Topical Application of Soybean Tar Alleviates Atopic Dermatitis Symptoms through Regulation of T Helper 2 Cells and Type 2 Innate Lymphoid Cells

Atopic dermatitis (AD) is an inflammatory skin disease. Recent studies have identified the CD4+T helper 2 (Th2) cells and type 2 innate lymphoid cells (ILC2s) as key drivers of AD. Soybean tar has been used to treat AD for centuries in China, but the mechanisms of action remain unknown. The aim of this study was to investigate whether soybean tar alleviates atopic dermatitis symptoms by inhibiting Th2 and ILC2s-mediated immune responses. Calcipotriol (a vitamin D3 analogue) was applied to mouse ears to trigger experimental atopic dermatitis in c57 mice. Topical application of soybean tar significantly improved AD symptoms determined by dermatitis score, ear thickness, and scratching frequency. Histological analyses showed that soybean tar reduced infiltration of eosinophils and mast cells in the lesioned skin. The Th2 cytokine IL-4 in skin lesions
was significantly reduced by soybean tar. Furthermore, soybean tar reduced CD4+/CD8+ T cell ratio, as well as Th2 cell and ILC2s populations in mouse cervical lymph nodes. These results indicate that topical application of soybean tar ameliorates AD symptoms by lowering Th2 and ILC2s-mediated immune responses and cytokine production.