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Background Inflammatory chemokines, such as macrophage-derived chemokine ( MDC/ CCL22), are elevated in the serum and lesioned skin of patients with atopic dermatitis ( AD), and are ligands for C-C chemokine receptor 4, which is predominantly expressed on T helper 2 lymphocytes, basophils and natural killer cells. We have previously reported that quercetagetin has an inhibitory activity on inflammatory chemokines, which is induced by interferon ( IFN)-γ and tumour necrosis factor ( TNF)-α, occurring via inhibition of the signal transducer and activator of transcription 1 ( STAT1) signal. Objectives To investigate the specific mechanisms of quercetagetin on the STAT1 signal. Methods We confirmed the inhibitory activity of quercetagetin on MDC and STAT1 in HaCaT keratinocytes. The interaction between STAT1 and IFN-γR1 was investigated using immunoprecipitation. The small interfering RNA approach was used to investigate the role of suppressor of cytokine signalling 1 ( SOCS1) and transforming growth factor ( TGF)-β1 induced by quercetagetin. Results Quercetagetin inhibited the expression of MDC at both the protein and m RNA levels in IFN-γ- and TNF-α-stimulated HaCaT human keratinocytes. Moreover, quercetagetin inhibited the phosphorylation of STAT1 through upregulation of SOCS1. Increased expression of SOCS1 disrupted the binding of STAT1 to IFN-γR1. Furthermore, quercetagetin augmented the expression of TGF-β1, which is known to modulate the immune response and inflammation. Conclusions These results suggest that quercetagetin may be a potent inhibitor of the STAT1 signal, which could be a new molecular target for anti-inflammatory treatment, and may thus have therapeutic applications as an immune modulator in inflammatory diseases such as AD. [ABSTRACT FROM AUTHOR]