Serum levels of CCL17/TARC in various skin diseases

Dear Editor, Chemokines have been identified as an attractant of different types of leukocytes to sites of infection and inflammation. They are produced locally in the tissues and act on the leukocytes through specific receptors. They also function as regulatory molecules in leukocyte maturation, trafficking and homing in the development of lymphoid tissues.1 Chemokines are a large family of chemotactic cytokines that can be divided into four subfamilies: CXC, CC, CX3C and C depending on their first two N-terminal cysteine residues.2 Among them, thymus and activationregulated chemokine (TARC/CCL17) is a member of CC chemokines, and is expressed in the thymus and peripheral blood monocytes.3 CCL17 is produced by monocyte-derived dendritic cells, endothelial cells, bronchial epithelial cells and epidermal keratinocyte (KC). 2 CCL17 functions as selective chemoattractant and serves for the recruitment and migration of T cells that express CC chemokine receptor 4 (CCR4). 4 We have shown that serum levels of CCL17 is elevated in patients with atopic dermatitis (AD) and reflect the disease activity of AD.5,6 We have also shown that serum levels of CCL17 are elevated in patients with bullous pemphigoid (BP) and mycosis fungoides (MF). 7,8 However, the relationship between disease activity and serum CCL17 levels is not clear. Furthermore, serum levels of CCL17 in other skin diseases, apart from psoriasis vulgaris and pemphigus vulgaris, are unknown. Therefore, we investigated serum levels of CCL17 in various skin diseases including AD, BP and MF. After taking informed consent, serum samples were stored at −20°C until measurement of serum CCL17 levels was performed using enzyme linked immunoabsorbent assay as previously described.6 We have shown that serum CCL17 levels are higher than plasma CCL17 levels and that platelets contain CCL17.6 In this study, we decided to measure serum levels rather than plasma levels because it is more convenient. As shown in Figure 1, AD (123 samples) showed variable and higher serum CCL17 levels compared to other skin diseases. Among other skin diseases, eczema (one sample), chronic actinic dermatitis (CAD) (one sample), prurigo nodularis (one sample), urticaria (one sample), pustular psoriasis (one sample), papulo-erythroderma syndrome (one sample), erythroderma (one sample), Stevens-Johnson syndrome (one sample), drug eruption (one sample), MF (three samples), Sezary syndrome (one sample), cutaneous T-cell lymphoma (one sample), staphylococcal scalded skin syndrome (SSSS) (one sample), angiosarcoma (two samples) and dermatomyositis (one sample) out of 149 samples showed higher serum CCL17 levels. Of note is that very high serum CCL17 levels are only seen in limited skin diseases such as CAD, papulo-erythroderma syndrome, MF, Sezary syndrome and SSSS. Interestingly, no BP patients showed higher serum CCL17 levels in this study. One possible explanation for this is that no severe BP patients were included in this study. In AD, serum CCL17 levels reflect disease severity as shown in Figure 2, consistent with the previous observation.5,6 Although larger scale studies are necessary, this study suggests that serum CCL17 levels may be a useful laboratory marker for the