Mycosis fungoides and Sézary syndrome tumor cells express epidermal fatty acid‐binding protein, whose expression decreases with loss of epidermotropism

Abstract

Fatty acid binding protein (FABP) is a family of transport proteins for fatty acid (FA). Epidermal FABP (E‐FABP) is highly expressed by resident memory T cells (TRM) in the skin. It supports the uptake of exogenous FA for long‐term survival of skin TRM. Mycosis fungoides (MF) is regarded as malignancy of skin TRM. In this study, we investigated E‐FABP expression in psoriasis vulgaris (PV), atopic dermatitis (AD), MF, and Sézary syndrome (SS). E‐FABP mRNA levels in PV were much higher than those in healthy controls. E‐FABP mRNA levels in AD and MF/SS lesional skin were also significantly higher than those of normal skin. By immunohistochemical staining, E‐FABP was positive in MF/SS lesional skin. Interestingly, E‐FABP was stained positive in epidermotropic lymphoid cells in patch, plaque, and erythrodermic lesions of MF/SS, suggesting that a part of tumor cells expressed E‐FABP. In tumorous lesions, however, most dermal tumor cells were negative for E‐FABP. Immunohistochemical staining using patch/plaque lesions and tumorous lesions from the same patients also revealed that E‐FABP expression decreased in tumorous lesions. Our study has suggested that MF/SS tumor cells express E‐FABP, whose expression decreases with loss of epidermotropism.