Human Β2m Research Articles

Xenogeneic β2-Microglobulin Substitution Affects Functional Binding of MHC Class I Molecules by CD8+ T Cells

NK cells and CD8+ T cells bind MHC-I molecules using distinct topological interactions. Specifically, murine NK inhibitory receptors bind MHC-I molecules at both the MHC-I H chain regions and beta2-microglobulin (beta2m) while TCR engages MHC-I molecules at a region defined solely by the class I H chain and bound peptide. As such, alterations in beta2m are not predicted to influence functional recognition of MHC-I by TCR. We have tested this hypothesis by assessing the capability of xenogeneic beta2m to modify the interaction between TCR and MHC-I. Using a human beta2m-transgenic C57BL/6 mouse model, we show that human beta2m supports formation and expression of H-2K(b) and peptide:H-2K(b) complexes at levels nearly equivalent to those in wild-type mice. Despite this finding, the frequencies of CD8+ single-positive thymocytes in the thymus and mature CD8+ T cells in the periphery were significantly reduced and the TCR Vbeta repertoire of peripheral CD8+ T cells was skewed in the human beta2m-transgenic mice. Furthermore, the ability of mouse beta2m-restricted CTL to functionally recognize human beta2m+ target cells was diminished compared with their ability to recognize mouse beta2m+ target cells. Finally, we provide evidence that this effect is achieved through subtle conformational changes occurring in the distal, peptide-binding region of the MHC-I molecule. Our results indicate that alterations in beta2m influence the ability of TCR to engage MHC-I during normal T cell physiology.

Regulation of Antigen Presentation by Amyloid Precursor-Like Protein 2 (36.1)

Abstract The amyloid precursor-like protein 2 (APLP2) is a secreted protein that is ubiquitously expressed. We have found that APLP2 over-expression decreases the quantity of H2-Kd molecules on the plasma membrane. In addition, Kd thermostability was improved by APLP2 down-regulation, suggesting that APLP2 affects Kd peptide selection and/or retention. The effects of APLP2 on Kd are likely related to their physical association, as pulse-chase experiments demonstrated interaction for up to two hours after Kd synthesis. Furthermore, significant co-localization of Kd molecules with APLP2 was observed in vesicular structures both at steady state and during endocytosis of Kd molecules from the cell surface. Mutagenesis studies revealed that APLP2/MHC association is influenced by sequences in the peptide-binding region and the α3 domain of the MHC class I heavy chain. β2m has an impact on APLP2/MHC interaction, since introduction of human β2m into mouse fibroblasts increased the level of interaction between H2-Dd and APLP2. In summary, APLP2 affects MHC class I cell surface expression and thermostability by an interaction controlled by more than one domain of the MHC class I heavy chain and by β2m. These data support a model in which APLP2 regulates MHC class I trafficking, and thereby antigen presentation. (NIH Grants AI54645, GM57428, and GM74876)

Conformation of Amyloid Fibrils of β2-Microglobulin Probed by Tryptophan Mutagenesis

Beta2-microglobulin (beta2-m), a protein responsible for dialysis-related amyloidosis, adopts an immunoglobulin domain fold in its native state. Although beta2-m has Trp residues at positions 60 and 95, both are located near the surface of the domain. Hence, beta2-m does not have a conserved Trp common to other immunoglobulin domains, which is buried in close proximity to the disulfide bond. To study the structure of amyloid fibrils in relation to their native fold, we prepared a series of Trp mutants. Trp60 and Trp95 were both replaced with Phe, and a single Trp was introduced at various positions. Among various mutants, W39-beta2-m, in which a Trp was introduced at the position corresponding to the conserved Trp, exhibited a remarkable quenching of fluorescence in the native state, as observed for other immunoglobulin domains. An x-ray structural analysis revealed that W39-beta2-m assumes the native fold with Trp39 located in the vicinity of the disulfide bond. Comparison of the fluorescence spectra of various mutants for the native and fibrillar forms indicated that, while the Trp residues introduced in the middle of the beta2-m sequence tend to be buried in the fibrils, those located in the C-terminal region are more exposed. In addition, the fluorescence spectra of fibrils prepared at pH 2.5 and 7.0 revealed a large difference in the fluorescence intensity for W60-beta2-m, implying a major structural difference between them.

