el-Ghorr A A, Norval M
Department of Medical Microbiology, University of Edinburgh Medical School, UK.
Photochem Photobiol. 1997 May;65(5):866-72. doi: 10.1111/j.1751-1097.1997.tb01936.x.
Trans-urocanic acid (trans-UCA) accumulates in the upper layers of the epidermis and can be isomerized to cis-UCA by UV light irradiation. Cis-urocanic acid possesses immunosuppressive properties that have led to its consideration as one of the initiators of UV-induced immunosuppression. High quantities of cis-UCA persist in human skin for prolonged periods in the summer months. In the present study, mice were injected intradermally with trans-UCA and cis-UCA three times a week for 4 weeks in order to ascertain the long-term effects of the presence of these compounds in the skin. The weight of mice and of their spleens were unaffected by the cis- or trans-UCA treatment. A decrease in thymus weight, accompanied by an increase in lymph node weight, was detected in the cis-UCA-treated mice compared with trans-UCA-treated mice and untreated controls. A net accumulation of lymphocytes and dendritic cells (DC) in lymph nodes was evident following cis-UCA treatment but the percentage of both CD4+ and CD8+ lymphocytes as well as Ia+ DC remained constant among the different treatment groups, indicating that there was no specific migration or proliferation of a particular subset of cells. The in vitro lymphoproliferative response of lymph node cells to the mitogen concanavalin A was significantly sup pressed by cis-UCA treatment. The density of Langerhans cells in the epidermis of the ears was not altered by the chronic cis-UCA treatment. However, chronic cis-UCA treatment did suppress the mixed skin lymphocyte reaction response utilizing epidermal cells from the ears (an uninjected area of skin), indicating a systemic suppression. Compared with trans-UCA treatment, chronic cis-UCA treatment did not cause a significant reduction in the contact hypersensitivity response to oxazolone or the delayed hypersensitivity response to herpes simplex virus. Thus, chronic treatment with cis-UCA led to the suppression of some, but not all, of the immune parameters that are affected by UVB irradiation.
反式尿刊酸（trans-UCA）积聚在表皮上层，经紫外线照射可异构化为顺式尿刊酸（cis-UCA）。顺式尿刊酸具有免疫抑制特性，这使其被视为紫外线诱导免疫抑制的引发因素之一。在夏季，大量的顺式尿刊酸会在人体皮肤中长期存在。在本研究中，每周给小鼠皮内注射三次反式尿刊酸和顺式尿刊酸，持续4周，以确定这些化合物在皮肤中存在的长期影响。顺式或反式尿刊酸处理对小鼠及其脾脏的重量没有影响。与反式尿刊酸处理的小鼠和未处理的对照组相比，顺式尿刊酸处理的小鼠胸腺重量下降，同时淋巴结重量增加。顺式尿刊酸处理后，淋巴结中淋巴细胞和树突状细胞（DC）明显净积聚，但不同处理组中CD4 +和CD8 +淋巴细胞以及Ia + DC的百分比保持不变，表明没有特定细胞亚群的特异性迁移或增殖。顺式尿刊酸处理显著抑制了淋巴结细胞对促有丝分裂原刀豆球蛋白A的体外淋巴细胞增殖反应。慢性顺式尿刊酸处理未改变耳部表皮中朗格汉斯细胞的密度。然而，慢性顺式尿刊酸处理确实抑制了利用耳部（未注射皮肤区域）表皮细胞的混合皮肤淋巴细胞反应，表明存在全身抑制。与反式尿刊酸处理相比，慢性顺式尿刊酸处理对恶唑酮的接触性超敏反应或对单纯疱疹病毒的迟发性超敏反应没有显著降低。因此，慢性顺式尿刊酸处理导致了紫外线B照射所影响的部分而非全部免疫参数的抑制。
