IL-4 acts on skin-derived dendritic cells to promote the T_H2 response to cutaneous sensitization and the development of allergic skin inflammation.

Abstract

Atopic dermatitis is characterized by scratching and a T_H2-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 naive T cells. We sought to determine whether non-T-cell-derived IL-4 acts on skin-derived DCs to promote the T_H2 response to cutaneously encountered antigen and allergic skin inflammation. DCs from dLNs of ovalbumin (OVA)-exposed skin were analyzed by flow cytometry and for their ability to polarize OVA-specific naive CD4⁺ T cells. Skin inflammation following epicutaneous sensitization of tape-stripped skin was assessed by flow cytometry of skin cells and real-time quantitative PCR of cytokines. Cytokine secretion and antibody levels were evaluated by ELISA. 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 T_H2 differentiation. DCs from dLNs of OVA-sensitized skin of Il4^-/- mice and CD11c-CreIl4r^flox/- mice, which lack IL-4Rα expression in DCs (DC^Δ/Δll4ra mice), were impaired in their capacity to drive T_H2 polarization compared with DCs from controls. Importantly, OVA-sensitized DC^Δ/Δll4ra mice demonstrated impaired allergic skin inflammation and OVA-specific systemic T_H2 response evidenced by reduced T_H2 cytokine secretion by OVA-stimulated splenocytes and lower levels of OVA-specific IgE and IgG1 antibodies, compared with controls. 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 T_H2 polarization and drive allergic skin inflammation.