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G T Nepom

Publications and source records attributed to G T Nepom.

At least 19 recordsLinked to original sources
PubMed2001

T cell selection and differential activation on structurally related HLA-DR4 ligands.

Plasticity of TCR interactions during CD4(+) T cell activation by an MHC-peptide complex accommodates variation in the peptide or MHC contact sites in which recognition of an altered ligand by the T cell can modify the T cell response. To explore the contribution of this form of TCR cross-recognition in the context of T cell selection on disease-associated HLA molecules, we have analyzed the relationship between TCR recognition of the DRB1*0401- and DRB1*0404-encoded HLA class II molecules associated with rheumatoid arthritis. Thymic reaggregation cultures demonstrated that CD4(+) T cells selected on either DRB1*0401 or DRB1*0404 could be subsequently activated by the other MHC molecule. Using HLA tetramer technology we identify hemagglutinin residue 307-319-specific T cells restricted by DRB1*0401, but activated by hemagglutinin residues 307-319, in the context of DRB1*0404. One such clone exhibits an altered cytokine profile upon activation with the alternative MHC ligand. This altered phenotype persists when both class II molecules are present. These findings directly demonstrate that T cells selected on an MHC class II molecule carry the potential for activation on altered self ligands when encountering Ags presented on a related class II molecule. In individuals heterozygous for these alleles the possibility of TCR cross-recognition could lead to an aberrant immune response.

Animals↗
PubMed2001

Tetramer-guided epitope mapping: rapid identification and characterization of immunodominant CD4+ T cell epitopes from complex antigens.

T cell responses to Ags involve recognition of selected peptide epitopes contained within the antigenic protein. In this report, we describe a new approach for direct identification of CD4+ T cell epitopes of complex Ags that uses human class II tetramers to identify reactive cells. With a panel of 60 overlapping peptides covering the entire sequence of the VP16 protein, a major Ag for HSV-2, we generated a panel of class II MHC tetramers loaded with peptide pools that were used to stain peripheral lymphocytes of an HSV-2 infected individual. With this approach, we identified four new DRA1*0101/DRB1*0401- and two DRA1*0101/DRB1*0404-restricted, VP16-specific epitopes. By using tetramers to sort individual cells, we easily obtained a large number of clones specific to these epitopes. Although DRA1*0101/DRB1*0401 and DRA1*0101/DRB1*0404 are structurally very similar, nonoverlapping VP16 epitopes were identified, illustrating high selectivity of individual allele polymorphisms within common MHC variants. This rapid approach to detecting CD4+ T cell epitopes from complex Ags can be applied to any known Ag that gives a T cell response.

CD4-Positive T-Lymphocytes↗
PubMed2001

Identification and modulation of a naturally processed T cell epitope from the diabetes-associated autoantigen human glutamic acid decarboxylase 65 (hGAD65).

T cell recognition of autoantigens is critical to progressive immune-mediated destruction of islet cells, which leads to autoimmune diabetes. We identified a naturally presented autoantigen from the human islet antigen glutamic acid decarboxylase, 65-kDa isoform (GAD65), by using a combination of chromatography and mass spectrometry of peptides bound by the type I diabetes (insulin-dependent diabetes mellitus, IDDM)-associated HLA-DR4 molecule. Peptides encompassing this epitope-stimulated GAD65-specific T cells from diabetic patients and a DR4-positive individual at high risk for developing IDDM. T cell responses were antagonized by altered peptide ligands containing single amino acid modifications. This direct identification and manipulation of GAD65 epitope recognition provides an approach toward dissection of the complex CD4(+) T cell response in IDDM.

Adolescent↗
PubMed2001

The role of the DR4 shared epitope in selection and commitment of autoreactive T cells in rheumatoid arthritis.

The mechanistic basis for HLA associations with RA is still unknown in spite of 20 years of disease association studies and a detailed characterization of HLA class II alleles associated with disease. Analysis of the structural interactions between DR4 susceptibility molecules and T cells specific for the peptide-MHC complex suggests a mechanism for directed T-cell selection and amplification in which RA-associated genetic polymorphisms bias intermolecular recognition. New immunologic models for illustrating the importance of regulated thresholds for T-cell activation based on avidity between the TCR, MHC, and peptide offer insight into a potential mechanism in which the disease-associated HLA molecules create an autoimmune-prone individual by virtue of a biased TCR selection and T-cell amplification process. New tools such as the use of HLA-DR4 tetramers provide the ability to identify and monitor the presence of such autoreactive T cells in the periphery of individuals and patients and should assist in further testing of the multistep model for RA pathways presented in this article.

Arthritis, Rheumatoid↗
PubMed2001

Activated human epitope-specific T cells identified by class II tetramers reside within a CD4high, proliferating subset.

