Failure of rIL-12 administration to inhibit established IgE responses in vivo is associated with enhanced IL-4 synthesis by non-B/non-T cells

PD-L2 modulates asthma severity by directly decreasing dendritic cell IL-12 production

Studies examining the role of programmed death 1 (PD-1) ligand 2 (PD-L2)/PD-1 in asthma have yielded conflicting results. To clarify its role, we examined the PD-L2 expression in biopsies from human asthmatics and the lungs of aeroallergen-treated mice. PD-L2 expression in bronchial biopsies correlated with the severity of asthma. In mice, allergen exposure increased PD-L2 expression on pulmonary myeloid dendritic cells (DCs), and PD-L2 blockade diminished allergen-induced airway hyperresponsiveness (AHR). By contrast, PD-1 blockade had no impact, suggesting that PD-L2 promotes AHR in a PD-1-independent manner. Decreased AHR was associated with enhanced serum interleukin (IL)-12 p40, and in vitro stimulation of DCs with allergen and PD-L2-Fc reduced IL-12 p70 production, suggesting that PD-L2 inhibits allergen-driven IL-12 production. In our model, IL-12 did not diminish T helper type 2 responses but rather directly antagonized IL-13-inducible gene expression, highlighting a novel role for IL-12 in regulation of IL-13 signaling. Thus, allergen-driven enhancement of PD-L2 signaling through a PD-1-independent mechanism limits IL-12 secretion, exacerbating AHR.

Oral administration of IL-12 suppresses anaphylactic reactions in a murine model of peanut hypersensitivity

There is no satisfactory therapeutic intervention for peanut allergy, which accounts for most life-threatening food allergic reactions. Since IL-12 has been found to inhibit allergic airway responses in a mouse model of asthma and to cure Th2 cytokine-mediated murine schistosomiasis, we hypothesized that IL-12 treatment might also inhibit peanut allergic reactions. Consequently, we investigated the effects of oral IL-12 treatment in a murine model of peanut allergy and found that oral administration of liposome encapsulated rIL-12 could both prevent and reverse peanut hypersensitivity and could reduce histamine release, peanut-specific serum IgE and IgG1, and fecal IgA levels. Oral IL-12 treatment also increased IFN-gamma but did not decrease IL-4 or IL-5 levels. We conclude that oral rIL-12 treatment has therapeutic as well as preventive effects on peanut allergy, which are associated with increased IFN-gamma production.

Il-18 gene transfer by adenovirus prevents the development of and reverses established allergen-induced airway hyperreactivity

We examined the role of IL-18 in preventing the development of and in reversing established allergen-induced airway inflammation and airway hyperreactivity (AHR), the cardinal features of asthma. IL-18, which potently induces IFN-gamma, was administered into the respiratory tract as cDNA in a replication-deficient adenovirus (Adv). Treatment of OVA-sensitized mice with the IL-18-expressing Adv reduced allergen-specific IL-4 production, airway eosinophilia, and mucus production, increased IFN-gamma production, and prevented the development of AHR. The effects of the IL-18 Adv treatment were dependent on the presence of IFN-gamma and IL-12. Moreover, administration of the IL-18 Adv to mice with established AHR greatly reduced AHR and IL-4 production and increased IFN-gamma production. These results demonstrate that IL-18, when administered by Adv into the respiratory tract, effectively reduces AHR and replaces an established Th2-biased immune response with a Th1-biased response.