The distribution of intimal white blood cells in the normal rabbit aorta.

Macrophages play an important role in atherogenesis and have been reported within the intima at lesion-prone sites in normocholesterolemic animals as well as infants and children. The objective of this study was to determine the spatial distribution of intimal white blood cells (WBC) in the normal rabbit aorta and the association of intimal WBC with replicating endothelial cells and sites of increased 125I-LDL permeability. Intimal WBC and macrophages were identified en face on whole aortic tissue and on Häutchen preparations based on their morphology, ingestion of exogenous horseradish peroxidase, non-specific esterase activity, and labeling with a monoclonal antibody for rabbit macrophages (RAM11). WBC were primarily located in the lesion-prone flow divider regions of the large abdominal branch arteries. Using [3H]thymidine autoradiography to determine cell proliferation, 4.4% of the WBC and 0.12% of the endothelial cells were labeled on the Häutchen preparations. The distribution of replicating endothelial cells was not localized to the arterial orifices and was not correlated with the distribution of intimal WBC. Intimal WBC were, however, spatially correlated with the distribution of 125I-LDL permeable sites about the celiac artery orifice and were directly associated with 31% of the LDL permeable spots. Moreover, mitotic endothelial cells accounted for only 8% of the total number of LDL permeable sites. The presence of intimal WBC at lesion-prone sites in the normocholesterolemic rabbit suggests that these cells may be important in the initiation of atherosclerotic lesions.