Defective Human Leukocyte Antigen Class I-associated Antigen Presentation Caused by a Novel β2-Microglobulin Loss-of-function in Melanoma Cells

The major histocompatibility complex class I molecules consist of three subunits, the 45-kDa heavy chain, the 12-kDa beta(2)-microglobulin (beta(2)m), and an approximately 8-9-residue antigenic peptide. Without beta(2)m, the major histocompatibility complex class I molecules cannot assemble, thereby abolishing their transport to the cell membrane and the subsequent recognition by antigen-specific T cells. Here we report a case of defective antigen presentation caused by the expression of a beta(2)m with a Cys-to-Trp substitution at position 25 (beta(2)m(C25W)). This substitution causes misfolding and degradation of beta(2)m(C25W) but does not result in complete lack of human leukocyte antigen (HLA) class I molecule expression on the surface of melanoma VMM5B cells. Despite HLA class I expression, VMM5B cells are not recognized by HLA class I-restricted, melanoma antigen-specific cytotoxic T lymphocytes even following loading with exogenous peptides or transduction with melanoma antigen-expressing viruses. Lysis of VMM5B cells is restored only following reconstitution with exogenous or endogenous wild-type beta(2)m protein. Together, our results indicate impairment of antigenic peptide presentation because of a dysfunctional beta(2)m and provide a mechanism for the lack of close association between HLA class I expression and susceptibility of tumor cells to cytotoxic T lymphocytes-mediated lysis in malignant diseases.

The Crystal Structure of H-2Db Complexed with a Partial Peptide Epitope Suggests a Major Histocompatibility Complex Class I Assembly Intermediate

In the absence of bound peptide ligands, major histocompatibility complex (MHC) class I molecules are unstable. In an attempt to determine the minimum requirement for peptide-dependent MHC class I stabilization, we have used short synthetic peptides derived from the Sendai virus nucleoprotein epitope (residues 324-332, 1FAPGNYPAL9) to promote its folding in vitro of H-2D(b). We found that H-2D(b) can be stabilized by the pentapeptide 5NYPAL9, which is equivalent to the C-terminal portion of the optimal nonapeptide and includes both the P5 and P9 anchor residues. We have crystallized the complex of the H-2D(b) molecule with the pentamer and determined the structure to show how a quasi-stable MHC class I molecule can be formed by occupancy of a single binding pocket in the peptide-binding groove.

Expression, refolding and crystallization of murine MHC class I H-2Dbin complex with human β2-microglobulin

Beta2-microglobulin (beta2m) is non-covalently linked to the major histocompatibility (MHC) class I heavy chain and interacts with CD8 and Ly49 receptors. Murine MHC class I can bind human beta2m (hbeta2m) and such hybrid molecules are often used in structural and functional studies. The replacement of mouse beta2m (mbeta2m) by hbeta2m has important functional consequences for MHC class I complex stability and specificity, but the structural basis for this is unknown. To investigate the impact of species-specific beta2m subunits on MHC class I conformation, murine MHC class I H-2Db in complex with hbeta2m and the peptide gp33 derived from lymphocytic choriomeningitis virus (LCMV) has been expressed, refolded in vitro and crystallized. Crystals containing two complexes per asymmetric unit and belonging to the space group P2(1), with unit-cell parameters a = 68.1, b = 65.2, c = 101.9 A, beta = 102.4 degrees, were obtained.

