ABSTRACT
BACKGROUND: Atopic dermatitis is characterized by scratching and a Th2-dominated local and systemic response to cutaneously encountered antigens. Dendritic cells (DCs) capture antigens in the skin and rapidly migrate to draining lymph nodes (dLNs) where they drive the differentiation of antigen-specific naïve T cells. OBJECTIVE: Determine whether non-T cell-derived IL-4 acts on skin-derived DCs to promote the Th2 response to cutaneously encountered antigen and allergic skin inflammation. METHODS: DCs from dLNs of ovalbumin (OVA)-exposed skin were analyzed by flow cytometry and for their ability to polarize OVA-specific naïve CD4+ T cells. Skin inflammation following epicutaneous (EC) sensitization of tape-stripped skin was assessed by flow cytometry of skin cells and qRT-PCR of cytokines. Cytokine secretion and antibody levels were evaluated by ELISA. RESULTS: Scratching upregulated IL4 expression in human skin. Similarly, tape stripping caused rapid basophil-dependent upregulation of cutaneous Il4 expression in mouse skin. In vitro treatment of DCs from skin dLNs with IL-4 promoted their capacity to drive Th2 differentiation. DCs from dLNs of OVA-sensitized skin of Il4-/- mice and CD11cCreIl4rflox/- mice that lack IL-4Rα expression in DCs (DCΔ/Δll4ra mice) were impaired in their capacity to drive Th2 polarization compared to DCs from controls. Importantly, OVA sensitized DCΔ/Δll4ra mice demonstrated impaired allergic skin inflammation and OVA-specific systemic Th2 response evidenced by reduced Th2 cytokine secretion by OVA-stimulated splenocytes and lower levels of OVA-specific IgE and IgG1 antibodies, compared to controls. CONCLUSION: Mechanical skin injury causes basophil-dependent upregulation of cutaneous IL-4. IL-4 acts on skin DCs that capture antigen and migrate to dLNs to promote their capacity for Th2 polarization and drive allergic skin inflammation.
ABSTRACT
BACKGROUND: Dedicator of cytokinesis 8 (DOCK8)-deficient patients have severe eczema, elevated IgE, and eosinophilia, features of atopic dermatitis (AD). OBJECTIVE: We sought to understand the mechanisms of eczema in DOCK8 deficiency. METHODS: Skin biopsy samples were characterized by histology, immunofluorescence microscopy, and gene expression. Skin barrier function was measured by transepidermal water loss. Allergic skin inflammation was elicited in mice by epicutaneous sensitization with ovalbumin (OVA) or cutaneous application of Staphylococcus aureus. RESULTS: Skin lesions of DOCK8-deficient patients exhibited type 2 inflammation, and the patients' skin was colonized by Saureus, as in AD. Unlike in AD, DOCK8-deficient patients had a reduced FOXP3:CD4 ratio in their skin lesions, and their skin barrier function was intrinsically intact. Dock8-/- mice exhibited reduced numbers of cutaneous T regulatory (Treg) cells and a normal skin barrier. Dock8-/- and mice with an inducible Dock8 deletion in Treg cells exhibited increased allergic skin inflammation after epicutaneous sensitization with OVA. DOCK8 was shown to be important for Treg cell stability at sites of allergic inflammation and for the generation, survival, and suppressive activity of inducible Treg cells. Adoptive transfer of wild-type, but not DOCK8-deficient, OVA-specific, inducible Treg cells suppressed allergic inflammation in OVA-sensitized skin of Dock8-/- mice. These mice developed severe allergic skin inflammation and elevated serum IgE levels after topical exposure to Saureus. Both were attenuated after adoptive transfer of WT but not DOCK8-deficient Treg cells. CONCLUSION: Treg cell dysfunction increases susceptibility to allergic skin inflammation in DOCK8 deficiency and synergizes with cutaneous exposure to Saureus to drive eczema in DOCK8 deficiency.
