Activation of peroxisome proliferator-activated receptor-gamma in dendritic cells inhibits the development of eosinophilic airway inflammation in a mouse model of asthma

Abstract

Peroxisome proliferator-activated receptors (PPARs) are activated by an array of polyunsaturated fatty acid derivatives, oxidized fatty acids, and phospholipids and are proposed to be important modulators of immune and inflammatory responses. Recently, we showed that activation of PPAR-gamma alters the maturation process of dendritic cells (DCs), the most potent antigen-presenting cells. In the present report, we investigated the possibility that, by targeting DCs, PPAR-gamma activation may be involved in the regulation of the pulmonary immune response to allergens. Using a model of sensitization, based on the intratracheal transfer of ovalbumin (OVA)-pulsed DCs, we show that rosiglitazone, a selective PPAR-gamma agonist, reduces the proliferation of Ag-specific T cells in the draining mediastinal lymph nodes but, surprisingly enough, dramatically increases the production of the immunoregulatory cytokine interleukin (IL)-10 by T cells, as compared to control mice sensitized with OVA-pulsed DCs. After aerosol challenge, the recruitment of eosinophils in the bronchoalveolar lavage fluids was strongly reduced compared to control mice. Finally, T cells from the mediastinal lymph nodes produced higher amounts of IL-10 and interferon-gamma. Inhibition of IL-10 activity with anti-IL-10R antibodies partly restored the inflammation. The specificity of the phenomenon was confirmed by treating OVA-pulsed DCs with ciglitazone, another PPAR-gamma agonist, and by using GW9662, a PPAR-gamma antagonist. Our data suggest that PPAR-gamma activation prevents induction of Th2-dependent eosinophilic airway inflammation and might contribute to immune homeostasis in the lung.

Figure 1

PPAR-γ expression in BM-DCs. DCs were fixed, permeabilized, and stained for PPAR-γ expression (black histogram). White histogram represents fluorochrome-matched isotype control mAbs.

Figure 2

Effect of RSG treatment on CCR7 expression by DCs. BM-DCs were pulsed or not overnight with 100 μg/ml of OVA in the presence or in the absence of 10 μmol/L of RSG. LPS at the dose of 500 ng/ml was also used as a positive control. Cells were incubated with CCL19-Fc for 30 minutes before addition of PE-labeled anti-human IgG (black histograms). White histogram represents fluorochrome-matched isotype control mAbs.

Figure 3

RSG treatment inhibits the migration of OVA-pulsed DCs. BM-DCs were pulsed or not with OVA overnight in the presence or in the absence of RSG (RSG/OVA-DCs). The next day, DCs were labeled with CFSE and 1 × 10⁶ OVA-DCs, RSG/OVA-DCs, or unpulsed DCs were instilled into the trachea of naïve BALB/c mice. Twenty-four hours later, the presence of migrating CFSE-labeled DCs was investigated in the MLNs. Top: Plots show one representative mouse of four. The histogram represents the mean number of CFSE⁺ DCs ± SEM from five mice per group.

Figure 4

RSG impairs T-cell proliferation in the MLNs. On day −2, BALB/c mice received a cohort of CFSE-labeled OVA-specific naïve T cells. On day 0, mice were administered intratracheally with OVA-DCs, RSG/OVA-DCs, or with unpulsed DCs. Four days later, the proliferation of CD4⁺ KJ1–26⁺ CFSE⁺ T cells was analyzed by flow cytometry. Results show one representative experiment of 10 to 12 mice per group. *, P < 0.05.

Figure 5

RSG-treated DCs modify the pattern of cytokine production of naïve T cells. On day −2, BALB/c mice received a cohort of CFSE-labeled OVA-specific naïve T cells. On day 0, mice were administered intratracheally with OVA-DCs, RSG/OVA-DCs, or with unpulsed DCs. Four days later, T cells from MLNs were collected and incubated for another 4-day period at 37°C. Supernatants were harvested and assayed for the presence of IL-4, IL-5, IL-10, and IFN-γ. Results are represented as mean ± SEM from 10 to 12 mice per group. *, P < 0.05.

Figure 6

RSG-treated DCs modify the cellular composition of BAL. On day 0, mice received an intratracheal injection of OVA-DCs, ciglitazone/OVA-DCs, RSG/OVA-DCs treated with the PPAR-γ antagonist GW9662 (GW9662/RSG/OVA-DCs), or unpulsed DCs. From days 10 to 13, mice were exposed to OVA aerosols. To test the role of IL-10 in RSG-induced effects, some mice that received RSG/OVA-DCs on day 0 were injected with anti-IL-10Rα (IL-10Ra/RSG/OVA-DCs) 24 hours before aerosol exposure. Twenty-four hours after the last aerosol, BAL was performed. Results are expressed as mean ± SEM from 8 to 10 mice per group. *, P < 0.05.

Figure 7

RSG-treated DCs reduce the pulmonary inflammatory response in the lung. On day 0, mice received an intratracheal injection of OVA-DCs, RSG/OVA-DCs, or unpulsed DCs. From days 10 to 13, mice were exposed to OVA aerosols. Four-μm sections of the lungs were stained with May-Grunwald Giemsa. Mice that received OVA-DCs revealed strong perivascular and peribronchial inflammatory lesions composed mainly of eosinophils and mononuclear cells. These features were strongly reduced in the lungs of mice injected with RSG/OVA-DCs. Original magnifications: ×20 (A, C); ×100 (B, D).

Figure 8

RSG-treated DCs modify the pattern of cytokine production of T cells after re-exposure of the mice to OVA aerosols. On day 0, mice received an intratracheal injection of OVA-DCs, RSG/OVA-DCs, or unpulsed DCs. From days 10 to 13, mice were exposed to OVA aerosols. Twenty-four hours after the last aerosol, cells from MLNs were collected and restimulated for 4 days in the presence of OVA. The supernatants were harvested and assayed for the presence of IL-5, IL-10, and IFN-γ. Results show the mean ± SEM from 8 to 10 mice per group. *, P < 0.05.