Threshold signaling of human Th0 cells in activation and anergy: Modulation of effector function by altered TCR ligand

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-gamma 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-IU 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-beta production was comparable for both peptides, whereas IL-IO secretion was markedly increased but more so in response to p 2, 28-40A3(4,36) Membrane expression of costimulatory ligands CD80 and CD86 was similar fur 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.