Targeting Toll-like receptors on dendritic cells modifies the T_H2 response to peanut allergens in vitro

Background: Delivery of allergens with bacterial adjuvants has been shown to be a successful immunotherapeutic strategy for food allergy treatment in animal models. How microbial signals, acting through the innate immune system, reshape ongoing allergic responses is poorly understood. Objective: To investigate the contribution of Toll-like receptors (TLRs) in the response to bacterial adjuvants, we designed an in vitro system to characterize the effect of heat-killed Escherichia coli vector (HKE) on peanut-induced responses of dendritic cells (DCs) and T cells. Methods: Wild-type or TLR signaling-deficient bone marrow-derived DCs were pulsed with crude peanut extract (CPE) alone (50 μg/mL) in the presence of HKE (10⁶/mL). DC maturation was analyzed by means of flow cytometry. Treated DCs were cocultured with carboxyfluorescein succinimidyl ester (CFSE)-labeled CD4⁺ T cells from sensitized mice. Cytokine production from DCs and T cells was measured by using Bioplex assays. Results: Peanut-pulsed DCs induced the production of IL-4, IL-5, and IL-13, as well as IL-17 and IFN-γ, from primed T cells. Adding HKE to CPE-pulsed DCs resulted in a significant decrease in T_H2 cytokine production associated with an increase in IFN-γ levels and profound attenuation of T-cell proliferation. These effects were linked to HKE-induced TLR-dependent changes in DC reactivity to CPE, especially the production of polarizing cytokines, such as IL-12. Conclusions: TLR signals modulate peanut-induced DC maturation in vitro, leading to changes in the T-cell response to peanut. These TLR effects must be confirmed in vivo and might constitute another alternative for allergen immunotherapies.