Chronic ultraviolet B (UVB) irradiation (290-320 nm) of the skin results in the degradation of extracellular matrix macromolecules, elastosis, formation of wrinkles [1] and enhanced risk for skin cancer [2]. We have previously found that chronic UVB irradiation of human and mouse skin induces pronounced angiogenesis of cutaneous blood vessels [3; 4]. Moreover, targeted overexpression of vascular endothelial growth factor (VEGF)-A enhanced the sensitivity to UVB-induced cutaneous photodamage [5], whereas transgenic overexpression of the angiogenesis inhibitor thrombospondin-1 in the epidermis completely prevented UVB-induced skin damage [3]. Together, these findings indicate that the cutaneous blood vasculature plays a critical role in the mediation of photodamage. In contrast, the role of cutaneous lymphatic vessels in the response to UVB irradiation has remained unknown.

Lymphatic vessels play a crucial role in the maintenance of tissue fluid homeostasis [6], and our recent results obtained in mouse models indicate that impairment of lymphatic vessel function is involved in the mediation of acute UVB-induced skin damage in mice because of increased leakiness of lymphatic vessels that was induced by enhanced levels of VEGF-A [7; 8]. To investigate the consequences of chronic UVB irradiation of human skin on cutaneous lymphatic vessels, we obtained skin samples from the face (sun-exposed skin; 2-mm punch biopsies from the crow's feet area not including wrinkles) and from the buttocks (non-sunexposed skin; 4-mm punch biopsies) of 17 healthy Korean volunteers. All procedures involving human subjects were approved by the Institutional Review Board of Seoul National University Hospital, and all subjects provided written informed consent. Facial skin samples were divided into 3 groups, according the the previously described scoring system for the severity of photodamage in Korean individuals [9]: Group 1: grades 1-3 (n= 6); group 2: grades 4-5 (n= 6); and group 3: grades 6-7 (n= 5). Grade1 corresponds to absence of wrinkles whereas grade 7 corresponds to severely wrinkled skin [9].