T cell receptor and peptide-contacting residues in the HLA-DR17(3) beta 1 chain

A Single Amino Acid Substitution Prevents Recognition of a Dominant Human Aquaporin-4 Determinant in the Context of HLA-DRB1*03:01 by a Murine TCR

Background

Aquaporin 4 (AQP4) is considered a putative autoantigen in patients with Neuromyelitis optica (NMO), an autoinflammatory disorder of the central nervous system (CNS). HLA haplotype analyses of patients with NMO suggest a positive association with HLA-DRB1* 03:01. We previously showed that the human (h) AQP4 peptide 281–300 is the dominant immunogenic determinant of hAQP4 in the context of HLA-DRB1*03:01. This immunogenic peptide stimulates a strong Th₁ and Th₁₇ immune response. AQP4_281-300-specific encephalitogenic CD4⁺ T cells should initiate CNS inflammation that results in a clinical phenotype in HLA-DRB1*03:01 transgenic mice.

Methods

Controlled study with humanized experimental animals. HLA-DRB1*03:01 transgenic mice were immunized with hAQP4_281-300, or whole-length hAQP4 protein emulsified in complete Freund’s adjuvant. Humoral immune responses to both antigens were assessed longitudinally. In vivo T cell frequencies were assessed by tetramer staining. Mice were followed clinically, and the anterior visual pathway was tested by pupillometry. CNS tissue was examined histologically post-mortem. Flow cytometry was utilized for MHC binding assays and to immunophenotype T cells, and T cell frequencies were determined by ELISpot assay.

Results

Immunization with hAQP4_281-300 resulted in an in vivo expansion of antigen-specific CD4⁺ T cells, and an immunoglobulin isotype switch. HLA-DRB1*03:01 TG mice actively immunized with hAQP4_281-300, or with whole-length hAQP4 protein were resistant to developing a neurological disease that resembles NMO. Experimental mice show no histological evidence of CNS inflammation, nor change in pupillary responses. Subsequent analysis reveals that a single amino acid substitution from aspartic acid in hAQP4 to glutamic acid in murine (m)AQP4 at position 290 prevents the recognition of hAQP4_281-300 by the murine T cell receptor (TCR).

Conclusion

Induction of a CNS inflammatory autoimmune disorder by active immunization of HLA-DRB1*03:01 TG mice with human hAQP4_281-300 will be complex due to a single amino acid substitution. The pathogenic role of T cells in this disorder remains critical despite these observations.

Immunopathogenesis of neuromyelitis optica

Neuromyelitis optica (NMO, Devic's syndrome) is a clinical syndrome characterized by optic neuritis and (mostly longitudinally extensive) myelitis. If untreated, NMO usually takes a relapsing course and often results in blindness and tetra- or paraparesis. The discovery of autoantibodies to aquaporin-4, the most abundant water channel in the CNS, in 70-80% of patients with NMO (termed NMO-IgG or AQP4-Ab) and subsequent investigations into the pathogenic impact of this new reactivity have led to the recognition of NMO as an autoimmune condition and as a disease entity in its own right, distinct from classic multiple sclerosis. Here, we comprehensively review the current knowledge on the role of NMO-IgG/AQP4-Ab, B cells, T cells, and the innate immune system in the pathogenesis of NMO.

Human aquaporin 4281-300 is the immunodominant linear determinant in the context of HLA-DRB1*03:01: relevance for diagnosing and monitoring patients with neuromyelitis optica

