Transgenic VEGF-A induces enlargement of lymphatic vessels in vivo. Fluorescently labeled dextran was injected into the ear skin of VEGF-A transgenic (VEGF-TG) and wild-type mice. In wild-type mice, lymphatic vessels were relatively small in vehicle-treated skin (A) and were dilated within 24 hours after initiation of DTH reactions (B). In VEGF-A transgenic mice, lymphatic vessels were larger than wild-type vessels under noninflamed conditions (C) and were further enlarged 24 hours after antigen challenge (D). In wild-type mice, lymphatic vessels returned to their normal size within 7 days after challenge (E-F). This is in contrast to VEGF-A transgenic mice, in which the lymphatic vessels in the inflamed skin remained dramatically enlarged (H) compared with vehicle-treated tissue (G) for more than 7 days. Differences in vessel diameters in vivo were calculated 24 hours (I) and 7 days (J) after antigen challenge and are expressed as mean plus or minus SEM (n = 90 regions of interest per genotype and time point). ***P < .001. Scale bar: 100 μm.