Antigen-specific T cells acquire a distinctive phenotype during activation, with characteristic acquisition of surface markers and patterns of gene expression. Early after antigen stimulation, CD4(+) T lymphocytes increase their surface density of the CD4 marker, a trait which has been used to identify antigen-activated cells. The recent development of MHC tetramer technologies has greatly improved the ability to detect HLA class I-restricted T cells specific for known antigen epitopes. We have recently extended these studies to human class II-restricted CD4(+) T cell responses and now describe antigen-specific T cell responses from human peripheral blood in which elevated CD4 expression levels in human T cells following antigen stimulation identify the activated and proliferating subset of cells. The CD4(high) population is substantially enriched in epitope-specific cells identified by class II tetramer staining and almost all tetramer-positive cells are contained within the CD4(high) population. T cell clones derived from the tetramer-positive, CD4(high) population demonstrate antigen specificity and maintain tetramer staining, while the substantial number of CD4(high) cells which fail to stain with tetramer appear to proliferate as a result of bystander activation. Epitope-specific components of a polyclonal immune response are directly visualized and quantitated by tetramer detection, providing a direct measure of the heterogeneity of the human immune response.

CD4 Antigens↗
PubMed2001

Low-dose streptozotocin induces sustained hyperglycemia in Macaca nemestrina.

The potential for using macaques to create a nonhuman primate diabetic model was investigated. The significant objectives were to determine a) prognosis of STZ induced permanent beta cell destruction in nonhuman primates, and b) the potential to use STZ treated animals in a model of autoimmune diabetes by following adoptively transferred lymphocytes into MHC identical macaques. Beta cell impairment was achieved by a single intravenous, low dose (10-40 mg/kg body weight) streptozotocin injection in a majority of pigtailed macaques (Macaca nemestrina). Multiple injections, even at low doses at close intervals affected liver and kidney functions in addition to beta cell destruction. Abnormal IVGTT were observed in all streptozotocin-treated animals, in some within a week to 10 days. The fasting blood glucose levels rose from <70 mg/dl in pre-STZ stage to above 400 mg/dl in severely diabetic macaques. Histological evidence suggests loss of beta cells when animals were euthanized within two to four weeks post-STZ treatment. Near complete destruction of beta cells was observed in animals maintained longer than three months on insulin. Donor T cells from STZ-treated animals were incubated overnight with 10U/ml IL-2 and 2.5 ug/ml PHA and then injected iv into a MHC-identical non-diabetic sibling. Three weeks later a second injection of donor PMBC labeled with vital dye Cell Tracker Green was given and the animal was euthanized after 24 hours. The recipient showed labeled donor T cells in the pancreas, spleen and peripheral blood, consistent with specific homing of activated lymphocytes from the diabetic donor.

Adoptive Transfer↗
PubMed2000

Distinct T cell interactions with HLA class II tetramers characterize a spectrum of TCR affinities in the human antigen-specific T cell response.

The polyclonal nature of T cells expanding in an ongoing immune response results in a range of disparate affinities and activation potential. Recently developed human class II tetramers provide a means to analyze this diversity by direct characterization of the trimolecular TCR-peptide-MHC interaction in live cells. Two HSV-2 VP16(369-379)-specific, DQA1*0102/DQB1*0602 (DQ0602)-restricted T cell clones were compared by means of T cell proliferation assay and HLA-DQ0602 tetramer staining. These two clones were obtained from the same subject, but show different TCR gene usage. Clone 48 was 10-fold more sensitive to VP16(369-379) peptide stimulation than clone 5 as assayed by proliferation assays, correlating with differences in MHC tetramer binding. Clone 48 gave positive staining with the DQ0602/VP16(369-379) tetramer at either 23 or 37 degrees C. Weak staining was also observed at 4 degrees C. Clone 5 showed weaker staining compared with clone 48 at 37 degrees C, and no staining was observed at 23 degrees C or on ice. Receptor internalization was not required for positive staining. Competitive binding indicates that the cell surface TCR of clone 48 has higher affinity for the DQ0602/VP16(369-379) complex than clone 5. The higher binding affinity of clone 48 for the peptide-MHC complex also correlates with a slower dissociation rate compared with clone 5.

Amino Acid Sequence↗
PubMed2000

Beta 57-Asp plays an essential role in the unique SDS stability of HLA-DQA1*0102/DQB1*0602 alpha beta protein dimer, the class II MHC allele associated with protection from insulin-dependent diabetes mellitus.

