ABSTRACT
It has been known for some time that endothelial cells can be found circulating in blood. Only recently, however, have studies begun to explore the utility of their enumeration and examination. An exciting related area pertains to the presence of endothelial progenitors in blood. Unfortunately the literature on this subject is replete with cell descriptions that are often ambiguous and sometimes simply incorrect. This chapter will utilize precise terminology (Table 1) to distinguish between the different endothelial cells found in blood, circulating endothelial cells (CEC) and endothelial progenitor cells (EPC), and for the endothelial-like cells that grow out from a culture of blood, blood outgrowth endothelial cells (BOEC) and spindle cells (SpC). We here will critically examine the literature on blood endothelial cells and attempt to correct the several misapprehensions that currently exist.
