV-specific activity is at the HLA-B locus. Furthermore, HLA-B gene frequencies in the population are those likely to be most influenced by HIV disease, consistent with the observation that B alleles evolve more rapidly than A alleles. The dominant involvement of HLA-B in influencing HIV disease outcome is of specific relevance to the direction of HIV research and to vaccine design.     

Common west African HLA antigens are associated with protection from severe malaria

A large case-control study of malaria in West African children shows that a human leucocyte class I antigen (HLA-Bw53) and an HLA class II haplotype (DRB1*1302-DQB1*0501), common in West Africans but rare in other racial groups, are independently associated with protection from severe malaria. In this population they account for as great a reduction in disease incidence as the sickle-cell haemoglobin variant. These data support the hypothesis that the extraordinary polymorphism of major histocompatibility complex genes has evolved primarily through natural selection by infectious pathogens.     

KIR expression on self-reactive CD8+ T cells is controlled by T-cell receptor engagement

Natural killer cell tolerance is maintained by the interaction of killer inhibitory receptors (KIRs) with self-major histocompatibility complex class I gene products. A subset of T cells also expresses inhibitory receptors, but the functional significance of these receptors on T cells is unclear. Here we show that, in the absence of T-cell receptor (TCR) engagement, KIRs expressed on CD8+ T cells are slowly downregulated by KIR ligands expressed on antigen-presenting cells. The resulting expression levels of KIR are no longer able to inhibit T-cell function. In contrast, TCR engagement sustains KIR expression, and re-induces functional levels of KIR expression after ligand-induced downregulation of KIR. Our data indicate that KIR expression on CD8+ T cells in vivo may be maintained through continuous encounters with antigen. As KIR-mediated inhibition of T-cell activation can be bypassed at high antigen concentrations, dynamic KIR expression may mediate T-cell tolerance to self-antigens by sparing self-reactive T cells, thus enabling them to mediate potentially useful immune functions to quantitatively or qualitatively different antigens.     

Unusual HLA-B alleles in two tribes of Brazilian Indians.

The Kaingang and Guarani are culturally and linguistically distinct tribes of southern Brazil. Like all Amerindian groups they show limited HLA polymorphism, which probably reflects the small founder populations that colonized America by overland migration from Asia 11,000-40,000 years ago. We find the nucleotide sequences of HLA-B alleles from the Kaingang and Guarani to be distinct from those characterized in caucasian, oriental and other populations. By comparison, the HLA-A and C alleles are familiar. These results and those reported in the accompanying paper on the Waorani of Ecuador reveal that a marked evolution of HLA-B has occurred since humans first entered South America. New alleles have been formed through recombination between pre-existing alleles, not by point mutation, giving rise to distinctive diversification of HLA-B in different South American Indian tribes.     

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.     

Innate immune recognition and regulation in liver injury: A brief report from a series of studies

The discovery of innate immune receptors and the emergence of liver immunology （high content of NK and NKT cells in liver） led to the second research summit in innate immunity since the finding of NK cells in the middle 1970s. Liver disease is one of the most dangerous threats to humans, and the progress in innate immunology and liver immunology made it possible to re-explain the cellular and mo- lecular immune mechanisms of liver disease. In the past ten years, we have found that innate recognition of hepatic NK and NKT subsets were involved in murine liver injury. We established a novel NK cell-dependent acute murine hepatitis model by activating Toll-like receptor-3 （TLR-3） with an injection of poly I：C, which may mimic mild viral hepatitis （such as Chronic Hepatitis B）. We observed that a network of innate immune cells including NK, NKT and Kupffer cells is involved in liver immune injury in our established NK cell-dependent murine,model. We noted that TLR-3 on Kupffer cells activated by pretreatment with poly I： C might protect against bacterial toxin （LPS）-induced fulminant hepatitis by down-regulating TLR-4 function, while TLR-3 pre-activation of NK cells might reduce Con A-induced NKT cell-mediated fulminant hepatitis by blocking NKT cell recruitment to the liver. We also found that the oversensitivity to injury by immune stimulation in HBV （hepatitis B virus） transgenic mice （full HBV gene-tg or HBs-tg） correlated to the over-expression of Real, an NKG2D （natural killer cell group 2D） ligand of NK cells or CDld, a ligand of TCR-V14 of NKT cells, on HBV＋ hepatocytes, which leads to an innate immune response against hepatocytes and is critical in liver immune injury and regeneration.     