OBJECTIVE To identify linear determinants of human aquaporin 4 (hAQP4) in the context of HLA-DRB1*03:01. DESIGN In this controlled study with humanized experimental animals, HLA-DRB1*03:01 transgenic mice were immunized with whole-protein hAQP4 emulsified in complete Freund adjuvant. To test T-cell responses, lymph node cells and splenocytes were cultured in vitro with synthetic peptides 20 amino acids long that overlap by 10 amino acids across the entirety of hAQP4. The frequency of interferon γ, interleukin (IL) 17, granulocyte-macrophage colony-stimulating factor, and IL-5-secreting CD4+ T cells was determined by the enzyme-linked immunosorbent sport assay. Quantitative immunofluorescence microscopy was performed to determine whether hAQP4281-300 inhibits the binding of anti-hAQP4 recombinant antibody to surface full-length hAQP4. SETTING Academic neuroimmunology laboratories. SUBJECTS Humanized HLA-DRB1*03:01+/+ H-2b-/- transgenic mice on a B10 background. RESULTS Peptide hAQP4281-300 generated a significantly (P <.01) greater TH1 and TH17 immune response than any of the other linear peptides screened. This 20mer peptide contains 2 dominant immunogenic 15mer peptides. hAQP4284-298 induced predominantly an IL-17 and granulocyte-macrophage colony-stimulating factor TH cell phenotype, whereas hAQP4285-299 resulted in a higher frequency of TH1 cells. hAQP4281-300 did not interfere with recombinant AQP4 autoantibody binding. CONCLUSIONS hAQP4281-330 is the dominant linear immunogenic determinant of hAQP4 in the context of HLA-DRB1*03:01. Within hAQP4281-330 are 2 dominant immunogenic determinants that induce differential TH phenotypes. hAQP4 determinants identified in this study can serve as diagnostic biomarkers in patients with neuromyelitis optica and may facilitate the monitoring of treatment responses to pharmacotherapies.

Crystallographic structure of the human leukocyte antigen DRA, DRB3*0101: models of a directional alloimmune response and autoimmunity

We describe structural studies of the human leukocyte antigen DR52a, HLA-DRA/DRB3*0101, in complex with an N-terminal human platelet integrin alphaII(B)betaIII glycoprotein peptide which contains a Leu/Pro dimorphism. The 33:Leu dimorphism is the epitope for the T cell directed response in neonatal alloimmune thrombocytopenia and post-transfusion purpura in individuals with the alphaII(B)betaIII 33:Pro allele, and defines the unidirectional alloimmune response. This condition is always associated with DR52a. The crystallographic structure has been refined to 2.25 A. There are two alphabeta heterodimers to the asymmetric unit in space group P4(1)2(1)2. The molecule is characterized by two prominent hydrophobic pockets at either end of the peptide binding cleft and a deep, narrower and highly charged P4 opening underneath the beta 1 chain. Further, the peptide in the second molecule displays a sharp upward turn after pocket P9. The structure reveals the role of pockets and the distinctive basic P4 pocket, shared by DR52a and DR3, in selecting their respective binding peptide repertoire. We observe an interesting switch in a residue from the canonically assigned pocket 6 seen in prior class II structures to pocket 4. This occludes the P6 pocket helping to explain the distinctive "1-4-9" peptide binding motif. A beta57 Asp-->Val substitution abrogates the salt-bridge to alpha76 Arg and along with a hydrophobic beta37 is important in shaping the P9 pocket. DRB3*0101 and DRB1*0301 belong to an ancestral haplotype and are associated with many autoimmune diseases linked to antigen presentation, but whereas DR3 is susceptible to type 1 diabetes DR52a is not. This dichotomy is explored for clues to the disease.

Frequency of DRB1–DQB1 two-locus haplotypes in tuberculosis: Preliminary report

Analysis of correlation between tuberculosis (TB) and human leukocyte antigen (HLA) in populations from Asia and Latin America has shown conflicting results. The aim of this study was to evaluate the frequency of HLA-DRB1-DQB1 two-locus haplotypes of 61 TB patients and 125 healthy volunteers in the same ethnic group in Poland. DRB1 and DQB1 alleles were determined by PCR-SSP "low-resolution" and "high-resolution" methods. Our study showed that DRB1*1601 and DQB1*0502 alleles were more frequent, whereas DQB1*0201 was rarer in TB than in controls. DRB1*16-DQB1*05, DRB1*04-DQB1*03 and DRB1*1601-DQB1*0502 haplotype were more common, and DRB1*11-DQB1*03 less frequent in TB in comparison to controls. Positive linkage disequilibrium (LD) for DRB1*01-DQB1*05, DRB1*03-DQB1*02, DRB1*11-DQB1*03, DRB1*13-DQB1*06 and DRB1*15-DQB1*06 was found in controls. A trend towards the positive LD for DRB1*01-DQB1*05, DRB1*03-DQB1*02, DRB1*11-DQB1*03, DRB1*15-DQB1*06 and DRB1*16-DQB1*05 was shown in TB. The trend towards the positive LD for DRB1*16-DQB1*05 haplotype in TB patients was not observed in the control group. It seems likely that the presence of DRB1*1601, DQB1*0502 alleles and DRB1*1601-DQB1*0502, DRB1*04-DQB1*03, DRB1*14-DQB1*05 haplotypes may be related to a higher risk of developing TB, whereas low frequency of DQB1*0201 and DRB1*11-DQB1*03 haplotype may be linked to the resistance to TB.

