Mechanisms of control of allergic skin inflammation by T regulatory cells

Most patients with Atopic dermatitis (AD) have a skin barrier defect. This allows cutaneous sensitizationto antigens that leads to allergic skin inflammation (ASI). In a minority of patients AD arises from an immunedeficiency. Patients with DOCK8 deficiency and WASP deficiency have a normal skin barrier but impaired Tregcell function. Dock8-/- mice developed exaggerated ASI following application of ovalbumin (OVA) to tape strippedskin. Adoptive transfer experiments demonstrate that defective Tregs underlie their exaggerated ASI. Wepropose to use the DOCK8 deficiency model to study of the pathways that drive AD independently of skin barrierdefects and determine the mechanisms by which Tregs restrain ASI. DOCK8 activates the GTPase CDC42. CDC42 activates the Ser/Thr kinase PAK2 as well as WASPwhich drives actin filaments branching. Preliminary data show that AD is more severe in DOCK8- deficient thanWASP-deficient patients. Similarly ASI is more severe in Dock8-/- than in Wasp-/- mice. Tregs in OVA sensitizedskin and their FOXP3 expression are decreased in Dock8-/- but not Wasp-/- mice. DOCK8 deficient inducedTregs (iTregs) have reduced stability in vitro particularly in the presence of IL-4. Tregs from Dock8-/ but notWasp-/- mice as well as WT Tregs treated with PAK inhibitors have decreased levels of pY-STAT5 followingIL-2 stimulation due to accelerated dephosphorylation. This suggests that the DOCK8-PAK2 axis but not theDOCK8-WASP axis is essential to maintain pY-STAT5 levels in Tregs AlphaFold Multimer modeling predicts adirect interaction between STAT5B and the tyrosine phosphatase SHP2 abolished by mimicking PAK2-mediatedserine phosphorylation of STAT5B. We will test the overall hypothesis that in DOCK8 deficiency loss of WASP activation whichdisrupts the cortical branched actin cytoskeleton and Treg cell interaction with target cells and loss ofPAK2 activation which reduces the levels of IL-2 driven pY-STAT5 and Treg stability synergize topromote ASI. We will test the following hypotheses 1) Reduced IL-2 driven STAT5 phosphorylation in DOCK8deficient Tregs impairs their stability in a Th2 milieu and ability to restrain ASI. 2) Defective WASP activation anddefective PAK activation independently impair Treg ability to suppress ASI in DOCK8 deficiency. 3) Serinephosphorylation of pY-STAT5 by IL-2 driven DOCK8 mediated activation of PAK2 promotes Treg stability byinhibiting the docking of SHP2 to STAT5. Many patients with AD remain resistant to current therapies.Understanding the roles of DOCK8 and associated proteins as well as the regulation of the STAT5 signaling axisin Treg function and the molecular pathogenesis of AD could inform novel therapies in AD particularly thosedesigned to boost Treg cells.