面向语义Web的直觉模糊粗描述逻辑

分析了面向语义Web的直觉模糊粗描述逻辑的研究现状和存在的问题,基于(I, T)-直觉模糊粗集理论将直觉模糊描述逻辑和粗描述逻辑进行了集成,即提出了一种新的直觉模糊粗描述逻辑．针对与本体语言OWL 2等价的描述逻辑SROIQ(D),对SROIQ(D)进行了扩充,具体提出了直觉模糊粗描述逻辑IFRSROIQ(D),给出了IFRSROIQ(D)的语法、语义和性质,证明了IFRSROIQ(D)的推理问题（包括知识库可满足性、概念可满足性、概念包含、逻辑推导、ABox一致性推理等）都可以归约到基于完备格的描述逻辑L*-SROIQ(D)上对应的推理．     

Peptide binding to empty HLA-B27 molecules of viable human cells

Intracellular binding of antigenic peptides by polymorphic class I major histocompatibility complex molecules creates the ligands recognized by receptors of CD8+ T cells. Previously described in vitro assays of peptide binding to class I molecules have been limited by either the low proportion of accessible binding sites or the lack of allelic specificity. Here we describe a system in which the human class I molecule HLA-B27 binds considerable amounts of an influenza peptide with precise allelic discrimination. Binding requires viable cells, is stimulated by gamma-interferon and is inhibited by brefeldin A. Our results are consistent with the presence of fairly stable 'empty' HLA-B27 molecules at the cell surface. By contrast, analysis of the binding of a second influenza peptide indicates that empty HLA-Aw68 molecules are relatively short-lived. We speculate that HLA-B27 might bind extracellular peptides in vivo and that this property could underlie its association with autoimmune disease.     

Direct binding of influenza peptides to class I HLA molecules

Activation of T lymphocytes requires the intracellular fragmentation of foreign antigens and their presentation by class I or class II major histocompatibility complex (MHC) glycoproteins. The direct binding of peptides to class II molecules has been demonstrated using equilibrium dialysis, gel filtration and fluorescence energy transfer at planar membranes, and its specificity compared to that of T-cell activation. In contrast, direct binding of peptides to class I molecules has been difficult to detect; although peptide sensitization experiments and the crystallographic structure of HLA-A2 (ref. 9) persuasively argue for its occurrence and importance. Here we describe a gel filtration assay from which we derive direct evidence for selective binding of an influenza matrix peptide to HLA-A2 and for binding of an influenza nucleoprotein peptide to HLA-B37. These two peptides have previously been shown to act respectively as targets for certain HLA-A2 or HLA-B37 restricted influenza-specific cytotoxic T lymphocytes (CTL). In addition we demonstrate binding to some, but not all, HLA allospecificities that cannot present these peptides to CTL. We estimate that less than 0.3% of the HLA molecules present in any given purified preparation were able to bind the added peptides.     

Strong xenogeneic HLA response in transgenic mice after introducing an alpha 3 domain into HLA B27.

The pronounced response by mouse T cells to the major histocompatibility complex (MHC) class I antigens of the same species is characterized by a relatively large fraction of responding cells. Responses to MHC class I allelles of other species are, however, generally much weaker. T lymphocytes are positively selected on thymic MHC antigens, resulting in a T-cell repertoire with strong alloreactivity. This has been explained in terms of a mouse T-cell repertoire that is not efficiently selected for recognition of HLA molecules owing to the absence of HLA in mice. Here we show that mice transgenic for HLA mount a T-cell response against allogeneic HLA that is no better than in normal mice. We decided instead to test whether the mouse accessory molecule Lyt-2 on cytotoxic T lymphocytes could interact efficiently with the alpha 3 domain of HLA. To do this, we replaced the alpha 3 domain of HLA-B27 by a murine alpha 3 domain in a gene construct used to produce transgenic mice, and then used the spleen cells from these mice to stimulate normal mouse T cells. Under these conditions cytotoxic T lymphocytes were generated with the same frequency against xenogeneic HLA-B27 determinants as against allogeneic mouse class I antigens. These findings indicate that the normally weak xeno-MHC response is due to the inefficient interaction of the murine Lyt-2 accessory molecule with HLA class I, and not to limitations of the mouse T-cell repertoire.     

