ANTAGONISTIC PEPTIDES SPECIFICALLY INHIBIT PROLIFERATION, CYTOKINE PRODUCTION, CD40L EXPRESSION, AND HELP FOR IGE SYNTHESIS BY DER-P-1-SPECIFIC HUMAN T-CELL CLONES

Background: Allergic disorders are characterized by IgE antibody respo nses to a multitude of allergens as a result of the ability of these a ntibodies to specifically bind to high-affinity IgE receptors on mast cells and basophils. This interaction results in receptor activation a nd release of soluble mediators such as histamine and leukotrienes, wh ich cause allergic reactions in various target organs. Because the syn thesis of IgE is tightly regulated by cytokines and CD40 ligand (L) in teractions, CD4(+) helper T cells are obvious targets, with the aim to modulate allergen-induced IgE responses. Objectives: Because of the c entral role of allergen-specific T-helper type 2 (T-H2) cells in the p athway leading to IgE synthesis in vitro and in vivo, we have evaluate d the possibility of inhibiting allergen-induced activation of these c ells by using allergen-derived peptides that have been modified by sin gle amino acid substitutions. Methods: Three cloned human T-H2-like CD 4(+) T-cell lines, specific for Der p 1, the major allergen in house d ust, were used in this study. Upon activation with Der p 1 or specific Der p 1-dervived wild-type peptides, these T-cell clones produce high levels of IL-4 and IL-5 and low levels of interferon-gamma and IL-2, respectively, and furthermore give help to B cells for the production of IgE in vitro. Modified synthetic peptides were generated by the int roduction of single amino acid substitutions into two different T-cell activation-inducing epitopes on Der p 1. The effects of these modifie d peptides were studied in Der p 1-induced proliferation, cytokine pro duction, and in vitro IgE production assays. Results: Several substitu ted Der p 1-derived peptides failed to induce T-cell proliferation, in contrast to the native peptides. In addition, some of these peptides acted as antagonists by strongly inhibiting wild-type peptide-induced proliferation as well as the production of interferon-gamma, IL-2, IL- 4, and IL-5, although the production of the latter two cytokines was l ess affected than that of interferon-gamma, even at a 100-fold molar e xcess of the antagonistic peptides, In addition, the presence of an ex cess of each of the antagonistic peptides during the activation of Der p I-specific T-cell clones prevented induction of CD40L expression, r esulting in a failure of these cells to give help to B cells for the p roduction of IgE in vitro, even in the presence of exogenous IL-4. Con clusions: Substitution of certain amino acid residues in immunogenic D er p 1-derived peptides results in the generation of peptides that fai l to induce proliferation of Der p 1-specific T-cell clones, In additi on, these modified peptides have strong antagonistic activities on Der p 1-induced proliferation, cytokine production, and CD40L expression by allergen-specific T-cell clones as well as on T cell-mediated IgE p roduction by B cells. These findings suggest that modified peptides in terfere with allergen-induced activation of T cells, including the pro duction of cytokines and the expression of surface molecules important for successful T cell-B cell interactions, and may therefore have the rapeutic potential by inhibiting the expansion and function of allerge n-specific T-H2 cells.