A single treatment with a CpG-containing immunostimulatory DNA sequence (ISS) given before allergen challenge can inhibit T helper type 2 cell (Th2)–mediated airway responses in animal models of allergic asthma; however, the mechanism of this inhibition remains largely undefined. Here, we demonstrate that airway delivery of ISS before allergen challenge in Th2-primed mice acts in two distinct ways to prevent the allergic responses to this challenge. The first is to prevent induction of cytokines from allergen-specific Th2 cells, as demonstrated by the nearly complete inhibition of Th2 cytokine production, Th2-dependent functional responses, and gene induction patterns. ISS inhibits the Th2 response by rendering lung antigen-presenting cells (APCs) unable to effectively present antigen to Th2 cells, but not to Th1 cells. This loss of APC function correlates with a reduced expression of costimulatory molecules, including programmed cell death ligand (PD-L)1, PD-L2, CD40, CD80, CD86, and inducible T cell costimulator, and of major histocompatibility complex class II on CD11c+APCs from the airways of ISS-treated mice. The second important action of ISS is inhibition of immunoglobulin E–dependent release of Th2 cytokines, especially interleukin 4, from basophils and/or mast cells in the airways of Th2-primed mice. Thus, inhibition by ISS of allergic responses can be explained by two novel mechanisms that culminate in the inhibition of the principal sources of type 2 cytokines in the airways.
Background CpG-containing oligodeoxynucleotides (CpG-ODN) are potent inhibitors of Th2-mediated allergic airway disease in sensitized mice challenged with allergen. A single treatment has transient effects but a limited series of treatments has potential to achieve clinically meaningful sustained inhibition of allergic airway disease. Objective To optimize the treatment regimen and determine the mechanisms of action in mice of an inhaled form of CpG-ODN being developed for human asthma treatment. Methods A limited series of weekly intranasal 1018 ISS (CpG-ODN; B-class) treatments were given to ragweed allergen-sensitized mice chronically exposed to allergen during and after the 1018 ISS treatment regimen. Treatment effects were evaluated by measuring effect on lung Th2 cytokines and eosinophilia as well as lung dendritic cell function and T cell responses. Results Twelve intranasal 1018 ISS treatments induced significant suppression of BAL eosinophilia and IL-4, IL-5, and IL-13 levels and suppression was maintained through 13 weekly ragweed exposures administered after treatment cessation. At least 5 treatments were required for lasting Th2 suppression. CpG-ODN induced moderate Th1 responses but Th2 suppression did not require IFN-γ. Th2 suppression was associated with induction of a regulatory T cell response. Conclusion A short series of CpG-ODN treatments results in sustained suppression of allergic lung inflammation induced by a clinically relevant allergen.
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