Studies of the stability of HLA-DQ have revealed a correlation between SDS stability of MHC class II alphabeta dimers and insulin-dependent diabetes mellitus (IDDM) susceptibility. The MHC class II alphabeta dimer encoded by HLA-DQA1*0102/DQB1*0602 (DQ0602), which is a dominant protective allele in IDDM, exhibits the greatest SDS stability among HLA-DQ molecules in EBV-transformed B-lymphoblastoid cells and PBLs. DQ0602 is also uniquely SDS stable in the HLA-DM-deficient cell line, BLS-1. We addressed the molecular mechanism of the stability of DQ0602 in BLS-1. A panel of mutants based on the polymorphic differences between HLA-DQA1*0102/DQB1*0602 and HLA-DQA1*0102/DQB1*0604 were generated and expressed in BLS-1. An Asp at beta57 was found to be critical for SDS stability, whereas Tyr at beta30, Gly at beta70, and Ala at beta86 played secondary roles. Furthermore, the level of class II-associated invariant chain peptide bound to HLA-DQ did not correlate with SDS stability, suggesting that class II-associated invariant chain peptide does not play a direct role in the unique SDS stability of DQ0602. These results support a role for DQB1 codon 57 in HLA-DQ alphabeta dimer stability and IDDM susceptibility.

Alleles↗
PubMed2000

HLA-DQ tetramers identify epitope-specific T cells in peripheral blood of herpes simplex virus type 2-infected individuals: direct detection of immunodominant antigen-responsive cells.

Ag-specific CD4+ T cells are present in peripheral blood in low frequency, where they undergo recruitment and expansion during immune responses and in the pathogenesis of numerous autoimmune diseases. MHC tetramers, which constitute a labeled MHC-peptide ligand suitable for binding to the Ag-specific receptor on T cells, provide a novel approach for the detection and characterization of such rare cells. In this study, we utilized this technology to identify HLA DQ-restricted Ag-specific T cells in the peripheral blood of human subjects and to identify immunodominant epitopes associated with viral infection. Peptides representing potential epitope regions of the VP16 protein from HSV-2 were loaded onto recombinant DQ0602 molecules to generate a panel of Ag-specific DQ0602 tetramers. VP16 Ag-specific DQ-restricted T cells were identified and expanded from the peripheral blood of HSV-2-infected individuals, representing two predominant epitope specificities. Although the VP16 369-380 peptide has a lower binding affinity for DQ0602 molecules than the VP16 33-52 peptide, T cells that recognized the VP16 369-380 peptide occurred at a much higher frequency than those that were specific for the VP16 33-52 peptide.

Amino Acid Sequence↗
PubMed2000

HLA class I and class II profiles of patients presenting with Sydenham's chorea.

Sydenham's chorea (SC) may occur in rheumatic fever (RF) patients without arthritis and carditis. In this study we typed HLA antigens and alleles in patients presenting with the distinct major clinical manifestations of RF, i.e., chorea, carditis, or arthritis, in population and family studies. We evaluated 91 patients with RF for HLA-A, HLA-B, and HLA-DR antigens; of these, 33 had pure chorea, 26 pure carditis, 16 pure arthritis, and 16 carditis plus arthritis. We also typed 24 SC patients and their unaffected siblings for HLA-DRB1 and HLA-DQB1 alleles using molecular methods. HLA-B49 and HLA-DR1 antigens were overrepresented in the total group of patients with RF and in all the subgroups studied, excluding the SC subgroup in which the frequency of HLA-DR1 antigen was not increased. The frequencies of the HLA-DRB1 and HLA-DQB1 alleles in patients with pure chorea were not significantly different from those observed in controls. Similarly, the frequencies of HLA class II alleles in SC patients did not differ significantly from those observed in unaffected siblings. These findings show that immunogenetic susceptibility to RF varies according to the major clinical manifestation presented by the patient.

Adolescent↗
PubMed2000

Increased frequency of HLA class II alleles DRB1*0301 and DQB1*0201 in Lambert-Eaton myasthenic syndrome without associated cancer.

Lambert-Eaton myasthenic syndrome (LEMS) is a rare autoimmune neuromuscular disorder characterized by pathogenic autoantibodies directed against the presynaptic voltage-gated calcium channels (VGCC), resulting in a clinical syndrome of proximal muscular weakness and autonomic dysfunction. Sixty percent of LEMS cases are associated with cancer, most commonly small cell carcinoma of the lung. In the 40% of LEMS patients without carcinoma, the stimulus for the production of VGCC autoantibodies is unknown; however, these LEMS patients have multiple other organ-specific autoantibodies. To investigate the autoimmune basis of noncancer associated LEMS (NCA-LEMS), high resolution typing of major histocompatibility loci was performed in 23 patients with NCA-LEMS. NCA-LEMS was strongly associated with DRB1*0301 (p<0.0001) and DQB1*0201 (p<0.0001), suggesting that NCA-LEMS is an autoimmune disorder associated with the DR3-DQ2 extended haplotype.

Adolescent↗
PubMed2000

Antigen recognition.

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Antigen Presentation↗
PubMed2000

GAD65-specific autoantibodies enhance the presentation of an immunodominant T-cell epitope from GAD65.

