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Threshold Signaling of Human Th0 Cells in Activation and Anergy: Modulation of Effector Function by Altered TCR Ligand¹

Adrienne Verhoef^* and Jonathan R. Lamb^2,

^* Department of Biology, Imperial College of Science, Technology and Medicine, London, United Kingdom; and Respiratory Medicine Unit, Edinburgh University Medical School, Edinburgh, United Kingdom

Molecular interactions between TCR and its natural ligand, in the presence of costimulatory signals, elicit T cell effector functions, whereas subtle changes in the structure of antigenic peptides may induce only selected T cell effector function including anergy. In this study, we have investigated the immunological activity of an altered TCR ligand (p 2, 28–40A^34,36) derived from the immunodominant T cell epitope of the group 2 allergen of house dust mite, in which residues at positions 34 and 36 were substituted by alanine. Elevated IFN- synthesis was induced by equimolar concentrations of the analogue compared with native peptide (p 2, 28–40) and was paralleled by increased down-regulation of cell surface CD3. IL-5 and IL-10 production exhibit the same sensitivity to both peptides, implying that the induction of T cell effector functions are not all proportional to TCR occupancy. Both native peptide and the analogue bound to MHC class II (DRB1*1101) molecules with similar affinities. Furthermore, p 2, 28–40A^34,36 induced T cell anergy at lower concentrations than native peptide. During the induction of anergy, TGF-ß production was comparable for both peptides, whereas IL-10 secretion was markedly increased but more so in response to p 2, 28–40A^34,36. Membrane expression of costimulatory ligands CD80 and CD86 was similar for native peptide and p 2, 28–40A^34,36 and increased in activation, whereas only CD86 was elevated during anergy. The modulation of T cell effector function with altered TCR ligands may have practical applications in reprogramming allergic inflammatory responses through the induction of T cell anergy and/or the promotion of Th1 cytokines.

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