Biological characteristics of the sensitive Japanese skin

It is well known that two different photobiologic processes mainly take place when the human skin is exposed to ultraviolet (UV) light. The long waves of UVA and visible light (320–400 nm) irradiation causes skin tanning by melanocytic activation and the short waves of UVB (280–320 nm) can elicit variety of biologic action in cutaneous keratinocytes, melanocytes and other skin component cells. The sensitivity to the UV lights is generally depending on the three kinds of the skin type classified by the proposal of Pathak et al. [1]. The skin sensitivity of Japanese population, however, seems to be different from that of Caucasian's population because of the differences in genetic background and skin color, as indicated by Satoh and Kawada [2]. They tried to classify into three groups as J-I (always burn and rarely tan), J-II (moderately burn and moderately tan) and J-III (never burn and always tan) by the skin types to UV lights for the sun-tanning and sun-burning. Comparing these two criteria, a general concern indicates that J-I–III may correspond to the skin type II–IV of the Fitzpatrick's classification, respectively. Based on the Japanese skin types, the incidence of skin cancers and precancerous lesions related to the long-term exposure of sun-light was epidemiologically estimated by Araki et al. [3]. According to their results for several years (1992–1998), the overall number of skin cancers and precancerous states in Japanese was demonstrated to be small in comparison with the incidence of Caucasian's population, even though the people sets in areas of higher ambient solar radiation. However, working outdoors having J-I and/or a history of severe sunburn during childhood were found to be important risk factors, particularly among people of over 60 years of age. Regarding skin cancers and sun-exposed areas, we compared between 20 patients with skin cancers (males 13 and females seven) (average 65 years old) (Table I) and 24 controls (males 10 and females 14), who were selected as similar ages to the patients at random, in their skin types and life environments by a questionnaire system. The skin types of the patients were J-I (15%), J-II (40%), and J-III (35%) and those of controls were J-I (4.2%), J-II (62.5%), and J-III (4.2%), respectively. The patient group tended not to protect from sun exposure and most of them were farmers. UV exposure is known to induce modulation of the skin immune system which Langerhans cells decrease in number in the epidermis, and on the other hand it is supposed that interleukin IL-10 producing macrophages (CD11b+) expand in the dermis. Not only IL-10, but also tumor necrosis factor (TNF)-α from macrophages and mast cells in the dermis seem to increase and suppress Th1 immune responses of the epidermis and Th2 immune responses might be induced by UV irradiation [4]. Recently, it has been reported, however, that in patients with polymorphous light eruption (PLE), the expression of TNF-α, IL-4, and IL-10 is reduced by UVB irradiation and that PLE appearance is related to UVB-induced immunosuppression [5]. Table I. Twenty patients with skin cancers (average ages: 65 years old) (Department of Dermatology, Fukushima Medical University Hospital, 2001–2002) Skin cancers Number of patients Malignant melanoma 8 Squamous carcinoma 4 Bowen's disease 4 Basal cell carcinomas 3 Eccrine porocarcinoma 1 Location of skin cancers Sun-exposed areas 9 Non-exposed areas 11 Then, we attempted to study UVB effects on atopic disease and chronic inflamed skin diseases in the therapeutic advantage, although it is harmful for the patients to be cutaneous carcinogenesis. The epidermal keratinocytes are capable of producing CC chemokines in the local Th2 response, as seen in atopic dermatitis, mycosis fungoides, etc. [6]. Thymus and activated-related chemokine (TARC) is one of the chemokines produced by keratinocytes which selectively activate lymphocytes of Th2 subset expressing CCR4 (receptor for TARC) [7]. Accumulating evidence has suggested that these chemokines have primary pathogenic importance in Th2 skin diseases. In order to find the effects of UVB irradiation on the production of TARC, we used a human keratinocyte HaCaT cell line. As assessed by RT-PCR and ELISA, UVB irradiation significantly decreased the expression of TARC mRNA and protein in HaCaT cells stimulated with interferon-γ (IFN-γ) and TNF-α in a dose-dependent manner. The down-regulation of TARC expression may be mediated in part by activation of the particular transcription, signal transducer and activator of transcription 1 (STAT 1), since it has shown that STAT 1 DNA-binding was down-regulated by UVB irradiation. Our results suggest that STAT 1 and other transcription factors play an important biological role in immune system of human skin irradiated by UVB and may support the results of Kolgen et al. [5]. In this point of view, UVB irradiation will be a therapeutic tool for skin diseases related to Th2 type reaction, such as atopic dermatitis, mycosis fungoides, etc., although we need to optimize adequately the use of UVB in patients with J-I skin type or those of whom have the episode of severe sun-burn after UVB irradiation. References 1. Pathak, M.A., Nghiem, P. and Fitzpatrick, T.B. Acute and chronic effects on the skin. In: Fitzpatrick's Dermatology in General Medicine, 5th edn (Freedberg, I.M., Eisen, A.Z., Wolf, K., Austen, K.F., Goldsmith, L.A., Katz, S.I. and Fitzpatrick, T.B. eds), pp. 1598–1607. McGraw-Hill, New York (1999). 2. Satoh, Y. and Kawada, A. Action spectrum for melanin pigmentation to ultraviolet light, and Japanese skin typing. In: Brown Melanoderma: Biology and Diseases of Epidermal Pigmentation (Fitzpatrick, T.B., Wick, M.M. and Toda, K. eds), pp. 87–95. University of Tokyo Press, Tokyo (1986). 3. Araki, K. , Nagano, T. , Ueda, M. , Washio, F. , Watanabe, S. , Yamaguchi, N. and Ichihashi, M. Incidence of skin cancers and precancerous lesions in Japanese- Risk factors and prevention. J. Epidemiol. 9, S14–S21 (1999). 4. Teunissen, M. B. , Piskin, G. , Nuzzo, S. et al. Ultraviolet B radiation induces a transient appearance of IL-4+ neutrophils, which support the development of Th2 responses. J Immunol. 168, 3732–3739 (2002). 5. Kolgen, W. , van Meurs, M. , Jongsma, M. et al. Differential expression of cytokines in UVB-exposed skin of patients with polymorphous light eruption. Arch. Dermatol. 140, 295–302 (2004). 6. Kakinuma, T. , Sugaya, M. , Nakamura, K. , Kaneko, F. , Wakugawa, M. , Matsushima, K. and Tamaki, K. Thymus and activation-regulated chemokine (TARC/CCL17) in mycosis fungoides: serum TARC levels reflect the disease activity of mycosis fungoides. J. Am. Acad. Dermatol. 48, 23–30 (2003). 7. Imai, T. , Nagira, M. , Tkagi, S. et al. Selective recruitment of CCR4-binding Th2 cells toward antigen-presenting cells by the CC chemokins thymus and activation-regulated chemokine and macrophage-derived chemokine. Int. Immunol. 11, 81–88 (1999).