GAD65 autoantibodies (GAD65Ab) are highly prevalent in type 1 diabetes, but their functional role in the pathogenesis of the disease and their relationship to T-cell reactivity to GAD65 is still unclear. We tested the hypothesis that GAD65Ab modulate presentation of GAD65 to T-cells. T-cell hybridoma T33.1, which recognizes the GAD65 274-286 epitope in the context of HLA-DRB 1*0401, was incubated with antigen-presenting cells exposed to recombinant human GAD65 alone or complexed with GAD65Ab' or GAD65Ab- sera. Stimulation of the T33.1 hybridoma was greatly enhanced by multiple GAD65Ab+ sera. The enhancement effect was most prominent with sera from patients with high GAD65 autoantibody levels. Sera from GAD65Ab- subjects had no effect. The correlation between T-cell stimulation and GAD65Ab levels was not absolute, suggesting that other variables such as autoantibody recognition of different regions of GAD65 and variable effects on processing of the 274-286 epitope may contribute. Uptake of antibody-complexed GAD65 was Fc receptor (FcR)-mediated because the enhancement of presentation was inhibited by monoclonal antibodies against FcR. Our results support the hypothesis that GAD65Ab modulate presentation of GAD65 to T-cells. Increased antigen uptake and heterogeneity in the autoantibody specificity may provide a mechanism for antibody-facilitated T-cell response influencing the progression of type 1 diabetes.

Adolescent↗
PubMed2000

Molecular aspects of HLA class II alphabeta heterodimers associated with IDDM susceptibility and protection.

HLA-DQ alleles are strongly associated with IDDM susceptibility and protection. Studies assessing the molecular properties of HLA-DR, a HLA class II locus in linkage disequilibrium with HLA-DQ, have made substantial contributions toward elucidating the structure and function of HLA class II molecules. Reports on the molecular properties of HLA-DQ are now following and have revealed interesting observations regarding the stability of HLA-DQ alphabeta heterodimers. Future work is expected to provide an understanding of the mechanism by which HLA-DQ is associated with IDDM susceptibility and protection.

Animals↗
PubMed1999

MHC-peptide ligand interactions establish a functional threshold for antigen-specific T cell recognition.

Antigen-specific T cell recognition is dependent on the functional density of the TCR-ligand, which consists of specific MHC molecules and a specifically bound peptide. We have examined the influence of the affinity and concentration of exogenous peptide and the density of specific MHC molecules on the proliferation of a CD4+, DQA1*0501/DQB1*0201 (DQ2.1)-restricted, HSV-2-specific T cell clone. Using antigen peptide analogs with different mutations of known DQ2-anchor residues, T cell response was reduced in an peptide-affinity and - concentration specific manner. The decrease using weaker binding peptides was gradual as stimulation with a peptide with intermediate affinity yielded intermediate T cell proliferation and the poorest binding peptide induced an even weaker T cell response. MHC class II density on the APC was modified using DQ2 homo- and heterozygous B-LCLs as APCs, however this variation of MHC concentration had no effect on T cell proliferation. We interpret this as a reflection of a low threshold for activation of the T cell clone, in which peptide-MHC avidity is the over-riding determinant of the strength of ligand signal.

Alleles↗
PubMed1999

Peptide binding affinity and pH variation establish functional thresholds for activation of HLA-DQ-restricted T cell recognition.

Peptides derived from the HSV-2 VP16 protein were utilized for studies of peptide binding to DQ0302 molecules and T cell activation at both neutral and acidic pH. The native peptide VP16 430-444 contains an Asp at position 442, binds to DQ0302 strongly, with a Kd value of 50nM at acidic pH and very weakly, with a Kd value of greater than 10 microM at neutral pH. A truncated version of 430-444, i.e., VP16 433-442, binds with an affinity 10-fold lower compared to 430-444 at acidic pH, and binding at neutral pH was barely detectable. The homologous peptide 430-444,442A has an Asp to Ala substitution at position 442 and binds to DQ0302 with a Kd similar to 433-442. The short truncated analog 433-442A binds very poorly at both acidic and neutral pH. Both the wild type 430-444 and 433-442 peptides stimulated a HSV-specific T cell clone after a brief incubation with antigen presenting cells (APC) expressing DQ0302 at acidic pH. Much higher concentrations of wild type peptides were needed to activate T cells at neutral pH. In contrast, APC pulsed with Ala-substituted peptides 430-444,442A or 433-442A at neutral pH failed to stimulate the T cell clone, while APC pulsed at acidic pH and subsequently washed led to successful T cell activation. The Ala-substituted peptide was recognized by the T cell clone at neutral pH only when it was present in the APC culture throughout the stimulation process. While the MHC-peptide complexes formed with the native peptide are stable, complexes formed with the Ala-substituted peptide had a functional t1/2 of less than 4 hr at neutral pH.

Amino Acid Sequence↗