Influence of Xenogeneic β2-Microglobulin on Functional Recognition of H-2Kb by the NK Cell Inhibitory Receptor Ly49C

NK cells maintain self-tolerance through expression of inhibitory receptors that bind MHC class I (MHC-I) molecules. MHC-I can exist on the cell surface in several different forms, including "peptide-receptive" or PR-MHC-I that can bind exogenous peptide. PR-MHC-I molecules are short lived and, for H-2K(b), comprise approximately 10% of total MHC-I. In the present study, we confirm that signaling through the mouse NK inhibitory receptor Ly49C requires the presence of PR-K(b) and that this signaling is prevented when PR-K(b) is ablated by pulsing with a peptide that can bind to it with high affinity. Although crystallographic data indicate that Ly49C can engage H-2K(b) loaded with high-affinity peptide, our data suggest that this interaction does not generate an inhibitory signal. We also show that no signaling occurs when the PR-K(b) complex has mouse beta(2)-microglobulin (beta(2)m) replaced with human beta(2)m, although replacement with bovine beta(2)m has no effect. Furthermore, we show that beta(2)m exchange occurs preferentially in the PR-K(b) component of total H-2K(b). These conclusions were reached in studies modulating the sensitivity to lysis of both NK-resistant syngeneic lymphoblasts and NK-sensitive RMA-S tumor cells. We also show, using an in vivo model of lymphocyte recirculation, that engrafted lymphocytes are unable to survive NK attack when otherwise syngeneic lymphocytes express human beta(2)m. These findings suggest a qualitative extension of the "missing self" hypothesis to include NK inhibitory receptors that are restricted to the recognition of unstable forms of MHC-I, thus enabling NK cells to respond more quickly to events that decrease MHC-I synthesis.

Report of the Wet Workshop for Quantification of Soluble HLA-G in Essen, 2004

Membrane-anchored and soluble human leukocyte antigen HLA-G (sHLA-G) molecules exert strong inhibiting signals after interaction with their cognate receptors ILT2 (CD85j), ILT4 (CD85d), and KIR2DL4 (CD158d) that are differentially expressed by natural killer cells, T cells, and antigen-presenting cells. These inhibitory functions can become operative in conditions in which such immune cells try to attack viral infected or tumor cells. Recently, clinical studies showed that sHLA-G molecules are also relevant in the prediction of allograft acceptance after heart transplantation, liver-kidney cotransplantation, and the successful implantation and development of embryos after in vitro fertilization. In view of this diagnostic potential, reliable methods for the measurement of sHLA-G molecules in various body fluids are of interest. Thus, the aims of the Wet Workshop for measurement of sHLA-G held in Essen, Germany (at the Institute of Immunology October 18–20, 2004) were to select and validate HLA-G–specific enzyme-linked immunosorbent assay (ELISA) formats and purified standard HLA-G proteins, which can be easily generated and used as consensual references. To this end, the antibody combinations monoclonal antibody (mAb) MEM-G/9 (capture) + anti-β2m (detection) and the mAb 5A6G7 (capture) + mAb W6/32 (detection) were chosen in an ELISA format for the simultaneous determination of shed HLA-G1 + soluble HLA-G5 (sHLA-G1 + HLA-G5) and for the exclusive detection of HLA-G5 molecules, respectively. As standard, protein HLA-G5 molecules were purified from insect SF9 cells coinfected by HLA-G5 + human β2m and characterized for their antigenic determinants. A total of 24 members in 13 teams participated in the 3-day sHLA-G Wet Workshop. All workshop materials, protocols, standard reagents, and samples were provided to each team by the organizers. The Wet-Workshop results clearly demonstrated that (1) the HLA-G5 standard reagent was equally detected by both ELISA formats; (2) sHLA-G1 + G5 and HLA-G5 molecules, respectively, were specifically detected by the two ELISA formats; and (3) both ELISA formats measure reproducibly the amounts of sHLA-G. The comparison of the two ELISA results obtained evidenced that in healthy donors sHLA-G1 molecules can exist in body fluids besides HLA-G5. Moreover, a novel soluble HLA-G structure can be predicted that is recognized by the mAb 5A6G7 + mAb W6/32 antibody combination, but not by the one of mAb MEM-G/9 + anti-β2m.

