Pinus densiflora bark extract ameliorates 2,4‐dinitrochlorobenzene‐induced atopic dermatitis in NC/Nga mice by regulating Th1/Th2 balance and skin barrier function

Korean red pine (Pinus densiflora) bark has been traditionally used in Korea and other parts of East Asia to relieve inflammatory diseases. Although many studies using P. densiflora bark have been reported, its effect on atopic dermatitis (AD) has not been elucidated. Thus, we investigated whether the P. densiflora bark extract (PBE) has potential to attenuate AD symptoms and elucidated the molecular mechanism. Oral administration of PBE to mice with 2,4‐dinitrochlorobenzene (DNCB)‐induced AD lessened dermatitis scores and scratching behavior and significantly reduced measures of epidermal thickness, infiltration of mast cells and eosinophils, levels of immunoglobulin E (IgE), and IgG₁/IgG_2a ratio in serum. PBE not only inhibited IL‐4, IL‐5, and IL‐13 but also increased IFN‐γ in splenic production. Furthermore, PBE significantly suppressed mRNA expression of thymic stromal lymphopoietin and further downregulated the mRNA expression of Th2 and Th17 cytokines such as IL‐4, IL‐13, IL‐17, IL‐31, and TNF‐α. In addition, the protein expressions of filaggrin, involucrin, and loricrin in lesional skin were recovered by PBE. These results suggest that PBE attenuates DNCB‐induced AD via regulating Th1/Th2 balance and skin barrier function.