IL-17A-Producing Innate Lymphoid Cells Promote Skin Inflammation by Inducing IL-33-Driven Type 2 Immune Responses

Atopic dermatitis (AD) is a chronic, pruritic, inflammatory skin disease characterized by type 2 cytokines secreted by T helper type 2 cells and group 2 innate lymphoid cells. Despite a high degree of heterogeneity, AD is still explained by type 2 immunity, and the role of IL-17A, which is increased in acute, pediatric, or Asian patients with AD, remains poorly understood. Here, we aimed to investigate the role of IL-17A-producing group 3 innate lymphoid cells (ILC3s), which are unexplored immune cells, in the pathogenesis of AD. We found that the numbers of ILC3s in the skin of AD-induced mice were increased, and that neutralizing IL-17A delayed development of AD. Moreover, adoptive transfer of ILC3s accelerated the symptoms of AD. Mechanically, ILC3s induced IL-33 production by nonimmune skin cells, keratinocytes, and fibroblasts, which promoted type 2 immune responses. Because AD has a complex pathophysiology and a broad spectrum of clinical phenotypes, the presence of ILC3s in the skin and their interaction with nonimmune skin cells could explain the pathogenesis of cutaneous AD.