Membrane-Anchored β2-Microglobulin Stabilizes a Highly Receptive State of MHC Class I Molecules

The magnitude of response elicited by CTL-inducing vaccines correlates with the density of MHC class I (MHC-I)-peptide complexes formed on the APC membrane. The MHC-I L chain, beta2-microglobulin (beta2m), governs complex stability. We reasoned that genetically converting beta2m into an integral membrane protein should exert a marked stabilizing effect on the resulting MHC-I molecules and enhance vaccine efficacy. In the present study, we show that expression of membranal human beta2m (hbeta2m) in mouse RMA-S cells elevates MHC-I thermal stability. RMA-S transfectants bind an exogenous peptide at concentrations 10(4)- to 10(6)-fold lower than parental RMA-S, as detected by complex-specific Abs and by T cell activation. Moreover, saturation of the transfectants' MHC-I by exogenous peptide occurs within 1 min, as compared with approximately 1 h required for parental cells. At saturation, however, level of peptide bound by modified cells is only 3- to 5-fold higher. Expression of native hbeta2m only results in marginal effect on the binding profile. Soluble beta2m has no effect on the accelerated kinetics, but the kinetics of transfectants parallel that of parental cells in the presence of Abs to hbeta2m. Ab inhibition and coimmunoprecipitation analyses suggest that both prolonged persistence of peptide-receptive H chain/beta2m heterodimers and fast heterodimer formation via lateral diffusion may contribute to stabilization. In vivo, peptide-loaded transfectants are considerably superior to parental cells in suppressing tumor growth. Our findings support the role of an allosteric mechanism in determining ternary MHC-I complex stability and propose membranal beta2m as a novel scaffold for CTL induction.

An HLA-E single chain trimer inhibits human NK cell reactivity towards porcine cells

HLA-E, when expressed by pig cells, could alleviate human natural killer (NK) cell-mediated rejection of porcine xenografts by providing a potent inhibitory ligand for human NK cells expressing CD94/NKG2A. Yet cell-surface expression of HLA-E on porcine epithelial (LLC-PK1) cells was not observed after transfection with an expression vector harboring HLA-E alone or in combination with an expression vector containing human β2m. A single chain trimer (SCT) of HLA-E consisting of, in the following order (from N- to C-terminus), the leader peptide of human β2m, VMAPRTLIL (an HLA-E-binding peptide), a 15 amino acid linker, mature human β2m, a 20 amino acid linker, and mature HLA-E heavy chain was engineered. Cell-surface expression and correct folding of HLA-E SCT was shown by FACS analyses of stably transfected LLC-PK1 cells. Untransfected LLC-PK1 cells were readily lysed by the NK cell lines NKL and NK-92, while LLC-PK1 cells expressing HLA-E SCT were almost completely protected. In addition, the HLA-E SCT recapitulates the peptide dependent properties of normal HLA-E trimeric complexes in that an HLA-E SCT with an hsp60 derived peptide, though expressed at the cell-surface, did not inhibit NK cell-mediated lysis. The HLA-E SCT, which conferred protection against NK cell-mediated killing, also inhibited NK cell IFN-γ secretion elicited by co-culture of NKL cells with LLC-PK1 cells. Thus, HLA-E SCT, in which all three components of a normal HLA-E protein complex are in one polypeptide chain, is immunologically functional as it is able to modulate NK cell cytotoxicity and cytokine secretion.

An amyloid-forming segment of beta2-microglobulin suggests a molecular model for the fibril.

In humans suffering from dialysis-related amyloidosis, the protein beta2-microglobulin (beta2M) is deposited as an amyloid; however, an amyloid of beta2M is unknown in mice. beta2M sequences from human and mouse are 70% identical, but there is a seven-residue peptide in which six residues differ. This peptide from human beta2M forms amyloid in vitro, whereas the mouse peptide does not. Substitution of the human peptide for its counterpart in the mouse sequence results in the formation of amyloid in vitro. These results show that a seven-residue segment of human beta2M is sufficient to convert beta2M to the amyloid state, and that specific residue interactions are crucial to the conversion. These observations are consistent with a proposed Zipper-spine model for beta2M amyloid, in which the spine of the fibril consists of an anhydrous beta-sheet.

