Robyn E. O'Hehir

Overlapping T-cell epitopes in the group I allergen of Dermatophagoides species restricted by HLA-DP and HLA-DR class II molecules

The induction of IgE antibodies reactive with the group I allergen of Dermatophagoides species (house dust mite [HDM]), which comprise a major component of the allergic immune response in HDM-atopic individuals, is dependent on the functional activity of specific CD4+ T cells. In this report we demonstrate that for a particular HDM-atopic individual the T-cell response to the group I allergen of Dermatophagoides pteronyssinus (Der p I) is limited to a single region (residues 101-143) of the protein. By mapping the fine antigen specificity with T-cell clones, we observed that the sequence 101-131 of Der p I contains a cluster of at least three overlapping T-cell epitopes. Analysis of the HLA class II restriction specificity of the T-cell clones revealed that the T-cell epitope, residues 110-131, was restricted by HLA-DRB1*0101. In contrast, peptide Der p I, 110-119 was recognized in association with HLA-DPB1*0402. However, the ability of cloned T cells to proliferate to the peptide Der p I, 107-119 presented by HLA-DPB1*0401, HLA-DPB1*0402, and HLA-DPB1*0501 expressing accessory cells illustrates the heterogeneity of the restriction specificity of this region of Der p I. The application of this information in the design of peptide-based immunotherapy in the management of allergic responses to HDM is discussed.

Functional inactivation of Dermatophagoides spp. (house dust mite) reactive human T‐cell clones

Staphylococcal enterotoxins are able both to stimulate powerful polyclonal proliferative responses and to induce non‐responsiveness of T lymphocytes expressing the appropriate T‐cell antigen receptor Vβ gene products. T‐cell clones representative of the human response to house dust mite were identified that express either Vβ3 or Vβ6 gene products. The specificity of the latter was confirmed by serology. Pre‐treatment of cloned Vβ3+ T cells with the Staphyhcoccus aureus enterotoxins B or C1 rendered them non‐responsive to immunogenic challenge with their natural ligand, while retaining responsiveness to exogenous IL‐2. Similarly, exposure of the Vβ6+ dust mite reactive T cells to the Staphylococcal enterotoxin of the appropriate specificity, SEE, induced specific anergy. The development of non‐responsiveness was associated with changes in the T‐cell phenotypes. Downreguiation of the T‐cell receptor, Ti‐CD3, was paralleled by enhanced expression of both CD2 and the IL‐2 receptor, CD25. Differential co‐modulation of CD4 and Ti‐CD3 suggested that for some T cells CD4 may form part of the specific antigen recognition structure. Toxicity of the Staphylococcal enterotoxins may be removed by chemical modification, thus their ability functionally to inactivate subpopulations of T cells expressing antigen‐specific receptors with shared characteristics may be of potential value in the regulation of allergic diseases if the diversity of the T‐cell repertoire proves to be limited.

An in vitro model of peptide-mediated immunomodulation of the human T cell response to Dermatophagoides spp (house dust mite)

Allergic sensitivity of Dermatophagoides spp (house dust mites) is mediated by specific IgE antibody, the production of which requires the presence of CD4+ helper T cells. Attempts to hyposensitize this response in allergic individuals have depended on the administration of extracts of specific allergen. However, the ability of peptides derived from unrelated antigens to inhibit specific immune responses offers an alternative approach to therapy. We have addressed this question by examining the ability of a nonstimulatory peptide analogue derived from influenza virus hemagglutinin to modulate T cell recognition of house dust mite. The peptide inhibited the response of mite-specific CD4+ T cell clones restricted by either the HLA-DRAB1 or DRAB3 gene products. Furthermore, mite-induced polyclonal T cell responses were negatively modulated by the peptide, whereas recognition of common recall antigens remained intact. The inhibitory effects were mediated at the level of the antigen-presenting cell, since no inhibition of mitogen or anti-CD3 antibody-driven T cell proliferation was observed. In direct binding assays, the peptide analogue bound to selected HLA-DR molecules expressed on the membrane of antigen-presenting cells, with specificity predominantly for those class II proteins capable of restricting house dust mite-allergen T cell recognition.

Contribution of T-cell receptor-contacting and peptide-binding residues of the class II molecule HLA-DR4 Dw10 to serologic and antigen-specific T-cell recognition

The relative contributions of putative T-cell receptor (TCR)-contacting and peptide-binding residues of a major histocompatibility complex (MHC) class II restriction element to serologic and antigen-specific T-cell recognition were investigated by site-specific mutagenesis. Amino acids 70 and 71 in the DR beta 1 domain of DR4 Dw10 are uniquely differnet from the other Dw subtypes of DR4. Residue 70 is predicted to be located at the membrane-distal surface of the class II molecule, where it may influence T-cell recognition by a direct interaction with a TCR. Residue 71 is predicted to form part of the antigen-binding groove where its influence on T-cell recognition may be mediated indirectly via an effect on peptide binding. Transfected murine L cells were produced expressing the products of DR4 Dw10B genes in which the codons for residues 70 and 71 had been mutated towards DR4 Dw14. Support for the predicted orientations of beta-chain residues 70 and 71 was lent by the observation that only residue 70 plays an important role in the formation of a serologic determinant. Mutation of this residue was sufficient to produce recovery of recognition by a human monoclonal antibody, NI, which has specificity for all the DR4 subtypes with the exception of DR4 Dw10. The human T-cell clone HA1.7, specific for influenza virus hemagglutinin (HA) peptide 307-319 and restricted by DR1 Dw1, exhibits degeneracy of MHC restriction on the DR4 Dw subtypes with the exception of DR4 Dw10.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of human T-cell responses to house dust mite allergens by a T-cell receptor peptide☆

