IL-31 uncouples skin inflammation from itch sensation in allergic dermatitis

Despite a robust literature associating IL-31 with pruritic inflammatory skin diseases, its influence on cutaneous inflammation and on the interplay between inflammatory and neurosensory pathways remain unmapped. Here, we examined the effects of IL-31 and its receptor IL31RA on both inflammation and pruritus in mouse models of dermatitis, including chronic topical house dust mite (HDM) exposure. Unexpectedly, Il31 deficiency increased cutaneous adaptive type 2 cytokine-producing cells and serum IgE. In addition, M2-like macrophages capable of fueling feedforward pro-inflammatory loops were selectively enriched in Il31ra-deficient skin. Thus, IL-31 is not strictly a pro-inflammatory cytokine, but rather an immunoregulatory factor that limits the magnitude of allergic skin inflammation. In contrast, Il31-deficient mice displayed a deficit in HDM-induced scratching. Itch reduction occurred despite intact - and in some cases increased - responsiveness of sensory neurons to other pruritogens released during HDM challenge, highlighting the non-redundant contribution of IL-31-receptive sensory afferents to pruritus in environmental allergen-induced dermatitis. When present, therefore, IL-31 uncouples circuits driven by sensory neurons and immune cells that converge in inflamed skin.