Lack of evidence for TARC/CCL17 production by normal human keratinocytes in vitro

BACKGROUND: thymus and activation-regulated chemokine (TARC)/CCL17 is a CC chemokine that selectively attracts Th2-type lymphocytes. Immunohistochemical analyses have revealed that TARC is expressed in the epidermal keratinocytes of atopic dermatitis (AD), suggesting TARC involvement in the pathogenesis of the disease. However, keratinocyte TARC production has been described only in the transformed keratinocyte cell line HaCaT. OBJECTIVE: to examine TARC production in normal human epidermal keratinocytes (NHEK) in vitro. METHODS: the expression of TARC mRNA and protein were examined in NHEK and HaCaT cells stimulated with various cytokines. RESULTS: stimulation with inflammatory cytokines, including interleukin (IL)-1, IL-4, IL-6, IL-10, interferon (IFN)-alpha, IFN-beta, IFN-gamma, and tumor necrosis factor (TNF)-alpha failed to induce TARC mRNA expression in NHEK. However, stimulation with IFN-gamma and TNF-alpha together enhanced expression slightly. ELISA analysis failed to detect TARC protein in NHEK culture supernatant, even following stimulation with IFN-gamma and TNF-alpha. In contrast, HaCaT cells produced TARC protein even without stimulation of cytokines. CONCLUSION: these results indicate that production of TARC by HaCaT cells is a phenomenon specific to the cell line and the observation on TARC in HaCaT cells can not be generalized. NHEK do not produce TARC protein in vitro.