Lung restricted T cell receptor AV2S3+ CD4+ T cell expansions in sarcoidosis patients with a shared HLA-DRbeta chain conformation

BACKGROUND

Sarcoidosis is a systemic disease of unknown aetiology frequently affecting the lungs. CD4+ T cells, in particular, accumulate in the lungs, implicating them in the pathogenesis of the disease.

METHODS

T cell receptor (TCR) variable (V) gene expression on bronchoalveolar lavage (BAL) fluid T cells and the HLA DR alleles of 121 Scandinavian patients with sarcoidosis was determined.

RESULTS

As expected from our previous results, almost every DRB1*0301 (i.e. DR17) positive patient (67/69) had significantly increased numbers of AV2S3+ CD4+ T cells in the BAL fluid but normal levels in peripheral blood (that is, lung restricted expansions) compared with only six of 52 DRB1*0301 negative patients. Detailed genotypic HLA analysis showed that these six DRB1*0301 negative patients with lung restricted AV2S3+ T cell expansions had another HLA allele in common-the HLA-DRB3*0101 allele (also called DR52a)-which was not found in any other DRB1*0301 negative patient. A new group of sarcoidosis patients was therefore identified, characterised by a strict correlation between a distinct HLA allele and lung accumulated T cells expressing a particular TCR V segment. Furthermore, the HLA-DRB1*0301 and HLA-DRB3*0101 encoded molecules showed similarities, with identical amino acid sequences in regions important for antigen binding which may enable them to bind and present the same or similar antigenic peptides.

CONCLUSIONS

HLA-DRB3*0101 as well as DRB1*0301 positive sarcoidosis patients may have the capacity to present specific sarcoidosis associated antigens in such a way that AV2S3+ CD4+ T cells are stimulated preferentially, generating lung restricted AV2S3+ T cell expansions.

Scanning a DRB3*0101 (DR52a)-Restricted Epitope Cross-Presented by DR3: Overlapping Natural and Artificial Determinants in the Human Acetylcholine Receptor

A recurring epitope in the human acetylcholine receptor (AChR) α subunit (α146–160) is presented to specific T cells from myasthenia gravis patients by HLA-DRB3*0101—“DR52a”—or by DR4. Here we first map residues critical for DR52a in this epitope by serial Ala substitution. For two somewhat similar T cells, this confirms the recently deduced importance of hydrophobic “anchor” residues at peptide p1 and p9; also of Asp at p4, which complements this allele’s distinctive Arg74 in DRβ. Surprisingly, despite the 9 sequence differences in DRβ between DR52a and DR3, merely reducing the bulk of the peptide’s p1 anchor residue (Trp149→Phe) allowed maximal cross-presentation to both T cells by DR3 (which has Val86 instead of Gly). The shared K71G73R74N77 motif in the α helices of DR52a and DR3 thus outweighs the five differences in the floor of the peptide-binding groove. A second issue is that T cells selected in vitro with synthetic AChR peptides rarely respond to longer Ag preparations, whereas those raised with recombinant subunits consistently recognize epitopes processed naturally even from whole AChR. Here we compared one T cell of each kind, which both respond to many overlapping α140–160 region peptides (in proliferation assays). Even though both use Vβ2 to recognize peptides bound to the same HLA-DR52a in the same register, the peptide-selected line nevertheless proved to depend on a recurring synthetic artifact—a widely underestimated problem. Unlike these contaminant-responsive T cells, those that are truly specific for natural AChR epitopes appear less heterogeneous and therefore more suitable targets for selective immunotherapy.

