IL-31/33 Axis in Atopic Dermatitis

Atopic dermatitis (AD) is a chronic inflammatory skin disorder characterized by impaired epidermal barrier function, immune dysregulation (e.g., Th2 polarization), genetic factors (e.g., filaggrin mutations), environmental triggers and microbial dysbiosis, leading to pruritus and eczematous lesions. In this review, we present the synergistic "IL-31/IL-33 axis." IL-33, released by damaged keratinocytes, acts as an alarmin, initiating inflammation via ST2 receptors and promoting Th2 cytokine production (IL-4, IL-5, IL-13). This upregulates IL-31, primarily from Th2 cells, which directly activates sensory neurons to induce pruritus and impairs keratinocyte differentiation. Together, IL-31 and IL-33 exacerbate the itch-scratch feedback loop, barrier disruption, and inflammation. Elevated levels of IL-31 and IL-33 correlate with disease severity. Targeting the IL-31/IL-33 axis represents an emerging therapeutic option, e.g., nemolizumab (anti-IL-31RA) significantly reduces pruritus and AD symptoms in clinical trials. However, anti-IL-33/ST2 agents (e.g., etokimab, tozorakimab) demonstrate variable efficacy, highlighting complexity in targeting IL-33. Future research should prioritize biomarker-driven patient stratification to optimize the clinical application of these novel antibody-based therapies.