TARC and sensitive skin
Authors: Nakamura K. 
Published: September 2010

Atopic dermatitis (AD) is a chronic inflammatory skin disease characterized by pruritic and dry skin lesions with elevated serum IgE levels. AD is characterized by predominant infiltration of Th2 type cells secreting cytokines such as interleukin‐4 (IL‐4) and IL‐5. Chemokines are chemotactic cytokines that regulate leukocyte trafficking into the inflamed tissues and are divided into four families: CC, CXC, C and CX3C. Among CC chemokines, thymus and activation regulated chemokine (TARC)/CCL17 and monocyte derived chemokine (MDC)/CCL22 attracts Th2 type T cells. This is produced by dendritic cells, endothelial cells and T cells. We have examined the expression of TARC in lesional skin. We have identified that keratinocytes (KCs) are major sources of TARC when stimulated by IFN‐γ and TNF‐α. We next examined the serum levels of TARC levels in AD patients [4]. Forty patients with AD, 20 healthy controls and 20 patients of psoriasis were examined. The serum TARC levels with AD patients were significantly higher than healthy controls and psoriasis patients (Fig. 1). The average levels of the serum TARC of AD was 2338.0 ± 302.8 pg mL–1, whereas that of healthy controls was 215.3 ± 26.8 pg mL–1 and that of psoriasis was 256.3 ± 25.3 pg mL–1. We compared serum TARC levels among three different stages (mild, moderate, and severe) of AD. Serum TARC levels of severe AD patients were significantly higher than those of mild and moderate group. The average levels of TARC in the mild, moderate and severe groups were 540.8 ± 111.6 pg mL–1, 2056.2 ± 290.3 pg mL–1, and 4812 ± 491 pg mL–1, respectively. The patients with old age who suffered from AD for a long period showed severe eruptions and the serum TARC levels of these aged group showed relatively higher CCL17 levels compared with those of young patients (2182.1 ± 312.0 pg mL–1, 1103.3 ± 240.2 pg mL–1). To determine the CCL17 localization in lesional skin, immunohistochemical analysis was performed using biopsy samples. Immunoreactive TARC was detected in the epidermal KC and dermal infiltrating cells in the acute and chronic lesional skin.

Serum TARC levels in patients with atopic dermatitis (AD psoriasis vulgaris and healthy controls.

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To elucidate the source of TARC producing cells in peripheral blood mononuclear cells (PBMCs) in AD patients, we purifed CD4+ T cell, CD8+ T cell, and monocytes. Both CD4+ and CD8+ T cells expressed TARC mRNA, and the level of TARC mRNA expression was more predominant in CD4+ T cells. Monocyte did not express TARC mRNA. Monocyte derived dendritic cells (MoDCs) were produced from monocytes cultured with both IL‐4 and GM‐CSF for 5 days. MoDCs expressed CD11c, CD1c, CD13 and HLA‐DR antigen. MoDCs expressed TARC mRNA and produced TARC protein in high levels in healthy controls. The level of TARC protein by MoDCs was more prominent in AD patients compared with healthy controls (20146.2 pg/ml vs 15654.7 pg/ml). The levels of TARC by MoDCs in different ages were examined and that was 24,281 pg/ml (10∼20 years old), 21389.7 pg/ml (20∼30 years old) and 18733.3 g/ml (30∼40 years old), respectively. MDC/CCL22 is another chemokine which attracts Th2 type T cells. We also examined the levels of MDC in the culture supernatants of MoDCs in AD patients. These were also higher in AD patients compared to healthy controls. The levels of MDC produced by MoDCs increased according to the aged people of AD patients as follows: 41,698 pg/ml (10∼20 years old), 41,987 pg/ml (20∼30 years old), 50,533 pg/ml (30∼40 years old). These results suggest that MDC, produced by MoDCs in AD patients, showed high levels in the aged people in severe AD, indicating that MDC is a good marker for the sensitive skin in AD.

KCs can produce various kinds of cytokines and chemokines such as TARC and MDC. IFN‐γ induced TARC and MDC production by KCs, and this is augmented by additional stimulation of TNF‐α. We examined that the activity of transcription factors such as NFkB and STAT‐1 in KCs in in vitro system. We showed that NFkB and STAT‐1 DNA binding activity in KCs significantly increased under the stimulation of IFN‐γ and TNF‐α by gel shift analysis. The NFkB DNA binding activity was partially blocked by genistein and LY294002, indicating that tyrosine kinase inhibitor and PI3kinase inhibitor can regulate NFkB DNA binding activity in KCs. Interestingly, TARC production by KCs, when stimulated by IFN‐γ and TNF‐α, was also inhibited by additional genistein and LY294002. These data indicated that TARC production in KCs was regulated by NFkB pathways.

CC chemokine receptor‐4 (CCR4) is a specific ligand for TARC/CCL17 and MDC/CCL22. We examined CCR4 and CXCR3 expression on peripheral blood memory T cells and found that the percentage of CCR4 expression on memory T cells was significantly higher in AD patients compared with normal controls and psoriasis patients [5]. The positivity of CCR4 expression on CD4+ CD45RO+ T cells in AD patients was 23.4 ± 18.1%, whereas that of healthy controls and patients with psoriasis was 5.3 ± 3.5%, 6.5 ± 5.0%, individually. The positivity of CCR expression on CD8+ CD45RO+ T cells in AD patients was 7.6 ± 5.3%, whereas that of healthy controls and patients with psoriasis was 4.9 ± 1.1%, 2.9 ± 5.2%, individually (AD versus control: P < 0.0005).CCR4 expression in the severe group was significantly higher than that seen in the healthy controls (P < 0.05). An immunohistochemical study of CCR4 and CXCR3 expression was also performed. In acute and chronic lesions, CCR4 was expressed on more than 70% of CD4+ T cells which had a higher ratio compared with that of psoriasis and healthy control. Taken together, these data indicate CCL17 and CCR4 play an important role in the pathogenesis of AD and may reflect the disease severity of AD.

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