show Abstracthide AbstractMechanisms by which regulatory T (Treg) cells fail to control inflammation in asthma remain poorly understood. We show that a severe asthma-associated polymorphism in the interleukin-4 receptor alpha chain (IL-4Ra-R576) biases induced Treg (iTreg) cells towards a T helper 17 (TH17) cell fate. This skewing reflects the recruitment by IL-4Ra-R576 of the adaptor protein growth factor receptor-bound protein 2 (GRB2), which drives IL-17 expression by an extracellular signal-regulated kinase-, IL-6- and STAT3-dependent mechanism. We showed that the IL-4Ra-R576 mutation elicits TH17 airway responses in vivo, in a house dust mite (HDM)- or ovalbumin (OVA)-driven model of airway inflammation in the mice carry the IL-4Ra-R576 mutation (Il4raR576 mice). Treg cell-specific deletion of genes encoding IL-6Ra or the master TH17 cell regulator Retinoid-related Orphan Receptor ?t (ROR?t), but not IL-4 and IL-13, protected mice against exacerbated airway inflammation induced by IL-4Ra--576. Analysis of lung tissue Treg cells revealed that the expression of IL-17 and the TH17 cell-associated chemokine receptor CCR6 was largely overlapping and highly enriched in Treg and conventional T (Tconv) cells of allergen-treated Il4raR576 mice. To further characterize the subset of IL-17 producing Foxp3+ Treg in the lung of OVA-treated mice we utilized CCR6 as a marker of Treg cells committed towards the TH17 cell lineage to examine their functional, epigenetic and transcriptional profiles. CCR6+Foxp3EGFP+ Treg cells isolated from OVA-sensitized and challenged Il4raR576 mice, by FACS (Fluorescence Activated Cell Sorting) exhibited decreased methylation of the Foxp3 CNS2 locus comparing to CCR6–Foxp3EGFP+ Treg cells from same animals, indicative of decreased stability. They also exhibited profoundly decreased suppressive function as compared to CCR6– WT and CCR6– Il4raR576 counterparts. Transcriptional profiling of CCR6+Foxp3EGFP+ Treg cells revealed increased relative expression in CCR6+ Il4raR576 Treg cells of genes associated with a TH17 cell signature, including Rorc, Ccr6, Il23r, Il17a, Il17f, Il1r1, Nr1d1, Cstl, and Ahr comparing to CCR6–Foxp3EGFP+ Treg cells from same animals. Overall design: Three CCR6+Foxp3EGFP+ Il4raR576 replicates and four CCR6–Foxp3EGFP+ Il4raR576 Treg replicates (controls) were sampled