Induction of angiogenesis in VEGF transgenic mice after long-term UVB irradiation. Immunofluorescence analysis with antibody against CD31 (A-L) demonstrated prominent vascularization in the papillary dermis of VEGF-overexpressing mice after 10 weeks of chronic UVB irradiation (D, arrowheads), whereas vessels were not altered in wild-type littermates that did or did not undergo UVB irradiation (A, C). VEGF-overexpressing mice also formed tortuous vessels in the upper dermis of nonirradiated skin (B). Expression of VEGFR-2 was up-regulated in the dermal blood vessels of UVB-treated, VEGF-overexpressing mice (H), and this expression colocalized with CD31 (L, arrows). VEGFR-2 expression (F) also colocalized with CD31 (B) at the tortuous vessels in the nonirradiated skin of VEGF-overexpressing mice (J, merged image), whereas VEGFR-2 was weakly expressed or absent in the skin of wild-type mice (I, K). Scale bars, 100 μm. A Plan Fluor 20 × objective with an aperture of 0.50 was used for panels A-L. Computer-assisted morphometric analysis of CD31-stained skin sections after 10 weeks of UVB irradiation revealed a significant increase in the relative area occupied by vessels (M), in average vessel size (N), and in vessel density (O) in VEGF transgenic mice (▪). In contrast, no significant differences were detected in the nonirradiated and irradiated skin of wild-type mice (□). Data are expressed as mean ± SD (n = 5). ^***P < .001; ^**P < .01; ^*P < .05.