P-selectin and Vascular Cell Adhesion Molecule-1 Are Focally Expressed in Aortas of Hypercholesterolemic Rabbits Before Intimal Accumulation of Macrophages and T Lymphocytes

The accumulation of monocyte/macrophages and T lymphocytes in arterial intima is a hallmark of early atherogenesis. To investigate the temporal relationships between endothelial expression of adhesion molecules (eg, P-selectin and vascular cell adhesion molecule-1 [VCAM-1]) and intimal accumulation of macrophages and T lymphocytes, immunostaining was performed by using serial frozen sections from intercostal branch points of thoracic aortas of New Zealand White rabbits that had been fed a 0.3% cholesterol diet. After 1 week of cholesterol feeding, neither macrophages nor T lymphocytes were detected, although endothelial expression of P-selectin and VCAM-1 was observed. After 3 weeks, macrophages were detectable in 75% and T lymphocytes were present in 25% of the rabbits. Expression of P-selectin and VCAM-1 was sustained until 10 weeks. Infiltration of T lymphocytes was restricted in areas in which macrophages were accumulated and did not appear to precede macrophage infiltration. E-selectin expression was not detectable before accumulation of mononuclear leukocytes; however, very few endothelial cells covering foam cell lesions expressed E-selectin after 6 weeks. Similar results were obtained in Watanabe heritable hyperlipidemic rabbits aged 1, 2, and 3 months. Taken together, localized expression of P-selectin and VCAM-1 may play a key role in the initial recruitment of macrophages and T lymphocytes in early atherogenesis.