T Cell Responses to Heat-Shock Protein 60: Differential Responses by CD4+ T Cell Subsets According to Their Expression of CD45 Isotypes

We demonstrate that human T lymphocytes proliferate in vitro to highly purified human heat-shock protein 60 (Hu.hsp60). The response to this self Ag was confined to the CD45RA+RO− T cell subset, with minimal responses by adult CD45RA−RO+ T cells. Experiments using keyhole limpet hemocyanin as a prototypic novel Ag, or tetanus toxoid as a recall Ag, were consistent with the notion that CD45RA+RO− and CD45RA−RO+ T cell subsets can be designated as naive and memory cells, respectively; thus, responses to Hu.hsp60 were confined to the putative naive subset. In contrast, both CD45RA+RO− and CD45RA−RO+ T cell populations proliferated to bacterial hsp60 from Mycobacterium leprae, Escherichia coli, or Chlamydia trachomatis. However, only CD45RA−RO+ (memory) T cells responded to a mycobacterial hsp60-derived peptide previously defined as a major bacteria-specific epitope. Experiments with cord blood T cells, which are CD45RA+RO− and can be considered truly naive, showed that the peptide could elicit responses from naive T cells in vitro; cord blood cells also responded to Hu.hsp60. Since bacterial hsp60 Ags contain both conserved and nonconserved epitopes, we speculate that in vivo challenge with bacterial hsp60 will activate T cells capable of seeing either type of epitope, but only those that see nonconserved epitopes maintain the CD45RA−RO+ memory phenotype. However, T cells recognizing conserved epitopes, while not apparently being recruited to the memory pool, may nevertheless play a role in immunoregulation, particularly in the context of inflammation, when expression of Hu.hsp60 is increased.

Human leukocyte antigens in tuberculosis and leprosy

Human mycobacterial infections are characterized by a spectrum of clinical and immunological manifestations. Specific human leukocyte antigen (HLA) factors are associated with the subtypes of leprosy that develop and the course of tuberculosis after infection. The identification of protective mycobacterial antigens presented by a broad variety of HLA molecules will have important implications for the design of vaccines.

Use of T cell receptor/HLA-DRB1*04 molecular modeling to predict site-specific interactions for the DR shared epitope associated with rheumatoid arthritis

OBJECTIVE

To use molecular modeling tools to analyze the potential structural basis for the genetic association of rheumatoid arthritis (RA) with the major histocompatibility complex (MHC) "shared epitope," a set of conserved amino acid residues in the third hypervariable region of the DRbeta chain.

METHODS

Homology model building techniques were used to construct molecular models of the arthritis-associated DRB1*0404 molecule and a T cell receptor (TCR) from T cell clone EM025, which is specific for DR4 molecules containing the shared epitope sequence. Interactive graphics techniques were used to orient the TCR on the DR molecule, guided by surface complementarity analysis.

RESULTS

The predicted TCR-MHC-peptide complex involved multiple interactions and specificity for the shared epitope. TCR residues CDR1beta D30, CDR2beta N51, and CDR3beta Q97 were positioned to potentially participate in hydrogen bond interactions with the shared epitope DRbeta residues Q70 and R71.

CONCLUSION

These results suggest a structural mechanism in which specific TCR recognition and possibly Vbeta selection are directly influenced by the disease-associated MHC polymorphisms.

The impact of DR3 microvariation on peptide binding: the combinations of specific DR beta residues critical to binding differ for different peptides