Recent analysis of the usage of T-cell receptor (TcR) beta chain variable region (V beta) gene elements by house dust mite (HDM)-reactive T cells from an atopic donor suggested that TcR-V beta 3 gene products may form a major component of the human T-cell repertoire reactive to this common allergen. In this study a peptide analog of the TcR-V beta 3 complementarity determining region 2 (CDR2) is shown to inhibit the polyclonal human T-cell response to HDM; this effect is specific because inhibition is dependent on the presence of V beta 3 + T cells. This experimental approach has been used to determine whether the pattern seen in T-cell clones derived from one atopic donor reflects TcR-V beta usage in the polyclonal response to allergen in the general population. Inhibition of more than 50% of the polyclonal response to allergen by V beta 3-CDR2 peptide was observed in 16 of 21 donors tested, suggesting that TcR-V beta 3 gene usage may form a major component of the human HDM repertoire and as such offer a suitable target for T cell-directed specific immunotherapy in HDM-allergic individuals. Depletion of CD8+ T cells abolishes peptide-mediated inhibition of CD4+ T-cell proliferation to HDM, suggesting that induction of a CD8+ regulatory T-cell subset by the CDR2 peptide may modulate HDM-specific allergic T-cell responses.

Differential induction of the NF-AT complex during restimulation and the induction of T-cell anergy

Stimulation of human CD4+ T-cell clones through the T-cell receptor (TcR) by high doses of specific peptide results in the induction of a long-lived state of nonresponsiveness that has been called anergy. During the induction of anergy, T cells are phenotypically similar to cells responding to an immunogenic stimulus. The amount of TcR at the cell surface is downmodulated, whereas the CD2 and CD25 receptors are increased. When restimulated, however, anergic T cells fail to up-regulate transcription of the IL-2 gene and in consequence do not produce IL-2. In this study, we have compared the ability of various transcription factors to bind to their appropriate site on DNA. Factors were isolated from the nuclei of T cells that were in the induction phase of anergy or were undergoing activation. The pattern of binding activity in restimulated T cells is consistent with the pattern that has previously been shown to regulate T-cell-specific expression of the IL-2 and the beta chain of the TcR genes. The measured binding to a TCF-1 site is the same in the nuclei of resting, activated, and anergized cells. The inducible factors NK-kappa B, beta E2, CD28RC, and AP-1 are not expressed in resting cells and are twofold lower in anergized as compared with activated cells. In contrast, anergic T cells express approximately eightfold lower amounts of NF-AT, a member of the class of inducible factors that regulates IL-2 gene transcription.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of cytokine and chemokine transcription in a human TH2 type T‐cell clone during the induction phase of anergy

Background Selected cytokines produced by allergen specific CD4+ T cells from atopic individuals contribute to both the specific and non‐specific effector mechanisms of the allergic itnmune response. The chemokine family of cytokines and tumour necrosis factor (TNF)‐α are leucocyte regulatory and proinflanimatory molecules. The chemokines include interleukin (IL)‐8 and the RANTES/SIS cytokines.

Staphylococcus aureus enterotoxin mediated specific non-responsiveness of human T cells

Exotoxins produced by certain strains of Staphylococcus aureus are able to both stimulate and induce non-responsiveness in T cells expressing specific T cell antigen receptor V beta gene elements. The exposure of human CD4+ T cells to the appropriate enterotoxin rendered them anergic to restimulation with their natural ligand, although responsiveness to exogenous IL-2 remained intact. The loss of antigen-dependent proliferation was associated with the down-regulation of the TCR complex that was paralleled by enhanced cell surface CD2 and CD25. Further analysis of the phenotypic changes revealed that membrane levels of CD28 were increased only on activation, suggesting a differential expression of this protein on activated and anergic T cells. During the induction of anergy it was observed that the synthesis of the lymphokines IL-2, IL-4 and IFN-gamma was differentially regulated. IL-4 and IFN-gamma, but not IL-2 were detected in the supernatants of overnight cultures of T cells exposed to tolerising concentrations of toxin. Transcription of IL-4, as determined by polymerase chain reaction at selected intervals, was elevated during the induction of anergy and accounted for the presence of the protein in the supernatants. In contrast, no tight coupling was observed between protein and mRNA levels for IL-2, suggesting post-translational regulation.

Clonal analysis of CD4 mediated accessory function on the effector activity of human CD4+ T cell subsets

Background: It has been reported for the peripheral T cell repertoire that CD4 molecules may enhance adhesion between T cells and antigen presenting cells and, through their physical association with T cell antigen receptors, contribute to signal transduction.

Differential dependence of TH‐0, TH‐1 and TH‐2 CD4 4+ T cells on co‐stimulatory activity provided by the accessory molecule LFA‐1

Background The adhesion molecule LFA‐1 contributes to the activation response of peripheral blood human CD4+ T cells. Less is known of its contribution to stimulation of long‐term CD4+ T cell lines and clones or of its potential to co‐stimulate CD4+ T cells of different functional phenotype.