β2-Microglobulin H31Y Variant 3D Structure Highlights the Protein Natural Propensity Towards Intermolecular Aggregation

β2-Microglobulin (β2m) is the non-covalently bound light chain of the human class I major histocompatibility complex (MHC-I). The natural turnover of MHC-I gives rise to the release of β2m into plasmatic fluids and to its catabolism in the kidney. β2m dissociation from the heavy chain of the complex is a severe complication in patients receiving prolonged hemodialysis. As a consequence of renal failure, the increasing β2m concentrations can lead to deposition of the protein as amyloid fibrils. Here we characterize the His31→Tyr human β2m mutant, a non-natural form of β2m that is more stable than the wild-type protein, displaying a ten-fold acceleration of the slow phase of folding. We report the 2.9Å resolution crystal structure and the NMR characterization of the mutant β2m, focussing on selected structural features and on the molecular packing observed in the crystals. Juxtaposition of the four mutant β2m molecules contained in the crystal asymmetric unit, and specific hydrogen bonds, stabilize a compact protein assembly. Conformational heterogeneity of the four independent molecules, some of their mutual interactions and partial unpairing of the N-terminal β-strand in one protomer are in keeping with the amyloidogenic properties displayed by the mutant β2m.

Crystal structure of monomeric human beta-2-microglobulin reveals clues to its amyloidogenic properties.

Dissociation of human beta-2-microglobulin (beta(2)m) from the heavy chain of the class I HLA complex is a critical first step in the formation of amyloid fibrils from this protein. As a consequence of renal failure, the concentration of circulating monomeric beta(2)m increases, ultimately leading to deposition of the protein into amyloid fibrils and development of the disorder, dialysis-related amyloidosis. Here we present the crystal structure of a monomeric form of human beta(2)m determined at 1.8-A resolution that reveals remarkable structural changes relative to the HLA-bound protein. These involve the restructuring of a beta bulge that separates two short beta strands to form a new six-residue beta strand at one edge of this beta sandwich protein. These structural changes remove key features proposed to have evolved to protect beta sheet proteins from aggregation [Richardson, J. & Richardson, D. (2002) Proc. Natl. Acad. Sci. USA 99, 2754-2759] and replaces them with an aggregation-competent surface. In combination with solution studies using (1)H NMR, we show that the crystal structure presented here represents a rare species in solution that could provide important clues about the mechanism of amyloid formation from the normally highly soluble native protein.

Spontaneous inflammatory disease in HLA-B27 transgenic mice does not require transporter of antigenic peptides.

HLA-B27 is strongly linked with a group of human diseases called spondyloarthropathies. Even though HLA-B27 as an MHC class I molecule would be expected to present endogenously processed peptides such as cytosolic or viral proteins, many of the B27-linked diseases begin after an infection with an enterobacteria, an exogenous antigen. In our previous studies, we have described development of spontaneous inflammatory disease in HLA-B27 transgenic mice expressing beta(2)m free heavy chains on the cell surface. In order to address the role of endogenous versus exogenous antigens and a role for Tap genes in the development of spontaneous diseases, mice lacking Tap-1 (knockout) were mated to HLA-B27/human beta(2)m transgenic mice. B27(+)/human beta(2)m(+) double-transgenic mice (without mouse beta(2)m) lacking the Tap-1 gene developed spontaneous inflammatory disease similar to wild-type Tap-1 gene-expressing counterparts. Our data demonstrate that peptide transporters (Tap) were not involved in the development of spontaneous inflammatory disease in B27(+)/human beta(2)m transgenic animals.

Covalent Linkage to β2-Microglobulin Enhances the MHC Stability and Antigenicity of Suboptimal CTL Epitopes

Abstract Many CTL epitopes of clinical importance, particularly those derived from tumor Ags, display relatively poor MHC binding affinity and stability. Because in vivo immunogenicity, and thus the efficacy of peptide-based vaccines, is thought to be determined by MHC/peptide complex stability, there is a need to develop a simple strategy for enhancing the binding of suboptimal epitopes. Toward this goal, the ability to enhance suboptimal peptides through covalent linkage to β2-microglobulin (β2m) was explored. Two suboptimal variants of a high-affinity Db-restricted influenza nucleoprotein peptide were covalently linked, via a polypeptide spacer, to the amino terminus of human β2m and the recombinant fusion proteins expressed in Escherichia coli. When compared with their uncoupled counterparts, the β2m-linked epitopes display enhanced MHC stabilization and antigenicity. Thus, tethering epitopes to β2m provides a simple method for augmenting the biological activity of suboptimal peptides and could be useful in the design of peptide-based vaccines or immunotherapeutics.