HLA-DR molecules are a group of highly polymorphic glycoprotein heterodimers that present peptide antigens to T lymphocytes for immune surveillance. To assess the significance of limited polymorphism on the functional differentiation of DR molecules, the binding of several immunogenic peptides to the DR3 microvariants [DR(alpha, beta 1*0302) and DR(alpha, beta 1*0301)] and to mutants of these DR3 molecules was examined. This analysis has shown that each residue (DR beta 26, DR beta 28, DR beta 47, and DR beta 86), which differentiates these two DR3 molecules, contributes to their functional distinction and that the relative contribution of each residue varies for different peptide/DR3 complexes. For example, DR beta 28 and DR beta 86 controlled the mycobacterium tuberculosis 65-kD heat shock protein peptides 3-13 and 4-15 (HSP) binding specificity to DR (alpha, beta 1*0301). [HSP does not bind to DR(alpha, beta 1*0302)], whereas DR beta 26, DR beta 28, and DR beta 86 controlled the influenza hemagglutinin peptide 306-318 (HA) binding specificity to DR(alpha, beta 1*0302). [HA does not bind to DR(alpha, beta 1*0301).] In comparison, DR beta 86 alone controlled the binding level difference of sperm whale myoglobin peptide 132-151 (SWM) and of myelin basic protein peptide 152-170 (MBP) [both bind to DR(alpha, beta 1*0301) at levels five times greater than to DR(alpha, beta 1*0302)] to the DR3 molecules. Although not critical, additional DR beta residues influenced the binding level of individual peptides of each of the DR3 molecules and, again, the combinations of these residues differed for different peptide/DR3 complexes. These data showed that individual DR residues vary in their relative contribution to the interaction between a specific DR molecule and different peptides and that limited polymorphism can create substantial differences in the peptide binding profiles among DR molecules.

The relative importance of individual DR binding motif positions as defined by peptide anchor analysis of influenza hemagglutinin peptide 306-318 and human myelin basic protein peptide 152-165 binding to several DR molecules: definition of a common extended DR binding motif

Definition of peptide binding motifs for DR molecules has proven difficult as the peptides that bind to a DR molecule have shown extensive variability at putative motif positions. Recent studies suggest that specific peptide anchor residues (motif positions) and specific DR residues can differ in importance for peptide binding to a DR molecule. To assess further the relevance of individual peptide anchor residues, the binding of serial alanine-substituted analogs of influenza virus hemagglutinin (HA) 306-318 and human myelin basic protein (MBP) 152-165 to a panel of transfected wild-type DR molecules was examined. This analysis included DR molecules from a wide range of allelic families and, unlike most earlier studies, multiple members of single DR allelic families. The data show that different peptide residues serve as critical anchors for binding to different DR molecules. For example, MBP binding to DR(alpha, beta 1*0303) required peptide residues F154 (i), R159 (i + 5) and R162 (i + 8). In contrast, MBP binding to DR(alpha, beta 1*0102) required peptide residues I153 (i) and L156 (i + 3). More importantly, the combination of critical anchor residues in HA and MBP differed for binding to a single DR molecule [e.g. V309 (i) for HA and I153 (i) and L156 (i + 3) for MBP binding to DR(alpha, beta 1*0102)]. Although the location of the binding pocket in each DR molecule compared to the DR (alpha, beta 1 *0101) crystal is expected to be similar and suggests a common extended DR binding motif, the present results suggest that the relative importance of individual peptide anchor residues and of the corresponding DR binding pockets will differ for each DR/peptide complex.

Changes in the peripheral blood T-Cell receptor V beta repertoire in vivo and in vitro during shigellosis

A sequential activation of T cells in peripheral blood during shigello sis has been observer (D. Islam, P.K. Bradham, A. A. Lindberg, and B. Christensson, Infect. Immun 63:2941-2949, 1995). To further investigate the cellular response during the course of Shigella infection, changes in the T-cell receptor (TCR) repertoire in the subsets in blood in patients during shigellosis was that Shigella antigens may modulate the function of T cells carrying TCRs capable of recognizing Shigella-specific epitopes or superantigens. Such a selective preference for T cells expressing certain TCR Vbeta types could lead to the expansion or deletion of these T cells. In the present study of 27 adult male Bangladeshi patients with dysentery (14 cases caused by Shigella Dysenteriae 1 and 13 cases caused by Shigella flexneri), the changes in the TCR Vbeta repertoire of peripheral blood CD4+ and CD8+ T-cell subsets have been analyzed with a panel of nine anti-Vbeta monoclonal antibodies by flow cytometry. Twenty healthy males from Bangladesh and 20 healthy males from Sweden served as controls. Compared with the Bangladeshi controls, the patients had an increased frequency of CD4+T cells expression Vbeta2, Vbeta3, and Vbeta17, with a maximum at day 7 after the onset of disease. The frequency of CD4+T cells expressing Vbeta5.1 was increased only in patients with S. flexneri infection. Peripheral blood T cells from Shigella-infected patients also responded to in vitro stimulation in a TCR Vbeta-specific manner. Stimulation with heat-killed S. dysenteriae 1 and Shiga toxin enhanced the frequency of cells expressing Vbeta2, Vbeta3, Vbeta5.1, Vbeta13.6, and Vbeta17, especially in samples obtained at day 7. The enhanced frequency of cells expressing Vbeta2, Vbeta3, Vbeta5.1, and Vbeta17 found both in in vivo and in vitro could suggest that in shigellosis antigens or superantigens are presented to the immune system and preferentially activate certain TCR Vbeta types in T-cell subsets. The kinetics of the change in the TCR Vbeta repertoire in blood during shigellosis may indicate that following local activation, the antigen activated T cells can be retrieved in the blood and restimulated in vitro. If confirmed by parallel analysis of T cells in the gut and blood by TCR sequence analysis, the possibility suggested by our findings would facilitate further analysis of the role of cell-mediated immune responses in the pathogenesis of and protection against Shigella infection.

