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.
To investigate the contribution of Toll-like receptors in the response to bacterial adjuvants, we designed an in vitro system to characterize the effect of heat-killed E.coli on peanut-induced responses of dendritic cells (DCs) and T cells.
Wild-type or Toll-Like Receptor (TLR) signaling-deficient bone-marrow derived DCs were pulsed with crude peanut extract alone (CPE) (50 µg/mL) in the presence of heat-killed E.coli (HKE) (106/mL). DC maturation was analyzed by flow cytometry. Treated DCs were co-cultured with CFSE-labeled CD4+ T cells from sensitized mice. Cytokine production from DCs and T cells was measured by bioplex assays.
Peanut pulsed DCs induced the production of IL-4, IL-5, 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 Th2 cytokine production, associated with an increase in IFN-γ 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.
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 may constitute another alternative for allergen immunotherapies.