Cell-Surface Expression and Alloantigenic Function of a Human Nonclassical Class I Molecule (HLA-E) in Transgenic Mice

We have introduced the gene (E*01033) encoding the heavy chain of the human nonclassical MHC class I Ag, HLA-E, into the mouse genome. Two founder mice carry a 21-kb fragment, the others bear an 8-kb fragment. Each of the founder mice was mated to mice of an already established C57BL/10 transgenic line expressing human beta2-microglobulin (beta2m). Cell surface HLA-E was detected on lymph node cells by flow cytometry only in the presence of endogenous human beta2m. However, HLA-E-reactive mouse CTL (H-2-unrestricted) lysed efficiently the target cells originating from HLA-E transgenic mice without human beta2m, showing that the HLA-E protein can be transported to the cell surface in the absence of human beta2m, presumably by association with murine beta2m. Rejection of skin grafts from HLA-E transgenic mice demonstrates that HLA-E behaves as a transplantation Ag in mice. HLA-E transgenic spleen cells are effective in stimulating an allogeneic CTL response in normal and human classical class I (HLA-B27) transgenic mice. Furthermore, results from split-well analysis indicate that the majority of the primary in vivo-induced CTL recognizes HLA-E as an intact molecule (H-2-unrestricted recognition) and not as an HLA-E-derived peptide presented by a mouse MHC molecule, although a small fraction (ranging from 4 to 21%) of the primary in vivo-induced CTL is able to recognize HLA-E in an H-2-restricted manner. Based on these observations, we conclude that HLA-E exhibits alloantigenic properties that are indistinguishable from classical HLA class I molecules when expressed in transgenic mice.

Cell surface expression of HLA-E: interaction with human β2-microglobulin and allelic differences

The formation of a trimeric complex composed of MHC class I heavy chain, beta2-microglobulin (beta2m) and peptide ligand is a prerequisite for its efficient transport to the cell surface. We have previously demonstrated impaired intracellular transport of the human class Ib molecule HLA-E in mouse myeloma X63 cells cotransfected with the genes for HLA-E and human beta2m (hbeta2m), which is most likely attributable to inefficient intracellular peptide loading of the HLA-E molecule. Here we demonstrate that cell surface expression of HLA-E in mouse cells strictly depends on the coexpression of hbeta2m and that soluble empty complexes of HLA-E and hbeta2m display a low degree of thermostability. Both observations imply that low affinity interaction of HLA-E with beta2m accounts to a considerable extent for the observed low degree of peptide uptake in the endoplasmic reticulum. Moreover, we show that the only allelic variation present in the caucasoid population located at amino acid position 107 (Gly or Arg) greatly affects intracellular transport and cell surface expression upon transfection of the respective alleles into mouse cells. No obvious difference was found with regard to the sequence of the peptide ligand.

Functional comparison of bovine, murine, and human β2-microglobulin: interactions with murine MHC i molecules

Fetal calf serum is a well known source of bovine β2-microglobulin (β2m) which can exchange with endogenous β2m from, as well as promote peptide binding to, class I major histocompatibility (MHC I) molecules on cells cultured in vitro. Recombinant bovine β2m was expressed and purified for direct functional comparison to human and murine β2m for interactions with murine MHC I molecules H-2Kb, Db, Kd, Ld, and Dd. Bovine and human β2m were equivalent in stabilizing MHC I heavy chains and facilitating peptide loading, suggesting similar affinities for murine MHC I heavy chains. The activity of murine β2m was significantly weaker, consistent with previous work that demonstrated the lower affinity of murine human β2m for murine heavy chains compared to human β2m. Analysis of bovine β2m in fetal calf serum revealed ten-fold higher concentrations than in adult bovine serum, levels shown to significantly affect MHC I stability and peptide loading. The ramifications for the study of MHC I molecules from cells in culture and the evolutionary implications of the higher affinity interactions of human and bovine β2m are discussed.

