Elevated serum galectin‐9 levels in patients with atopic dermatitis

Galectin‐9 is a member of the galectin family that has a wide spectrum of biological functions. Among them, galectin‐9 has been known mainly as a potent chemoattractant for eosinophils. In addition, galectin‐9 alters the T‐cell balance by negatively regulating T‐helper (Th)1 and Th17 cells, resulting in Th2 polarization. Atopic dermatitis (AD) is a skin allergic disease characterized by peripheral eosinophilia, mast cell activation and predominance of Th2 cells. To investigate possible roles of galectin‐9 in AD, we measured serum galectin‐9 levels in AD patients and investigated galectin‐9 expression in lesional skin by immunohistochemistry. Serum galectin‐9 levels in patients with AD were significantly higher than those in healthy controls and correlated with the Eczema Area and Severity Index. Serum galectin‐9 levels were decreased after treatment, accompanied by improvement of skin lesions. Immunohistochemical study revealed that galectin‐9 was expressed on epidermal keratinocytes and mast cells in lesional skin of AD. Our results suggest that elevated galectin‐9 expression is associated with progression of AD and that galectin‐9 could be a therapeutic target in AD.