Which of the following statements regarding endothelial cells in acute inflammation are true?

b. Specific patterns of receptor expression regulate leukocyte adherence

 c. Endothelial cell nitric oxide generation regulates regional blood flow and leukocyte adhesion

d. Endothelial cells may be capable of phagocytosis

Endothelial cells are increasingly recognized to be phenotypically heterogeneous. Specific receptor molecules are expressed at various sites where they help to direct lymphocytes and other leukocytes to their appropriate target organ. In the high endothelial venues, these receptor molecules are known as vascular addressing. Endothelial cells play a major role in regulating vascular tone. This is the result of angiotensin-converting enzyme on the cell surface as well as the production of both endothelia (a potent vasoconstrictor) and nitric oxide (a potent vasodilator). Both play important physiologic roles in determining the distribution of blood flow. In addition, recent evidence suggests that NO may have direct effects upon the expression of a variety of leukocyte adhesion molecules. Under unusual circumstances, endothelial cells can exhibit macrophage-like properties in that they can act as antigen-presenting cells and also phagocytose particles. They may also be a significant source of oxidants in inflammatory reactions after ischemic injury. Endothelial cells are not passive participants in inflammatory processes; rather, they possess the ability to direct and focus many aspects of an inflammatory event