Adventitial lymphatics and atherosclerosis.

Lymphatic vessels are important in reverse cholesterol transport and play a crucial role in regression of atherosclerotic plaque in experimental animal models. Therefore, we attempted to analyze adventitial microcirculation including lymphatic vessels and adventitial macrophages in large human arteries in various stages of atherosclerosis. Eighty-one arterial segments of large arteries (iliac arteries and abdominal aortas) were obtained from deceased organ donors. Lymphatic vessels were identified using anti-LYVE-1 and anti-D2-40/podoplanin immunohistochemical staining. Adventitial blood vessels and macrophages were visualized using anti-CD-31 and anti-CD-68. Intimal thickness was measured under 100x magnification with an Olympus BX 41 light microscope using the visual mode analySIS 3.2 software. Lymphatic vessels were counted in each cross section of the examined arteries, and adventitial blood vessels (CD31+) were counted using the "hot spot" method. Statistical analysis was performed with Statistica 9.1 PL software (StatSoft, Cracow, Poland). Mann-Whitney, F-Cox, Chi-square, and Spearman's correlation tests were performed and the differences were considered significant at p < 0.05. Lymphatic and blood vessels in the adventitia of examined arteries were identified and quantified. Significant positive correlations were found between the number of adventitial lymphatics (LYVE-L +) and intimal thickness (r = 0.37; p < 0.05) as well as with age of the subjects (r = 0.3; p < 0.05). Thus, lymphatic vessels are present in the adventitia of large arteries in humans and the number of adventitial lymphatic vessels increases with progression of atherosclerosis as assessed by intimal thickness.