Fms-Like Tyrosine Kinase 3 Ligand Decreases T Helper Type 17 Cells and Suppressors of Cytokine Signaling Proteins in the Lung of House Dust Mite-Sensitized and -Challenged Mice

We previously reported that Fms-like tyrosine kinase 3 ligand (Flt3-L) reversed airway hyperresponsiveness (AHR) and airway inflammation, and increased the number of regulatory CD11c(high)CD8 alpha(high)CD11b(low) dendritic cells and CD4(+)CD25(+)ICOS(+)Foxp3(+)IL-10(+) T-regulatory cells in the lung of allergen-sensitized and -challenged mice. In this study, we evaluated the effect of Flt3-L on Th17 cells and expression of suppressors of cytokine signaling (SOCS) proteins in the lungs of house dust mite (HDM)-sensitized and -challenged mice. BALB/c mice were sensitized and challenged with HDM, and AHR to methacholine was established. Mice were treated with Flt3-L (5 mu g, intraperitoneal) daily for 10 days. Levels of IL-4, -5, -6, -8, and -13, and transforming growth factor (TGF)-beta in the bronchoalveolar lavage fluid (BALF) were examined by ELISA. Flt3-L treatment reversed existing AHR to methacholine and substantially decreased eosinophils, neutrophils, IL-5, -6, -8, and IL-13, and TGF-beta levels in the BALF. HDM-sensitized and -challenged mice showed a significant increase in lung CD4(+)IL-17(+)IL-23R(+)CD25(-) T cells with high expression of retinoic acid-related orphan receptor (ROR)-gamma t transcripts. However, administration of Flt3-L substantially decreased the number of lung CD4(+)IL-17(+)IL-23R(+)CD25(-) T cells, with significantly decreased expression of ROR-gamma t mRNA in these cells. HDM sensitization caused a significant increase in the expression of SOCS-1, -3, and -5 in the lung. Flt3-L treatment abolished the increase in SOCS-1 and SOCS-3 proteins, whereas SOCS-5 expression was significantly reduced. These data suggest that the therapeutic effect of Flt3-L in reversing the hallmarks of allergic asthma in a mouse model is mediated by decreasing IL-6 and TGF-beta levels in the BALF, which, in turn, decrease CD4(+)IL-17(+)IL-23R(+)ROR-gamma t(+)CD25(-) T cells and the expression of SOCS-1 and SOCS-3 in the lung of HDM-sensitized and -challenged mice.