Clip binds to HLA class II using methionine-based, allele-dependent motifs as well as allele-independent supermotifs

The invariant chain (Ii) region that interacts with class II and inhibits premature peptide binding has been mapped to amino acids 82-107, known as CLIP. It is unclear whether CLIP binds directly to the class II peptide binding groove and thus competitively blocks binding of other peptides, or whether it binds to conserved class II sites and indirectly inhibits peptide binding by inducing conformational changes in class II. Here we show evidence that strongly suggests that CLIP binds within the peptide binding groove, as CLIP binds to various HLA-DR alleles using allele-dependent as well as allele-independent, methionine-based binding motifs. First, a core sequence of 12 amino acids was identified within CLIP which is required for optimal binding to DR1, DR2, DR3(17) and DR7. This sequence is composed of CLIP p88-99 (SKMRMATPLLMQ). By substitution analysis, all three methionine residues appeared to control CLIP binding to HLA-DR. However, whereas M90 controlled binding to all four alleles, M92 and M98 were of different importance for the various alleles: M92 is involved in CLIP binding to DR1 and DR3(17) but not to DR2 or DR7, and M98 controls CLIP binding to DR2, DR3(17) and DR7 but not DR1. Also, CLIP competes with known immunogenic peptides for class II binding in a manner indistinguishable from regular, class II binding competitor peptides. Finally, the dissociation rates of CLIP-class II complexed are similar to those of antigenic peptide-class II complexes. Thus, CLIP most likely binds to the class II peptide binding groove, since most allelic class II differences are clustered here. CLIP uses unconventional methionine anchor residues representing an allele-independent supermotif (M90) as well as allele-dependent motifs (M92 and M98).

HLA-DR residues accessible under the peptide-binding groove contribute to polymorphic antibody epitopes

Many residues involved in polymorphic antibody-binding epitopes on class II molecules are located on the alpha-helix of DR beta chains. Although they have received less attention, residues in the peptide-binding groove and second domain of the DR beta chain may also be critical for polymorphic anti-DR antibody epitopes. In this study, we used transfectants expressing site-directed mutations at positions in the HLA-DR beta 1 and beta 2 domains and flow cytometry to define the epitopes of several polymorphic anti-DR antibodies. Both DR(beta 1*0403) residues 14 and 25 were shown to be involved in the epitopes of mAbs DA6. 164, HU-20, Q5/6, and 50D6, and DR(beta 1*0701) residue 14 was shown to be critical for the epitopes of two DR7-specific mAbs, SFR 16-DR7M and TAL13.1. Unlike most other residues shown to be important in antibody-binding epitopes, residue 14 is located in the floor of the peptide-binding groove and residue 25 is in an outer loop, each with their side chains pointing down, such that antibodies may directly contact these residues from below the binding groove. Two residues in the beta 2 domain, beta 180 and beta 181, were also shown to be involved in the epitopes of three polymorphic anti-DR mAbs, NFLD.D1, NFLD.M1, and LY9. Although these two residues are close to the transmembrane domain in the linear sequence, their solvent accessibility in the DR1 structures is quite impressive. Our data provide new evidence that residues accessible under the peptide-binding groove contribute to polymorphic antibody-binding epitopes.