Interaction of HLA-E with Peptides and the Peptide Transporter In Vitro: Implications for its Function in Antigen Presentation

The assembly of MHC Ia molecules in the endoplasmic reticulum requires the presence of peptide ligands and beta2m and is facilitated by chaperones in an ordered sequence of molecular interactions. A crucial step in this process is the interaction of the class I alpha-chain/beta2m dimer with TAP, which is believed to ensure effective peptide loading of the empty class I molecule. We have previously demonstrated impaired intracellular transport of the class Ib molecule HLA-E in mouse myeloma cells cotransfected with the genes for HLA-E and human beta2m, which is most likely attributable to inefficient intracellular peptide loading of the HLA-E molecule. We therefore analyzed the ability of HLA-E in the transfectant cell line to bind synthetic peptides by means of their ability to enhance cell surface expression of HLA-E. Peptide binding was confirmed by testing the effect on the thermostability of soluble empty HLA-E/human beta2m dimers. Two viral peptides binding to HLA-E were thus identified, for which the exact positioning of the N terminus appeared critical for binding, whereas the contribution of the length of the C terminus seemed to be minor, allowing peptides as short as seven amino acids and up to 16 amino acids to exhibit considerable binding activity. Furthermore, we demonstrate that HLA-E interacts with TAP and that this interaction can be prolonged by the proteasome inhibitor N-acetyl-L-leucyl-L-leucyl-L-norleucinal, which reduces the intracellular peptide pool. The presented data indicate that HLA-E is capable of presenting peptide ligands similar to the repertoire of HLA class Ia molecules.

Ankylosing spondylitis, HLA B27, and beyond

Publication of the landmark Lancet paper showing the strong association between HLA B27 and ankylosing spondylitis 25 years ago 1 Brewerton DA Hart FD Nicholls A Caffrey M James DCO Sturrock RD Ankylosing spondylitis and HLA-27. Lancet. 1973; ii: 904-907 Summary Scopus (1410) Google Scholar stimulated an avalanche of research into HLA/disease associations. The subsequent weaker associations of HLA B27 with anterior uveitis, reactive arthritis, sacroiliitis, late-onset pauciarticular juvenile chronic arthritis in boys, and inflammatory bowel disease with axial joint involvement suggested a common genetic determinant for a group of disorders already linked as seronegative spondyloarthropathies by the clinical observations and family studies of the late Verna Wright, 2 Wright V Moll JMH Seronegative polyarthritis. North Holland Publishing Company, Amsterdam1976: 1-483 Google Scholar and others. Because reactive arthritis can be precipitated in B27-positive individuals by sexually acquired chlamydial infection or by enteric infections with Campylobacter, Clostridium, Salmonella, Shigella, and Yersinia spp, induction of disease by “arthritogenic” bacterial strains in genetically predisposed individuals has become a compelling idea for the pathogenesis of these disorders. This idea is supported by experiments in transgenic rats expressing HLA B27 and human β2-microglobulin. Such animals develop gut and joint inflammatory disease, 3 Hammer RE Maika SD Richardson JA Tang JP Taurog JD Spontaneous inflammatory disease in transgenic rats expressing HLA B27 and human β2m: an animal model of HLA B27 associated with human disorders. Cell. 1990; 63: 1099-1112 Summary Full Text PDF PubMed Scopus (814) Google Scholar which is mediated by normal gut bacteria, including Bacteroides species, 4 Rath HC Herfarth HH Ikeda JS et al. Normal luminal bacteria, especially bacteroides species, mediate chronic colitis, gastritis, and arthritis in HLA B27/human beta2 microglobulin transgenic rats. J Clin Invest. 1996; 98: 945-953 Crossref PubMed Scopus (677) Google Scholar and which does not occur when the animals are maintained in a germfree environment. 5 Taurog JD Richardson JA Croft JT et al. The germ free state prevents development of gut and joint inflammatory disease in HLA B27 transgenic rats. J Exp Med. 1994; 180: 2359-2364 Crossref PubMed Scopus (914) Google Scholar