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 ^highCD8α ^highCD11b ^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 mg, intraperitoneal) daily for 10 days. Levels of IL-4, -5, -6, -8, and -13, and transforming growth factor (TGF)-β 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-β 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)-γt 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-γt 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-β levels in the BALF, which, in turn, decrease CD4 ⁺IL-17 ⁺IL-23R ⁺ROR-γt ⁺CD25 ^- T cells and the expression of SOCS-1 and SOCS-3 in the lung of HDM-sensitized and -challenged mice.