Structural basis of Dscam isoform specificity

The Dscam gene gives rise to thousands of diverse cell surface receptors thought to provide homophilic and heterophilic recognition specificity for neuronal wiring and immune responses. Mutually exclusive splicing allows for the generation of sequence variability in three immunoglobulin ecto-domains, D2, D3 and D7. We report X-ray structures of the amino-terminal four immunoglobulin domains (D1-D4) of two distinct Dscam isoforms. The structures reveal a horseshoe configuration, with variable residues of D2 and D3 constituting two independent surface epitopes on either side of the receptor. Both isoforms engage in homo-dimerization coupling variable domain D2 with D2, and D3 with D3. These interactions involve symmetric, antiparallel pairing of identical peptide segments from epitope I that are unique to each isoform. Structure-guided mutagenesis and swapping of peptide segments confirm that epitope I, but not epitope II, confers homophilic binding specificity of full-length Dscam receptors. Phylogenetic analysis shows strong selection of matching peptide sequences only for epitope I. We propose that peptide complementarity of variable residues in epitope I of Dscam is essential for homophilic binding specificity.     

HBK - SPF 鸭 MHC I 区域微卫星标记分析

摘要: 禽主要组织相容性复合体是一组紧密连锁高度多态的基因群,与免疫反应或敏感性密切相关,鸭 MHC I 区域全长 36. 8 kb,由 TAP1、TAP2 和 5 个 MHC I 拷贝基因( UAA-UEA) 组成。HBK-SPF 鸭是中国农业科学院哈尔滨兽医研究所培育的无特定病原体种鸭,分为 B 和 Q 2 个品系,已封闭繁育了 7 个世代。本文在鸭 MHC I 区域筛选了 4个微卫星位点,通过单链构象多态性分析和聚合酶链式反应直接测序,发现 A 位点具有多态性,为( GT) n 的重复结构,第 6 代 HBK-B 和 HBK-Q 的31 个个体和第 7 代 的140 个个体进行聚合酶链式反应,结果直接测序,在重复结构之前的 108bp 中,发现了 4 种纯合单倍型和 6 种杂合单倍型; B 位点未得到目的产物; C 位点位于 MHC I 拷贝基因UDA 和 UEA 之间,扩增结果与 UAA 和 UBA 之间序列高度同源,无法判断基因型; D 位点表现为单态,为( ATA) 15的固定重复结构。本研究为进一步研究鸭 MHC I 基因结构和建立家系提供了依据。     

HLA-DR products are a subset of human Ia antigens

Human Ia antigens are polymorphic cell-surface sialoglycoproteins which have restricted tissue distribution. They are bimolecular complexes of 34,000 (alpha) and 28,000 (beta) molecular weight and most of the polymorphism is found in the smaller polypeptides. They are involved in the initiation of immune responses and particular Ia antigens are associated with increased susceptibility to certain diseases. They are also the major barrier to human allogeneic tissue transplantation. Whereas serological analysis and mixed lymphocyte typing have defined three polymorphic families of Ia antigens, HLA-DR, -DC and -SB, protein sequencing results and studies with monoclonal antibodies indicate that the complexity is much greater. Thus the HLA-DR and DC specificities as defined by alloantisera, could represent groups of antigens which are controlled by HLA genes in linkage disequilibrium. Here, we have used a monoclonal antibody specific for HLA-DR2 to show that this determinant is carried by molecules which are distinct from those of the DC series and which represent 30% of the Ia antigens expressed on the cell surface of an HLA homozygous line PGF.