Immature dendritic cells expressing indoleamine 2,3-dioxygenase suppress ovalbumin-induced allergic airway inflammation in mice.

Background: Proliferation of activated CD4+ T lymphocytes is inhibited by indoleamine 2,3-dioxygenase (IDO).

Objective: We undertook the present study to test the hypothesis that IDO-expressing immature DCs (imDCs) can restore immune tolerance in mice suffering from allergic airway inflammation.

Methods: imDCs were generated from murine bone marrow cells using granulocyte-macrophage colony-stimulating factor.The imDCs were subsequently transfected with an IDO expression vector (pEGFP-N1-IDO). Surface marker expression, including CD11c, MHCII, CD80, and CD86, was analyzed using flow cytometry. IDO-expressing imDCs were injected into the trachea of ovalbumin (OVA)-sensitized mice, and lung histopathology and cytokine expression in bronchoalveolar lavage fluid were assessed. The splenic CD4+ T cells of OVA-sensitized mice were isolated and co-cultured with pEGFP-N1-IDO-expressing imDCs, and apoptosis of CD4+ T cells was detected using the terminal deoxynucleotidyl transferase dUTP nick end labeling assay.

Results: Expression of IDO in imDCs did not alter cell surface molecule expression. We observed marked lung inflammation, elevated total cell and eosinophil count, and altered cytokine levels in OVA-sensitized mice. These parameters improved upon inoculation with IDO-expressing imDCs. Co-culture with IDO-expressing imDCs also induced apoptosis, inhibited IL-4 and IL-5 expression, and upregulated IFN-gamma expression in CD4+ T cells.

Conclusions: IDO-expressing imDCs induced T(H)2 cell apoptosis and reduced T(H)2 cell activation and allergic airway inflammation in OVA-sensitized mice. Thus, upregulation of IDO expression may provide a novel immunointervention strategy for asthma treatment.