Demonstration of TARC and CCR4 mRNA expression and distribution using in situ RT-PCR in the lesional skin of atopic dermatitis.

Thymus- and activation-regulated chemokine (TARC/CCL17) and its receptor, CC chemokine receptor 4 (CCR4), have been proven to be involved in a number of allergic diseases, especially atopic dermatitis (AD). The purpose of this study was to examine the expression and distribution of TARC and CCR4 mRNAs in samples of AD (n=15, acute lesions 8, chronic lesions 7) and normal skin (n=6). The expression and distribution of TARC and CCR4 mRNAs were detected with the in situ reverse transcription (RT) -polymerase chain reaction (PCR) technique. TARC mRNA was expressed in epidermal keratinocytes, dermal endothelial cells and infiltrating cells. CCR4 mRNA was expressed in dermal endothelial cells and infiltrating cells. In acute AD lesional skin, there were more positive cells, and the staining intensity was stronger than in chronic lesions (p<0.05). The distribution of positive cells was as follows: In the epidermis, keratinocytes in the basal layer showed the strongest staining, and keratinocytes in the spinous layer showed moderate staining; the superficial area showed faint staining. In the dermis, infiltrating cells located in the superficial area of the dermis showed the strongest staining, positive staining intensity became weaker and the percentage of positive cells became less as the location became deeper. There were no positive cells in normal skin. These data further substantiate the role of TARC/CCR4 in the pathogenesis of AD.